Interplay between bandwidth-controlled and filling-controlled pressure-induced Mott insulator to metal transition in the molecular compound [Au(Et-thiazdt) 2]

Optical properties of the quasi-two-dimensional single-component molecular Mott insulator [Au(Et-thiazdt)2] (Et-thiazdt = N-ethyl-1,3-thiazoline-2-thione-4,5-dithiolate) have been investigated under pressure at room temperature. At 1.5 GPa, [Au(Et-thiazdt)2] undergoes an insulator to metal transition (IMT). Optical conductivity spectra exhibit a clear Drude peak at high pressure. In addition, we observed a clear anisotropy of pressure-induced modifications of the electronic structure. With increasing pressure, along the molecule stacks, a strong increase of the spectral weight below 1 eV is observed, while in the transverse direction, it remains barely constant with a redistribution from midinfrared to low energy. Besides the increase of the singly occupied molecular orbital (SOMO) bandwidth, calculations show that the SOMO-1 bands cross the Fermi level at the transition. Moreover, we have calculated the optical conductivity as a function of pressure to provide a picture of the compound physics under 1 eV. Our results indicate that the pressure-induced IMT is simultaneously due to a bandwidth and a band-filling phenomenon that imply both Mott physics and uncorrelated charge carriers.