Topological Valley Currents in Gapped Dirac Materials

TL;DR

This paper explores dissipationless valley currents in gapped 2D Dirac materials, highlighting their topological nature, bulk origin, and quantized Hall conductivity, even without edge modes.

Contribution

It reveals that topological valley currents are primarily bulk-driven and quantized, independent of edge states, in gapped Dirac materials with broken inversion symmetry.

Findings

Bulk valley currents dominate over edge modes.

Valley Hall conductivity is quantized at half-integer values.

Under-gap currents significantly influence magnetization and charge Hall effects.

Abstract

Gapped 2D Dirac materials, in which inversion symmetry is broken by a gap-opening perturbation, feature a unique valley transport regime. The system ground state hosts dissipationless persistent valley currents existing even when topologically protected edge modes are absent or when they are localized due to edge roughness. Topological valley currents in such materials are dominated by bulk currents produced by electronic states just beneath the gap rather than by edge modes. Dissipationless currents induced by an external bias are characterized by a quantized half-integer valley Hall conductivity. The under-gap currents dominate magnetization and the charge Hall effect in a light-induced valley-polarized state.