Spectroscopy of the electron–phonon interaction in the layered two-dimensional dichalcogenide 1T–VSe2

Abstract

The vibrational spectra of the layered two-dimensional transition-metal dichalcogenide 1T–VSe2 are investigated by the methods of point-contact and Raman spectroscopy. The measured point-contact spectra and the Raman scattering spectra contain features that coincide in position and relative intensity. Various regimes of current passage (ballistic, diffusive, and thermal) in 1T–VSe2/Cu point contacts are investigated. Both direct and inverse point-contact spectra are recorded, the former demonstrating the effect of the electron–phonon interaction in 1T–VSe2 and the latter reflecting the destruction of localization of the electronic states in the region near the contact, which leads to growth of the contact conductance. A study of the point contacts in the regime of small energy and momentum mean free paths of the electrons reveals nonlinearities caused by a phase transition of the material to a state with a charge density wave. The point-contact electron–phonon interaction function, previously unknown for this compound, is recovered from the data, and the values of the mean and rms phonon frequencies in 1T–VSe2 are calculated. An estimate of the Debye temperature is made.