The importance of three-dimensional effects in the electronic structure of the quasi two-dimensional layered crystal $1T$-Ti${\mathrm{Se}}_2$ is demonstrated by means of high-resolution angle-resolved photoemission excited by synchrotron radiation. By resolving the spin-orbit splitting of the upper Se-$4p$ valence band in $\Gamma A$ we found strong evidence for hole states at $\Gamma$. The overlap (<120 meV) between these states and the Ti-$3d$ states measured exactly at $\Gamma$ and $L$, respectively, is much smaller than previously suggested and is discussed in relation to the structural phase transition below $T_c\simeq 200$ K.

• Received 29 July 1985

DOI:https://doi.org/10.1103/PhysRevLett.55.2188