First-order metal-to-metal phase transition and non-Fermi-liquid behavior in a two-dimensional Mott insulating layer adsorbed on a metal substrate

Abstract

The electronic structure of a two-dimensional Mott insulating layer in contact with a semi-infinite metal substrate is studied within cluster dynamical mean field theory. For this purpose, the overlayer forming a square lattice is divided into an array of ($2\ifmmode\times\else\texttimes\fi{}2$)-site clusters in which interatomic electron correlations are taken into account explicitly. In striking contrast to the single-site approximation, where substrate-adsorbate hybridization gives rise to Fermi-liquid properties at low temperature, short-range correlations lead to bad metallicity in a much wider parameter range as a function of temperature and overlayer-substrate coupling strength. The $(\ensuremath{\pi},0)$ component of the self-energy exhibits a finite low-energy scattering rate, which increases with decreasing temperature even when hybridization between overlayer and substrate states is as large as the nearest-neighbor hopping energy within the overlayer. In addition, at moderate overlayer-substrate coupling and in the presence of the second nearest-neighbor hopping interaction, the overlayer undergoes a first-order phase transition between two correlated metallic phases when electron doping is increased by changing the chemical potential. These results suggest that normal metal proximity effects are strongly modified when spatial fluctuations in the overlayer are taken into consideration.