Ginzburg-Landau theory of noncentrosymmetric superconductors

TL;DR

This paper develops a Ginzburg-Landau theory for noncentrosymmetric superconductors with Rashba spin-orbit coupling, explaining observed anomalies in superfluid density and penetration depth data through a two-transition temperature model.

Contribution

It introduces a microscopic Ginzburg-Landau framework for noncentrosymmetric superconductors, predicting two distinct transition temperatures and explaining experimental features like the superfluid density kink.

Findings

Prediction of two transition temperatures, T_c and T^*.

Explanation of the superfluid density kink at T^*.

Estimation of critical field near T_c.

Abstract

The data of temperature dependent superfluid density $n_s(T)$ in Li$_2$Pd$_3$B and Li$_2$Pt$_3$B [Yuan {\it et al.}, \phrl97, 017006 (2006)] show that a sudden change of the slope of $n_s (T)$ occur at slightly lower than the critical temperature. Motivated by this observation, we microscopically derive the Ginzburg-Landau (GL) equations for noncentrosymmetric superconductors with Rashba type spin orbit interaction. Cooper pairing is assumed to occur between electrons only in the same spin split band and pair scattering is allowed to occur between two spin split bands. The GL theory of such a system predicts two transition temperatures, the higher of which is the conventional critical temperature $T_c$ while the lower one $T^*$ corresponds to the cross-over from a mixed singlet-triplet phase at lower temperatures to only spin-singlet or spin-triplet (depending on the sign of the interband scattering potential) phase at higher temperatures. As a consequence, $n_s (T)$ shows a kink at this cross-over temperature. We attribute the temperature at which sudden change of slope occurs in the observed $n_s (T)$ to the temperature $T^*$. This may also be associated with the observed kink in the penetration depth data of CePt$_3$Si. We have also estimated critical field near critical temperature.