Spectroscopic investigations of the interaction of low-lying crystal-field excitations and optical phonons in TmVO4: Electronic davydov and magnetic phonon splitting

Abstract

Abstract We have studied by means of infrared and Raman spectroscopy the effects of mutual energy renormalisation of a 4f-crystal field transition coupled resonantly to an optical E g -phonon in tetragonal TmVO 4 . As a consequence of this coupling a phonon-mediated interionic interaction between the Tm 3+ -ions and a delocalisation of the electronic excitation energy (Davydov splitting into two exciton states with odd and even parity) is observed. The E g -phonon transition demonstrates a splitting in an external magnetic field B ext ‖ z and a strong field-dependent level anticrossing of one component with the E g -exciton. As interactions with other transitions practically do not interfere, this system presents a simple “picture-book example” of magneto-elastic effects, which can be treated theoretically in a quantitative manner.