Experimental Confirmation of Quantum Hall Ferromagnetic State in an Organic Dirac Fermion System

TL;DR

This paper experimentally confirms a quantum Hall ferromagnetic state with a helical edge state in an organic Dirac fermion system, demonstrating topological phase behavior in organic molecular crystals.

Contribution

First experimental observation of a topological quantum Hall ferromagnetic state with helical edge states in an organic material.

Findings

Interlayer resistance saturates at low temperatures and high magnetic fields.

Resonant dependence of resistance on magnetic field direction.

Evidence that helical edge states dominate transport.

Abstract

We have experimentally confirmed the quantum Hall ferromagnetic state with Chern number \nu=0, characterized by the helical edge state, in a layered organic Dirac fermion system \alpha-(BEDT-TTF)_2I_3. The interlayer resistance saturates at low temperatures and high magnetic fields. It does not scale with the sample cross-sectional area in the saturating region, and resonantly depends on the magnetic field direction. These results strongly suggest that the helical edge state dominates transport. This is the first observation of the topological phase in organic molecular crystals.