Time-Reversal Symmetry-Breaking Flux State in an Organic Dirac Fermion System

TL;DR

This paper explores how pressure induces a flux state in an organic Dirac fermion system, breaking time-reversal symmetry and producing measurable thermoelectric effects consistent with experiments.

Contribution

It demonstrates the emergence of a flux state with broken time-reversal symmetry in an organic Dirac fermion system due to Coulomb interactions, supported by theoretical calculations matching experimental data.

Findings

Broken time-reversal symmetry via flux formation

Large Nernst signal observed and computed

Thermopower consistent with experimental results

Abstract

We investigate symmetry breaking in the Dirac fermion phase of the organic compound $\alpha$-(BEDT-TTF)$_2$I$_3$ under pressure, where BEDT-TTF denotes bis(ethylenedithio)tetrathiafulvalene. The exchange interaction resulting from inter-molecule Coulomb repulsion leads to broken time-reversal symmetry and particle-hole symmetry while preserving translational symmetry. The system breaks time-reversal symmetry by creating fluxes in the unit cell. This symmetry-broken state exhibits a large Nernst signal as well as thermopower. We compute the Nernst signal and thermopower, demonstrating their consistency with experimental results.