Experimental Confirmation of Massive Dirac Fermions in Weak Charge-Ordering State in \alpha-(BEDT-TTF)_2I_3

TL;DR

This study provides experimental evidence that the weak charge-ordering state in -(BEDT-TTF)_2I_3 exhibits characteristics of a massive Dirac fermion system, confirmed through magnetoresistance measurements and Landau level analysis.

Contribution

First experimental confirmation that the weak charge-ordering state in -(BEDT-TTF)_2I_3 is a massive Dirac fermion state based on magnetoresistance data.

Findings

MR peak observed in weak CO state consistent with massive Dirac fermion behavior.

Magnetic-field dependence matches Landau level predictions for a massive Dirac fermion.

Weak CO state in -(BEDT-TTF)_2I_3 is identified as a massive Dirac fermion system.

Abstract

The electronic structure of weak charge-ordering (CO) state just below the critical pressure in an organic conductor \alpha-(BEDT-TTF)_2I_3 was experimentally investigated using peak structure in the temperature dependence of interlayer magnetoresistance (MR). Based on a minimal model considering multiple Landau levels (LLs), we discuss herein the MR peak as characteristic to multilayer massless/massive Dirac fermion (DF) systems. MR measured in the weak CO state exhibited a clear MR peak, and its magnetic-field dependence was consistent with the LL behavior of a massive DF with a small gap. Results indicate that the weak CO state in \alpha-(BEDT-TTF)_2I_3 is a massive DF state.