Emergent Quantum-Geometric Equivalence of Injection and Shift Currents

TL;DR

This paper reveals a fundamental connection between injection and shift currents in nonlinear optics, showing they can be governed by the same quantum geometric properties in certain materials.

Contribution

It uncovers a hidden relation between injection and shift currents via interband Berry-curvature and quantum-metric dipoles, especially in Dirac and Weyl semimetals.

Findings

Injection and shift currents are governed by the same quantum-geometric dipole in certain regimes.

In Dirac and Weyl semimetals, these currents probe a unified geometric property.

The relation simplifies the interpretation of nonlinear optical measurements.

Abstract

Injection and shift currents are generally regarded as distinct nonlinear optical responses with separate microscopic origins. Here, we uncover a general hidden connection between them through interband Berry-curvature and quantum-metric dipoles. In systems with approximately linear electronic dispersion near the Fermi level and at low photon energies, this relation sharpens into an emergent equivalence, with injection and shift currents governed by the same interband quantum-geometric dipole. This regime is naturally realized in Dirac and Weyl semimetals, as well as in strained graphene, where measurements of injection and shift currents probe a unified geometric property of the electronic wavefunctions rather than distinct dynamical processes. Our results establish a new framework for interpreting nonlinear optical experiments and suggest that quantum geometry may provide a broader organizing principle linking seemingly distinct nonlinear optical responses in solids.