Charge-density-wave STM observation in η-Mo4O11 -: art. no. 165428

We present scanning tunneling microscopy (STM) measurements of the two-dimensional eta -Mo4O11 com pound, which exhibits Peierls transitions at 30 and 109 K. Using a homemade UHV low-temperature STM, we observe at 50 K (between the two transitions) the formation of an incommensurate charge-density wave (CDW) along the b direction. STM images provide an accurate measurement of the wave vector of this CDW, which is the "nesting'' vector characterizing the transition at 109 K. The measured value is in perfect agreement with previous electron diffraction and x-ray diffuse scattering measurements. Finally, recording simultaneously STM images at positive and negative sample bias, we observe the expected pi phase shift of the CDW, due to a full spatial separation of the occupied and empty electronic states of the CDW.