Surface Charge Ordering Transition:<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="italic">α</mml:mi></mml:math>Phase of Sn/Ge(111)

Abstract

We have identified and characterized a charge-density wave transition $({T}_{c}\ensuremath{\sim}\ensuremath{-}60\ifmmode^\circ\else\textdegree\fi{}\mathrm{C})$ in the low-coverage \ensuremath{\alpha} phase of the Sn/Ge(111) interface both experimentally and theoretically. Charge ordering is accompanied by a structural distortion from $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ to $(3\ifmmode\times\else\texttimes\fi{}3)$ symmetry. Density-functional theory calculations are unable to correctly reproduce the observed ground state and, more importantly, indicate that Fermi surface nesting does not play a role in this transition. Both signal the importance of many-body effects in this system. Experiment and theory indicate that the Sn/Ge(111) overlayer is fundamentally different from the Pb/Ge(111) overlayer previously reported.