Berry Phase Dynamics of Sliding Electron Crystals

TL;DR

This paper theoretically investigates the unique sliding dynamics of topologically nontrivial electron crystals in two-dimensional materials, revealing how Berry curvature and quantum geometry influence their transport properties and Hall conductance.

Contribution

It introduces a model for the sliding behavior of anomalous Hall crystals considering quantum geometry effects, highlighting non-quantized Hall conductance contributions.

Findings

Transverse anomalous velocity arises from Berry curvature and non-invariance.

Acceleration modifies internal current beyond static values.

Net Hall conductance is generally not quantized due to internal and center-of-mass contributions.

Abstract

Systems such as Wigner crystals and incommensurate charge density waves that spontaneously break a continuous translation symmetry have unusual transport properties arising from their ability to slide coherently in space. Recent experimental and theoretical studies suggest that spontaneous translation symmetry breaking in some two-dimensional materials with nontrivial quantum geometry (e.g., rhombohedral pentalayer graphene) leads to a topologically nontrivial electron crystal state called the anomalous Hall crystal and characterized by a vanishing linear-response dc longitudinal conductivity and a non-vanishing Hall conductivity. In this work we present a theoretical investigation of the sliding dynamics of this new type of electron crystal, taking into account the system's nontrivial quantum geometry. We find that when accelerated by an external electric field, the crystal acquires a transverse anomalous velocity that stems from not only the Berry curvature of the parent band but also the Galilean non-invariance of the crystal state (i.e., crystal states with different momenta are not related by simple momentum boosts). We further show that acceleration of the crystal modifies its internal current from the static crystal value that is determined by the Chern number of the crystal state. The net Hall conductance including contributions from center-of-mass motion and internal current is in general not quantized. As an experimentally relevant example, we present numerical results in rhombohedral pentalayer graphene and discuss possible experimental implications.