Scanning tunneling microscopy of the charge-density-wave structure in 1T-TaS2.

Abstract

Using scanning tunneling microscopy (STM), we studied 1T-${\mathrm{TaS}}_{2}$ in all four of its charge-density-wave (CDW) supporting phases over the temperature range 360--143 K. Special attention was given to the search for discommensurate structures and the distinguishing of true CDW discommensurations and domains from apparent discommensurations and domains formed by interference between the CDW and the atomic lattice. In the lowest-temperature commensurate (C) phase, we find that the CDW is in the commensurate configuration as expected. We use the C phase to investigate the effects of multiple tips and find that shifts in the apparent registration of the CDW relative to the atomic lattice result. In the nearly commensurate (NC) phase, the CDW is in a true domain structure as evidenced by satellite spots in the Fourier transforms of the STM images. In the triclinic (T) phase, the STM data indicate that the CDW is in a striped domain phase, which is significantly different from the domain model previously proposed. Finally, in the high-temperature incommensurate (I) phase, we find unexpected satellite spots in the STM Fourier transforms, suggesting that a CDW modulation is also present in this phase.