arXiv subjects

Kyohei Nakamura

Publications and source records attributed to Kyohei Nakamura.

3 recordsLinked to original sources

arXiv2026

Superconducting diode effect in correlated electron systems by nonreciprocal magnetism

The superconducting diode effect (SDE), characterized by a nonreciprocal critical current in superconductors, has recently been observed in strongly correlated electron systems and near quantum criticality, pointing to unconventional mechanisms beyond weak-coupling theories. Here we investigate the SDE in the Rashba-Zeeman-Hubbard model, which captures $d$-wave superconductivity in an antiferromagnetic quantum critical regime, using the Dyson-Gor'kov equation with the fluctuation exchange approximation. We show that electron correlations suppress the conventional intrinsic SDE arising from depairing currents. More importantly, a supercurrent nonreciprocally induces antiferromagnetic order, which fundamentally governs the critical current and enables perfect diode efficiency. Our results reveal a previously unrecognized correlation-driven mechanism of the SDE and establish strongly correlated superconductors as a platform for superconducting diode physics.

cond-mat.supr-con↗

arXiv2025

Supercurrent-induced antiferromagnetic order and spin-triplet pair generation in quantum critical d-wave superconductors

A supercurrent is well recognized as being of prime importance within mean-field theory, but remains largely unexplored in strongly correlated electron systems (SCES) and the quantum critical region. To clarify the impact of the supercurrent on magnetism and superconductivity near an antiferromagnetic quantum critical point, we study the two-dimensional Hubbard model based on a fluctuation exchange approximation for a current-carrying superconducting state. We show a supercurrent-induced antiferromagnetism and emergence of spin-triplet Cooper pairs. The former results from Bogoliubov Fermi surfaces, suppression in the superconducting gap, and strong correlation effects beyond the mean-field theory. Our results suggest that the supercurrent can bring out rich phenomena of superconductivity in SCES.

cond-mat.supr-con↗

arXiv2023

Orbital effect on intrinsic superconducting diode effect

Much ink has recently been spilled on nonreciprocal phenomena in superconductors, especially the superconducting diode effect (SDE) characterized by the nonreciprocity of the critical current $ΔJ_c$. Contrary to the fundamental and practical significance of the SDE, the precise underlying mechanism remains unclear. In this paper, we investigate the impact of an orbital effect on the intrinsic SDE in a bilayer superconductor with Rashba spin-orbit coupling and an in-plane magnetic field. We show that a small orbital effect leads to the sign reversal of $ΔJ_c$ and a crossover of the helical superconducting state at a lower magnetic field than the monolayer superconductor. On the other hand, a large orbital effect induces a decoupling transition, stabilizing a finite momentum Cooper pairing state called the orbital Fulde-Ferrell-Larkin-Ovchinnikov state, and results in the drastic change of the SDE. Owing to the orbital effect, the field dependence of the SDE may show oscillations several times. The results shed light on the mechanism of the SDE in atomically-thin multilayer superconductors.

cond-mat.supr-con↗