Temperature-dependent pseudogap and electron localization in 1T-${\mathrm{TaS}}_2$

Photoelectron spectroscopy reveals a striking correspondence between charge-density-wave-related phase transitions and modifications of the electronic structure in 1T-${\mathrm{TaS}}_2$. High-energy-resolution spectra indicate that the collapse of the Fermi surface is abrupt at the quasicommensurate-commensurate transition (∼185 K) and that, below this critical temperature, the Fermi level lies in a deep, temperature-dependent pseudogap. These results strongly suggest successive localizations due to electron correlations and disorder, and resolve an outstanding contradiction between transport data and previous spectroscopic results with lower resolution.