All-Optical Steering of Competing Topological Pathways in ZrTe₅.

Abstract

All-optical topological control offers a pathway toward ultrafast manipulation of quantum phases with minimal dissipation. Here we demonstrate that mode-selective coherent-phonon excitation in ZrTe₅ enables deterministic steering of the lattice across symmetry-distinct topological phases. Displacive driving of the Raman-active <i>A</i>_1<i>g</i> mode reshapes the potential energy surface and induces a femtosecond transition sequence from a strong topological insulator to a Dirac semimetal and subsequently to a weak topological insulator. Beyond a critical atomic displacement, nonlinear phonon coupling activates the infrared <i>B</i>_1<i>u</i> mode, breaks inversion symmetry, and opens an alternative route to a Weyl semimetal. At higher excitation strengths, bandgap renormalization and modified electron-phonon coupling induce a nonmonotonic <i>B</i>_1<i>u</i> response, revealing competing symmetry-preserving and symmetry-breaking pathways. Building on these insights, we propose a dual-color control scheme that enables directional phase selection. These results establish a mode-resolved framework for ultrafast navigation of topological phase space, verifiable via ultrafast transport or diffraction techniques.