arXiv subjects

Shin-ichi Hikino

Publications and source records attributed to Shin-ichi Hikino.

7 recordsLinked to original sources

arXiv2026

Spin Josephson diode effect induced by higher-harmonic spin Josephson currents in a diffusive Josephson junction

We theoretically investigate the spin Josephson diode effect (SJDE) in a diffusive Josephson junction with a Rashba metal layer under a ferromagnetic exchange field. Within the quasiclassical Green's function framework, we derive analytical expressions for the first- and second-harmonic spin Josephson currents. The interplay between Rashba spin-orbit interaction and the exchange field breaks inversion and time-reversal symmetries, generating additional cosine terms in the spin current-phase relations and a finite phi0 phase shift. This phase shift induces an intrinsic asymmetry between forward and backward spin currents, leading to the SJDE without an external magnetic field. Numerical results show that the efficiency decreases with increasing metal thickness due to suppression of the second-harmonic component, while its dependence on spin-orbit interaction strength reflects competing effects between phase shift enhancement and harmonic suppression. These findings demonstrate that the interplay between harmonic components provides a mechanism for nonreciprocal spin transport without requiring suppression of spin-singlet correlations.

cond-mat.supr-con↗

arXiv2025

Perturbative Analysis of the Field-Free Josephson Diode Effect in a Multilayered Josephson Junction

The Josephson diode effect (JDE) is a novel phenomenon in which a superconducting junction exhibits asymmetric Josephson currents with respect to the superconducting phase difference. In this study, we theoretically investigate how the interplay between a static exchange field and Rashba spin-orbit interaction (RSOI) influences the JDE. By employing the quasiclassical Green's function method and perturbative calculations, we derive analytical expressions for the Josephson current in a junction composed of a ferromagnetic layer and a normal metal with RSOI. Remarkably, the JDE is found to emerge even in the absence of any external magnetic field. In this regime, the Josephson current is exclusively carried by spin-triplet Cooper pairs, as spin-singlet components are strongly suppressed by the ferromagnet. Furthermore, our results show that the efficiency of the JDE can be enhanced by tuning the thickness of the normal metal and the strength of the RSOI. These findings offer valuable theoretical guidelines for the design of superconducting devices exhibiting nonreciprocal transport effects.

cond-mat.supr-con↗

arXiv2018

Magnetization Reversal by Tuning Rashba Spin-Orbit Interaction and Josephson Phase in a Ferromagnetic Josephson Junction

We theoretically investigate the magnetization inside a normal metal containing the Rashba spin-orbit interaction (RSOI) induced by the proximity effect in an s-wave superconductor/normal metal/ferromagnetic metal/s-wave superconductor (S/N/F/S) Josephson junction. By solving the linearized Usadel equation taking account of the RSOI,we find that the direction of the magnetization induced by the proximity effect in N can be reversed by tuning the RSOI.Moreover, we also find that the direction of the magnetization inside N can be reversed by changing the superconducting phase difference, i.e., Josephson phase. From these results, it is expected that the dependence of the magnetization on the RSOI and Josephson phase can be applied to superconducting spintronics.

cond-mat.supr-con↗

arXiv2017

Theoretical study of magnetism induced by proximity effect in a ferromagnetic Josephson junction with a normal metal

We theoretically study the magnetism induced by the proximity effect in the normal metal of ferromagnetic Josephson junction composed of two $s$-wave superconductors separated by ferromagnetic metal/normal metal/ferromagnetic metal junction (${S}/{F}/{N}/{F}/{S}$ junction). We calculate the magnetization in the $N$ by solving the Eilenberger equation. We show that the magnetization arises in the ${N}$ when the product of anomalous Green's functions of the spin-triplet even-frequency odd-parity Cooper pair and spin-singlet odd-frequency odd-parity Cooper pair in the ${N}$ has a finite value. The induced magnetization $M(d,θ)$ can be decomposed into two parts, $M(d,θ)=M^{\rm I}(d)+M^{\rm II}(d,θ)$, where $d$ is the thickness of $N$ and $θ$ is superconducting phase difference between two ${S}$s. Therefore, $θ$ dependence of $M(d,θ)$ allows us to control the amplitude of magnetization by changing $θ$. The variation of $M(d,θ)$ with $θ$ is indeed the good evidence of the magnetization induced by the proximity effect, since some methods of magnetization measurement pick up total magnetization in the ${S}/{F}/{N}/{F}/{S}$ junction.

cond-mat.supr-con↗

arXiv2014

0-$π$ transition driven by magnetic proximity effect in a Josephson junction

We theoretically study the Josephson effect in a superconductor/normal metal/superconductor ({\it S}/{\it N}/{\it S}) Josephson junction composed of $s$-wave {\it S}s with {\it N} which is sandwiched by two ferromagnetic insulators ({\it F}s), forming a spin valve, in the vertical direction of the junction. We show that the 0-$π$ transition of the Josephson critical current occurs with increasing the thickness of {\it N} along the junction. This transition is due to the magnetic proximity effect (MPE) which induces ferromagnetic magnetization in the {\it N}. Moreover, we find that, even for fixed thickness of {\it N}, the proposed Josephson junction with the spin valve can be switched from $π$ to 0 states and vice versa by varying the magnetization configuration (parallel or antiparallel) of two {\it F}s. We also examine the effect of spin-orbit scattering on the Josephson critical current and argue that the 0-$π$ transition found here can be experimentally observed within the current nanofabrication techniques, thus indicating a promising potential of this junction as a 0-$π$ switching device operated reversibly with varying the magnetic configuration in the spin valve by, e.g., applying an external magnetic field. %with the magnetization configuration in the spin valve. Our results not only provide possible applications in superconducting electronics but also suggest the importance of a fundamental concept of MPE in nanostructures of multilayer {\it N}/{\it F} systems.

cond-mat.supr-con↗

arXiv2012

Towards precise measurement of oscillatory domain wall by ferromagnetic Josephson junction

We theoretically propose a principle for precise measurement of oscillatory domain wall (DW) by a ferromagnetic Josephson junction, which is composed of a ferromagnetic wire with DW and two superconducting electrodes. The current-voltage curve exhibits stepwise structures, only when DW oscillates in the ferromagnetic wire. The voltage step appears at V = n(\hbar/2e)ω_DW with the fundamental constant \hbar/e, integer number n, and the DW frequency ω_DW. Since V can be determined in the order of 10^9 accuracy, the oscillatory DW will be measured more precisely than present status by conventional method.

cond-mat.supr-con↗

arXiv2011

First-principles study of the spin-mixing conductance in Pt/Ni$_{81}$Fe$_{19}$ junctions

Based on the spin-pumping theory and first-principles calculations, the spin-mixing conductance (SMC) is theoretically studied for Pt/Permalloy (Ni$_{81}$Fe$_{19}$, Py) junctions. We evaluate the SMC for ideally clean Pt/Py junctions and examine the effects of interface randomness. We find that the SMC is generally enhanced in the presence of interface roughness as compared to the ideally clean junctions. Our estimated SMC is in good quantitative agreement with the recent experiment for Pt/Py junctions. We propose possible routes to increase the SMC in Pt/Py junctions by depositing a foreign magnetic metal layer in Pt, offering guidelines for designing the future spintronic devices.

cond-mat.mes-hall↗