(a,b) Frequency spectra of displacements at various temperatures in run-1 (a) and run-2 (b). The current-induced signals are highlighted by green arrows. (c) Temperature dependence of the MPE signals (dots) and background (BG) signals (closed triangles) in run-1 and run-2. These plots are obtained from the data in (a,b). Background levels are estimated by the 10-kHz values of the fitted curves for the spectra: A/f + B, where f is the frequency and A and B are fitting parameters. (d) Temperature dependence of the displacement signal at 10 kHz minus the background (BG) signal in run-1 and run-2. The data are obtained from (c). Temperature dependence of electrical conductivity measured along the interlayer direction (= 1/ρzz) is also shown.