Organic superconductors revisited STM imaging and DFT based simulations of the bc plane of rc-(BEDT-TTF)2Cu(NCS)2

摘要

The surfaces of a ten years aged crystal and a freshly prepared k-(BEDT-TTF)_2Cu(NCS)_2 crystal were compared by scanning tunneling microscopy (STM). The molecularly-resolved STM images of the bc plane of the crystals agree with each other and with the electronic contrast obtained by new density functional theory (DFT) based simulations. Even after ten years STM images of the molecular stacking of BEDT-TTF display a variation in brightness at the positions of different molecules. We attribute this symmetry breaking concerning the brightness in the STM images of the otherwise equivalent BEDT-TTF dimers to the electronic states of a relaxed surface.