High-temperature Josephson diode

Many superconducting systems with broken time-reversal and inversion symmetry show a superconducting diode effect, a non-reciprocal phenomenon analogous to semiconducting p-n-junction diodes. While the superconducting diode effect lays the foundation for realizing ultralow dissipative circuits, Josephson-phenomena-based diode effect (JDE) can enable the realization of protected qubits. The superconducting diode effect and JDE reported thus far are at low temperatures (~4 K), limiting their applications. Here we demonstrate JDE persisting up to 77 K using an artificial Josephson junction of twisted layers of Bi2Sr2CaCu2O8+δ. JDE manifests as an asymmetry in the magnitude and distributions of switching currents, attaining the maximum at 45° twist. The asymmetry is induced by and tunable with a very small magnetic field applied perpendicular to the junction and arises due to interaction between Josephson and Abrikosov vortices. We report a large asymmetry of 60% at 20 K. Our results provide a path towards realizing superconducting Josephson circuits at liquid-nitrogen temperature.

Crossover from gapped-to-gapless Dirac surface states in magnetic topological insulator MnBi2Te4

Intrinsic magnetic topological insulators (MTIs) host exotic topological phases such as quantized anomalous Hall insulating phase, arising due to the large magnetic exchange gap. However, the interplay of magnetism and topology in these systems in different temperature regimes remains elusive. In this work, we present the logarithmic temperature-dependence of conductivity for sub-100 nm thick exfoliated flakes of MTI MnBi2Te4in the presence of out-of-plane magnetic fields and extracted the linear slope,κ. We observed a characteristic change,Δκ∼-0.5in the low-temperature regime, indicating the gapped Dirac surface state according to Lu-Shen theory. We also report the recovery of topological properties in the system via the weak-antilocalization effect in the vicinity of antiferromagnetic to paramagnetic transition and in the paramagnetic regime. Hikami-Larkin-Nagaoka analysis suggested the presence of topological surface states. Therefore, our study helps in understanding how intrinsic magnetism masks topological properties in an MTI as long as magnetic ordering persists.

Layer-resolved electronic behavior in a Kondo lattice system, CeAgAs2

We investigate the electronic structure of an antiferromagnetic Kondo lattice system CeAgAs₂employing hardx-ray photoemission spectroscopy. CeAgAs₂, an orthorhombic variant of HfCuSi₂structure, exhibits antiferromagnetic ground state, Kondo like resistivity upturn and compensation of magnetic moments at low temperatures. The photoemission spectra obtained at different photon energies suggest termination of the cleaved surface at cis-trans-As layers. The depth-resolved data show significant surface-bulk differences in the As and Ce core level spectra. The As 2pbulk spectrum shows distinct two peaks corresponding to two different As layers. The peak at higher binding energy correspond to cis-trans-As layers and is weakly hybridized with the adjacent Ce layers. The As layers between Ce and Ag-layers possess close to trivalent configuration due to strong hybridization with the neighboring atoms and the corresponding feature appear at lower binding energy. Ce 3dcore level spectra show multiple features reflecting strong Ce-As hybridization and strong correlation. Intensef₀peak is observed in the surface spectrum while it is insignificant in the bulk. In addition, we observe a features at binding energy lower than the well-screened feature indicating the presence of additional interactions. This feature becomes more intense in the bulk spectra suggesting it to be a bulk property. Increase in temperature leads to a spectral weight transfer to higher binding energies in the core level spectra and a depletion of spectral intensity at the Fermi level as expected in a Kondo material. These results reveal interesting surface-bulk differences, complex interplay of intra- and inter-layer covalency, and electron correlation in the electronic structure of this novel Kondo lattice system.

Evidence of the Anomalous Fluctuating Magnetic State by Pressure-Driven 4f Valence Change in EuNiGe3

In rare-earth compounds with valence fluctuation, the proximity of the 4f level to the Fermi energy leads to instabilities of the charge configuration and the magnetic moment. Here, we provide direct experimental evidence for an induced magnetic polarization of the Eu³⁺ atomic shell with J = 0, due to intra-atomic exchange and spin-orbital coupling interactions with the Eu²⁺ atomic shell. By applying external pressure, a transition from antiferromagnetic to a fluctuating behavior in EuNiGe₃ single crystals is probed. Magnetic polarization is observed for both valence states of Eu²⁺ and Eu³⁺ across the entire pressure range. The anomalous magnetism is discussed in terms of a homogeneous intermediate valence state where frustrated Dzyaloshinskii-Moriya couplings are enhanced by the onset of spin-orbital interaction and engender a chiral spin-liquid-like precursor.

Shubnikov-de Haas and de Haas-van Alphen oscillations in Czochralski grown CoSi single crystal

Anisotropic transport, Shubnikov-de Haas (SdH), and de Haas-van Alphen (dHvA) quantum oscillations studies are reported on a high-quality CoSi single crystal grown by the Czochralski method. Temperature-dependent resistivities indicate the dominating electron-electron scattering. Magnetoresistance (MR) at 2 K reaches 610% forI ∥ [111]andB ∥ [011-], whereas it is 500% forI ∥ [011-] andB ∥ [111]. A negative slope in field-dependent Hall resistivity suggests electrons are the majority carriers. The carrier concentration extracted from Hall conductivity indicates no electron-hole compensation. In 3D CoSi, the electron transport lifetime is found to be approximately in the same order as the quantum lifetime, whereas in 2Delectron gas the long-range scattering drives the transport life much larger than the quantum lifetime. From MR and Hall SdH oscillations, the effective masses and Dingle temperatures have been calculated. The dHvA oscillation reveals three frequencies at 18 T (γ), 558 T (α) and 663 T (β), whereas, SdH oscillation results in only two frequenciesαandβ. Theγfrequency observed in dHvA oscillation is a tiny hole pocket at the Γ point.

Orthorhombic charge density wave on the tetragonal lattice of EuAl4

EuAl₄ possesses the BaAl₄ crystal structure type with tetragonal symmetry I4/mmm. It undergoes a charge density wave (CDW) transition at T _CDW = 145 K and features four consecutive antiferromagnetic phase transitions below 16 K. Here we use single-crystal X-ray diffraction to determine the incommensurately modulated crystal structure of EuAl₄ in its CDW state. The CDW is shown to be incommensurate with modulation wave vector q = (0,0,0.1781 (3)) at 70 K. The symmetry of the incommensurately modulated crystal structure is orthorhombic with superspace group Fmmm(00σ)s00, where Fmmm is a subgroup of I4/mmm of index 2. Both the lattice and the atomic coordinates of the basic structure remain tetragonal. Symmetry breaking is entirely due to the modulation wave, where atoms Eu and Al1 have displacements exclusively along a, while the fourfold rotation would require equal displacement amplitudes along a and b. The calculated band structure of the basic structure and interatomic distances in the modulated crystal structure both indicate the Al atoms as the location of the CDW. The tem-per-ature dependence of the specific heat reveals an anomaly at T _CDW = 145 K of a magnitude similar to canonical CDW systems. The present discovery of orthorhombic symmetry for the CDW state of EuAl₄ leads to the suggestion of monoclinic instead of orthorhombic symmetry for the third AFM state.

Superconductivity in Heusler compound ScAu2Al

We report superconducting state properties and electronic structure of a full Heusler material ScAu₂Al. The resistivity measurement indicates a zero-field (at nominal Earth's field) superconducting transition temperature,T_c= 5.12 K (in contrary to the previously reported value of 4.4 K), which falls in the highestT_c-regime among the Heusler superconductors. The magnetization data shows that ScAu₂Al is a moderate type-II superconductor, where the critical field values can be estimated from the Ginzburg-Landau-Abrikosov-Gorkov theory. The field-dependent magnetization response further shows signatures of flux jump in ScAu₂Al. A sharp jump in the temperature dependent specific heat (C_p) data confirms bulk superconductivity. We report that the electron-phonon coupling constant,λ_e-ph= 0.77, suggesting a moderate electron-phonon coupling in ScAu₂Al. Further, we show that the observedλ_e-phvalue in ScAu₂Al is the highest amongst the reported Heusler superconductors, indicating strong correlation betweenT_candλ_e-phvalues and significant role of electron-phonon coupling in mediating superconductivity in Heusler superconductors. Finally, we discuss the electronic properties and reveal the existence of van Hove singularity near the Fermi level in ScAu₂Al.

Evolution of local structure and superconductivity in CaFe2As2

We investigate the evolution of the local structural parameters and their implication in unconventional superconductivity of 122 class of materials employing extended x-ray absorption fine structure studies. The spectral functions near the FeK- and AsK-absorption edges of CaFe₂As₂and its superconducting composition, CaFe_1.9Co_0.1As₂(T_c= 12 K) exhibit evidence of enhancement of Fe contributions near the Fermi level with Co substitution, which becomes more prominent at low temperatures indicating enhanced role of Fe in the electronic properties with doping. As-Fe and Fe-Fe bondlengths derived from the experimental data reveal evolution with temperature across the magneto-structural transition in the parent compound. The evolution of these parameters in Co-doped superconducting composition is similar to its parent compound although no magneto-structural transition is observed in this system. These results reveal an evidence of doping induced evolution to the proximity to critical behavior and/or strong nematic fluctuations which might be important for superconductivity in this system.

Observation of Standing Spin Waves in a van der Waals Magnetic Material

Spin waves are studied for data storage, communication, and logic circuits in the field of spintronics based on their potential to substitute electrons. The recent discovery of magnetism in 2D systems such as monolayer CrI₃ and Cr₂ Ge₂ Te₆ has led to a renewed interest in such applications of magnetism in the 2D limit. Here, direct evidence of standing spin waves is presented along with the uniform precessional resonance modes in the van der Waals magnetic material, CrCl₃ . This is the first direct observation of standing spin-wave modes, set up along a thickness of 20 mm, in a van der Waals material. Standing spin waves are detected in the vicinity of both branches, optical and acoustic, of the antiferromagnetic resonance. Magnon-magnon coupling and softening of resonance modes with temperature enable extraction of interlayer exchange field as a function of temperature.

On-Demand Local Modification of High-Tc Superconductivity in Few Unit-Cell Thick Bi2 Sr2 CaCu2 O8+δ

High-temperature superconductors (HTSs) are important for potential applications and for understanding the origin of strong correlations. Bi₂ Sr₂ CaCu₂ O_8+δ (BSCCO), a van der Waals material, offers a platform to probe the physics down to a unit-cell. Guiding the flow of electrons by patterning 2DEGS and oxide heterostructures has brought new functionality and access to new science. Similarly, modifying superconductivity in HTS locally, on a small length scale, is of immense interest for superconducting electronics. A route to modify superconductivity locally by depositing metal on the surface is reported here by transport studies on few unit-cell thick BSCCO. Deposition of chromium (Cr) on the surface over a selected area of BSCCO results in insulating behavior of the underlying region. Cr locally depletes oxygen in CuO₂ planes and disrupts the superconductivity in the layers below. This technique of modifying superconductivity is suitable for making sub-micrometer superconducting wires and more complex superconducting devices.

Magnetotransport properties of noncentrosymmetric CaAgBi single crystal

We report on the single crystal growth and transport properties of a topological semimetal CaAgBi which crystallizes in the hexagonal ABC-type structure with the non-centrosymmetric space groupP63mc(No. 186). The transverse magnetoresistance measurements with current in the basal plane of the hexagonal crystal structure reveal a value of about 30% forI∥[10̄0] direction and about 50% forI∥[1̅10] direction at 10 K in an applied magnetic field of 14 T. The magnetoresistance shows a cusp-like behavior in the low magnetic field region, suggesting the presence of weak antilocalization effect for temperatures less than 100 K. The Hall measurements reveal that predominant charge carriers are p-type, exhibiting a linear behavior at high fields. The magnetoconductance of CaAgBi is analyzed based on the modified Hikami-Larkin-Nagaoka model. Our first-principle calculations within a density-functional theory framework reveal that the Fermi surface of CaAgBi consists of both the electron and hole pockets and the size of the hole pocket is much larger than electron pockets suggesting the dominant p-type carriers in accordance with our experimental results.

Complex hybridization physics in CaFe2As2- a high resolution hard x-ray photoemission study

Employing high resolution hard x-ray photoemission spectroscopy, we investigate the electronic structure of an exotic Fe-based superconductor, CaFe2As2, which exhibits rich temperature pressure phase diagram and dichotomy on achieving superconductivity on application of pressure. The experimental valence band spectra exhibit significant differences for experiments at different surface sensitivities. We discover that the change in angle between light polarization and surface normal leads to similar orbital selective spectral response suggesting requirement of different methodology to probe the surface-bulk differences. Thus, the final state effects of the core level spectroscopy has been exploited to reveal the depth-resolved information. Strong features related to plasmon excitations have been observed in various core level spectra. Ca 2p spectra exhibit evidence of significant hybridization with the conduction electrons, and distinct features corresponding to the surface and bulk electronic structures while As core levels remain unaffected. The depth-resolved Fe 2p spectra at different temperatures exhibit interesting features suggesting structural anomaly may be a bulk property. All these results reveal complexity in the hybridization physics between Fe, As and Ca states presumably leading to exoticity in this material.

Anisotropic magnetic properties of trigonal ErAl2Ge2 single crystal

We report the anisotropic magnetic properties of the ternary compound ErAl₂Ge₂. Single crystals of this compound were grown by high temperature solution growth technique,using Al:Ge eutectic composition as flux. From the powder x-ray diffraction we confirmed that ErAl₂Ge₂ crystallizes in the trigonal CaAl₂Si₂-type crystal structure. The anisotropic magnetic properties of a single crystal were investigated by measuring the magnetic susceptibility, magnetization, heat capacity and electrical resistivity. A bulk antiferromagnetic ordering occurs around 4 K as inferred from the magnetic susceptibility and the heat capacity. The susceptibility is larger along the ab-plane and flattens out below the magnetic transition temperature ([Formula: see text]) and the magnetization in the ordered state increases more rapidly along the ab-plane than along the c-axis suggesting that the moments are inclined more towards the ab-plane. The magnetic susceptibility, magnetization and the 4f -derived part of the heat capacity in the paramagnetic regime analysed based on the point charge model of the crystalline electric field (CEF) indicate a relatively low CEF energy level splitting.

Zigzag spin chains in the spin-5/2 antiferromagnet Ba2Mn(PO4)2

One-dimensional magnets, where spins interact only along a particular spatial direction, are of special interest due to their quantum mechanical behaviors, viz., spin liquid, spin glass, quantum phase transition, even superconductivity etc.

Superconducting properties and μSR study of the noncentrosymmetric superconductor Nb0.5Os0.5

The properties of the noncentrosymmetric superconductor (α-[Formula: see text] structure) Nb_0.5Os_0.5 have been investigated using resistivity, magnetization, specific heat, and muon spin relaxation and rotation (μSR) measurements. These measurements suggest that Nb_0.5Os_0.5 is a weakly coupled ([Formula: see text]) type-II superconductor ([Formula: see text]), having a bulk superconducting transition temperature T _c   =  3.07 K. The specific heat data fits well with the single-gap BCS model indicating nodeless s-wave superconductivity in Nb_0.5Os_0.5. The μSR measurements also confirm [Formula: see text]-wave superconductivity with the preserved time-reversal symmetry.

Superconducting and charge density wave transition in single crystalline LaPt2Si2

We present results of our comprehensive studies on single crystalline LaPt₂Si₂. Pronounced anomaly in electrical resistivity and heat capacity confirms the bulk nature of superconductivity (SC) and charge density wave (CDW) transition in the single crystals. While the charge density wave transition temperature is lower, the superconducting transition temperature is higher in single crystal compared to the polycrystalline sample. This result confirms the competing nature of CDW and SC. Another important finding is the anomalous temperature dependence of upper critical field H _C2(T). We also report the anisotropy in the transport and magnetic measurements of the single crystal.

Giant Rashba effect at the topological surface of PrGe revealing antiferromagnetic spintronics

Rashba spin-orbit splitting in the magnetic materials opens up a new perspective in the field of spintronics. Here, we report a giant Rashba spin-orbit splitting on the PrGe [010] surface in the paramagnetic phase with Rashba coefficient α R  = 5 eVÅ. We find that α R can be tuned in this system as a function of temperature at different magnetic phases. Rashba type spin polarized surface states originates due to the strong hybridization between Pr 4f states with the conduction electrons. Significant changes observed in the spin polarized surface states across the magnetic transitions are due to the competition between Dzyaloshinsky-Moriya interaction and exchange interaction present in this system. Presence of Dzyaloshinsky-Moriya interaction on the topological surface give rise to Saddle point singularity which leads to electron-like and hole-like Rashba spin split bands in the [Formula: see text] and [Formula: see text] directions, respectively. Supporting evidences of Dzyaloshinsky-Moriya interaction have been obtained as anisotropic magnetoresistance with respect to field direction and first-order type hysteresis in the X-ray diffraction measurements. A giant negative magnetoresistance of 43% in the antiferromagnetic phase and tunable Rashba parameter with temperature makes this material a suitable candidate for application in the antiferromagnetic spintronic devices.

Growth of high-quality Bi2Sr2 CaCu2O8+δ whiskers and electrical properties of resulting exfoliated flakes

In this work, we demonstrate a simple technique to grow high-quality whiskers of Bi₂ Sr₂ CaCu₂ O_8+δ – a high T_c superconductor. Structural analysis shows the single-crystalline nature of the grown whiskers. To probe electrical properties, we exfoliate these whiskers into thin flakes (~50 nm thick) using the scotch-tape technique and develop a process to realize good electrical contacts. We observe a superconducting critical temperature, T_c, of 86 K. We map the evolution of the critical current as a function of temperature. With 2-D materials emerging as an exciting platform to study low-dimensional physics, our work paves the way for future studies on two-dimensional high-T_c superconductivity.

Probing the magnetic ground state of single crystalline Ce3TiSb5

Motivated by the report of superconductivity in R₃TiSb₅ (R  =  La and Ce) and possibly Nd₃TiSb₅ at  ∼4 K, we grew single crystals of La₃TiSb₅ and Ce₃TiSb₅ by the high-temperature solution method using Sn as a flux. While in both compounds we observed a superconducting transition at 3.7 K for resistivity and low-field magnetization, our data conclusively show that it arose from residual Sn flux present in the single crystals. In particular, the heat capacity data do not present any of the anomalies expected from a bulk superconducting transition. The anisotropic magnetic properties of Ce₃TiSb₅, crystallizing in a hexagonal P6₃/mcm structure, were studied in detail. We find that the Ce ions in Ce₃TiSb₅ form a Kondo lattice and exhibited antiferromagnetic ordering at 5.5 K with a reduced moment and a moderately normalized Sommerfeld coefficient of 598 mJ/mol K². The characteristic single-ion Kondo energy scale was found to be  ∼8 K. The magnetization data were subjected to a crystal electric field (CEF) analysis. The experimentally observed Schottky peak in the 4f-electron heat capacity of Ce₃TiSb₅ was reproduced fairly well by the energy levels derived from the CEF analysis.

Evidence for bulk superconductivity in pure bismuth single crystals at ambient pressure

At ambient pressure, bulk rhombohedral bismuth is a semimetal that remains in the normal state down to at least 10 millikelvin. Superconductivity in bulk bismuth is thought to be unlikely because of the extremely low carrier density. We observed bulk superconductivity in pure bismuth single crystals below 0.53 millikelvin at ambient pressure, with an estimated critical magnetic field of 5.2 microteslas at 0 kelvin. Superconductivity in bismuth cannot be explained by the conventional Bardeen-Cooper-Schrieffer theory because its adiabatic approximation does not hold true for bismuth. Future theoretical work will be needed to understand superconductivity in the nonadiabatic limit in systems with low carrier densities and unusual band structures, such as bismuth.

Magnetic, specific heat and electrical transport properties of Frank-Kasper cage compounds RTM2Al20 [R = Eu, Gd and La; TM = V, Ti]

Single crystals of Frank-Kasper compounds RTM2Al20 (R  =  Eu, Gd and La; TM  =  V and Ti) were grown by self-flux method and their physical properties were investigated through magnetization (M), magnetic susceptibility (χ), specific heat (C P) and electrical resistivity (ρ) measurements. Powder x-ray diffraction studies and structural analysis showed that these compounds crystallize in the cubic crystal structure with the space group [Formula: see text]. The magnetic susceptibility for the compounds EuTi2Al20 and GdTi2Al20 showed a sudden jump below the Néel temperature T N indicative of plausible double magnetic transition. Specific heat (C P) and electrical resistivity (ρ) measurements also confirm the first-order magnetic transition (FOMT) and possible double magnetic transitions. Temperature variation of heat capacity showed a sharp phase transition and huge C P value for the (Eu/Gd)Ti2Al20 compounds' full width at half-maximum (FWHM) (<0.2 K) which is reminiscent of a first-order phase transition and a unique attribute among RTM2Al20 compounds. In contrast, linear variation of C P is observed in the ordered state for (Eu/Gd)V2Al20 compounds suggesting a λ-type transition. We observed clear anomaly between heating and cooling cycle in temperature-time relaxation curve for the compounds GdTi2Al20 (2.38 K) and EuTi2Al20 (3.2 K) which is indicating a thermal arrest due to the latent heat. The temperature variation of S mag for GdTi2Al20 saturates to a value [Formula: see text] while the other magnetic systems exhibited still lower entropy saturation values in the high temperature limit. [Formula: see text] versus T plot showed a maximum near 27 K for all the compounds indicating the presence of low frequency Einstein modes of vibrations. Resistivity measurements showed that all the samples behave as normal Fermi liquid type compounds and [Formula: see text] due to electron-phonon scattering follows Bloch-Grüneisen-Mott relation in the paramagnetic region.

Orientational coupling between the vortex lattice and the crystalline lattice in a weakly pinned Co(0.0075)NbSe2 single crystal

We report experimental evidence of strong orientational coupling between the crystal lattice and the vortex lattice in a weakly pinned Co-doped NbSe2 single crystal through direct imaging using low temperature scanning tunneling microscopy/spectroscopy. When the magnetic field is applied along the six-fold symmetric c-axis of the NbSe2 crystal, the basis vectors of the vortex lattice are preferentially aligned along the basis vectors of the crystal lattice. The orientational coupling between the vortex lattice and crystal lattice becomes more pronounced as the magnetic field is increased. This orientational coupling enhances the stability of the orientational order of the vortex lattice, which persists even in the disordered state at high fields where dislocations and disclinations have destroyed the topological order. Our results underpin the importance of crystal lattice symmetry on the vortex state phase diagram of weakly pinned type II superconductors.

Unconventional Superconductivity in La(7)Ir(3) Revealed by Muon Spin Relaxation: Introducing a New Family of Noncentrosymmetric Superconductor That Breaks Time-Reversal Symmetry

The superconductivity of the noncentrosymmetric compound La(7)Ir(3) is investigated using muon spin rotation and relaxation. Zero-field measurements reveal the presence of spontaneous static or quasistatic magnetic fields below the superconducting transition temperature T(c)=2.25  K-a clear indication that the superconducting state breaks time-reversal symmetry. Furthermore, transverse-field rotation measurements suggest that the superconducting gap is isotropic and that the pairing symmetry of the superconducting electrons is predominantly s wave with an enhanced binding strength. The results indicate that the superconductivity in La(7)Ir(3) may be unconventional and paves the way for further studies of this family of materials.

Enhanced conduction band density of states in intermetallic EuTSi3 (T = Rh, Ir)

We report on the physical properties of single crystalline EuRhSi3 and polycrystalline EuIrSi3, inferred from magnetization, electrical transport, heat capacity and (151)Eu Mössbauer spectroscopy. These previously known compounds crystallise in the tetragonal BaNiSn3-type structure. The single crystal magnetization in EuRhSi3 has a strongly anisotropic behaviour at 2 K with a spin-flop field of 13 T, and we present a model of these magnetic properties which allows the exchange constants to be determined. In both compounds, specific heat shows the presence of a cascade of two close transitions near 50 K, and the (151)Eu Mössbauer spectra demonstrate that the intermediate phase has an incommensurate amplitude modulated structure. We find anomalously large values, with respect to other members of the series, for the RKKY Néel temperature, for the spin-flop field (13 T), for the spin-wave gap (≃20-25 K) inferred from both resistivity and specific heat data, for the spin-disorder resistivity in EuIrSi3 (≃240 μΩ cm) and for the saturated hyperfine field (52 T). The enhanced values of the quantities that depend on the electronic density of states at the Fermi level, imply that the latter must be strongly enhanced in these two materials. EuIrSi3 exhibits a giant magnetoresistance ratio, with values exceeding 600% at 2 K in a field of 14 T.

Disordering of the vortex lattice through successive destruction of positional and orientational order in a weakly pinned Co0.0075NbSe2 single crystal

The vortex lattice in a Type II superconductor provides a versatile model system to investigate the order-disorder transition in a periodic medium in the presence of random pinning. Here, using scanning tunnelling spectroscopy in a weakly pinned Co(0.0075)NbSe(2) single crystal, we show that the vortex lattice in a 3-dimensional superconductor disorders through successive destruction of positional and orientational order, as the magnetic field is increased across the peak effect. At the onset of the peak effect, the equilibrium quasi-long range ordered state transforms into an orientational glass through the proliferation of dislocations. At a higher field, the dislocations dissociate into isolated disclination giving rise to an amorphous vortex glass. We also show the existence of a variety of additional non-equilibrium metastable states, which can be accessed through different thermomagnetic cycling.

Estimate of the Coulomb correlation energy in CeAg2Ge2 from inverse photoemission and high resolution photoemission spectroscopy

The occupied and the unoccupied electronic structure of CeAg2Ge2 single crystal has been studied using high resolution photoemission and inverse photoemission spectroscopy, respectively. High resolution photoemission reveals the clear signature of Ce 4f states in the occupied electronic structure which was not observed clearly in our earlier studies. The Coulomb correlation energy in this system has been determined experimentally from the position of the 4f states above and below the Fermi level. Theoretically, the correlation energy has been determined by using the first principles density functional calculations within the generalized gradient approximations taking into account the strong intra-atomic (on-site) interaction Hubbard Ueff term. The calculated valence band shows minor changes in the spectral shape with increasing Ueff due to the fact that the density of Ce 4f state is narrow in the occupied part and is hybridized with the Ce 5d, Ag 4d and Ge 4p states. On the other hand, substantial changes are observed in the spectral shape of the calculated conduction band with increasing Ueff since the density of Ce 4f state is very large in the unoccupied part, compared to other states. The estimated value of correlation energy for CeAg2Ge2 from the experiment and the theory is ≈ 4.2 eV. The resonant photoemission data are analyzed in the framework of the single-impurity Anderson model which further confirms the presence of the Coulomb correlation energy and small hybridization in this system.

Anisotropic magnetic behavior of single crystalline CeTiGe3 and CeVGe3

We have grown the single crystals of iso-structural CeTiGe3 and CeVGe3 compounds by using Ce-Ge eutectic as flux. Using the techniques of magnetization, electrical resistivity and heat capacity, our data on single crystals reveal pronounced magnetic anisotropies in these compounds with hexagonal symmetry. The c-axis is the easy axis of magnetization in CeTiGe3 which orders ferromagnetically at 14 K, and a gap in the magnon excitation spectra of ∼ 28 K is inferred from both electrical resistivity and heat capacity. The electrical resistivity of CeTiGe3 shows anisotropic Kondo behavior and the heat capacity indicates the existence of the first excited crystal electric field split doublet lying at about ∼ 50 K. The nature of magnetic ordering changes to antiferromagnetic in CeVGe3, which undergoes a magnetic transition at TN ∼ 6 K with the a - b plane as the easy plane of magnetization. Below TN, the electrical resistivity of CeVGe3 along the c axis shows an upturn due to the opening of a gap. The 4f contribution to the resistivity ρ4f establishes that CeVGe3, like the Ti analog, is also a Kondo lattice compound. The present work on single crystals further advances our understanding of these materials based on polycrystalline samples which have been studied earlier in the literature.

EuNiGe₃, an anisotropic antiferromagnet

Single crystals of EuNiGe3, crystallizing in the non-centrosymmetric BaNiSn3-type structure, were grown using In flux, enabling us to explore the anisotropic magnetic properties, which was not possible with previously reported polycrystalline samples. The EuNiGe3 single crystalline sample is found to order antiferromagnetically at 13.2 K, as revealed from the magnetic susceptibility, heat capacity and electrical resistivity data. The low temperature magnetization M (H) is distinctly different for the field parallel to the ab-plane and c-axis; the ab-plane magnetization varies almost linearly with the field before the occurrence of an induced ferromagnetic (FM) phase (spin-flip) at 6.2 Tesla. On the other hand M (H) along the c-axis is accompanied by two metamagnetic transitions followed by a spin-flip at 4.1 T. A model including anisotropic exchange and dipole-dipole interactions reproduces the main features of magnetization plots but falls short of full representation. (H,T) phase diagrams have been constructed for the field applied along the principal directions. From the (151)Eu Mössbauer spectra, we determine that the 13.2 K transition leads to an incommensurate antiferromagnetic (AFM) intermediate phase followed by a transition near 10.5 K to a commensurate AFM configuration.

Synthesis, crystal and electronic structure of the quaternary magnetic EuTAl4Si2 (T = Rh and Ir) compounds

Single crystals of the quaternary europium compounds EuRhAl4Si2 and EuIrAl4Si2 were synthesized by using the Al-Si binary eutectic as a flux. The structure of the two quaternary compounds has been refined by single crystal X-ray diffraction. Both compounds are stoichiometric and adopt an ordered derivative of the ternary KCu4S3 structure type (tetragonal tP8, P4/mmm). The two compounds reported here represent the first example of a quaternary and truly stoichiometric 1:1:4:2 phase crystallizing with this structure type. In light of our present results, the structure of the BaMg4Si3 compound given in literature as representing a new prototype is actually isotypic with the KCu4S3 structure. Local spin density approximation including the Hubbard U parameter (LSDA + U) calculations show that Eu ions are in the divalent state, with a significant hybridization between the Eu 5d, Rh (Ir) 4d (5d), Si 3p and Al 3p states. Magnetic susceptibility measured along the [001] direction confirms the divalent nature of the Eu ions in EuRhAl4Si2 and EuIrAl4Si2, which order magnetically near ∼11 and ∼15 K, respectively.

Anisotropic magnetic properties and crystal electric field studies on CePd2Ge2 single crystal

The anisotropic magnetic properties of the antiferromagnetic compound CePd2Ge2, crystallizing in the tetragonal crystal structure have been investigated in detail on a single crystal grown by the Czochralski method. From the electrical transport, magnetization and heat capacity data, the Néel temperature is confirmed to be 5.1 K. Anisotropic behaviour of the magnetization and resistivity is observed along the two principal crystallographic directions-namely, [100] and [001]. The isothermal magnetization measured in the magnetically ordered state at 2 K exhibits a spin reorientation at 13.5 T for the field applied along the [100] direction, whereas the magnetization is linear along the [001] direction attaining a value of 0.94 μ(B)/Ce at 14 T. The reduced value of the magnetization is attributed to the crystalline electric field (CEF) effects. A sharp jump in the specific heat at the magnetic ordering temperature is observed. After subtracting the phononic contribution, the jump in the heat capacity amounts to 12.5 J K(-1)mol(-1) which is the expected value for a spin ½ system. From the CEF analysis of the magnetization data the excited crystal field split energy levels were estimated to be at 120 K and 230 K respectively, which quantitatively explains the observed Schottky anomaly in the heat capacity. A magnetic phase diagram has been constructed based on the field dependence of magnetic susceptibility and the heat capacity data.

Electronic structure of EuFe2As2

Employing high resolution photoemission spectroscopy, we studied the temperature evolution of the electronic structure of EuFe2As2, a unique pnictide, where antiferromagnetism of the Eu layer survives within the superconducting phase due to 'FeAs' layers, achieved via substitution and/or pressure. High energy and angle resolution helped to reveal the signature of peak-dip features, having significant p orbital character and spin density wave transition induced band folding in the electronic structure. A significant spectral weight redistribution is observed below 20 K manifesting the influence of antiferromagnetic order on the conduction electrons.

Plasmon mode modifies the elastic response of a nanoscale charge density wave system

The elastic response of suspended NbSe(3) nanowires is studied across the charge density wave phase transition. The nanoscale dimensions of the resonator lead to a large resonant frequency (~10-100 MHz), bringing the excited phonon frequency in close proximity of the plasmon mode of the electronic condensate-a parameter window not accessible in bulk systems. The interaction between the phonon and plasmon modes strongly modifies the elastic properties at high frequencies. This is manifested in the nanomechanics of the system as a sharp peak in the temperature dependence of the elastic modulus (relative change of 12.8%) in the charge density wave phase.

Antiferro- and ferromagnetic ordering in a PrGe single crystal

An equiatomic PrGe single crystal was grown by the Czochralski pulling method. The grown single crystal was found to have CrB-type orthorhombic crystal structure with the space group Cmcm (no. 63). Transport and magnetization data reveal large anisotropy in the electrical resistivity, magnetic susceptibility and magnetization. PrGe was found to exhibit two consecutive magnetic orderings at 44 K and 41.5 K, respectively. The magnetic susceptibility measurement along the three principal directions in low applied fields revealed a cusp-like behaviour at 44 K while at 41.5 K a ferromagnetic-like increase was observed. The hysteretic behaviour in the magnetization measurement at 1.8 K confirmed the ferromagnetic nature of PrGe at low temperatures. The heat capacity data clearly revealed the bulk nature of two magnetic transitions by the presence of two sharp peaks attaining values exceeding 40 J K(-1) mol(-1) at the respective temperatures. The absence of a Schottky contribution in the magnetic part of the heat capacity indicates a quasi-ninefold degenerate J = 4 magnetic ground state in this system. The low temperature data of electrical resistivity and the magnetic part of the heat capacity show the existence of a gap in the spin-wave spectrum.

Complex magnetic order in Pr₂Pd₃Ge₅: a single crystal study

We have investigated the magnetic and electronic transport properties of single crystal Pr(2)Pd(3)Ge(5) grown by the Czochralski method. Complex magnetic behaviour (multiple magnetic transitions) is clearly seen in this compound from the magnetic susceptibility χ(T), isothermal magnetization M(H) and electrical resistivity ρ(T) data. For the magnetic field applied along the crystallographic c-axis (H ‖ [001]) the χ(T) data exhibit two sharp transitions at 6.9 and 6.3 K and a broad hump near 8 K. Four anomalies at 8.0, 7.3, 6.2 and 4.9 K are observed for the magnetic field along both a- and b-directions (H ‖ [100] and H ‖ [010]). Further, the ordered state χ(T) presents a large anisotropy with an easy axis along the c-axis. The presence of magnetocrystalline anisotropy is also inferred from the isothermal M(H) data. The M(H) data measured at 1.9 K for H ‖ [001] exhibit a step-like increase due to field-induced metamagnetic transitions at [Formula: see text] T and [Formula: see text] T. For H ‖ [100] and H ‖ [010] sharp step-like field-induced metamagnetic transitions occur at [Formula: see text] T and [Formula: see text] T which are accompanied by a weak S-shaped spin-flop metamagnetic transition at [Formula: see text] T. We have extracted the H-T phase diagram from the M(H) data collected at different temperatures in the magnetically ordered state which shows the existence of three magnetic phases below T(N) for H ‖ [100] and H ‖ [010], and two magnetic phases for H ‖ [001]. A sharp transition due to the onset of long range antiferromagnetic order is also seen in the ρ(T) data which also exhibit anisotropic behaviour. The observation of an upturn near T(N) in the ρ(T) data suggests the formation of a super-zone gap and hence the existence of incommensurate magnetic structure. Further, in the ordered state, the ρ(T) data present a gap in the excitation spectrum of magnons with a characteristic energy gap Δ ∼ 0.23 meV.

Anisotropic magnetic properties and superzone gap formation in CeGe single crystal

Single crystals of CeGe and its non-magnetic analog LaGe have been grown by the Czochralski method. The CeGe compound crystallizes in the orthorhombic FeB-type crystal structure with the space group Pnma (#62). The anisotropic magnetic properties have been investigated for well oriented single crystals by measuring the magnetic susceptibility, electrical resistivity and heat capacity. It has been found that CeGe orders antiferromagnetically at 10.5 K. Both transport and magnetic studies have revealed large anisotropy, reflecting the orthorhombic crystal structure. The magnetization data at 1.8 K reveal metamagnetic transitions along the [010] direction at 4.8 and 6.4 T and along the [100] direction at a critical field of 10.7 T, while the magnetization along the [001] direction increases linearly without any anomaly up to a field of 16 T. From the magnetic susceptibility and the magnetization measurements it has been found that the [010] direction is the easy axis of magnetization. The electrical resistivity along the three crystallographic directions exhibits an upturn at T(N), indicating superzone gap formation below T(N) in this compound. We have performed crystal electric field analysis on the magnetic susceptibility and the heat capacity data and found that the ground state is a doublet, and the energies of splitting from the ground state to the first and second excited doublet states were estimated to be 39 and 111 K, respectively.

Antiferromagnetic ordering in EuPtGe3

The magnetic properties of single crystalline EuPtGe(3), crystallizing in the non-centrosymmetric BaNiSn(3)-type crystal structure, have been studied by means of magnetization, electrical resistivity, heat capacity and (151)Eu Mössbauer spectroscopy. The susceptibility and heat capacity data indicate a magnetic transition at T(N) = 11 K. The Mössbauer data confirm this conclusion, but evidence a slight first-order character of the transition. Analysing the magnetization data using a mean field model with two antiferromagnetically coupled sublattices allows us to explain some aspects of the magnetic behaviour, and to derive the first- and second-neighbour exchange integrals in EuPtGe(3).

Surfactant free rapid synthesis of hydroxyapatite nanorods by a microwave irradiation method for the treatment of bone infection

Mesoporous nanocrystalline hydroxyapatite (nHAp) rods of size 40-75 nm long and 25 nm wide (resembling bone mineral) were synthesized under microwave irradiation without using any surfactants or modifiers. The surface area and average pore size of the nHAp were found to be 32 m(2) g(-1) and 4 nm, respectively. Rifampicin (RIF) and ciprofloxacin (CPF) loaded nHAp displayed an initial burst followed by controlled release (zero order kinetics). Combination of CPF and RIF loaded nHAp showed enhanced bacterial growth inhibition against Staphylococcus aureus (S. aureus), Staphylococcus epidermidis (S. epidermidis) and Escherichia coli (E. coli) compared to individual agent loaded nHAp and pure nHAp. In addition, decreased bacterial adhesion (90%) was observed on the surface of CPF plus RIF loaded nHAp. The biocompatibility test toward MG63 cells infected with micro-organisms showed better cell viability and alkaline phosphatase activity (ALP) for the combination of CPF and RIF loaded nHAp. The influence on cell viability of infected MG63 cells was attributed to the simultaneous and controlled release of CPF and RIF from nHAp, which prevented the emergence of subpopulations that were resistant to each other. Hence, apart from the issue of the rapid synthesis of nHAp without surfactants or modifiers, the simultaneous and controlled release of dual drugs from nHAp would be a simple, non-toxic and cost-effective method to treat bone infections.

The effect of chemical substitution in Rh(17)S(15)

Rh(17)S(15) has recently been shown to be a strongly correlated superconductor with a transition temperature of 5.4 K. In order to understand the nature of the strong correlations we study the effect of replacement of some of the Rh and S atoms by other elements such as Fe, Pd, Ir and Ni on the Rh side and Se on the S side in this work. We find that while replacements of Ir and Se lower the transition temperature considerably, those of Fe, Pd and Ni destroy the superconductivity down to 1.5 K. The resistivity data for these doped samples show a minimum which is presumably disorder induced. A reduction of T(c) is always accompanied by a reduction of electron correlations, as deduced from heat capacity and magnetization data. Interestingly, the Fe doped sample shows evidence of spin glass formation at low temperatures.

Measurement of anomalous phonon dispersion of CaFe2As2 single crystals using inelastic neutron scattering

We measured phonon dispersions of CaFe2As2 using inelastic neutron scattering and compared our results to predictions of density functional theory in the local density approximation. The calculation gives correct frequencies of most phonons if the experimental crystal structure is used, except observed linewidths/frequencies of certain modes were larger/softer than predicted. Strong temperature dependence of some phonons near the structural phase transition near 172 K may indicate strong electron-phonon coupling and/or anharmonicity, which may be important for superconductivity.

Strongly correlated superconductivity in Rh17S15

In this Letter, we report resistivity, susceptibility, heat capacity, and upper critical field studies on a polycrystalline Rh17S15 sample which exhibits superconductivity below 5.4 K. Detailed studies suggest that the superconductivity in this compound arises from strongly correlated charge carriers presumably due to the high density of states of Rh d bands at the Fermi level. Moreover, the Hall coefficient shows a sign change and increases at low temperature before the sample becomes a superconductor below 5.4 K.