Nonlinear bulk photocurrent probe Z2 topological phase transition

TL;DR

This paper demonstrates that nonlinear bulk photocurrents, such as shift and injection currents, can effectively detect Z2 topological phase transitions by exhibiting polarity reversal, providing a direct optical signature of the transition.

Contribution

It introduces nonlinear bulk photocurrents as a novel, robust probe for Z2 topological phase transitions, validated through theoretical models and first-principles calculations.

Findings

Photocurrent polarity reverses across the topological transition.

Band inversion drives the topological phase change.

Nonlinear photocurrents serve as sensitive probes for Z2 phases.

Abstract

Detecting topological phase transitions in bulk is challenging due to the limitations of surface sensitive probes like ARPES. Here, we demonstrate that nonlinear bulk photocurrents, specifically shift and injection currents, serve as effective probes of Z_2 topological transitions. These photocurrents show a robust polarity reversal across the Z_2 phase transition, offering a direct optical signature that distinguishes strong topological phases from weak or trivial ones. This effect originates from a reorganization of key band geometric quantities, the Berry curvature and shift vector, on time-reversal-invariant momentum planes. Using a low energy Dirac model, we trace this behaviour to a band inversion in the time-reversal-invariant momentum plane that drives the topological transition. We validate these findings through tight-binding model for Bi_2Te_3 and first-principles calculations for ZrTe_5 and BiTeI, where the topological phase can be tuned by pressure or temperature. Our results establish nonlinear photocurrent as a sensitive and broadly applicable probe of Z_2 topological phase transitions.