An alternative interpretation of recent ARPES measurements on TiSe ₂

Abstract

Recently there has been a renewed interest in the charge density wave transition of TiSe2, fuelled by the possibility that this transition may be driven by the formation of an excitonic insulator or even an excitonic condensate. We show here that the recent ARPES measurements on TiSe2 can also be interpreted in terms of an alternative scenario, in which the transition is due to a combination of Jahn-Teller effects and exciton formation. The hybrid exciton-phonons which cause the CDW formation interpolate between a purely structural and a purely electronic type of transition. Above the transition temperature, the electron-phonon coupling becomes ineffective but a finite mean-field density of excitons remains and gives rise to the observed diffuse ARPES signals.