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

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 A1g 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 × 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 A1g phonon mode.

NMR determination of Van Hove singularity and Lifshitz transitions in nodal-line semimetal ZrSiTe

“…In ZrSiSe, transport results were recently proposed to give evidence for even larger T -induced changes of µ [15]. For the present case, we assume it is relative shifts of band energies that contribute to this process causing the node to shift relative to µ, perhaps induced by the promotion of carriers from donor states, in a manner akin to the changes that have been proposed [17] to accompany the optical promotion of carriers in ZrSiTe.…”

“…The sharp VHS adjacent to the protected nodal line implies that additional electronic features relying upon the enhanced g(E) could be engineered into this system [26][27][28][29][30], by tuning E F to the VHS. Tuning could be accomplished by chemical pressure [43], physical pressure or strain [16,44], and light activation [17] with the re-quired energy difference being quite small. This could be another avenue for switching the topological behavior for quantum computing applications.…”

“…Its large region of topologically protected drumhead surface states [13] as well as very large spin Berry curvature and associated spin Hall and Nernst response [14] suggest spintronic and related applications. Suggested changes of Fermi surface topology in this family include a temperature-induced Lifshitz transition in ZrSiSe [15], and a pressure-induced Lifshitz transition in ZrSiTe [16] as well as indications of photo-induced phonon driven transformation [17].…”