Orbital design of Berry curvature: pinch points and giant dipoles induced by crystal fields

TL;DR

This paper explores how crystal fields in low-symmetry materials can induce localized and singular Berry curvature features, leading to giant dipoles and enhanced nonlinear transport effects without the need for hole excitations.

Contribution

It reveals that crystal fields can generate Berry curvature hot-spots and pinch points in materials with orbital degrees of freedom, independent of hole excitations, which is a novel mechanism.

Findings

Crystal fields induce Berry curvature hot-spots and pinch points.

Giant Berry curvature dipoles are observed in these materials.

Enhanced nonlinear transport responses are achieved without hole excitations.

Abstract

The Berry curvature (BC) - a quantity encoding the geometric properties of the electronic wavefunctions in a solid - is at the heart of different Hall-like transport phenomena, including the anomalous Hall and the non-linear Hall and Nernst effects. In non-magnetic quantum materials with acentric crystalline arrangements, local concentrations of BC are generally linked to single-particle wavefunctions that are a quantum superposition of electron and hole excitations. BC-mediated effects are consequently observed in two-dimensional systems with pairs of massive Dirac cones and three-dimensional bulk crystals with quartets of Weyl cones. Here, we demonstrate that in materials equipped with orbital degrees of freedom local BC concentrations can arise even in the complete absence of hole excitations. In these solids, the crystals fields appearing in very low-symmetric structures trigger BCs characterized by hot-spots and singular pinch points. These characteristics naturally yield giant BC dipoles and large non-linear transport responses in time-reversal symmetric conditions.