Symmetry-breaking-induced topology in FeSe

TL;DR

This paper demonstrates that breaking tetragonal symmetry in bulk FeSe via strain or structural changes can induce a strong topological insulating phase, supported by DFT and many-body calculations, revealing a new route to topological phases in this material.

Contribution

The study introduces a novel approach to realize topological phases in bulk FeSe by symmetry-breaking, supported by comprehensive theoretical calculations including DFT and dynamical mean field theory.

Findings

Breaking $C_4$ symmetry induces topological insulating phase in FeSe.

Uniaxial strain and temperature changes lead to non-trivial band topology.

Topological features remain robust under electronic correlations.

Abstract

FeSe has been one of the most intensively studied iron-based superconductors over the past two decades, exhibiting a wide range of phenomena such as unconventional superconductivity, nematic order, magnetism, orbital-selective correlations, and structural phase transitions. While topologically non-trivial phases have been identified in certain cases -- such as Te-doped FeSe and monolayer FeSe -- topology in bulk FeSe has largely remained unexplored. In this work, we propose a new route to realize topological phases directly in bulk FeSe. We demonstrate that breaking the tetragonal $C_4$ rotational symmetry, thereby lowering the crystal symmetry, can drive FeSe into a strong topological insulating phase. To support this, we perform density functional theory calculations and analyze the band structure using Topological Quantum Chemistry and symmetry-based indicators. Our results show that both uniaxial strain and temperature-induced structural changes lead to non-trivial band topology. Moreover, incorporating electronic correlations through dynamical mean field theory reveals that the topological characteristics near the Fermi level remain robust, as the relevant bands experience only moderate renormalization. These findings highlight strain as a promising mechanism to induce topological phases in FeSe