arXiv subjects

Saori I. Kawaguchi

Publications and source records attributed to Saori I. Kawaguchi.

6 recordsLinked to original sources

arXiv2026

Unveiling pressurized bulk superconductivity in a trilayer nickelate Pr4Ni3O10 single crystal

The recent discovery of superconductivity in pressurized Ruddlesden-Popper (RP) nickelates has provided new perspectives on the mechanism of high-temperature superconductivity. Up to now, most experiments concentrated on the lanthanum-related RP phase, so the discovery of new superconducting RP nickelates is highly desirable to reveal their generality. Here we report that high-quality Pr4Ni3O10 single crystal is grown with an optical floating zone furnace under high oxygen pressure. High-pressure transport measurements show that the superconducting state arises above 10 GPa, and the maximum Tc reaches 39 K without saturation, significantly exceeding the value of 25-30 K of La4Ni3O10. Ultrasensitive d.c. magnetic susceptibility measurements under high pressure indicate bulk superconductivity with appreciable superconducting volume fractions. By performing in situ high-pressure synchrotron X-ray diffraction measurements at 16 K, a structural transition is found from monoclinic to tetragonal. Unlike La4Ni3O10, the electronic structure of the high-pressure phase of Pr4Ni3O10 from density functional theory exhibits a dramatic metallization of the sigma-bonding band consisting of three dz2 orbitals and van Hove singularity of coupled bands of dx2-y2 orbitals near the Fermi level, similar to the bilayer nickelate La3Ni2O7. These findings reveal some generic features of both crystal and electronic structures for high-temperature superconductivity in nickelates and multi-layer cuprates.

cond-mat.supr-con↗

arXiv2025

Superconducting-insulating phase transition in pressurized Ba1-xKxBiO3

We report the first observation of a pressure-induced transition from a superconducting (SC) to an insulating (I) phase in single-crystal Ba1-xKxBiO3 (x = 0.4, 0.43, 0.52, and 0.58) superconductors. X-ray diffraction measurements conducted at 20 K reveal a direct relationship between this SC-I transition and a pressure-induced distortion of crystal structure. With increasing pressure, the lattice parameters a and c of the ambient-pressure superconducting tetragonal (T) phase are compressed continuously below a critical pressure (Pc1), wherein the pressure (P) dependence of superconducting transition temperature (Tc) displays a small variation. However, upon further compression, the lattice of the compressed T phase displays an anisotropic change, and Tc shows a monotonous decrease. When the pressure reaches Pc2 (Pc2 > Pc1), the compressed T phase collapses along the c axis, followed by the disappearance of superconductivity and the appearance of the insulating phase. This SC-I transition is fully reversible, with the critical pressure increasing alongside K doping concentration. These findings are strikingly similar to the SC-I transition observed in hole-doped high-Tc cuprate superconductors under pressure. Identifying their commonalities could deepen our understanding of the mechanisms that underlie high- Tc superconductivity in these two oxide superconductors with a perovskite structure.

cond-mat.supr-con↗

arXiv2023

Superconductivity above 30 K achieved in dense scandium

Superconductivity is one of most intriguing quantum phenomena, and the quest for elemental superconductors with high critical temperature (Tc) is of great scientific significance due to their relatively simple material composition and the underlying mechanism. Here we report the experimental discovery of densely compressed scandium (Sc) becoming the first elemental superconductor with Tc breaking into 30 K range, which is comparable to the Tc values of the classic La-Ba-Cu-O or LaFeAsO superconductors. Our results show that Tconset of Sc increases from ~3 K at around 43 GPa to ~32 K at about 283 GPa (Tczero ~ 31 K), which is well above liquid neon temperature. Interestingly measured Tc shows no sign of saturation up to the maximum pressure achieved in our experiments, indicating that Tc might be even higher upon further compression.

cond-mat.supr-con↗

arXiv2023

Structure responsible for the superconducting state in La3Ni2O7 at high pressure and low temperature conditions

Very recently, a new superconductor with Tc = 80 K was reported in nickelate (La3Ni2O7) at around 15 - 40 GPa conditions (Nature, 621, 493, 2023) [1], which is the second type of unconventional superconductor, beside the cuprates, with Tc above liquid nitrogen temperature. However, the phase diagram plotted in this report was mostly based on the transport measurement at low temperature and high pressure conditions, and the assumed corresponding X-ray diffraction (XRD) results was carried out at room temperature. This encouraged us to carry out in situ high pressure and low temperature synchrotron XRD experiments to determine which phase is responsible for the high Tc state. In addition to the phase transition from orthorhombic Amam structure to orthorhombic Fmmm structure, a tetragonal phase with space group of I4/mmm was discovered when the sample was compressed to 19 GPa at 40 K where the superconductivity takes palce in La3Ni2O7. The calculations based on this tetragonal structure reveal that the electronic states approached to the Fermi energy were mainly dominated by the eg orbitals (3dz2 and 3dx2-y2) of Ni atoms, which are located in the oxygen octahedral crystal field. The correlation between Tc and this structural evolution, especially Ni-O octahedra regularity and the in-plane Ni-O-Ni bonding angles, are analyzed. This work sheds new lights to identify what is the most likely phase responsible for superconductivity in the double layered nickelate.

cond-mat.supr-con↗

arXiv2023

Absence of Tc-Pinning Phenomenon Under High Pressure in High-Entropy REO0.5F0.5BiS2 Layered Superconductor

Recently, robustness of superconductivity (transition temperature, Tc) under high pressures has been observed in high-entropy alloy (HEA), bcc-type Ti-Zr-Hf-Nb-Ta, and HEA-type compounds (Ag,In,Sn,Pb,Bi)Te with a NaCl-type structure. Since those materials have three-dimensional crystal structure, investigation on the pressure dependence of Tc of low-dimensional materials is needed to understand the phenomena. Here, we investigated the superconducting properties and the crystal structure of BiS2-based layered system REO0.5F0.5BiS2. Although the robustness of Tc was induced in MTe with increasing M-site configurational entropy, the increase in RE-site configurational entropy does not induce robustness of Tc under high pressures in REO0.5F0.5BiS2. The crystal structure of HEA-type REO0.5F0.5BiS2 was confirmed as monoclinic P21/m, which is the same space group as the zero-entropy counterpart LaO0.5F0.5BiS2. The results suggest that an increase in configurational entropy at blocking layers do not affect crystal structure and superconducting properties under high pressures in the BiS2-based layered system.

cond-mat.supr-con↗

arXiv2020

High-pressure effects on superconducting properties and crystal structure of Bi-based layered superconductor La2O2Bi3Ag0.6Sn0.4S6

The effects of pressure on the superconducting properties of a Bi-based layered superconductor La2O2Bi3Ag0.6Sn0.4S6, which possesses a four-layer-type conducting layer, have been studied through the electrical resistance and magnetic susceptibility measurements. The crystal structure under pressure was examined using synchrotron X-ray diffraction at SPring-8. In the low-pressure regime, bulk superconductivity with a transition temperature Tc of ~ 4.5 K was induced by pressure, which was achieved by in-plane chemical pressure effect owing to the compression of the tetragonal structure. In the high-pressure regime above 6.4 GPa, a structural symmetry lowering was observed, and superconducting transitions with a Tc ~ 8 K were observed. Our results suggest the possible commonality on the factor essential for Tc in Bi-based superconductors with two-layer-type and four-layer-type conducting layers.

cond-mat.supr-con↗