Electronic instabilities of the two-dimensional Sn/Ge(111) alpha-phase

The Sn/Ge(111) interface presents at room temperature an ordered root 3 x r oot 3R(30 degrees) surface reconstruction, formed by a submonolayer array o f tin adatoms, which reversibly transforms upon cooling into a 3 x 3 struct ure. Recently, it has been claimed that the formation of a commensurate cha rge density wave is responsible for this transition. We present high-resolu tion synchrotron radiation photoemission results which support, instead, th at the driving force of the transition is rehybridization: fluctuations in the tin adatom type of bonding freeze-in at low temperature to yield the st atic long-range ordering of the 3 x 3 ground state which is governed by an ideal 1/2 ratio of the sp(3)/sp(2) hybridization balance. (C) 1999 Elsevier Science B.V. All rights reserved.