# A Hybrid-Monte-Carlo study of monolayer graphene with partially screened Coulomb interactions at finite spin density

## TL;DR

This study uses Hybrid-Monte-Carlo simulations to explore the effects of partially screened Coulomb interactions on monolayer graphene at finite spin density, revealing interaction-driven Fermi surface warping and a potential quantum phase transition at the van Hove singularity.

## Contribution

It provides the first non-perturbative simulation evidence that interactions can turn the Lifshitz transition into a quantum phase transition in graphene.

## Key findings

- Interaction-induced warping of Fermi contours
- Reduction of bandwidth consistent with experiments
- Lifshitz transition becomes a quantum phase transition

## Abstract

We report on Hybrid-Monte-Carlo simulations at finite spin density of the $\pi$-band electrons in monolayer graphene with realistic inter-electron interactions. Unlike simulations at finite charge-carrier density, these are not affected by a fermion-sign problem. Our results are in qualitative agreement with an interaction-induced warping of the Fermi contours, and a reduction of the bandwidth as observed in angle resolved photoemission spectroscopy experiments on charge-doped graphene systems. Furthermore, we find evidence that the neck-disrupting Lifshitz transition, which occurs when the Fermi level traverses the van Hove singularity (VHS), becomes a true quantum phase transition due to interactions. This is in-line with an instability of the VHS towards the formation of electronic ordered phases, which has been predicted by a variety of different theoretical approaches.