Fluctuation-Induced Magnetoelectric Effect in Noncentrosymmetric Superconductors

Abstract

We study the effect of superconducting fluctuations on the spin susceptibility and NMR relaxation rate in noncentrosymmetric two-dimensional materials above the superconducting transition temperature, considering arbitrary strength of impurity scattering. Employing a microscopic model with linear Rashba spin-orbit coupling, we show that superconducting fluctuations give rise to a direct contribution to the spin susceptibility through fluctuation-induced Cooper pairs. This fluctuation-driven magnetoelectric effect is possible even for purely $s$-wave singlet pairing, a mechanism that is forbidden in centrosymmetric systems. It competes with the reduction of the susceptibility below the Pauli value arising from the combined effects of the suppression of the density of states and quantum-interference localization processes. In contrast, superconducting fluctuations enhance the NMR relaxation rate above its normal-state Korringa value, with spin-orbit coupling providing an additional amplification of this effect.