P. Mallet et al., Contrast reversal of the charge density wave STM image in purple potassiummolybdenum bronze K0.9Mo6O17, PHYS REV B, 60(3), 1999, pp. 2122-2126
We report on a scanning tunneling microscopy (STM) investigation of the cha
rge density wave (CDW) state of a layered oxide compound, the purple bronze
K0.9Mo6O17 The experiments have been carried out in an ultra-high-vacuum v
ariable-temperature STM. At low temperature, we have observed a (2X2) super
structure due to the CDW state, superimposed on the atomic lattice. Spectro
scopic measurements reveal a strong decrease of the density of states near
the Fermi energy, consistent with the suppression of a sizable fraction of
the Fermi surface below the CDW transition temperature. Finally, by simulta
neous imaging at negative and positive biases, we show a complete spatial s
eparation between occupied and empty states involved in the CDW modulation,
resulting in a contrast reversal of the CDW images. [S0163-1829(99)03127-6
].