We present a first detailed study of the charge density wave (CDW) contrast inversion in scanning tunneling microscopy (STM) images. Combining high resolution STM imaging at different tunneling biases and density functional theory, we demonstrate that contrast inversion is very sensitive to the position of the CDW gap with respect to the Fermi level. We establish that the absence of contrast inversion at zero-bias is a direct consequence of the CDW gap opening away from the Fermi level, well inside the valence band in TiSe2. Our original analysis reveals a shift of the CDW gap to higher and higher binding energy with increasing electron doping. This finding has important consequences on the CDW formation mechanism and on the understanding of the interplay of the CDW with superconductivity in Cu intercalated TiSe2.
Collaboration with UCL/LCN.