arXiv subjects

Riku Iimori

Publications and source records attributed to Riku Iimori.

3 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

Electrical manipulation of magnetic domain structure in van der Waals ferromagnetic Fe$_3$GaTe$_2$ using ferroelectric PMN-PT single crystal

2D van der Waals (vdW) ferromagnets have emerged as promising materials for spintronic applications due to their unique magnetic properties and tunability. Controlling ferromagnetism via external stimuli is critical for both fundamental research and device integration. In particular, modulation of magnetic anisotropy and exchange interactions through strain offers a viable pathway for functional control. Owing to their weak interlayer coupling, vdW ferromagnets exhibit pronounced sensitivity to strain, enabling effective tuning of their magnetic states. In this study, electric-field-induced magnetoelectric coupling is investigated in the above-room-temperature vdW ferromagnet Fe$_3$GaTe$_2$ integrated on a ferroelectric PMN-PT substrate. It is demonstrated that application of an electric field leads to a substantial reduction in coercive force along with dynamic reconfiguration of the magnetic domain structure. These effects are attributed to electric-field-induced modulation of the vdW interlayer gap and enhancement of the Dzyaloshinskii-Moriya interaction. These findings reveal a strong interplay between electric fields and magnetism in vdW systems, offering a viable route toward the development of low-power, multifunctional magnetic devices. This work establishes a foundation for the electric-field control of magnetic properties in vdW ferromagnets and highlights their potential in next-generation spintronic technologies.

cond-mat.mtrl-sci↗

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↗