Adam Tsen, Columbia University
Among the most intriguing aspects of reduced dimensionality in solids is the enhancement of correlation effects (electron-electron, electron-phonon, etc.). In the layered metallic chalcogenides, this gives rise to the formation of various collective electron phases such as charge density waves (CDWs), spin density waves, and superconductivity. In the past, studies on monolayer graphene and various semiconducting dichalcogenides have shown that taking layered materials to their physical two-dimensional limit leads to fundamental changes in band structure, allowing for a powerful experimental knob to tune for electronic functionality. In contrast, the effect of thickness control over these collective electron phases has been largely unexplored. By combining cryogenic transmission electron microscopy with electrical transport measurements, we investigate how the various CDW structures in 1T-TaS2 change with lower dimensionality. We find that in well-controlled samples, the discommensuration melting transition at low temperatures gradually disappears with reduced thickness. I will discuss the physical reasons underlying this behavior as well as demonstrate how to further manipulate this phase transition in few-layer devices by application of an in-plane electric field.