Pairing mechanism of unconventional superconductivity in doped Kane-Mele model

TL;DR

This paper investigates how spin-orbit coupling influences the pairing symmetry in a doped Kane-Mele model, revealing a transition from spin-singlet to spin-triplet pairing as spin-orbit coupling increases.

Contribution

It demonstrates the emergence of spin-triplet f-wave pairing in the Kane-Mele model due to increased spin-orbit coupling, using RPA calculations.

Findings

Weak spin-orbit coupling favors ESE pairing.

Strong spin-orbit coupling favors ETO f-wave pairing.

Longitudinal spin fluctuations support ETO pairing.

Abstract

We study the pairing symmetry of a doped Kane-Mele model on a honeycomb lattice with on-site Coulomb interaction. The pairing instability of Cooper pair is calculated based on the linearized Eliashberg equation within the random phase approximation (RPA). When the magnitude of the spin-orbit coupling is weak, even-frequency spin-singlet even-parity (ESE) pairing is dominant. On the other hand, with the increase of the spin-orbit coupling, we show that the even-frequency spin-triplet odd-parity (ETO) f-wave pairing exceeds ESE one. ETO f-wave pairing is supported by the longitudinal spin fluctuation. Since the transverse spin fluctuation is strongly suppressed by spin-orbit coupling, ETO f-wave pairing becomes dominant for large magnitude of spin-orbit coupling.