Strain-induced quantum phase transitions in magic angle graphene

TL;DR

This paper studies how tiny uniaxial strains in magic-angle twisted bilayer graphene can induce quantum phase transitions, explaining some experimental variability through theoretical calculations.

Contribution

It demonstrates that small strains can cause phase transitions in magic-angle graphene, highlighting strain as a key factor in experimental observations.

Findings

Strain induces a transition from a Kramers intervalley-coherent insulator to a nematic semi-metal.

Critical strain values match those observed experimentally.

Strain effects are significant in understanding sample-dependent behaviors.

Abstract

We investigate the effect of uniaxial heterostrain on the interacting phase diagram of magic-angle twisted bilayer graphene. Using both self-consistent Hartree-Fock and density-matrix renormalization group calculations, we find that small strain values ($\epsilon \sim 0.1 - 0.2 \%$) drive a zero-temperature phase transition between the symmetry-broken Kramers intervalley-coherent insulator and a nematic semi-metal. The critical strain lies within the range of experimentally observed strain values, and we therefore predict that strain is at least partly responsible for the sample-dependent experimental observations.