Low-Frequency Noise and Sliding of the Charge Density Waves in Two-Dimensional Materials.

There has been a recent renewal of interest in charge-density-wave (CDW) phenomena, primarily driven by the emergence of two-dimensional (2D) layered CDW materials, such as 1T-TaS2, characterized by very high transition temperatures to CDW phases. In the extensively studied classical bulk CDW materials with quasi-1D crystal structure, the charge carrier transport exhibits intriguing sliding behavior, which reveals itself in the frequency domain as "narrowband" and "broadband" noise. Despite the increasing attention on physics of 2D CDWs, there have been few reports of CDW sliding, specifically in quasi-2D rare-earth tritellurides and none on the noise in any of 2D CDW systems. Here we report the results of low-frequency noise (LFN) measurements on 1T-TaS2 thin films - archetypal 2D CDW systems, as they are driven from the nearly commensurate (NC) to incommensurate (IC) CDW phases by voltage and temperature stimuli. We have found that noise in 1T-TaS2 devices has two pronounced maxima at the bias voltages, which correspond to the onset of CDW sliding and the NC-to-IC phase transition. We observed unusual Lorentzian noise features and exceptionally strong noise dependence on electric bias and temperature. We argue that LFN in 2D CDW systems has unique physical origin, different from known fundamental noise types. The specifics of LFN in 2D CDW materials can be explained by invoking the concept of interacting discrete fluctuators in the NC-CDW phase. Noise spectroscopy can serve as a useful tool for understanding electronic transport phenomena in 2D CDW materials characterized by coexistence of different phases and strong CDW pinning.