SURFACE-STRUCTURE AND SPECTROSCOPY OF CHARGE-DENSITY WAVE MATERIALS USING SCANNING TUNNELING MICROSCOPY

The scanning tunneling microscope (STM) has been used to study the effects of Fe doping on the charge-density wave (CDW) structure in NbSe3 and 1T-TaS2. In NbSe3 small amounts of Fe reduce both CDW gaps by 25%-30% and change the relative CDW amplitudes of the high- and low-temperature CDWs. The CDW amplitudes remain strong on all three chains of the surface unit cell with no evident disorder. In IT-Fe0.05Ta0.95S2 the Fe introduces substantial disorder in the CDW pattern, but the local CDW amplitude remains strong. The CDW energy gap is reduced by approximately 50% and the resistive anomaly at the commensurate-incommensurate transition is removed. The STM in both the image and spectroscopy modes can detect subtle changes in CDW structure due to impurities.