Surface structure and spectroscopy of charge-density wave materials using scanning tunneling microscopy

Abstract

The Scanning tunneling microscope (STM) has been used to study the effects of Fe doping on the charge-density wave (CDW) structure in NbSe{sub 3} and 1T-TaS{sub 2}. In NbSe{sub 3} 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 1T-Fe{sub 0.05}Ta{sub 0.95}S{sub 2} 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.