Mott transition in the Hubbard model on anisotropic honeycomb lattice with implications for strained graphene: Gutzwiller variational study

TL;DR

This study investigates how applying strain to a honeycomb lattice, similar to graphene, induces a Mott transition, revealing that electron correlations become significant even without a full transition to an insulator.

Contribution

It introduces a computationally efficient Gutzwiller-based approach to predict strain-induced Mott transitions in honeycomb lattices, with implications for strained graphene.

Findings

Critical Hubbard $U$ decreases significantly under uniaxial strain.

Graphene remains semimetallic even at high strains, but shows signs of electron correlation effects.

Band narrowing and reduced double occupancies are observable signatures of correlations.

Abstract

Modification of interatomic distances due to high pressure leads to exotic phenomena, including metallicity, superconductivity and magnetism, observed in materials not showing such properties in normal conditions. In two-dimensional crystals, such as graphene, atomic bond lengths can be modified by more that 10 percent by applying in-plane strain, i.e., without generating high pressure in the bulk. In this work, we study the strain-induced Mott transition on a honeycomb lattice by using computationally inexpensive techniques, including Gutzwiller Wave Function (GWF) and different variants of Gutzwiller Approximation (GA), obtaining the lower and upper bounds for critical Hubbard repulsion ($U$) of electrons. For uniaxial strain in the armchair direction the band gap is absent, and electron correlations play a dominant role. A significant reduction of the critical Hubbard $U$ is predicted. Model considerations are mapped onto tight-binding Hamiltonian for monolayer graphene by the auxiliary Su-Schrieffer-Heeger model for acoustic phonons, assuming zero stress in the direction perpendicular to the strain applied. Our results suggest that graphene, although staying in semimetallic phase even for extremely high uniaxial strains, may show measurable signatures of electron correlations, such as the band narrowing and the reduction of double occupancies.