arXiv subjects

Masanobu Shiga

Publications and source records attributed to Masanobu Shiga.

6 recordsLinked to original sources

arXiv2026

Multiple Superconducting Phases in Palladium Deuteride Induced by Nuclear-Spin Isotope Effect

We study the superconducting properties of high-quality PdD$_{x}$ films. The resistivity shows a sharp drop at $T$ $\sim$1.7 K, marking the superconducting transition. However, a finite resistivity persists and vanishes at $\sim$0.6 K. The temperature and magnetic-field dependences of the resistivity exhibit multiple anomalies within the superconducting state, revealing distinct superconducting phases. Such anomalies are absent in PdH$_{x}$ films. These results demonstrate a clear qualitative difference between the superconducting phase diagrams of PdD$_{x}$ and PdH$_{x}$, highlighting the role of nuclear-spin isotope effects.

cond-mat.supr-con↗

arXiv2025

New quantum state formed by highly concentrated protons in superconducting palladium hydride

Hydrogen exhibits quantum phenomena, such as tunneling in materials. According to theory, the quantum properties of hydrogen change significantly in superconductors due to the emergence of an energy gap on the Fermi surface, which reduces the interaction between hydrogen nucleus (i.e., proton) and conduction electrons. This reduction is predicted to enhance the tunneling probability of protons. Here, we report the double transitions of the electrical resistivity in high-quality palladium hydride (PdHx) and deuteride (PdDx) prepared by low-temperature absorption below T = 180 K. After a sharp drop in the resistivity at T ~ 2 K owing to the superconducting transition of PdH(D)x, a large residual resistivity remained. Additionally, the resistivity dropped to zero below T = 1 K. The experimental results suggest that the quantum tunneling of highly concentrated protons (deuterons) in the superconducting state is responsible for the observed features: the residual resistivity arises from the weakening of the global coherence of superconductivity owing to the tunneling motion of protons (deuterons), while the zero resistivity is caused by long-range ordering of the protons (deuterons). This system offers a new platform for investigating the quantum many-body properties of tunneling particles.

cond-mat.supr-con↗

arXiv2024

Spin polarization driven by molecular vibrations leads to enantioselectivity in chiral molecules

Chirality pervades multiple scientific domains-physics, chemistry, biology, and astronomy-and profoundly influences their foundational principles. Recently, the chirality-induced spin selectivity (CISS) phenomenon has captured significant attention in physical chemistry due to its potential applications and intriguing underlying physics. Despite its prominence, the microscopic mechanisms of CISS remain hotly debated, hindering practical applications and further theoretical advancements. Here we challenge the established view that attributes CISS-related phenomena to current-induced spin polarization and electron transport across interfaces. We propose that molecular vibrations in chiral molecules primarily drive spin polarization, thereby governing CISS. Employing an electrochemical cell paired with a precisely engineered magnetic multilayer, we demonstrate that the magnetic interactions akin to interlayer exchange coupling are crucial for CISS. Our theoretical study suggests that molecular vibrations facilitate chirality-dependent spin polarization, which plays a pivotal role in CISS-related phenomena such as magnetoresistance and enantiomer separation using ferromagnets. These findings necessitate a paradigm shift in the design and analysis of systems in various scientific fields, extending the role of spin dynamics from traditional areas such as solid-state physics to chemical reactions, molecular biology, and even drug discovery.

cond-mat.mtrl-sci↗

arXiv2022

Observation of gigantic spin conversion anisotropy in bismuth

Whilst the g-factor can be anisotropic due to the spin-orbit interaction (SOI), its existence in solids cannot be simply asserted from a band structure, which hinders progress on studies from such the viewpoints. The g-factor in bismuth (Bi) is largely anisotropic; especially for holes at T-point, the g-factor perpendicular to the trigonal axis is negligibly small (< 0.112), whereas the g-factor along the trigonal axis is very large (62.7). We clarified in this work that the large g- factor anisotropy gives rise to the gigantic spin conversion anisotropy in Bi from experimental and theoretical approaches. Spin-torque ferromagnetic resonance was applied to estimate the spin conversion efficiency in rhombohedral (110) Bi to be 17%, which is unlike the negligibly small efficiency in Bi(111). Harmonic Hall measurements supports the large spin conversion efficiency in Bi(110). This is the first observation of gigantic spin conversion anisotropy as the clear manifestation of the g-factor anisotropy. Beyond the emblematic case of Bi, our study unveiled the significance of the g-factor anisotropy in condensed-matter physics and can pave a pathway toward establishing novel spin physics under g-factor control.

cond-mat.mtrl-sci↗

arXiv2021

Current-in-plane magnetoresistance in chiral-molecule/ferromagnetic metal bilayer due to thermally induced spin polarization

We report chirality-induced current-in-plane magnetoresistance (CIP-MR) in chiral molecule/ferromagnetic metal bilayer at room temperature. The previously reported chiralityinduced current-perpendicular-to-plane magnetoresistance (CPP-MR) originates from the chiral induced spin-selectivity (CISS) effect that needs charge-current passing through the molecule. In contrast, the observed CIP-MR in the present study requires no bias charge current through the molecule. The temperature dependence of CIP-MR suggests thermally induced spin-polarization in the chiral molecules is the key for the observed MR.

cond-mat.mtrl-sci↗

arXiv2021

Observation of spontaneous x-ray magnetic circular dichroism in a chiral antiferromagnet

X-ray magnetic circular dichroism (XMCD) signals are usually absent in antiferromagnets. In this letter, we report the observation of spontaneous XMCD spectra originating from the inverse triangular spin structure, or the polarization of the cluster magnetic octupole, in the chiral antiferromagnet Mn$_{3}$Sn thin film. The result is consistent with the recent theoretical predictions that the inverse triangular spin structure can give rise to finite XMCD signals in the absence of net magnetization [J. Phys. Soc. Jpn. 89, 083703 (2020) and Phys. Rev. Lett. 126, 157402 (2021)].

cond-mat.mtrl-sci↗