Fulde-Ferrel-Larkin-Ovchinnikov Inhomogeneous Superconducting State and Phase Transitions Induced by Spin Accumulation in a Ferromagnet-$ d_{x^{2}-y^{2}}$-Wave Superconductor-Ferromagnet Tunnel Junction

TL;DR

This paper theoretically predicts the emergence of FFLO inhomogeneous superconducting states and various phase transitions induced by spin accumulation in a ferromagnet-d-wave superconductor-ferromagnet tunnel junction, revealing a complex phase diagram with critical points.

Contribution

It introduces a theoretical model predicting FFLO states, phase transitions, and critical points in a ferromagnet-d-wave superconductor-ferromagnet junction, expanding understanding of spin accumulation effects.

Findings

First-order transitions from homogeneous to inhomogeneous states.

Second-order transitions from superconducting to normal state.

Identification of Lifshitz, bicritical, and quantum critical points.

Abstract

Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) inhomogeneous superconducting (SC) state, first- and second-order phase transitions, and quantum criticality induced by spin accumulation in a ferromagnet-$d_{x^{2}-y^{2}}$-wave superconductor-ferromagnet tunnel junction are theoretically predicted. A complex phase diagram in the temperature-bias voltage plane is determined. It is found that the phase transitions from the homogeneous BCS state to the inhomogeneous FFLO state, and from the FFLO state with the momentum $\mathbf{% q}$'s azimuthal angle $\theta_{\mathbf{q}}=0$ to that with $\theta_{% \mathbf{q}}=\pi /4$, are of the first-order; while the transitions from all SC states to the normal state at critical voltages are of the second-order. A Lifshitz point, a bicritical point and a quantum critical point are identified.