arXiv subjects

Ryohei Oishi

Publications and source records attributed to Ryohei Oishi.

5 recordsLinked to original sources

arXiv2026

Piezomagnetic effect of a rare-earth-based altermagnet TbPt6Al3

We have investigated the piezomagnetic (PZM) effect of the rare-earth-based g-wave altermagnet TbPt6Al3 by magnetization measurements of single-crystalline samples under uniaxial stress sigma. The magnetization in magnetic field along the trigonal a axis increases linearly with sigma for T < TN, indicating the emergence of PZM effect, while the theoretically predicted nonlinear PZM effect was not observed. PZM coefficient of Q11 at 2 K is obtained as 9.1 times 10^-3 mu_B/(f.u. MPa), which is larger by more than two orders of magnitude than those for other altermagnets and noncollinear antiferromagnets. Temperature dependence of Q11 below TN yielded the critical component beta as 0.28, whose value is close to that of the magnetic moment estimated by the neutron powder diffraction. We propose that the large Q11 and the large poling field of 10000 Oe to achieve the single-domain state in TbPt6Al3 are due to the strong relativistic spin-orbit coupling of the 4f electrons in the Tb3+ ions.

cond-mat.str-el↗

arXiv2025

Antiferromagnetic Order and Magnetic Frustration in the Honeycomb Heavy-Fermion System Ce(Pt$_{1-x}$Pd$_{x}$)$_6$Al$_3$: $^{27}$Al and $^{195}$Pt NMR Studies

Heavy-fermion systems with magnetic frustration offer a rich platform for investigating the interplay among Kondo screening, magnetic frustration, and quantum criticality. We report comprehensive $^{27}$Al and $^{195}$Pt nuclear magnetic resonance measurements on polycrystalline Ce(Pt$_{1-x}$Pd$_{x}$)$_6$Al$_3$ ($x = 0$, 0.1, 0.2, and 0.3). For $x = 0$, the Knight shift, linewidth, and nuclear spin-lattice relaxation rate reveal a paramagnetic heavy-fermion ground state persisting down to 0.1~K, characterized by a coherence temperature $T_{\mathrm{coh}} \simeq 15$~K. Substituting Pd induces antiferromagnetic order at $T_{\mathrm{N}} \simeq 3.5$~K, while suppressing $T_{\mathrm{coh}}$. Comparison between $x = 0.1$ and $x = 0.3$ reveals a crossover from itinerant spin-density-wave antiferromagnetism to more localized-moment antiferromagnetism, indicating a shift toward the localized side of the Doniach phase diagram. These findings establish Ce(Pt$_{1-x}$Pd$_{x}$)$_6$Al$_3$ as a tunable platform to explore the competition between Kondo screening and magnetic frustration.

cond-mat.str-el↗

arXiv2024

Electronic states in superconducting type-II Dirac semimetal: 1T-PdSeTe

We have investigated the surface and bulk electronic structures of the superconducting type-II Dirac semimetal 1T-PdSeTe. The superconducting transition temperature $T_C = 3.2$ K was almost twice as high as $T_C = 1.6$ K in 1T-PdTe$_2$. Scanning transmission electron microscopy measurements showed homogeneously mixed Se and Te atoms in the chalcogen layers, consistent with the CdI$_2$-type crystal structure. Angle-resolved photoemission spectroscopy measurements and density functional theory calculations indicated the existence of the topological surface states, and the overall band structures were similar to those of 1T-PdTe$_2$. These results suggest that CdI$_2$-type lattice symmetry dictates the band dispersion, regardless of atomic disorder in the chalcogen layers. As the electronic band dispersion and the local structures were persistent upon substitution, the enhancement of $T_C$ is likely associated with the chemical pressure. Our results provide insight into the effects of the solid solution on the surface and bulk electronic states as well as the superconducting transition temperature.

cond-mat.supr-con↗

arXiv2024

Structural Evolution from Hyper-Honeycomb to Honeycomb Networks and Superconductivity in LaPt$_x$Si$_{2-x}$

We report the crystal structures and superconductivity (SC) of LaPt$_{x}$Si$_{2-x}$ ($0.5 \leq x \leq 1.0$) that are solid solutions of LaSi$_{2}$ and LaPtSi with centrosymmetric tetragonal ($I4_{1}/amd$, $D_{4h}^{19}$, \#141) and non-centrosymmetric tetragonal ($I4_{1}md$, $C_{4v}^{11}$, \#109) structures, respectively. It was found that at $0.86 \leq x \leq 1.00$, the non-centrosymmetric tetragonal symmetry is preserved, while partial disorder appears in alternating Pt and Si of the hyper-honeycomb network. The superconducting transition temperature $T_{\rm c}$ was drastically reduced from 3.9 K to 1.5 K as $x$ varies from 1.0 to 0.86. Additionally, a hexagonal phase with an AlB$_{2}$-type structure ($P6/mmm$, $D_{6h}^{1}$, \#191) has been discovered at $0.50 \leq x \leq 0.71$ with a honeycomb network of statistically distributed Pt and Si atoms. The hexagonal phase exhibited SC at $T_{\rm c} = 0.38$ K. This system provides an opportunity to investigate the relationship between topological electronic states, SC, and disorders

cond-mat.supr-con↗

arXiv2023

Enhancement of density of states and suppression of superconductivity in site-disordered topological metal LaPtSi

Single crystals of non-centrosymmetric $s$-wave superconductor LaPt$_{0.88}$Si$_{1.12}$ have been grown by the Czochralski (Cz) technique, whose crystal structure is described by the space group $I4{_1}md$ at ambient conditions. The inter-site mixing between platinum and silicon is confirmed by both single-crystal x-ray diffraction (SXRD) and electron probe micro-analyzer (EPMA). The disordered material exhibits a lower superconducting (SC) transition temperature $T_c$ at 2.02 K as opposed to the highest value of 3.9 K reported in polycrystalline LaPtSi without inter-site mixing. From specific heat, the Sommerfeld coefficient ($γ$) is estimated to be 7.85 mJ/mol K$^2$, which is much larger than the values reported for the samples exhibiting higher $T_c$. This is unprecedented as $T_c$ seems to decrease with increase in the electron density of states (DOS) at the Fermi energy and thus $γ$. The present work reports on the anomalous behaviour of SC and normal state properties of LaPt$_{x}$Si$_{2-x}$, presumably caused due to the existence of non-trivial topological bands.

cond-mat.supr-con↗