Charge-density-wave phase transition in $1T-{\mathrm{TiSe}}_2:$  Excitonic insulator versus band-type Jahn-Teller mechanism

The influence of the charge-density-wave phase transition on the electronic structure of $1T-{\mathrm{TiSe}}_2$ is studied by means of high-resolution angle-resolved photoemission spectroscopy with synchrotron radiation. We find that both the Se $4p$-type valence band maximum at $\Gamma$ and the Ti $3d$-type conduction band minimum at L are lowered upon cooling. Our photoemission results explain the observed anomalies in the transport data and appear to be consistent with the band-type Jahn-Teller mechanism rather than with excitonic electron-hole interaction.