Resonant ultrasound spectroscopy in the charge density wave and Weyl semimetal candidate compounds NbTe₄ and TaTe₄

Transition metal chalcogenides are an example of quantum materials, which show, topological states, charge density wave (CDW) formation, and ferroic orders. Within this family, the transition metal tetracalcogenides, NbTe4 and TaTe4, have captured the interest of the scientific community for being candidates to present axionic states connecting different Weyl points on the fermi surface through CDW formation. This represents a possibility to study the relationship between topological states of matter and correlated electronic states such as CDW. Diffraction, scanning tunneling spectroscopy, angle resolved photoemission spectroscopy and transport measurements have revealed important information about the CDW formation in these compounds. For instance, resistivity measurements as a function of temperature in these materials suggest possible phase transitions at certain temperatures, which, for the case of NbTe4, could be related to reconfigurations of the CDW order. However, bulk thermodynamic measurements that can give more insight into the nature of such transitions are still missing. Here we will present resonant ultrasound spectroscopy (RUS) measurements for NbTe4 and TaTe4 single crystals, in order to get thermodynamic information of the reported putative phase transitions at different temperatures, through the determination of the temperature dependence of the elastic constants. For NbTe4 we find that the resonance frequencies, directly related to the elastic constants, are highly hysteretical in the temperature range of 100K to 300K, which can be directly related to the presence and dynamics of the recently reported CDW domain walls (DWs)[1]. In contrast, TaTe4 do not show such hysteretical behavior. These results suggest that DWs in NbTe4 play a fundamental role in both, the electronic and elastic properties of NbTe4.

[1] Galvis, J. A. and Fang, A. and Jim'enez-Guerrero, D. and Rojas-Castillo, J. and Casas, J. and Herrera, O. and Garcia-Castro, A. C. and Bousquet, E. and Fisher, I. R. and Kapitulnik, A. and Giraldo-Gallo, P. Nanoscale phase-slip domain walls in the charge density wave state of the Weyl semimetal candidate NbTe4,American Physical Society 2023