Lattice distortion induced first and second order topological phase transition in rectangular high-T$_{\rm c}$ superconducting monolayer

TL;DR

This paper theoretically investigates how lattice distortions in a rectangular FeSeTe monolayer induce topological phase transitions, enabling the coexistence of topological states and high-temperature superconductivity, with implications for Majorana states.

Contribution

It demonstrates that unidirectional pressure causes band inversion and C4 symmetry breaking, facilitating topological phases and Majorana corner states in FeSeTe monolayers without detailed pairing assumptions.

Findings

Band inversion occurs over a wide doping range under unidirectional pressure.

C4 symmetry breaking enables Majorana corner states in the monolayer.

Edge states exhibit different Dirac energies along different directions.

Abstract

We theoretically study the lattice distortion induced first and second order topological phase transition in rectangular FeSe$_{x}$Te$_{1-x}$ monolayer. When compressing the lattice constant in one direction, our first principles calculation shows that the FeSe$_x$Te$_{1-x}$ undergoes a band inversion at $\Gamma$ point in a wide dopping range, say $x\in(0.0,0.7)$, which ensures coexistence of the topological band state and the high-T$_{\rm c}$ superconductivity. This unidirectional pressure also leads to the C$_4$ symmetry breaking which is necessary for the monolayer FeSe$_x$Te$_{1-x}$ to support Majorana corner states in the either presence or absence of time-reversal symmetry. Particularly, we use $k\cdot p$ methods to fit the band structure from the first principles calculation and found that the edge states along the $(100)$ and $(010)$ directions have different Dirac energy due to C$_4$ symmetry breaking. This is essential to obtain Majorana corner states in D class without concerning the details of the superconducting pairing symmetries and Zeeman form, which can potentially bring advantages in the experimental implementation.