Charge Density Wave Vortex Lattice Observed in Graphene-Passivated 1T-TaS<sub>2</sub> by Ambient Scanning Tunneling Microscopy
Michael Altvater, Nikhil Tilak, Skandaprasad Rao, Guohong Li, Choongjae Won, Sang‐Wook Cheong, Eva Y. Andrei
Abstract
The nearly commensurate charge density wave (CDW) excitations native to the transition-metal dichalcogenide crystal, 1T-TaS2, under ambient conditions are revealed by scanning tunneling microscopy (STM) and spectroscopy (STS) measurements of a graphene/TaS2 heterostructure. Surface potential measurements show that the graphene passivation layer prevents oxidation of the air-sensitive 1T-TaS2 surface. The graphene protective layer does not however interfere with probing the native electronic properties of 1T-TaS2 by STM/STS, which revealed that nearly commensurate CDW hosts an array of vortex-like topological defects. We find that these topological defects organize themselves to form a lattice with quasi-long-range order, analogous to the vortex Bragg glass in type-II superconductors but accessible in ambient conditions.