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

The vibrational spectra of the layered two-dimensional transition-metal dic halcogenide 1T-VSe2 are investigated by the methods of point-contact and Ra man spectroscopy. The measured point-contact spectra and the Raman scatteri ng spectra contain features that coincide in position and relative intensit y. Various regimes of current passage (ballistic, diffusive, and thermal) i n 1T-VSe2/Cu point contacts are investigated. Both direct and inverse point -contact spectra are recorded, the former demonstrating the effect of the e lectron-phonon interaction in 1T-VSe2 and the latter reflecting the destruc tion of localization of the electronic states in the region near the contac t, which leads to growth of the contact conductance. A study of the point c ontacts in the regime of small energy and momentum mean free paths of the e lectrons reveals nonlinearities caused by a phase transition of the materia l to a state with a charge density wave. The point-contact electron-phonon interaction function, previously unknown for this compound, is recovered fr om the data, and the values of the mean and rms phonon frequencies in 1T-VS e2 are calculated. An estimate of the Debye temperature is made. (C) 2001 A merican Institute of Physics.