Time resolved core level spectroscopy reveals light-induced structural changes in GdTe3

Abstract

Complex materials frequently exhibit broken symmetry phases, driven by a delicate balance of electronic, lattice, spin and orbital anisotropies. In this context, new phases of matter may emerge when this equilibrium is disturbed by photoexcitation. Here we investigate the response to ultrafast optical excitation of the GdTe₃ charge density wave (CDW) compound, by time-resolved X-ray photoemission spectroscopy (TR-XPS). By measuring the energy separation between two atomic species of Te 4d core levels, we identify a sharp discontinuity occurring precisely at the CDW transition temperature, confirming the sensitivity of this technique to the onset of the CDW order. Optical excitation with a novel Echelon-based pulse-replication scheme reveals the formation of a third low-valence tellurium specie, absent under equilibrium conditions, indicative of a light-induced structural rearrangement. The study provides new information on the rich dynamics in GdTe₃ and opens new avenues for research in this field by using TR-XPS at synchrotron sources.