Control of Metastable Charge Density Wave Phases in Ultrathin 1T-TaS$_{2}$

Among the most intriguing aspects of reduced dimensionality in condensed matter systems is the enhancement of various correlation effects (electron-electron, electron-phonon, etc.). In quasi-2D metallic chalcogenides, they lead to electronic instabilities that give rise to a wealth of exotic ground states such as charge density waves (CDWs), spin density waves, and superconductivity. 1T-TaS$_{2}$ is a unique layered material which exhibits a number of different CDW states as well as a Mott phase at low temperatures. Although its electronic structure is largely two dimensional, the CDWs are stabilized by an out-of-plane stacking. By combining low temperature transmission electron microscopy with electrical transport measurements, we investigate how the various CDW phases in 1T-TaS$_{2}$ change as it approaches the physical 2D limit. We find that in well-controlled samples, the lock-in transition from a nearly commensurate CDW to a fully commensurate CDW gradually disappears with reduced thickness as both phases become increasingly metastable. I will discuss the physical reasons underlying this behavior as well as demonstrate how to manipulate this phase transition in few-layer samples by application of an in-plane electric field.