Quasilinear quantum magnetoresistance in pressure-induced nonsymmorphic superconductor chromium arsenide

Ratio of 4:1 between ZnGeAs2and MnAs phases in a single composite and its impact on the structure-driven magnetoresistance

A strong influence of the lattice degree of freedom on magnetoresistance (MR) under high pressure underlies the conception of 'structure-driven' magnetoresistance (SDMR). In most magnetic or topological materials, the suppression of MR with increasing pressure is a general trend, while for some magnetic composites the MR enhances and even shows unusual behavior as a consequence of structural transition. Here we investigated the SDMR in the composite material based on the ZnGeAs2semiconductor matrix and MnAs magnetic inclusions in a phase ratio of 4:1. At ambient pressure, its magnetic and transport properties are governed by MnAs inclusions, i.e. it shows a Curie temperatureTC≈ 320 K and metallic-like conductivity. Under high pressure, the low-field room temperature MR undergoes multiple changes in the pressure range up to 7.2 GPa. The structural transition in the ZnGeAs2matrix has been found at ∼6 GPa, slightly lower than in the pure ZnGeAs2(6.2 GPa). The huge SDMR as high as 85% at 6.8 GPa and 2.5 kOe, which contains both positive and negative MR components, is accompanied by a pressure-induced metallic-like-to-semiconductor-like transition and the enhanced ferromagnetic order of MnAs inclusions. This observation offers a competing mechanism between the robust extrinsic ferromagnetism and high-pressure electronic properties of ZnGeAs2.

Shubnikov-de Haas oscillations and nontrivial topological states in Weyl semimetal candidate SmAlSi

The RAlX (R = Light rare earth; X = Ge, Si) compounds, as a family of magnetic Weyl semimetal, have recently attracted growing attention due to the tunability of Weyl nodes and its interactions with diverse magnetism by rare-earth atoms. Here, we report the magnetotransport evidence and electronic structure calculations on nontrivial band topology of SmAlSi, a new member of this family. At low temperatures, SmAlSi exhibits large non-saturated magnetoresistance (MR) (as large as ∼5500% at 2 K and 48 T) and distinct Shubnikov-de Haas (SdH) oscillations. The field dependent MRs at 2 K deviate from the semiclassical (μ₀H)²variation but follow the power-law relation MR∝(μ₀H)^mwith a crossover fromm∼ 1.52 at low fields (μ₀H< 15 T) tom∼ 1 under high fields (μ₀H> 18 T), which is attributed to the existence of Weyl points and electron-hole compensated characteristics with high mobility. From the analysis of SdH oscillations, two fundamental frequencies originating from the Fermi surface pockets with non-trivialπBerry phases and small cyclotron mass can be identified, this feature is supported by the calculated electronic band structures with two Weyl pockets near the Fermi level. Our study establishes SmAlSi as a paradigm for researching the novel topological states of RAlX family.

Effect of pressure on electronic, mechanical, and dynamic properties for orthorhombic WP

The structural, mechanical, electronic, and dynamic features of MnP-type WP have been presented under 0-50 GPa hydrostatic pressure utilizing density functional theory. The lattice constants, values of volume, and bond lengths are decreased with increasing pressure. It is found that the results of electronic band structures show that WP preserves its metallic feature under the pressure. The electronic band structures are shifted up in Y–Γ and Γ–X symmetry points under pressure. The partial density of the states indicates that hybridization occurs between W-d and P-p orbitals and also W–d orbital is dominated at all pressures. It is obtained that the mechanical properties of WP are increased with the increasing pressure. Additionally, the WP becomes more ductile under pressure. According to phonon dispersions, it is investigated that WP is dynamically stable under pressure.

Patterned diamond anvils prepared via laser writing for electrical transport measurements of thin quantum materials under pressure

Quantum materials exhibit intriguing properties with important scientific values and huge technological potential. Electrical transport measurements under hydrostatic pressure have been influential in unraveling the underlying physics of many quantum materials in bulk form. However, such measurements have not been applied widely to samples in the form of thin flakes, in which new phenomena can emerge, due to the difficulty in attaching fine wires to a thin sample suitable for high-pressure devices. Here, we utilize a home-built direct laser writing system to functionalize a diamond anvil to directly integrate the capability of conducting electrical transport measurements of thin flakes with a pressure cell. With our methodology, the culet of a diamond anvil is equipped with a set of custom-designed conducting tracks. We demonstrate the superiority of these tracks as electrodes for the studies of thin flakes by presenting the measurement of pressure-enhanced superconductivity and quantum oscillations in a flake of MoTe₂.

Dimensionality of the Superconductivity in the Transition Metal Pnictide WP

We report theoretical and experimental results on the transition metal pnictide WP. The theoretical outcomes based on tight-binding calculations and density functional theory indicate that WP is a three-dimensional superconductor with an anisotropic electronic structure and nonsymmorphic symmetries. On the other hand, magnetoresistance experimental data and the analysis of superconducting fluctuations of the conductivity in external magnetic field indicate a weakly anisotropic three-dimensional superconducting phase.

Topologically driven linear magnetoresistance in helimagnetic FeP

The helimagnet FeP is part of a family of binary pnictide materials with the MnP-type structure, which share a nonsymmorphic crystal symmetry that preserves generic band structure characteristics through changes in elemental composition. It shows many similarities, including in its magnetic order, to isostructural CrAs and MnP, two compounds that are driven to superconductivity under applied pressure. Here we present a series of high magnetic field experiments on high-quality single crystals of FeP, showing that the resistance not only increases without saturation by up to several hundred times its zero-field value by 35 T, but that it also exhibits an anomalously linear field dependence over the entire range when the field is aligned precisely along the crystallographic c-axis. A close comparison of quantum oscillation frequencies to electronic structure calculations links this orientation to a semi-Dirac point in the band structure, which disperses linearly in a single direction in the plane perpendicular to field, a symmetry-protected feature of this entire material family. We show that the two striking features of magnetoresistance-large amplitude and linear field dependence-arise separately in this system, with the latter likely due to a combination of ordered magnetism and topological band structure.

Z_{4} Topological Superconductivity in UCoGe

Topological nonsymmorphic crystalline superconductivity (TNCS) is an intriguing phase of matter, offering a platform to study the interplay between topology, superconductivity, and nonsymmorphic crystalline symmetries. Interestingly, some of TNCSs are classified into Z_{4} topological phases, which have unique surface states referred to as a Möbius strip or an hourglass, and they have not been achieved in symmorphic superconductors. However, material realization of Z_{4} TNCS has never been known, to the best of our knowledge. Here, we propose that the paramagnetic superconducting phase of UCoGe under pressure is a promising candidate of Z_{4}-nontrivial TNCS enriched by glide symmetry. We evaluate Z_{4} invariants of UCoGe by deriving the formulas relating Z_{4} invariants to the topology of Fermi surfaces. Applying the formulas and previous ab initio calculations, we clarify that three odd-parity representations out of four are Z_{4}-nontrivial TNCS, whereas the other is also Z_{2}-nontrivial TNCS. We also discuss possible Z_{4} TNCS in CrAs and related materials.

Progress in Cr- and Mn-based superconductors: a key issues review

The presence of magnetic ions was first believed to be detrimental to superconductivity. However, unconventional superconductivity has been widely induced by doping or applying external pressure in magnetic systems such as heavy fermion, cuprate and iron-based superconductors in which magnetic fluctuations are suggested to serve as the pairing glue for Cooper pairs. The discovery of superconductivity in the magnetic compounds CrAs and MnP under high pressures has further expanded this family of superconductors and provided new platforms for investigating the interplay between magnetism and superconductivity. CrAs and MnP represent the first superconductors among the transition metal Cr- and Mn-based compounds in which the electronic states near the Fermi level are dominated by Cr/Mn 3d electrons. Shortly after their discovery, new types of Cr-based quasi-one-dimensional superconductors A₂Cr₃As₃ and ACr₃As₃ (A [Formula: see text] K, Rb, Cs or Na) were discovered at ambient pressure. The close proximity of superconductivity to magnetic instability in these systems suggests that spin fluctuations may play crucial roles in mediating the Cooper pairing. In this article we review the basic physical properties of these novel superconductors and the progress achieved in recent studies.