Ta4SiTe4 is a one-dimensional van der Waals material that exhibits an exceptionally large thermoelectric power factor below room temperature. However, since this material has been available only in the form of acicular microcrystals, experimental exploration of the electronic properties responsible for its giant thermoelectric performance has long been challenging. In this study, we quantitatively evaluated the one-dimensional electronic nature of Ta4SiTe4 by combining micro-spot angle-resolved photoemission spectroscopy and transport measurements on focused-ion-beam-processed samples. The angle-resolved photoemission spectroscopy measurements reveal anisotropic band dispersions along and perpendicular to the crystallographic c axis. Consistently, transport measurements demonstrate that the resistivity perpendicular to the c axis is approximately five times larger than that along the c axis at 200 K. These results provide direct experimental evidence for the quasi-one-dimensional electronic character of Ta4SiTe4, which underlies its giant thermoelectric response reported previously, and offer fundamental insights into the role of electronic dimensionality in enhancing thermoelectric performance.

The superconducting gap symmetry is investigated by 125Te NMR measurements on Sc6MTe2 (M = Fe, Co) without spatial inversion symmetry. The spin susceptibility obtained from the Knight shift K is suppressed below the superconducting transition temperature, while leaving a finite value down to the lowest temperature ( 0.4 K). The nuclear spin-lattice relaxation rate 1/T1 follows a power law against temperature T without showing a coherence peak characteristic of the isotropic gap. The result implies a pairing admixture or a residual density of states under magnetic field. The normal metallic state has a Korringa scaling relation between 1/T1T and the Knight shift, reflecting a weak electron correlation.

High-entropy compounds, where multiple elements occupy a single crystallographic site in a highly disordered manner, challenge conventional understandings of electronic structures based on periodicity and well-defined band dispersion. Here, we report a detailed nuclear magnetic resonance study of the high-entropy superconductor X0.6Pt0.4Sb (X = Ru, Rh, Pd, Ir), revealing a spatially homogeneous electronic environment in the normal state, in stark contrast to its crystallographically disordered lattice. The superconducting state exhibits a small but solid Hebel-Slichter coherence peak followed by a significant decrease in the nuclear spin-lattice relaxation rate, providing compelling evidence for fully gapped s-wave pairing. Our findings not only deepen the understanding of superconductivity in highly disordered quantum materials but also open an alternative pathway for exploring superconducting states in entropy-stabilized systems.

Double perovskite compounds containing 5d transition metal elements have been extensively studied as platforms for multipolar order phenomena stemming from spin-orbit-entangled 5d electrons. In this study, we examine the interplay between crystal structure, multipolar order, and magnetic order in solid solutions of double perovskites with the 5d1 electronic configuration: Ba2CdReO6 and Ba2CaReO6, which exhibit distinct electronic orders. The substitution of larger Ca2+ ions for Cd2+ in Ba2CdReO6, systematically increases the lattice constant with increasing the amount of substitution x. Although the spin-orbit-entangled J = 3/2 state remains intact upon substitution, both the quadrupolar order below Tq = 25 K and the canted antiferro-magnetic (AFM) order below Tm = 12 K in Ba2CdReO6 are progressively suppressed as x increases. Magnetization measurements reveal that the canted AFM order is suppressed at x = 0.6, transitioning to a colinear AFM order, while the quadrupolar order persists up to x = 0.9. The experimental electronic phase diagram, summarizing the dependence of electronic orders on lattice constants, aligns well with the theoretical phase diagram considering electric quadrupolar interactions [G. Chen et al., Phys. Rev. B 82, 174440 (2010)]. This correspondence confirms that chemical pressure induced by substitution effectively tunes the interaction between 5d electrons. The results highlight the potential of chemical pressure to modulate multipolar interactions, paving the way for novel multipolar properties in 5d electron systems.

High-entropy compounds (HECs) have attracted interest for their unique properties driven by the so-called "cocktail effect." While HECs have been widely studied, germanium-based high-entropy compounds (HEGs) remain largely unexplored. In this study, we synthesized (RuRhPdPt)1-xIrxGe (0.2 ≤ x ≤ 1) and investigated its structural and transport properties. X-ray diffraction confirmed the formation of a single-phase MnP-type (Pnma) structure across the entire composition range, stabilized by entropy-driven effects. The phase transition between single- and multiphase states, controlled by annealing temperature, further supports entropy stabilization. Transport measurements revealed temperature-independent resistivity for x ≤ 0.6, indicating strong electron scattering from extreme chemical disorder. Hall effect measurements for x = 0.2 showed an ultrashort mean free path comparable to atomic spacing. Superconductivity observed in IrGe (x = 1) was systematically suppressed with increasing disorder, suggesting a disorder-induced breakdown of superconducting coherence. This study expands high-entropy materials to germanide systems and highlights the role of anions in tuning electronic and structural properties. Our findings provide insight into entropy-driven phase stabilization and disorder-induced transport phenomena, paving the way for novel high-entropy materials with tunable functionalities.

Double perovskite compounds containing 5d transition metal elements have been extensively studied as platforms for multipolar order phenomena stemming from spin-orbit-entangled 5d electrons. In this study, we examine the interplay between crystal structure, multipolar order, and magnetic order in solid solutions of double perovskites with the 5d1 electronic configuration: Ba2CdReO6 and Ba2CaReO6, which exhibit distinct electronic orders. The substitution of larger Ca2+ ions for Cd2+ in Ba2CdReO6, systematically increases the lattice constant with increasing the amount of substitution x. Although the spin-orbit-entangled J = 3/2 state remains intact upon substitution, both the quadrupolar order below Tq = 25 K and the canted antiferro-magnetic (AFM) order below Tm = 12 K in Ba2CdReO6 are progressively suppressed as x increases. Magnetization measurements reveal that the canted AFM order is suppressed at x = 0.6, transitioning to a colinear AFM order, while the quadrupolar order persists up to x = 0.9. The experimental electronic phase diagram, summarizing the dependence of electronic orders on lattice constants, aligns well with the theoretical phase diagram considering electric quadrupolar interactions [G. Chen et al., Phys. Rev. B 82, 174440 (2010)]. This correspondence confirms that chemical pressure induced by substitution effectively tunes the interaction between 5d electrons. The results highlight the potential of chemical pressure to modulate multipolar interactions, paving the way for novel multipolar properties in 5d electron systems.

We elucidate the transport properties and electronic structures of distorted rutile-type WO2. Electrical resistivity and Hall effect measurements of high-quality single crystals revealed the transport property characteristics of topological materials; these characteristics included an extremely large magnetoresistance of 13 200% (2 K and 9 T) and a very high carrier mobility of 25 700 cm2 V−1 s−1 (5 K). First-principles calculations revealed Dirac nodal lines (DNLs) near the Fermi energy in the electronic structure when spin–orbit interactions (SOIs) were absent. Although these DNLs mostly disappeared in the presence of SOIs, band crossings at high-symmetry points in the reciprocal space existed as Dirac points. Furthermore, DNLs protected by nonsymmorphic symmetry persisted on the ky = π/b plane. The unique transport properties originating from the topological electronic structure of chemically and thermally stable WO2 could represent an opportunity to investigate the potential electronic applications of the material.

Double perovskite compounds containing 5d transition metal elements have been extensively studied as platforms for multipolar order phenomena stemming from spin-orbit-entangled 5d electrons. In this study, we examine the interplay between crystal structure, multipolar order, and magnetic order in solid solutions of double perovskites with the 5d1 electronic configuration: Ba2CdReO6 and Ba2CaReO6, which exhibit distinct electronic orders. The substitution of larger Ca2+ ions for Cd2+ in Ba2CdReO6, systematically increases the lattice constant with increasing the amount of substitution x. Although the spin-orbit-entangled J = 3/2 state remains intact upon substitution, both the quadrupolar order below Tq = 25 K and the canted antiferromagnetic (AFM) order below Tm = 12 K in Ba2CdReO6 are progressively suppressed as x increases. Magnetization measurements reveal that the canted AFM order is suppressed at x = 0.6, transitioning to a colinear AFM order, while the quadrupolar order persists up to x = 0.9. The experimental electronic phase diagram, summarizing the dependence of electronic orders on lattice constants, aligns well with the theoretical phase diagram considering electric quadrupolar interactions [G. Chen et al., Phys. Rev. B 82, 174440 (2010)]. This correspondence confirms that chemical pressure induced by substitution effectively tunes the interaction between 5d electrons. The results highlight the potential of chemical pressure to modulate multipolar interactions, paving the way for novel multipolar properties in 5d electron systems.

The appearance of broken time-reversal symmetry (TRS) in superconducting states is an intriguing issue in solid-state physics because of the incompatibility of the spontaneous magnetic field and the Meissner effect. We identify broken TRS in Pd-doped CaAgP (CaAg0.9Pd0.1P) by point-contact spectroscpy through the magnetic-field response of conductance spectra. CaAg0.9Pd0.1P is a nodal-line semi-metal with exotic electronic states such as drumhead surface states and surface superconductivity. Tunneling conductance spectra acquired at the side surfaces of CaAg0.9Pd0.1P under an applied magnetic field exhibit broad zero-bias peaks with small asymmetric structures. Surprisingly, the asymmetric structures are reversed exactly by flipping the field direction. On the basis of an analysis which stands on the formula of tunneling junctions for unconventional superconductors, these results are consistent with the pair potential of the superconductivity breaks with the TRS and is strongly coupled to an external magnetic field. We reveal the novel character of superconducting nodal-line semi-metals by developing the TRS sensitivity of point-contact spectroscopy. Our results serve as an exploration of broken TRS in superconducting states realized in topological materials.

The appearance of broken time-reversal symmetry (TRS) in superconducting states is an intriguing issue in solid-state physics because of the incompatibility of the spontaneous magnetic field and the Meissner effect. We identify broken TRS in Pd-doped CaAgP (CaAg_0.9Pd_0.1P) by tunneling spectroscopy through the magnetic field response of conductance spectra. CaAg_0.9Pd_0.1P is a nodal-line semimetal with exotic electronic states such as drumhead surface states and surface superconductivity. Tunneling conductance spectra acquired at the side surfaces of CaAg_0.9Pd_0.1P under an applied magnetic field exhibit broad zero-bias peaks with small asymmetric structures. Surprisingly, the asymmetric structures are reversed exactly by flipping the field direction. On the basis of an analysis which stands on the formula of tunneling junctions for unconventional superconductors, these results are consistent with the pair potential of the superconductivity breaks the TRS and is strongly coupled to an external magnetic field. We reveal the novel character of superconducting nodal-line semimetals by developing the TRS sensitivity of tunneling spectroscopy. Our results serve as an exploration of broken TRS in superconducting states realized in topological materials.

Thermal expansion, by which a material's volume increases when heated, is a universal phenomenon deriving from the thermal vibration of the atoms that constitute solids. Since the discovery of low thermal expansion in Invar alloys at the end of the 19th century, the "abnormality" of thermal expansion has given birth to new sciences and technologies. This article describes studies of thermal expansion anomalies from low thermal expansion of Invar alloys to the giant negative thermal expansion (giant NTE) materials recently discovered. Moreover, prospects for future research are presented. One turning point is the large isotropic NTE of ZrW2O8 discovered in 1996. Starting with manganese nitride in 2005, various materials have been found to have negative linear expansion coefficients that are many times larger than those of conventional NTE materials, although some operating-temperature constraints exist. These achievements have overturned the conventional wisdom which holds that negative coefficients of linear expansion do not engender large values. Additionally, the achievements established the concept of "giant" or "colossal" NTE. This article emphasizes recent important findings of enhanced NTE caused by material microstructural effects that are peculiar to ceramic bodies, and "hybrid" NTE by which multiple mechanisms work simultaneously. Additionally, this article introduces an attempt to produce fine particles of NTE material and use them as a thermal expansion compensator, especially for thermal-expansion control of resin. [doi:10.2320/matertrans.MT-Y2023008]

We investigated the optical properties of single crystals of one-dimensional telluride Ta4SiTe4, which shows high thermoelectric performance below room temperature. Optical conductivity estimated from reflectivity spectra indicates the presence of a small energy gap of 0.1-0.15 eV at the Fermi energy. At the lowest energy, optical conductivity along the Ta4SiTe4 chain is an order of magnitude higher than that perpendicular to this direction, reflecting the anisotropic electron conduction in Ta4SiTe4. These results indicate that coexistence of a very small band gap and anisotropic electron conduction is a promising strategy to develop a high-performance thermoelectric material for low temperature applications.

We fabricated Cu matrix composites with low thermal expansion and high thermal conductivity using Zn2P2O7-based negative thermal expansion (NTE) filler. Magnesium and aluminum co-doped Zn2−x−yMgxAlyP2O7 exhibits large NTE over a wide temperature range including room temperature. While achieving high density of the phosphate filler using spark plasma sintering and its uniform dispersion by an ultrasonic process, we reduced thermal expansion of the Cu matrix composites and retained their high thermal conductivity. Particularly, the 30 vol. %-Zn1.70Mg0.25Al0.05P2O7/Cu composite had a linear expansion coefficient as low as 5.1 ppm/K at temperatures of 300–400 K. The results reported herein demonstrate that Zn pyrophosphates, which are superior in terms of environmental impact and cost, are effective for controlling the thermal expansion of metals and are expected to support widely diverse engineering applications in the future.

The electronic properties of ScPdGe and ScPdSi, crystallizing in the hexagonal ZrNiAl and orthorhombic TiNiSi structures, respectively, are investigated. ScPdGe and ScPdSi are found to show bulk superconductivity below 0.9 and 1.7 K, respectively, based on electrical resistivity and heat capacity data measured using synthesized polycrystalline samples. First principles calculations indicate the presence of large contributions of Sc 3d and Pd 4d electrons at the Fermi energy in both materials. The electronic properties and electronic states of these materials are discussed in comparison with those of several superconductors containing scandium and a 4d transition metal element.

We discovered large electric-field-induced strain in pyro-vanadate-phosphate Cu2−xZnxV1.8P0.2O7. Distinct from conventionally used piezoelectric materials including lead-zirconate-titanate, this material expands almost isotropically at room temperature when an electric field is applied. This volume change, exceeding 1000 ppm under the field of E = 3900 V/cm, is of the largest class induced by an electric field. The strain is phenomenologically interpreted as electrostriction because it is symmetric about E = 0 and because it obeys a higher term than E-linear such as E squared. The present x-ray diffraction experiments suggest that the applied electric field distorts the crystal lattice, although there is no structural phase transition. This material performs a volume-change-driven actuator function that is distinct from the strain-driven counterpart of piezoelectric materials. The discovery of actuator functionality in a material system with a non-perovskite structure, unlike the actuator materials developed to date, is a major breakthrough for future actuator engineering.

High-entropy compounds have garnered significant interest in recent years owing to their exceptional properties and functionalities derived from the cocktail effect, which indicates that the properties of high-entropy compounds will be significantly enhanced compared to the average properties obtained from the individual properties of the constituent elements. Herein, we report an increased superconducting transition temperature (T-c) and upper critical field (H-c2) as a new cocktail effect in the high-entropy antimonide superconductor (RuRhPdIr)(1-x)PtxSb, where x denotes the Pt content. Transport measurements revealed a composition-dependent systematic change from unusual transport properties due to the extremely strong scattering of electrons and phonons for x = 0.2 to a normal metallic state for x = 1 (PtSb). T-c also varied with the Pt content, which could be attributed to the change in the electron-phonon coupling, reaching a maximum of 3.1 K at x = 0.4. This was the highest value among the transition metal mono antimonides. The H-c2 value for x = 0.2 was 7 times higher than that for x = 1, which is likely attributed to the shortening of the coherence length due to chemical disorder. This study demonstrates that extremely strong chemical disorders in high-entropy compounds may be effective in improving their superconducting properties.

The pyrochlore oxide Pb2Re2O7-delta (PRO) is a candidate spin-orbit coupled metal (SOCM) that exhibits a structural phase transition with inversion symmetry breaking. In this paper, we report on the results of detailed x-ray diffraction (XRD) measurements on single crystals of PRO to clarify the crystal structure below the phase transition temperature at Ts = 300 K. In the XRD patterns, a clear peak splitting is observed below Ts, indicating a cubic-to-tetragonal transition. Based on the group-subgroup relationship and the observed reflection conditions, the space group of the low-temperature phase is proposed to be I4122, which agrees with optical second harmonic generation measurements. This space group is the same as that of the lowest-temperature structure of the analogous SOCM Cd2Re2O7 (CRO), which is realized by the emergence of odd-parity multipole order. The comparison between PRO and CRO allows for advancing our understanding of the symmetry-lowering complex order exhibited by SOCMs.

We report the discovery of bulk superconductivity in Sc6MTe2 with seven kinds of transition-metal elements M. The critical temperatures for M=3d elements are higher than those for 4d and 5d elements and increase in the order of M=Ni, Co, and Fe with the highest Tc of 4.7 K in Sc6FeTe2. First principles calculations indicate the presence of significant contribution of Fe 3d orbitals at the Fermi energy, which most likely enhance the Tc of Sc6FeTe2. The upper critical field for M=Os is considerably enhanced by the strong spin-orbit coupling. These results show Sc6MTe2 to constitute a unique family of d-electron superconductors, in which d electrons of 3d and 5d M atoms strongly influence the superconducting properties.

An entry from the Inorganic Crystal Structure Database, the world’s repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

NaPrTe2, NaNdTe2, and NaTbTe2 are found to be triangular lattice magnets with the alpha-NaFeO2 structure, where lanthanoid atoms with 4f electrons form a triangular lattice, based on the structural analysis and physical property measurements of synthesized polycrystalline samples. The alpha-NaFeO2 structure is a new polymorph of NaPrTe2, which has been reported to crystallize in the cubic LiTiO2 structure. Polytypism in NaPrTe2 was discussed based on the structural parameters determined by the Rietveld analysis. NaPrTe2 is suggested to be in the proximity of the phase boundary between the LiTiO2 and alpha-NaFeO2 types, as compared to NaNdTe2 and NaTbTe2, indicating that this compound might be interesting from the perspectives of the dimensional control of geometrically frustrated lattices. The magnetic susceptibility and heat capacity data indicated that NaPrTe2 do not show long-range magnetic order or a spin-glass transition above 2 K.