H. Kadobayashi | Searcharxiv

arXiv2026

Coupled structural and electronic evolution under pressure in CuIr2Se4, CuRh2S4, and CuRh2Se4

Spinel chalcogenides provide a platform for investigating the interplay among metallic, superconducting, and pressure-induced insulating states. Here, we combine synchrotron powder X-ray diffraction and electrical-resistivity measurements to investigate the pressure evolution of CuIr2Se4, CuRh2S4, and CuRh2Se4 over pressure ranges extending beyond those previously explored. High-pressure diffraction reveals closely related monoclinic supercells in all three compounds. For CuIr2Se4 and CuRh2S4, constrained profile fits based on structural models relaxed using density functional theory are compatible with Phase-IV-type bond-disproportionated structures, whereas the data for CuRh2Se4 establish a compatible monoclinic unit cell without resolving its atomic-scale ordering pattern. Insulating-like transport develops abruptly over a narrow pressure range in CuIr2Se4 but more gradually over broader pressure ranges in the Rh-based compounds, in close correspondence with their respective structural transformations. We also establish previously unreported bulk superconductivity in CuIr2Se4 at ambient pressure: zero resistance is attained at 0.29 K, and the accompanying ac diamagnetic response is consistent with nearly complete superconducting shielding. These results establish a close relationship between the formation of the high-pressure monoclinic phases and the evolution toward insulating transport, and demonstrate that transition-metal and chalcogen substitutions tune the characteristic pressure scales and the competition with superconductivity within a closely related structural framework.

cond-mat.mtrl-sci↗

arXiv2023

Anomalous charge transport upon quantum melting of chiral spin order

A plethora of correlated and exotic metallic states have been identified on the border of itinerant magnetism, where the long-range spin texture is melted by tuning the magnetic transition temperature (T$_C$) towards zero, referred to as the quantum phase transition (QPT). So far, the study of QPT in itinerant magnets has mainly focused on low-T$_C$ materials (i.e., typically T$_C$ ~ 10 K) where the modification of electronic band structure is subtle, and only makes a small contribution to the QPT. Here we report a distinct example of a magnetic QPT accompanied by a gigantic modification of the electronic structure in FeGe, i.e., a well-studied itinerant chiral magnet hosting near-room-temperature (T$_C$ = 278 K) helical/skyrmion spin texture. The pressure-driven modification of the band structure (e.g., reduction of exchange splitting) is evidenced by magneto-transport study, suggesting a Fermi-surface reconstruction around the magnetic QPT (P ~19 GPa), in stark contrast to the case of typical metallic ferromagnets. Further application of pressure leads to a metal-to-insulator transition above P > 30 GPa, as also corroborated by our density-functional theory (DFT) calculation. Of particular interest is the occurrence of anomalous magneto-transport in the inhomogeneous short-range chiral-spin ground state (P = 20-30 GPa) above the QPT, with longitudinal fluctuations of magnetization. The unexpected observation of spontaneous anomalous Hall effect in this exotic quantum regime suggests macroscopic time-reversal symmetry (TRS) breaking, even in the absence of long-range magnetic order. Our findings mark the large body of unexplored high-T$_C$ itinerant magnets with broken inversion-symmetry as promising candidates of novel ground state formation near QPT.

cond-mat.str-el↗