Signature of an Ultrafast Photo-Induced Lifshitz Transition in the Nodal-Line Semimetal ZrSiTe

TL;DR

This study demonstrates an ultrafast Lifshitz transition in ZrSiTe triggered by a coherent phonon mode, revealing a rapid change in electronic topology driven by photo-excitation and lattice dynamics.

Contribution

It provides direct evidence of a symmetry-preserving phonon-induced Lifshitz transition in a nodal-line semimetal using ultrafast spectroscopy and DFT calculations.

Findings

Coherent $A_{1g}$ phonon mode strongly modifies atomic distances.

Large displacements alter the electronic band structure significantly.

A sudden change in electronic response indicates an ultrafast Lifshitz transition.

Abstract

Here we report an ultrafast optical spectroscopic study of the nodal-line semimetal ZrSiTe. Our measurements reveal that, converse to other compounds of the family, the sudden injection of electronic excitations results in a strongly coherent response of an $A_{1g}$ phonon mode which dynamically modifies the distance between Zr and Te atoms and Si layers. "Frozen phonon" DFT calculations, in which band structures are calculated as a function of nuclear position along the phonon mode coordinate, show that large displacements along this mode alter the material's electronic structure significantly, forcing bands to approach and even cross the Fermi energy. The incoherent part of the time domain response reveals that a delayed electronic response at low fluence discontinuously evolves into an instantaneous one for excitation densities larger than $3.43 \times 10^{17}$ cm$^{-3}$. This sudden change of the dissipative channels for electronic excitations is indicative of an ultrafast Lifshitz transition which we tentatively associate to a change in topology of the Fermi surface driven by a symmetry preserving $A_{1g}$ phonon mode.