Monitoring and Controlling Charge-Density-Waves in 2D Materials*

Several layered transition metal dichalcogenides (TMDs) exhibit unusually high transition temperatures to different charge-density-wave (CDW) symmetry-reducing phases, revealing interesting physics, and opening possibility for practical applications of such materials. One of the most promising materials, 1T-TaS2, has the CDW transition between the nearly-commensurate (NC-CDW) and the incommensurate (IC-CDW) phases at 350 K, the transition to the normal metal phase at 550 K − 600 K. In this invited talk, I will review our recent results on controlling the CDW phase transitions in 2D materials with applied electric bias, and monitoring them via low-frequency electronic noise spectroscopy [1-6]. The noise spectroscopy has been particularly effective for monitoring the switching from the IC-CDW phase to the normal metal phase in 1T-TaS2. The noise spectral density exhibits sharp increases at the phase transition points, which correspond to the step-like changes in resistivity. The noise spectroscopy was instrumental in revealing the “hidden phase transitions” in vertical 1T-TaS2 devices. Preliminary data on the “narrow-band noise” in quasi-2D CDW devices will also be presented. We found that the 1T-TaS2 CDW devices reveal exceptional hardness against X-ray and proton radiations. We explained this property of the CDW devices by the high carrier concentration in all their phase states, two-terminal design, and the thin-film channel geometry.
[1] G. Liu, et al., Nature Nanotechnology, 11, 845 (2016); [2] G. Liu, et al., IEEE Electron Device Letters, 38, 1724 (2017); [3] A. K. Geremew, et al., Nanoscale, 11, 8380 (2019); [4] A. K. Geremew, et al., ACS Nano, 13, 7231 (2019); [5] R. Salgado, et al., Appl. Phys. Express, 12, 037001 (2019).