Tunable correlation-driven symmetry breaking in twisted double bilayer graphene

TL;DR

This study investigates the correlated phases in twisted double bilayer graphene, revealing spontaneous symmetry breaking as a key mechanism behind resistivity drops and nonlinear transport, with implications for broader flat band heterostructures.

Contribution

It provides the first detailed electrical transport measurements showing spontaneous symmetry breaking in tDBG, highlighting its role in correlated metallic phases.

Findings

Resistivity drops indicate symmetry breaking rather than superconductivity.

Hall coefficient reversals suggest spontaneous symmetry breaking.

Nonlinear $I$-$V$ characteristics are due to Joule heating.

Abstract

A variety of correlated phases have recently emerged in select twisted van der Waals (vdW) heterostructures owing to their flat electronic dispersions. In particular, heterostructures of twisted double bilayer graphene (tDBG) manifest electric field-tunable correlated insulating (CI) states at all quarter fillings of the conduction band, accompanied by nearby states featuring signatures suggestive of superconductivity. Here, we report electrical transport measurements of tDBG in which we elucidate the fundamental role of spontaneous symmetry breaking within its correlated phase diagram. We observe abrupt resistivity drops upon lowering the temperature in the correlated metallic phases neighboring the CI states, along with associated nonlinear $I$-$V$ characteristics. Despite qualitative similarities to superconductivity, concomitant reversals in the sign of the Hall coefficient instead point to spontaneous symmetry breaking as the origin of the abrupt resistivity drops, while Joule heating appears to underlie the nonlinear transport. Our results suggest that similar mechanisms are likely relevant across a broader class of semiconducting flat band vdW heterostructures.