# Topological pairings in Janus monolayer TaSSe

## TL;DR

This study investigates the topological superconducting states in Janus monolayer H-TaSSe, revealing the emergence of full-gap, topologically nontrivial pairings influenced by strong Rashba effects, with potential for helical or chiral topological superconductivity.

## Contribution

It is the first to analyze the pairing symmetry and topological states in Janus monolayer H-TaSSe, highlighting the influence of Rashba effects on topological superconductivity.

## Key findings

- Identified a full-gap, topologically nontrivial s+f+p-wave pairing at higher chemical potentials.
- Discovered a time-reversal broken d+p+f pairing with large Chern number at lower chemical potentials.
- Suggested H-TaSSe as a candidate for helical or chiral topological superconductor.

## Abstract

The Janus monolayer transition metal dichalcogenides[TMDs] MXY[M=Mo,W, etc. and X,Y=S,Se, etc.] has been synthesized recently, and the Rashba spin splitting arises in it owing to the breaking of out-of-plane mirror symmetry[\href{https://journals.aps.org/prb/abstract/10.1103/PhysRevB.97.235404}{Phys. Rev. B 97, 235404 (2018)}]. Here we study the pairing symmetry of superconducting Janus monolayer H-TaSSe by solving the linearized gap equation at the critical temperature $T_c$. We find that the strong Rashba effect in H-TaSSe could produce topological superconducting states which differs from that in its parent monolayer H-TaS$_2$ and H-TaSe$_2$. More specifically, at the chemical potential $\mu>-0.08$eV, we obtain a time-reversal invariant s+f+p-wave mixed pairing state. This pairing state is full-gap and topologically nontrivial, i.e. $\mathbb{Z}_2=1$. However, a time-reversal broken d+p+f pairing belonging to the 2-dimensional irreducible representation $E$ appears at lower chemical potential. It can host a large Chern number $C=-6$ at appropriate pairing strengths. The results suggest the monolayer H-TaSSe to be a candidate helical or chiral topological superconductor.