Scanning tunneling microscopy observation of sliding charge-density wave in blue bronze

Abstract

We investigated the sliding motion of charge-density wave (CDW) in K0.3 MoO3 with scanning tunneling microscopy (STM). With fixed position of the tunneling tip, a sharp peak was found in the spectra of tunneling current for sample bias current exceeding the threshold for the CDW depinning. The peak frequency increased with the extra current carried by the CDW condensate. This peak is understood to be generated by the modulation of gap distance between the tunneling tip and sample atom due to the sliding motion of CDW. The velocity of CDW at the surface was obtained directly: vs =5.7×10−3 cm/s just above the threshold. The corresponding sliding velocity in the interior of the same sample was obtained as vb =6.3×10−4 cm/s from the narrow band noise frequency. It was confirmed that the CDW is easily depinned at the surface and begins to slide with much higher velocity than the interior of sample. Tunneling spectroscopy was also measured and the CDW gap structure was obtained as a preliminary result.