Zero-field and time-reserval-symmetry-broken topological phase transitions in graphene

TL;DR

This paper predicts a zero-field topological phase transition in strained graphene nanoribbons, enabling control of quantum spin Hall and quantum anomalous Hall states through strain, SOC, and exchange fields, without magnetic fields.

Contribution

It introduces a novel zero-field topological phase transition in graphene, controllable via strain and SOC, expanding possibilities for quantum device manipulation.

Findings

Zero-field topological phase transition predicted between QSH and QAH states.

Strain-induced pseudomagnetic field couples to spin, affecting edge states.

Controllable transition via strain strength and direction.

Abstract

We propose a quantum electronic device based on strained graphene nanoribbon. Mechanical strain, internal exchange field and spin-orbit couplings (SOCs) have been exploited as principle parameters to tune physical properties of the device. We predict a remarkable zero-field topological quantum phase transition between the time-reversal-symmetry broken quantum spin hall (QSH) and quantum anomalous hall (QAH) states, which was previously thought to take place only in the presence of finite magnetic field. We illustrate as intrinsic SOC is tuned, how two different helicity edge states located in the opposite edges of the nanoribbon exchange their locations. Our results indicates that pseudomagnetic field induced by the strain could be coupled to the spin degrees of freedom through the SOC responsible for the stability of QSH state. The controllability of this zero-field phase transition with strength and direction of the strain is also demonstrated. Our prediction offers a tempting prospect of strain, electric and magnetic manipulation of the QSH effect.