Magnetic exchange interactions at the proximity of a superconductor

Interfacing magnetism with superconductivity gives rise to a wonderful playground for intertwining key degrees of freedom: Cooper pairs, spin, charge, and spin-orbit interaction, from which emerge a wealth of exciting phenomena, fundamental in the nascent field of superconducting spinorbitronics and topological quantum technologies. Magnetic exchange interactions (MEIs), being isotropic or chiral such as the Dzyaloshinskii-Moriya interactions, are vital in establishing the magnetic behavior at these interfaces as well as in dictating not only complex transport phenomena, but also the manifestation of topologically trivial or non-trivial objects. Here, we propose a methodology enabling the extraction of the tensor of MEI from electronic structure simulations accounting for superconductivity. We apply our scheme to the case of a Mn layer deposited on Nb(110) surface and explore proximity-induced impact on the MEI. The latter are weakly modified by a realistic electron-phonon coupling. However, tuning the superconducting order parameter, we unveil potential change of the magnetic order accompanied with chirality switching, as induced by the interplay of spin-orbit interaction and Cooper pairing. Owing to its simple formulation, our methodology can be readily implemented in state-of-the-art frameworks capable of tackling superconductivity and magnetism. We thus foresee implications in the simulations and prediction of topological superconducting bits as well as of cryogenic superconducting hybrid devices involving magnetic units.

Toward Reliable Synthesis of Superconducting Infinite Layer Nickelate Thin Films by Topochemical Reduction

Infinite layer (IL) nickelates provide a new route beyond copper oxides to address outstanding questions in the field of unconventional superconductivity. However, their synthesis poses considerable challenges, largely hindering experimental research on this new class of oxide superconductors. That synthesis is achieved in a two-step process that yields the most thermodynamically stable perovskite phase first, then the IL phase by topotactic reduction, the quality of the starting phase playing a crucial role. Here, a reliable synthesis of superconducting IL  nickelate films is reported after successive topochemical reductions of a parent perovskite phase with nearly optimal stoichiometry. Careful analysis of the transport properties of the incompletely reduced films reveals an improvement in the strange metal behavior of their normal state resistivity over subsequent topochemical reductions, offering insight into the reduction process.

Enhanced weak superconductivity in trigonalγ-PtBi2

Electrical resistivity experiments show superconductivity atTc=1.1K in a high-quality single crystal of trigonalγ-PtBi2, with an enhanced critical magnetic fieldμ0Hc2(0)≳1.5Tesla and a low critical current-densityJc(0)≈40 A cm-2atH = 0. BothTcandHc2(0)are the highest reported values for stoichiometric bulk samples at ambient pressure. We found a weakHc2anisotropy withΓ=Hc2ab/Hc2c<1, which is unusual among superconductors. Under a magnetic field, the superconducting transition becomes broader and asymmetric. Along with the low critical currents, this observation suggests an inhomogeneous superconducting state. In fact, no trace of superconductivity is observed through field-cooling-zero-field-cooling magnetization experiments.

Topological band inversion and chiral Majorana mode in hcp thallium

The chiral Majorana fermion is an exotic particle that is its own antiparticle. It can arise in a one-dimensional edge of topological materials, and especially that in a topological superconductor can be exploited in non-Abelian quantum computation. While the chiral Majorana mode (CMM) remains elusive, a promising situation is realized when superconductivity coexists with a topologically non-trivial surface state. Here, we perform fully non-empirical calculation for the CMM considering superconductivity and surface relaxation, and show that hexagonal close-packed thallium (Tl) has an ideal electronic state that harbors the CMM. Thekz=0plane of Tl is a mirror plane, realizing a full-gap band inversion corresponding to a topological crystalline insulating phase. Its surface and hinge are stable and easy to make various structures. Another notable feature is that the surface Dirac point is very close to the Fermi level, so that a small Zeeman field can induce a topological transition. Our calculation indicates that Tl will provide a new platform of the Majorana fermion.

Chemical bonding dictates drastic critical temperature difference in two seemingly identical superconductors

Though YB6 and LaB6 share the same crystal structure, atomic valence electron configuration, and phonon modes, they exhibit drastically different phonon-mediated superconductivity. YB6 superconducts below 8.4 K, giving it the second-highest critical temperature of known borides, second only to MgB2. LaB6 does not superconduct until near-absolute zero temperatures (below 0.45 K), however. Though previous studies have quantified the canonical superconductivity descriptors of YB6's greater Fermi-level (Ef) density of states and higher electron-phonon coupling (EPC), the root of this difference has not been assessed with full detail of the electronic structure. Through chemical bonding, we determine low-lying, unoccupied 4f atomic orbitals in lanthanum to be the key difference between these superconductors. These orbitals, which are not accessible in YB6, hybridize with π B-B bonds and bring this π-system lower in energy than the σ B-B bonds otherwise at Ef. This inversion of bands is crucial: the optical phonon modes we show responsible for superconductivity cause the σ-orbitals of YB6 to change drastically in overlap, but couple weakly to the π-orbitals of LaB6. These phonons in YB6 even access a crossing of electronic states, indicating strong EPC. No such crossing in LaB6 is observed. Finally, a supercell (the M k-point) is shown to undergo Peierls-like effects in YB6, introducing additional EPC from both softened acoustic phonons and the same electron-coupled optical modes as in the unit cell. Overall, we find that LaB6 and YB6 have fundamentally different mechanisms of superconductivity, despite their otherwise near-identity.

Bands renormalization and superconductivity in the strongly correlated Hubbard model using composite operators method

We use the composite operator method (COM) to analyze the strongly correlated repulsive Hubbard model, investigating the effect of nearest-neighbor hoppings up to fourth order on a square lattice. We consider two sets of self-consistent equations, one enforcing the Pauli principle and the other imposing charge-charge, spin-spin, and pair-pair correlations using a decoupling scheme developed by Roth (1969Phys. Rev.184451-9). We extract three distinct solutions from these equations: COM1 and COM2 by imposing the Pauli principle and one from Roth decoupling. An overview of the method studying the validity of particle-hole symmetry and the Luttinger theorem for each solution is presented. Additionally, we extend the initial basis to study superconductivity, concluding that it is induced by the Van Hove singularity. Finally, we include higher-order hoppings using realistic estimates for tight binding parameters and compare our results with ARPES measurements on cuprates.

Build Borophite from Borophenes: A Boron Analogue Graphite

Unlike graphene derived from graphite, borophenes represent a distinct class of synthetic two-dimensional materials devoid of analogous bulk-layered allotropes, leading to covalent bonding within borophenes instead of van der Waals (vdW) stacking. Our investigation focuses on 665 vdW-stacking boron bilayers to uncover potential bulk-layered boron allotropes through vdW stacking. Systematic high-throughput screening and stability analysis reveal a prevailing inclination toward covalently bonded layers in the majority of boron bilayers. However, an intriguing outlier emerges in δ5 borophene, demonstrating potential as a vdW-stacking candidate. We delve into electronic and topological structural similarities between δ5 borophene and graphene, shedding light on the structural integrity and stability of vdW-stacked boron structures across bilayers, multilayers, and bulk-layered allotropes. The δ5 borophene analogues exhibit metallic properties and characteristics of phonon-mediated superconductors, boasting a critical temperature near 22 K. This study paves the way for the concept of "borophite", a long-awaited boron analogue of graphite.

Collective neural network behavior in a dynamically driven disordered system of superconducting loops

Collective properties of complex systems composed of many interacting components such as neurons in our brain can be modeled by artificial networks based on disordered systems. We show that a disordered neural network of superconducting loops with Josephson junctions can exhibit computational properties like categorization and associative memory in the time evolution of its state in response to information from external excitations. Superconducting loops can trap multiples of fluxons in many discrete memory configurations defined by the local free energy minima in the configuration space of all possible states. A memory state can be updated by exciting the Josephson junctions to fire or allow the movement of fluxons through the network as the current through them surpasses their critical current thresholds. Simulations performed with a lumped element circuit model of a 4-loop network show that information written through excitations is translated into stable states of trapped flux and their time evolution. Experimental implementation on a high-Tc superconductor YBCO-based 4-loop network shows dynamically stable flux flow in each pathway characterized by the correlations between junction firing statistics. Neural network behavior is observed as energy barriers separating state categories in simulations in response to multiple excitations, and experimentally as junction responses characterizing different flux flow patterns in the network. The state categories that produce these patterns have different temporal stabilities relative to each other and the excitations. This provides strong evidence for time-dependent (short-to-long-term) memories, that are dependent on the geometrical and junction parameters of the loops, as described with a network model.

Emerging complexity in the self-dual theory of superconductivity

To describe the way complexity emerges in seemingly simple systems of nature requires one to attend to two principal questions: how complex patterns appear spontaneously and why a single system can accommodate their inexhaustible variety. It is commonly assumed the pattern formation phenomenon is related to the competition of several types of interactions with disparate length scales. The existence of configurations of qualitatively distinct morphology is attributed to the system frustration induced by the multi-scale interactions. This work explores an alternative approach through a mechanism that leads to a wide range of intricate and topologically non-trivial patterns. The mechanism is described by the self-dual Ginzburg-Landau theory and, possibly, other Maxwell-Higgs models. It gives rise to unique spatial flux profiles observed in superconductors between the two conventional superconductivity types, I and II. .

Van Hove singularity driven enhancement of superconductivity in two-dimensional tungsten monofluoride (WF)

Superconductivity in two-dimensional materials has gained significant attention in the last few years. In this work, we report phonon-mediated superconductivity investigations in monolayer Tungsten monofluoride (WF) by solving anisotropic Migdal Eliashberg equations as implemented in EPW. By employing first-principles calculations, our examination of phonon dispersion spectra suggests that WF is dynamically stable. Our results show that WF has weak electron-phonon coupling (EPC) strength (λ) of 0.49 with superconducting transition temperature (Tc) of 2.6 K. A saddle point is observed at 0.11 eV below the Fermi level (EF) of WF, which corresponds to the Van Hove singularity (VHS). On shifting the Fermi level to the VHS by hole doping (3.7 × 1014cm-2), the EPC strength increases to 0.93, which leads to an increase in theTcto 11 K. However, the superconducting transition temperature of both pristine and doped WF increases to approximately 7.2 K and 17.2 K, respectively, by applying the Full Bandwidth (FBW) anisotropic Migdal-Eliashberg equations. Our results provide a platform for the experimental realization of superconductivity in WF and enhancement of the superconducting transition temperature by adjusting the position ofEFto the VHS.

Steering of Vortices by Magnetic Field Tilting in Open Superconductor Nanotubes

In planar superconductor thin films, the places of nucleation and arrangements of moving vortices are determined by structural defects. However, various applications of superconductors require reconfigurable steering of fluxons, which is hard to realize with geometrically predefined vortex pinning landscapes. Here, on the basis of the time-dependent Ginzburg-Landau equation, we present an approach for the steering of vortex chains and vortex jets in superconductor nanotubes containing a slit. The idea is based on the tilting of the magnetic field B at an angle α in the plane perpendicular to the axis of a nanotube carrying an azimuthal transport current. Namely, while at α=0∘, vortices move paraxially in opposite directions within each half-tube; an increase in α displaces the areas with the close-to-maximum normal component |Bn| to the close(opposite)-to-slit regions, giving rise to descending (ascending) branches in the induced-voltage frequency spectrum fU(α). At lower B values, upon reaching the critical angle αc, the close-to-slit vortex chains disappear, yielding fU of the nf1 type (n≥1: an integer; f1: the vortex nucleation frequency). At higher B values, fU is largely blurry because of multifurcations of vortex trajectories, leading to the coexistence of a vortex jet with two vortex chains at α=90∘. In addition to prospects for the tuning of GHz-frequency spectra and the steering of vortices as information bits, our findings lay the foundation for on-demand tuning of vortex arrangements in 3D superconductor membranes in tilted magnetic fields.

Is La3Ni2O6.5 a Bulk Superconducting Nickelate?

Superconducting states onsetting at moderately high temperatures have been observed in epitaxially stabilized RENiO2-based thin films. However, recently, it has also been reported that superconductivity at high temperatures is observed in bulk La3Ni2O7-δ at high pressure, opening further possibilities for study. Here we report the reduction profile of La3Ni2O7 in a stream of 5% H2/Ar gas and the isolation of the metastable intermediate phase La3Ni2O6.45, which is based on Ni2+. Although this reduced phase does not superconduct at ambient or high pressures, it offers insights into the Ni-327 system and encourages future study of nickelates as a function of oxygen content.

Metal-bonded perovskite lead hydride with phonon-mediated superconductivity exceeding 46 K under ambient pressure

In the search for high-temperature superconductivity in hydrides, a plethora of multi-hydrogen superconductors have been theoretically predicted, and some have been synthesized experimentally under ultrahigh pressures of several hundred GPa. However, the impracticality of these high-pressure methods has been a persistent issue. In response, we propose a new approach to achieve high-temperature superconductivity under ambient pressure by implanting hydrogen into lead to create a stable few-hydrogen binary perovskite, Pb4H. This approach diverges from the popular design methodology of multi-hydrogen covalent high critical temperature (Tc) superconductors under ultrahigh pressure. By solving the anisotropic Migdal-Eliashberg equations, we demonstrate that perovskite Pb4H presents a phonon-mediated superconductivity exceeding 46 K with inclusion of spin-orbit coupling, which is six times higher than that of bulk Pb (7.22 K) and comparable to that of MgB2, the highestTcachieved experimentally at ambient pressure under the Bardeen, Cooper, and Schrieffer framework. The highTccan be attributed to the strong electron-phonon coupling strength of 2.45, which arises from hydrogen implantation in lead that induces several high-frequency optical phonon modes with a relatively large phonon linewidth resulting from H atom vibration. The metallic-bonding in perovskite Pb4H not only improves the structural stability but also guarantees better ductility than the widely investigated multi-hydrogen, iron-based and cuprate superconductors. These results suggest that there is potential for the exploration of new high-temperature superconductors under ambient pressure and may reignite interest in their experimental synthesis in the near future.

Design, fabrication, and characterization of kinetic-inductive force sensors for scanning probe applications

We describe a transducer for low-temperature atomic force microscopy based on electromechanical coupling due to a strain-dependent kinetic inductance of a superconducting nanowire. The force sensor is a bending triangular plate (cantilever) whose deflection is measured via a shift in the resonant frequency of a high-Q superconducting microwave resonator at 4.5 GHz. We present design simulations including mechanical finite-element modeling of surface strain and electromagnetic simulations of meandering nanowires with large kinetic inductance. We discuss a lumped-element model of the force sensor and describe the role of an additional shunt inductance for tuning the coupling to the transmission line used to measure the microwave resonance. A detailed description of our fabrication is presented, including information about the process parameters used for each layer. We also discuss the fabrication of sharp tips on the cantilever using focused electron beam-induced deposition of platinum. Finally, we present measurements that characterize the spread of mechanical resonant frequency, the temperature dependence of the microwave resonance, and the sensor's operation as an electromechanical transducer of force.

Exploring disorder correlations in superconducting systems: spectroscopic insights and matrix element effects

Understanding the intricate interplay between disorder and superconductivity has become a key area of research in condensed matter physics, with profound implications for materials science. Recent studies have shown that spatial correlations of disorder potential can improve superconductivity, prompting a re-evaluation of some theoretical models. This paper explores the influence of disorder correlations on the fundamental properties of superconducting systems, going beyond the traditional assumption of spatially uncorrelated disorder. In particular, we investigate the influence of disorder correlations on key spectroscopic superconductor properties, including the density of states, as well as on the matrix elements of the superconducting coupling constant and their impact on the localization length. Our findings offer valuable insights into the role of disorder correlations in shaping the behavior of superconducting materials.

Resonant x-ray diffraction measurements in charge ordered kagome superconductors KV3Sb5and RbV3Sb5

We report on (resonant) x-ray diffraction experiments on the normal state properties of kagome-lattice superconductors KV3Sb5and RbV3Sb5. We have confirmed previous reports indicating that the charge density wave (CDW) phase is characterized by a doubling of the unit cell in all three crystallographic directions. By monitoring the temperature dependence of Bragg peaks associated with the CDW phase, we ascertained that it develops gradually over several degrees, as opposed to CsV3Sb5, where the CDW peak intensity saturates promptly just below the CDW transition temperature. Analysis of symmetry modes indicates that this behavior arises due to lattice distortions linked to the formation of CDWs. These distortions occur abruptly in CsV3Sb5, while they progress more gradually in RbV3Sb5and KV3Sb5. In contrast, the amplitude of the mode leading to the crystallographic symmetry breaking fromP6/mmmtoFmmmappears to develop more gradually in CsV3Sb5as well. Diffraction measurements close to the V K edge and the Sb L1edge show no sensitivity to inversion- or time-symmetry breaking, which are claimed to be associated with the onset of the CDW phase. The azimuthal angle dependence of the resonant diffraction intensity observed at the Sb L1edge is associated with the difference in the population of unoccupied states and the anisotropy of the electron density of certain Sb ions.

The Coexistence of Superconductivity and Topological Order in Van der Waals InNbS2

The research on systems with coexistence of superconductivity and nontrivial band topology has attracted widespread attention. However, the limited availability of material platforms severely hinders the research progress. Here, it reports the first experimental synthesis and measurement of high-quality single crystal van der Waals transition-metal dichalcogenide InNbS2 , revealing it as a topological nodal line semimetal with coexisting superconductivity. The temperature-dependent measurements of magnetization susceptibility and electrical transport show that InNbS2 is a type-II superconductor with a transition temperature Tc of 6 K. First-principles calculations predict multiple topological nodal ring states close to the Fermi level in the presence of spin-orbit coupling. Similar features are also observed in the as-synthesized BiNbS2 and PbNbS2 samples. This work provides new material platforms ANbS2 (A = In, Bi, and Pb) and uncovers their intriguing potential for exploring the interplay between superconductivity and band topology.

Anharmonic theory of superconductivity and its applications to emerging quantum materials

The role of anharmonicity on superconductivity has often been disregarded in the past. Recently, it has been recognized that anharmonic decoherence could play a fundamental role in determining the superconducting properties (electron-phonon coupling, critical temperature, etc) of a large class of materials, including systems close to structural soft-mode instabilities, amorphous solids and metals under extreme high-pressure conditions. Here, we review recent theoretical progress on the role of anharmonic effects, and in particular certain universal properties of anharmonic damping, on superconductivity. Our focus regards the combination of microscopic-agnostic effective theories for bosonic mediators with the well-established BCS theory and Migdal-Eliashberg theory for superconductivity. We discuss in detail the theoretical frameworks, their possible implementation within first-principles methods, and the experimental probes for anharmonic decoherence. Finally, we present several concrete applications to emerging quantum materials, including hydrides, ferroelectrics and systems with charge density wave instabilities.

Superconductivity in the High-Entropy Ceramics Ti0.2 Zr0.2 Nb0.2 Mo0.2 Ta0.2 Cx with Possible Nontrivial Band Topology

Topological superconductors have drawn significant interest from the scientific community due to the accompanying Majorana fermions. Here, the discovery of electronic structure and superconductivity (SC) in high-entropy ceramics Ti0.2 Zr0.2 Nb0.2 Mo0.2 Ta0.2 Cx (x = 1 and 0.8) combined with experiments and first-principles calculations is reported. The Ti0.2 Zr0.2 Nb0.2 Mo0.2 Ta0.2 Cx high-entropy ceramics show bulk type-II SC with Tc ≈ 4.00 K (x = 1) and 2.65 K (x = 0.8), respectively. The specific heat jump (∆C/γTc ) is equal to 1.45 (x = 1) and 1.52 (x = 0.8), close to the expected value of 1.43 for the BCS superconductor in the weak coupling limit. The high-pressure resistance measurements show a robust SC against high physical pressure in Ti0.2 Zr0.2 Nb0.2 Mo0.2 Ta0.2 C, with a slight Tc variation of 0.3 K within 82.5 GPa. Furthermore, the first-principles calculations indicate that the Dirac-like point exists in the electronic band structures of Ti0.2 Zr0.2 Nb0.2 Mo0.2 Ta0.2 C, which is potentially a topological superconductor. The Dirac-like point is mainly contributed by the d orbitals of transition metals M and the p orbitals of C. The high-entropy ceramics provide an excellent platform for the fabrication of novel quantum devices, and the study may spark significant future physics investigations in this intriguing material.

Bosonic excitation spectra of superconductingBi2Sr2CaCu2O8+δandYBa2Cu3O6+xextracted from scanning tunneling spectra

A detailed interpretation of scanning tunneling spectra obtained on unconventional superconductors enables one to gain information on the pairing boson. Decisive for this approach are inelastic tunneling events. Due to the lack of momentum conservation in tunneling from or to the sharp tip, those are enhanced in the geometry of a scanning tunneling microscope compared to planar tunnel junctions. This work extends the method of obtaining the bosonic excitation spectrum by deconvolution from tunneling spectra to nodald-wave superconductors. In particular, scanning tunneling spectra of slightly underdopedBi2Sr2CaCu2O8+δwith aTcof 82 K and optimally dopedYBa2Cu3O6+xwith aTcof 92 K reveal a resonance mode in their bosonic excitation spectrum atΩres≈63 meVandΩres≈61 meVrespectively. In both cases, the overall shape of the bosonic excitation spectrum is indicative of predominant spin scattering with a resonant mode atΩres<2Δand overdamped spin fluctuations for energies larger than 2Δ. To perform the deconvolution of the experimental data, we implemented an efficient iterative algorithm that significantly enhances the reliability of our analysis.

Superconductivity in Nb: Impact of Temperature, Dimensionality and Cooper-Pairing

The ability to realistically simulate the electronic structure of superconducting materials is important to understand and predict various properties emerging in both the superconducting topological and spintronics realms. We introduce a tight-binding implementation of the Bogoliubov-de Gennes method, parameterized from density functional theory, which we utilize to explore the bulk and thin films of Nb, known to host a significant superconducting gap. The latter is useful for various applications such as the exploration of trivial and topological in-gap states. Here, we focus on the simulation's aspects of superconductivity and study the impact of temperature, Cooper-pair coupling and dimensionality on the value of the superconducting pairing interactions and gaps.

Superconducting ternary hydrides in Ca-U-H under high pressure

The research on hydrogen-rich ternary compounds attract tremendous attention for it paves new route to room-temperature superconductivity at lower pressures. Here, we study the crystal structures, electronic structures, and superconducting properties of the ternary Ca-U-H system, combining crystal structure predictions withab-initiocalculations under high pressure. We found four dynamically stable structures with hydrogen clathrate cages: CaUH12-Cmmm, CaUH12-Fd-3m, Ca2UH18-P-3m1, and CaU3H32-Pm-3m. Among them, the Ca2UH18-P-3m1 and CaU3H32-Pm-3mare likely to be synthesized below 1 megabar. Thefelectrons in U atoms make dominant contribution to the electronic density of states around the Fermi energy. The electron-phonon interaction calculations reveal that phonon softening in the mid-frequency region can enhance the electron-phonon coupling significantly. TheTcvalue of Ca2UH18-P-3m1 is estimated to be 57.5-65.8 K at 100 GPa. Our studies demonstrate that introducing actinides into alkaline-earth metal hydrides provides possibility in designing novel superconducting ternary hydrides.

Atomic Diffusion-Induced Polarization and Superconductivity in Topological Insulator-Based Heterostructures

The proximity effect at a highly transparent interface of an s-wave superconductor (S) and a topological insulator (TI) provides a promising platform to create Majorana zero modes in artificially designed heterostructures. However, structural and chemical issues pertinent to such interfaces have been poorly explored so far. Here, we report the discovery of Pd diffusion-induced polarization at interfaces between superconductive Pd1+x(Bi0.4Te0.6)2 (xPBT, 0 ≤ x ≤ 1) and Pd-intercalated Bi2Te3 by using atomic-resolution scanning transmission electron microscopy. Our quantitative image analysis reveals that nanoscale lattice strain and QL polarity synergistically suppress and promote Pd diffusion at the normal and parallel interfaces, formed between Te-Pd-Bi triple layers (TLs) and Te-Bi-Te-Bi-Te quintuple layers (QLs), respectively. Further, our first-principles calculations unveil that the superconductivity of the xPBT phase and topological nature of the Pd-intercalated Bi2Te3 phase are robust against the broken inversion symmetry. These findings point out the necessity of considering the coexistence of electric polarization with superconductivity and topology in such S-TI systems.

Designing the stripe-ordered cuprate phase diagram through uniaxial-stress

The ability to efficiently control charge and spin in the cuprate high-temperature superconductors is crucial for fundamental research and underpins technological development. Here, we explore the tunability of magnetism, superconductivity, and crystal structure in the stripe phase of the cuprate La[Formula: see text]Ba[Formula: see text]CuO[Formula: see text], with [Formula: see text] = 0.115 and 0.135, by employing temperature-dependent (down to 400 mK) muon-spin rotation and AC susceptibility, as well as X-ray scattering experiments under compressive uniaxial stress in the CuO[Formula: see text] plane. A sixfold increase of the three-dimensional (3D) superconducting critical temperature [Formula: see text] and a full recovery of the 3D phase coherence is observed in both samples with the application of extremely low uniaxial stress of [Formula: see text]0.1 GPa. This finding demonstrates the removal of the well-known 1/8-anomaly of cuprates by uniaxial stress. On the other hand, the spin-stripe order temperature as well as the magnetic fraction at 400 mK show only a modest decrease under stress. Moreover, the onset temperatures of 3D superconductivity and spin-stripe order are very similar in the large stress regime. However, strain produces an inhomogeneous suppression of the spin-stripe order at elevated temperatures. Namely, a substantial decrease of the magnetic volume fraction and a full suppression of the low-temperature tetragonal structure is found under stress, which is a necessary condition for the development of the 3D superconducting phase with optimal [Formula: see text]. Our results evidence a remarkable cooperation between the long-range static spin-stripe order and the underlying crystalline order with the three-dimensional fully coherent superconductivity. Overall, these results suggest that the stripe- and the SC order may have a common physical mechanism.

High-temperature superconductivity up to 223 K in the Al stabilized metastable hexagonal lanthanum superhydride

As compressed hydrides constantly refresh the records of superconducting critical temperatures (Tc) in the vicinity of room temperature, this further reinforces the confidence to find more high-temperature superconducting hydrides. In this process, metastable phases of superhydrides offer enough possibilities to access superior superconducting properties. Here we report a metastable hexagonal lanthanum superhydride (P63/mmc-LaH10) stabilized at 146 GPa by introducing an appropriate proportion of Al, which exhibits high-temperature superconductivity with Tc ∼ 178 K, and this value is enhanced to a maximum Tc ∼ 223 K at 164 GPa. A huge upper critical magnetic field value Hc2(0) reaches 223 T at 146 GPa. The small volume expansion of P63/mmc-(La, Al) H10 compared with the binary LaH10 indicates the possible interstitial sites of Al atoms filling into the La-H lattice, instead of forming conventional ternary alloy-based superhydrides. This work provides a new strategy for metastable high-temperature superconductors through the multiple-element system.

Anisotropic Superconducting Nb2 CTx MXene Processed by Atomic Exchange at the Wafer Scale

Superconductivty has recently been induced in MXenes through surface modification. However, the previous reports have mostly been based on powders or cold-pressed pellets, with no known reports on the intrinsic superconsucting properties of MXenes at the nanoale. Here, it is developed a high-temperature atomic exchange process in NH3 atmosphere which induces superconductivity in either singleflakes or thin films of Nb2 CTx MXene. The exchange process between nitrogen atoms and fluorine, carbon, and oxygen atoms in the MXene lattice and related structural adjustments are studied using both experiments and density functional theory. Using either single-flake or thin-film devices, an anisotropic magnetic response of the 2D superconducting transformation has been successfully revealed. The anisotropic superconductivity is further demonstrated using superconducting thin films uniformly deposited over a 4 in. wafers, which opens up the possibility of scalable MXene-based superconducting devices.

Sampling the Materials Space for Conventional Superconducting Compounds

A large scale study of conventional superconducting materials using a machine-learning accelerated high-throughput workflow is performed, starting by creating a comprehensive dataset of around 7000 electron-phonon calculations performed with reasonable convergence parameters. This dataset is then used to train a robust machine learning model capable of predicting the electron-phonon and superconducting properties based on structural, compositional, and electronic ground-state properties. Using this machine, the transition temperatures (Tc ) of approximately 200 000 metallic compounds are evaluated, all of which are on the convex hull of thermodynamic stability (or close to it) to maximize the probability of synthesizability. Compounds predicted to have Tc values exceeding 5 K are further validated using density-functional perturbation theory. As a result, 541 compounds with Tc values surpassing 10 K, encompassing a variety of crystal structures and chemical compositions, are identified. This work is complemented with a detailed examination of several interesting materials, including nitrides, hydrides, and intermetallic compounds. Particularly noteworthy is LiMoN2 , which is predicted to be superconducting in the stoichiometric trigonal phase, with a Tc exceeding 38 K. LiMoN2 has previously been synthesized in this phase, further heightening its potential for practical applications.

Universal Stripe Symmetry of Short-Range Charge Density Waves in Cuprate Superconductors

The omnipresence of charge density waves (CDWs) across almost all cuprate families underpins a common organizing principle. However, a longstanding debate of whether its spatial symmetry is stripe or checkerboard remains unresolved. While CDWs in lanthanum- and yttrium-based cuprates possess a stripe symmetry, distinguishing these two scenarios is challenging for the short-range CDW in bismuth-based cuprates. Here, high-resolution resonant inelastic x-ray scattering is employed to uncover the spatial symmetry of the CDW in Bi2 Sr2 - x Lax CuO6 + δ . Across a wide range of doping and temperature, anisotropic CDW peaks with elliptical shapes are found in reciprocal space. Based on Fourier transform analysis of real-space models, the results are interpreted as evidence of unidirectional charge stripes, hosted by mutually 90°-rotated anisotropic domains. This work paves the way for a unified symmetry and microscopic description of CDW order in cuprates.

Investigation of Hafnium Thin Films for Design of TES Microcalorimeters

Hafnium is a superconductor with a transition temperature slightly above 100 mK. This makes it attractive for such applications as microcalorimeters with high energy resolution. We report the superconducting properties of Hf films of thicknesses ranging from 60 to 115 nm, deposited on Si and Al2O3 substrates by electron beam evaporation. Besides that, we fabricated and measured combinations of hafnium with thin layers of normal metals, decreasing the critical temperature by the proximity effect. The critical temperature of the studied films varied from 56 to 302 mK. We have observed a significant change in the critical temperature of some films over time, which we propose to prevent by covering hafnium films with a thin layer of titanium.

Shaping Graphene Superconductivity with Nanometer Precision

Graphene holds great potential for superconductivity due to its pure 2D nature, the ability to tune its carrier density through electrostatic gating, and its unique, relativistic-like electronic properties. At present, still far from controlling and understanding graphene superconductivity, mainly because the selective introduction of superconducting properties to graphene is experimentally very challenging. Here, a method is developed that enables shaping at will graphene superconductivity through a precise control of graphene-superconductor junctions. The method combines the proximity effect with scanning tunnelling microscope (STM) manipulation capabilities. Pb nano-islands are first grown that locally induce superconductivity in graphene. Using a STM, Pb nano-islands can be selectively displaced, over different types of graphene surfaces, with nanometre scale precision, in any direction, over distances of hundreds of nanometres. This opens an exciting playground where a large number of predefined graphene-superconductor hybrid structures can be investigated with atomic scale precision. To illustrate the potential, a series of experiments are performed, rationalized by the quasi-classical theory of superconductivity, going from the fundamental understanding of superconductor-graphene-superconductor heterostructures to the construction of superconductor nanocorrals, further used as "portable" experimental probes of local magnetic moments in graphene.

Pressure-Induced Superconductivity and Topological Quantum Phase Transitions in the Topological Semimetal ZrTe2

Topological transition metal dichalcogenides (TMDCs) have attracted much attention due to their potential applications in spintronics and quantum computations. In this work, the structural and electronic properties of topological TMDCs candidate ZrTe2 are systematically investigated under high pressure. A pressure-induced Lifshitz transition is evidenced by the change of charge carrier type as well as the Fermi surface. Superconductivity is observed at around 8.3 GPa without structural phase transition. A typical dome-shape phase diagram is obtained with the maximum Tc of 5.6 K for ZrTe2 . Furthermore, the theoretical calculations suggest the presence of multiple pressure-induced topological quantum phase transitions, which coexists with emergence of superconductivity. The results demonstrate that ZrTe2 with nontrivial topology of electronic states displays new ground states upon compression.

Crystal structure prediction and non-superconductivity of N-doped LuH3at near ambient pressure

Lanthanide polyhydrides, which have attracted the attention of researchers, are considered as a potential candidate material for high-temperature superconductivity. Especially, it is reported that N-doped LuH3exhibits near ambient superconductivity recently. It has attracted attention to room temperature superconductivity of ternary Lu-N-H systems at near ambient pressure. Here, we constructed a LuNH3(N-doped LuH3) compound to predict the crystal structural at relatively low pressures. We found a stable ternary LuNH3structure with a tetragonalP4mmphase under 5 GPa. In addition, ourTccalculations show that theP4mmLuNH3structure does not exhibit superconductivity down to 0.3 K at near ambient pressure due to the H atoms hardly contribute to acoustical phonons.

Pressure-induced disorder and nanosizing inhibits superconductivity in In2Te3

The generation of disorder often gives rise to profound and irreversible physical phenomena. Here, we explore the influence of disorder on the superconducting properties of In2Te3through comprehensive high-pressure investigations. Building upon previous findings, we investigated the progressive suppression of superconductivity in In2Te3during the depressurization process: the increased disorder that ultimately leads to the complete disappearance of the superconducting state. Simultaneously, our high-pressure x-ray diffraction analysis reveals an irreversible structural phase transition. Furthermore, microstructure analysis using transmission electron microscopy clearly demonstrates both grain refinement and a substantial enhancement of disorder. These findings not only provide valuable insights into the mechanism by which disorder suppresses superconductivity, but also offer guidance for future advancements in the fabrication of atmospheric-pressure superconductors.

Perturbing finite temperature multicomponent DFT 1D Kohn-Sham systems: Peierls gap & Kohn anomaly

One of the greatest challenges when designing new technologies that make use of non-trivial quantum materials is the difficulty associated with predicting material-specific properties, such as critical temperature, gap parameter, etc. There is naturally a great amount of interest in these types of condensed matter systems because of their application to quantum sensing, quantum electronics, and quantum computation; however, they are exceedingly difficult to address from first principles because of the famous many-body problem. For this reason, a full electron-nuclear quantum calculation will likely remain completely out of reach for the foreseeable future. A practical alternative is provided by finite temperature, multi component density functional theory, which is a formally exact method of computing the equilibrium state energy of a many-body quantum system. In this work, we use this construction alongside a perturbative scheme to demonstrate that the phenomena Peierls effect and Kohn anomaly are both natural features of the Kohn-Sham (KS) equations without additional structure needed. We find the temperature dependent ionic density for a simple 1D lattice which is then used to derive the ionic densities temperature dependent affect on the electronic band structure. This is accomplished by Fourier transforming the ionic density term found within this KS electronic equation. Using the Peierls effect phonon distortion gap openings in relation to the Fermi level, we then perturb the KS ionic equation with a conduction electron density, deriving the Kohn anomaly. This provides a workable predictive strategy for interesting electro-phonon related material properties which could be extended to 2D and 3D real materials while retaining the otherwise complicated temperature dependence.

Synthesis of superconducting phase of La0.5Ce0.5H10at high pressures

Clathrate hydrideFm3-m-LaH10has been proven as the most extraordinary superconductor with the critical temperatureTcabove 250 K upon compression of hundreds of GPa in recent years. A general hope is to reduce the stabilization pressure and maintain the highTcvalue of the specific phase in LaH10. However, strong structural instability distortsFm3-mstructure and leads to a rapid decrease ofTcat low pressures. Here, we investigate the phase stability and superconducting behaviors ofFm3-m-LaH10with enhanced chemical pre-compression through partly replacing La by Ce atoms from both experiments and calculations. For explicitly characterizing the synthesized hydride, we choose lanthanum-cerium alloy with stoichiometry composition of 1:1. X-ray diffraction and Raman scattering measurements reveal the stabilization ofFm3-m-La0.5Ce0.5H10in the pressure range of 140-160 GPa. Superconductivity withTcof 175 ± 2 K at 155 GPa is confirmed with the observation of the zero-resistivity state and supported by the theoretical calculations. These findings provide applicability in the future explorations for a large variety of hydrogen-rich hydrides.

Superconductivity Above 100 K Predicted in Carbon-Cage Network

To explore carbide superconductors with higher transition temperature, two novel carbon structures of cage-network are designed and their superconductivity is studied by doping metals. MC6 and MC10 are respectively identified as C24 and C32 cage-network structures. This study finds that both carbon structures drive strong electron-phonon interaction and can exhibit superconductivity above liquid nitrogen temperature. Importantly, the superconducting transition temperatures above 100 K are predicted to be achieved in C24 -cage-network systems doped by Na, Mg, Al, In, and Tl at ambient pressure, which is far higher than those in graphite, fullerene, and other carbides. Meanwhile, the superconductivity of cage-network carbides is also found to be sensitive to the electronegativity and concentration of dopant M. The result indicates that the higher transition temperatures can be obtained by optimizing the carbon-cage-network structures and the doping conditions. The study suggests that the carbon-cage-network structure is a direction to explore high-temperature superconducting carbides.

Kondo scattering in underdoped Nd1-xSrxNiO2 infinite-layer superconducting thin films

The recent discovery of superconductivity in infinite-layer nickelates generates tremendous research endeavors, but the ground state of their parent compounds is still under debate. Here, we report experimental evidence for the dominant role of Kondo scattering in the underdoped Nd1-xSrxNiO2 thin films. A resistivity minimum associated with logarithmic temperature dependence in both longitudinal and Hall resistivities are observed in the underdoped Nd1-xSrxNiO2 samples before the superconducting transition. At lower temperatures down to 0.04 K, the resistivities become saturated, following the prediction of the Kondo model. A linear scaling behavior [Formula: see text] between anomalous Hall conductivity [Formula: see text] and conductivity [Formula: see text]is revealed, verifying the dominant Kondo scattering at low temperature. The effect of weak (anti-)localization is found to be secondary. Our experiments can help in clarifying the basic physics in the underdoped Nd1-xSrxNiO2 infinite-layer thin films.

Ubiquitous coexisting electron-mode couplings in high-temperature cuprate superconductors

In conventional superconductors, electron-phonon coupling plays a dominant role in generating superconductivity. In high-temperature cuprate superconductors, the existence of electron coupling with phonons and other boson modes and its role in producing high-temperature superconductivity remain unclear. The evidence of electron-boson coupling mainly comes from angle-resolved photoemission (ARPES) observations of [Formula: see text]70-meV nodal dispersion kink and [Formula: see text]40-meV antinodal kink. However, the reported results are sporadic and the nature of the involved bosons is still under debate. Here we report findings of ubiquitous two coexisting electron-mode couplings in cuprate superconductors. By taking ultrahigh-resolution laser-based ARPES measurements, we found that the electrons are coupled simultaneously with two sharp modes at [Formula: see text]70meV and [Formula: see text]40meV in different superconductors with different dopings, over the entire momentum space and at different temperatures above and below the superconducting transition temperature. These observations favor phonons as the origin of the modes coupled with electrons and the observed electron-mode couplings are unusual because the associated energy scales do not exhibit an obvious energy shift across the superconducting transition. We further find that the well-known "peak-dip-hump" structure, which has long been considered a hallmark of superconductivity, is also omnipresent and consists of "peak-double dip-double hump" finer structures that originate from electron coupling with two sharp modes. These results provide a unified picture for the [Formula: see text]70-meV and [Formula: see text]40-meV energy scales and their evolutions with momentum, doping and temperature. They provide key information to understand the origin of these energy scales and their role in generating anomalous normal state and high-temperature superconductivity.

Current-voltage characteristics of focused ion beam fabricated superconducting tungsten meanders

We report on the superconducting properties and intermediate resistive steps (IRS) observed in the current-voltage characteristics (IVC) of tungsten meander (MW) structures fabricated using focused ion beam (FIB) technique. Three number of MWs were studied with individual wire widths of 240 nm, 640 nm and 850 nm with superconducting transition temperatures (TC) of 4.5 K, 4.55 K and 4.60 K respectively. The measured normal state resistance values at 8 K for these wires are of ∼182 kΩ, ∼49 kΩ and ∼32 kΩ, respectively as a function of increasing wire widths; are higher than the quantum of resistance (h/4e2=6.45kΩ,his a Planck constant andeis electronic charge) indicating extreme disorder nature of the fabricated samples. The variation of resistance with respect to temperature (forT Collapse

Key Words

• focused ion beam deposition
• intermediate resistive steps (IRS)
• meander structures
• phase slip (PS)
• superconductivity

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MESH Headings Collapse

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Affiliation(s)

Abhishek Kumar Quantum Nanophotonics Metrology Division, CSIR-National Physical Laboratory, Dr K. S. Krishnan Marg, New Delhi 110012, India Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
Sudhir Husale Quantum Nanophotonics Metrology Division, CSIR-National Physical Laboratory, Dr K. S. Krishnan Marg, New Delhi 110012, India Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
M P Saravanan Low Temperature Laboratory, UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452001, India
Bikash Gajar Quantum Nanophotonics Metrology Division, CSIR-National Physical Laboratory, Dr K. S. Krishnan Marg, New Delhi 110012, India Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
Majid Yousuf Quantum Nanophotonics Metrology Division, CSIR-National Physical Laboratory, Dr K. S. Krishnan Marg, New Delhi 110012, India Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
Abhilasha Saini Quantum Nanophotonics Metrology Division, CSIR-National Physical Laboratory, Dr K. S. Krishnan Marg, New Delhi 110012, India Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
Mahesh Gaurav Yadav Quantum Nanophotonics Metrology Division, CSIR-National Physical Laboratory, Dr K. S. Krishnan Marg, New Delhi 110012, India Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
R P Aloysius Quantum Nanophotonics Metrology Division, CSIR-National Physical Laboratory, Dr K. S. Krishnan Marg, New Delhi 110012, India Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India

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Anisotropy and isotope effect in superconducting solid hydrogen

Elucidating the phase diagram of solid hydrogen is a key objective in condensed matter physics. Several decades ago, it was proposed that at low temperatures and high pressures, solid hydrogen would be a metal with a high superconducting transition temperature. This transition to a metallic state can happen through the closing of the energy gap in the molecular solid or through a transition to an atomic solid. Recent experiments have managed to reach pressures in the range of 400-500 GPa, providing valuable insights. There is strong evidence suggesting that metallization via either of these mechanisms occurs within this pressure range. Computational and experimental studies have identified multiple promising crystal phases, but the limited accuracy of calculations and the limited capabilities of experiments prevent us from determining unequivocally the observed phase or phases. Therefore, it is crucial to investigate the superconducting properties of all the candidate phases. Recently, we reported the superconducting properties of theC2/c-24,Cmca-12,Cmca-4 andI41/amd-2 phases, including anharmonic effects. Here, we report the effects of anisotropy on superconducting properties using Eliashberg theory. Then, we investigate the superconducting properties of deuterium and estimate the size of the isotope effect for each phase. We find that the isotope effect on superconductivity is diminished by anharmonicity in theC2/c-24 andCmca-12 phases and enlarged in theCmca-4 andI41/amd-2 phases. Our anharmonic calculations of theC2/c-24 phase of deuterium agree closely with the most recent experiment by Loubeyreet al(2022Phys. Rev. Lett.29035501), indicating that theC2/c-24 phase remains the leading candidate in this pressure range, and has a strong anharmonic character. These characteristics can serve to distinguish among crystal phases in experiment. Furthermore, expanding our understanding of superconductivity in pure hydrogen holds significance in the study of high-Tchydrides.

Pseudogap in BaPbxBi1‒xO3(x = 0.7, 0.75 and 1.0)

In this work, we have investigated the crystal and electronic structure of the orthorhombic phase of BaPbxBi1-xO3(BPBO) forx = 0.7 (BPBO70), 0.75 (BPBO75) and 1.0 (BPO), using temperature dependent x-ray diffraction measurements, photoemission spectroscopy, and electronic structure calculations. Our results show the importance of particle size and strain in governing superconductivity. Interestingly, the temperature evolution of the structural parameters in the case of BPBO70 is similar to that of BPBO75 but the magnitude of the change is diminished. The BPBO75 and BPO compounds exhibit metallic nature, which is corroborated by the core level studies. The electronic structure calculations in conjunction with the core level studies suggest that oxygen vacancies play an important role for metallicity observed in the end compound. The exponent to the spectral line shape close to the Fermi level suggests the origin of pseudogap to be due to other contributions in addition to disorder in the case of BPBO70 and BPO. The core level studies also show that as one goes fromx = 0.70 to 1.0, there occurs chemical potential shift towards the valence band suggesting hole doping. Our results open the venue to further study these compounds as a function of particle size, nature of carriers for its transport behaviour, electronic structure belowTC, composition at the grain boundaries and microscopic origin of pseudogap in the non-superconducting phase. We believe that our results call for a revision of the temperature-doping phase diagram of BPBO to include the pseudogap phase.

Non-Fermi-Liquid Behavior of Superconducting SnH4

The chemical interaction of Sn with H2 by X-ray diffraction methods at pressures of 180-210 GPa is studied. A previously unknown tetrahydride SnH4 with a cubic structure (fcc) exhibiting superconducting properties below TC  = 72 K is obtained; the formation of a high molecular C2/m-SnH14 superhydride and several lower hydrides, fcc SnH2 , and C2-Sn12 H18 , is also detected. The temperature dependence of critical current density JC (T) in SnH4 yields the superconducting gap 2Δ(0) = 21.6 meV at 180 GPa. SnH4 has unusual behavior in strong magnetic fields: B,T-linear dependences of magnetoresistance and the upper critical magnetic field BC2 (T) ∝ (TC - T). The latter contradicts the Wertheimer-Helfand-Hohenberg model developed for conventional superconductors. Along with this, the temperature dependence of electrical resistance of fcc SnH4 in non-superconducting state exhibits a deviation from what is expected for phonon-mediated scattering described by the Bloch-Grüneisen model and is beyond the framework of the Fermi liquid theory. Such anomalies occur for many superhydrides, making them much closer to cuprates than previously believed.

Discovery of a Superconductor Bi5 O4 S3 Cl Containing the Unique BiS3 Layer

The BiS2 -based layered superconductors with structures similar to those of cuprates and iron-based superconductors have stimulated much research interest. Here, a new quaternary compound is reported, Bi5 O4 S3 Cl, which crystalizes in a tetragonal structure with P4/mmm (No. 123) space group having alternately stacking unique BiS3 layers and Bi2 O2 layers along the c-axis with a Cl atom located at the center of the unit cell. A superconducting transition above 3 K is observed for both electrical transport and magnetic measurements. Hall resistivity measurements show its multiband character with a conduction dominated by electron-like charge carriers. The first-principles calculations exhibit that the semiconducting parent phase Bi5 O4 S3 Cl becomes metallic when sulfur vacancies are introduced, which hints the origin of superconductivity in Bi5 O4 S3 Cl. The findings will inspire the exploration of new BiS-based superconductors.

Promoted Electronic Coupling of Acoustic Phonon Modes in Doped Semimetallic MoTe2

As a prototype of the Weyl superconductor, layered molybdenum ditelluride (MoTe2) encompasses two semimetallic phases (1T' and Td) which differentiate from each other via a slight tilting of the out-of-plane lattice. Both phases are subjected to serious phase mixing, which complicates the analysis of its origin of superconductivity. Herein, we explore the electron-phonon coupling (EPC) of the monolayer semimetallic MoTe2, without phase ambiguity under this thickness limit. Apart from the hardening or softening of the phonon modes, the strength of the EPC can be strongly modulated by doping. Specifically, longitudinal and out-of-plane acoustic modes are significantly activated for electron doped MoTe2. This is ascribed to the presence of rich valley states and equispaced nesting bands, which are dynamically populated under charge doping. Through comparing the monolayer and bilayer MoTe2, the strength of EPC is found to be less likely to depend on thickness for neutral samples but clearly promoted for thinner samples with electron doping, while for hole doping, the strength alters more significantly with the thickness than doping. Our work explains the issue of the doping sensitivity of the superconductivity in semimetallic MoTe2 and establishes the critical role of activating acoustic phonons in such low-dimensional materials.

Superconductivity and phase transitions in Kagome compound Pd3P2S8from first-principles calculation

Pd3P2S8is a semiconductor that contains Kagome lattices, which exhibits various physical phenomena. Structural searches of Pd3P2S8in the pressure range from 0 to 120 GPa have revealed two phases of the space groupP3‾m1(designated asP3‾m1-1 andP3‾m1-2) and two phases of the space groupC2/m(designated asC2/m-1 andC2/m-2), with all butC2/m-2 phase being dynamically stable. Electron-phonon calculations combined with Bardeen-Cooper-Schrieffer's argument have shown that both phases are superconductors. Notably, theP3‾m1-1 phase undergoes a semiconductor-to-superconductor transition, with superconducting critical temperature (Tc) increasing up to a maximum of 9.13 K at 70 GPa. BothC2/m-1 andP3‾m1-2 phases exhibit superconductivity at 0 GPa. Our calculations demonstrate several new superconducting phases of Pd3P2S8, providing a pathway and platform for exploring superconductivity in materials with Kagome lattices and expanding the options for studying such lattices.

Thickness-Dependent Superconductivity in a Layered Electride on Silicon

Layered materials exhibit a plethora of fascinating properties. The challenge is to make the materials into epitaxial films, preferably integrated with mature technological platforms to facilitate their potential applications. Progress in this direction can establish the film thickness as a valuable parameter to control various phenomena, superconductivity in particular. Here, a synthetic route to epitaxial films of SrAlSi, a layered superconducting electride, on silicon is designed. A set of films ranging in thickness is synthesized employing a silicene-based template. Their structure and superconductivity are explored by a combination of techniques. Two regimes of TC dependence on the film thickness are identified, the coherence length being the crossover parameter. The results can be extended to syntheses of other honeycomb-lattice ternary compounds on Si or Ge exhibiting superconducting, magnetic, and other properties.

Gate-Defined Josephson Weak-Links in Monolayer WTe2

Systems combining superconductors with topological insulators offer a platform for the study of Majorana bound states and a possible route to realize fault tolerant topological quantum computation. Among the systems being considered in this field, monolayers of tungsten ditelluride (WTe2 ) have a rare combination of properties. Notably, it has been demonstrated to be a quantum spin Hall insulator (QSHI) and can easily be gated into a superconducting state. Measurements on gate-defined Josephson weak-link devices fabricated using monolayer WTe2 are reported. It is found that consideration of the 2D superconducting leads are critical in the interpretation of magnetic interference in the resulting junctions. The reported fabrication procedures suggest a facile way to produce further devices from this technically challenging material and the results mark the first step toward realizing versatile all-in-one topological Josephson weak-links using monolayer WTe2 .

Enhanced Superconducting Critical Parameters in a New High-Entropy Alloy Nb0.34Ti0.33Zr0.14Ta0.11Hf0.08

The structural and physical properties of the new titanium- and niobium-rich type-A high-entropy alloy (HEA) superconductor Nb0.34Ti0.33Zr0.14Ta0.11Hf0.08 (in at.%) were studied by X-ray powder diffraction, energy dispersive X-ray spectroscopy, magnetization, electrical resistivity, and specific heat measurements. In addition, electronic structure calculations were performed using two complementary methods: the Korringa-Kohn-Rostoker Coherent Potential Approximation (KKR-CPA) and the Projector Augmented Wave (PAW) within Density Functional Theory (DFT). The results obtained indicate that the alloy exhibits type II superconductivity with a critical temperature close to 7.5 K, an intermediate electron-phonon coupling, and an upper critical field of 12.2(1) T. This finding indicates that Nb0.34Ti0.33Zr0.14Ta0.11Hf0.08 has one of the highest upper critical fields among all known HEA superconductors.

Atomic-Layer Engineering of La2-xSrxCuO4-La2-xSrxZnO4 Heterostructures

The fabrication of trilayer superconductor-insulator-superconductor (SIS) Josephson junctions with high-temperature superconductor (HTS) electrodes requires atomically perfect interfaces. Therefore, despite great interest and efforts, this remained a challenge for over three decades. Here, we report the discovery of a new family of metastable materials, La2-xSrxZnO4 (LSZO), synthesized by atomic-layer-by-layer molecular beam epitaxy (ALL-MBE). We show that LSZO is insulating and epitaxially compatible with an HTS compound, La2-xSrxCuO4 (LSCO). Since the "parent" compound La2ZnO4 (LZO) is easier to grow, here we focus on this material as our insulating layer. Growing LZO at very low temperatures to reduce cation interdiffusion makes LSCO/LZO interfaces atomically sharp. We show that in LSCO/LZO/LSCO trilayers, the superconducting properties of the LSCO electrodes remain undiminished, unlike in previous attempts with insulator barriers made of other materials. This opens prospects to produce high-quality HTS tunnel junctions.

Bio-Inspired Design of Superconducting Spiking Neuron and Synapse

The imitative modelling of processes in the brain of living beings is an ambitious task. However, advances in the complexity of existing hardware brain models are limited by their low speed and high energy consumption. A superconducting circuit with Josephson junctions closely mimics the neuronal membrane with channels involved in the operation of the sodium-potassium pump. The dynamic processes in such a system are characterised by a duration of picoseconds and an energy level of attojoules. In this work, two superconducting models of a biological neuron are studied. New modes of their operation are identified, including the so-called bursting mode, which plays an important role in biological neural networks. The possibility of switching between different modes in situ is shown, providing the possibility of dynamic control of the system. A synaptic connection that mimics the short-term potentiation of a biological synapse is developed and demonstrated. Finally, the simplest two-neuron chain comprising the proposed bio-inspired components is simulated, and the prospects of superconducting hardware biosimilars are briefly discussed.