Correlated quantum shift vector of particle-hole excitations

TL;DR

This paper reveals that excitonic electron-hole pairs exhibit a unique, polarization-independent quantum shift vector, highlighting the non-perturbative effects of electron interactions on quantum geometric responses in materials.

Contribution

It introduces the concept of a correlated quantum shift vector for excitons, showing its independence from light polarization and its role as a diagnostic for particle-hole pair localization.

Findings

Excitonic shift vectors are polarization-independent, unlike non-interacting excitations.

Vanishing shift vectors in certain materials suppress shift photocurrent.

Shift vector behavior reveals electron interaction effects on quantum geometry.

Abstract

Excitons are a prime example of how electron interactions affect optical response and excitation. We demonstrate that, beyond its spectra, the bound nature of an exciton's electron-hole pair produces a correlated quantum geometry: excitonic excitations possess a quantum shift vector that is independent of light polarization. We find this counterintuitive behavior has dramatic consequences for geometric response: e.g., in noncentrosymmetric but non-polar materials, vertical excitonic transitions possess vanishing shift vector zeroing their shift photocurrent; this contrasts with finite and strongly light polarization dependent shift vectors for non-interacting delocalized particle-hole excitations. This dichotomy makes shift vector a sharp diagnostic of the pair localization properties of particle-hole excitations and demonstrates the non-perturbative effects of electron interactions in excited state quantum geometric response.