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.

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.

Pick-up and assembling of chemically sensitive van der Waals heterostructures using dry cryogenic exfoliation.

Assembling atomic layers of van der Waals materials (vdW) combines the physics of two materials, offering opportunities for novel functional devices. Realization of this has been possible because of advancements in nanofabrication processes which often involve chemical processing of the materials under study; this can be detrimental to device performance. To address this issue, we have developed a modified micro-manipulator setup for cryogenic exfoliation, pick up, and transfer of vdW materials to assemble heterostructures. We use the glass transition of a polymer PDMS to cleave a flake into two, followed by its pick-up and drop to form pristine twisted junctions. To demonstrate the potential of the technique, we fabricated twisted heterostructure of Bi2Sr2CaCu2O8+x (BSCCO), a van der Waals high-temperature cuprate superconductor. We also employed this method to re-exfoliate NbSe2 and make twisted heterostructure. Transport measurements of the fabricated devices indicate the high quality of the artificial twisted interface. In addition, we extend this cryogenic exfoliation method for other vdW materials, offering an effective way of assembling heterostructures and twisted junctions with pristine interfaces.

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.

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.

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,Tc= 5.12 K (in contrary to the previously reported value of 4.4 K), which falls in the highestTc-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 (Cp) data confirms bulk superconductivity. We report that the electron-phonon coupling constant,λe-ph= 0.77, suggesting a moderate electron-phonon coupling in ScAu2Al. Further, we show that the observedλe-phvalue in ScAu2Al is the highest amongst the reported Heusler superconductors, indicating strong correlation betweenTcandλe-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.

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 (ß), whereas, SdH oscillation results in only two frequenciesαandß. Theγfrequency observed in dHvA oscillation is a tiny hole pocket at the Γ point.

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.

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, CaFe1.9Co0.1As2(Tc= 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.

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.

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.

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

The properties of the noncentrosymmetric superconductor (α-[Formula: see text] structure) Nb0.5Os0.5 have been investigated using resistivity, magnetization, specific heat, and muon spin relaxation and rotation (µSR) measurements. These measurements suggest that Nb0.5Os0.5 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 Nb0.5Os0.5. The µSR measurements also confirm [Formula: see text]-wave superconductivity with the preserved time-reversal symmetry.

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.

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.

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.

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.

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.

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.

Magnetic anisotropy, unusual hysteresis and putative "up-up-down" magnetic structure in EuTAl4Si2 (T = Rh and Ir).

We present detailed investigations on single crystals of quaternary EuRhAl4Si2 and EuIrAl4Si2. The two compounds order antiferromagnetically at TN1 = 11.7 and 14.7 K, respectively, each undergoing two magnetic transitions. The magnetic properties in the ordered state present a large anisotropy despite Eu(2+)being an S-state ion for which the single-ion anisotropy is expected to be weak. Two features in the magnetization measured along the c-axis are prominent. At 1.8 K, a ferromagnetic-like jump occurs at very low field to a value one third of the saturation magnetization (1/3 M0) followed by a wide plateau up to 2 T for Rh and 4 T for Ir-compound. At this field value, a sharp hysteretic spin-flop transition occurs to a fully saturated state (M0). Surprisingly, the magnetization does not return to origin when the field is reduced to zero in the return cycle, as expected in an antiferromagnet. Instead, a remnant magnetization 1/3 M0 is observed and the magnetic loop around the origin shows hysteresis. This suggests that the zero field magnetic structure has a ferromagnetic component, and we present a model with up to third neighbor exchange and dipolar interaction which reproduces the magnetization curves and hints to an "up-up-down" magnetic structure in zero field.

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.