Surface superstructures of quasi-one-dimensional organic conductor beta -(BEDT-TTF)2PF6 crystal studied by scanning tunneling microscopy.

Abstract

Two kinds of superstructures were found at \ensuremath{\sim}280 K by scanning tunneling microscopy on the crystal surface of \ensuremath{\beta}-(BEDT-TFF${)}_{2}$${\mathrm{PF}}_{6}$, a quasi-one-dimensional organic conductor with a metal-insulator phase transition at \ensuremath{\sim}297 K. One has a structural modulation which is perpendicular to the one-dimensional conductive axis, similar to that previously observed on a TTF-TCNQ crystal surface. The other has a twofold periodicity along the one-dimensional conductive axis, as expected from the theory. Under the assumption that the former is an intermediate structure caused by the interaction between neighboring one-dimensional molecular chains, superstructures which have been observed in BEDT-TTF compounds could be explained well.