Three Dimensional Metallic and Two Dimensional Insulating Behavior in   Tantalum Dichalcogenides
  Using density functional theory with added on-site interactions (DFT+U), we study the electronic structure of bulk, monolayer, and bilayer of the layered transition-metal dichalcogenide $1T-TaS_2$. We show that a two-dimensional spin--$\frac{1}{2}$ Mott-phase exists for the monolayer in the charge-density wave state (CDW) and that such a phase is systematically destroyed by packing of the distorted layers leading to a one dimensional metal for bulk, CDW-distorted TaS$_2$. The latter finding is in contrast with previous DMFT predictions --disagreement we explain by the weak effective interaction felt by the electrons in the CDW state. Experimental observations of insulating behavior may arise from disorder due to stacking faults. 
Pierre Darancet, Andrew J. Millis, Chris A. Marianetti
cond-mat.mtrl-sci cond-mat.mes-hall