Optical conductivity as a probe of the interaction-driven metal in rhombohedral trilayer graphene

TL;DR

This paper demonstrates how optical conductivity measurements can distinguish between various interaction-driven metallic states in rhombohedral trilayer graphene, providing clear experimental signatures for identifying the ground state.

Contribution

The study introduces a theoretical framework showing how optical conductivity can differentiate candidate metallic phases in RTG, guiding experimental identification.

Findings

Single peak in fully gapped valence-bond state

Two peaks in bond-current state optical conductivity

Minimal conductivity independent of order parameter in charge-density wave

Abstract

Study of the strongly correlated states in van der Waals heterostructures is one of the central topics in modern condensed matter physics. Among these, the rhombohedral trilayer graphene (RTG) occupies a prominent place since it hosts a variety of interaction-driven phases, with the metallic ones yielding exotic superconducting orders upon doping. Motivated by these experimental findings, we show within the framework of the low-energy Dirac theory that the optical conductivity can distinguish different candidates for a paramagnetic metallic ground state in this system. In particular, this observable shows a single peak in the fully gapped valence-bond state. On the other hand, the bond-current state features two pronounced peaks in the optical conductivity as the probing frequency increases. Finally, the rotational symmetry breaking charge-density wave exhibits a minimal conductivity with the value independent of the amplitude of the order parameter, which corresponds precisely to the splitting of the two cubic nodal points at the two valleys into two triplets of the band touching points featuring linearly dispersing quasiparticles. These features represent the smoking gun signatures of different candidate order parameters for the paramagnetic metallic ground state, which should motivate further experimental studies of the RTG.