Temperature-Dependent Anomalies in the Structure of the (001) Surface of LiCu2O2

Abstract

Surface corrugation functions, derived from elastic helium atom scattering (HAS) diffraction patterns at different temperatures, reveal that the Cu2+ rows in the (001) surface of LiCu2O2 undergo an outward displacement of about 0.15 {\AA} as the surface was cooled down to 140 K. This is probably the first time that isolated one-dimensional magnetic ion arrays were realized, which qualifies the Li1+Cu2+O2-2 surface as a candidate to study one-dimensional magnetism. The rising Cu2+ rows induce a surface incommensurate structural transition along the a-direction. Surface equilibrium analysis showed that the surface Cu2+ ions at bulk-like positions experience a net outward force along the surface normal which is relieved by the displacement. Temperature-dependent changes of the surface phonon dispersions obtained with the aid of inelastic HAS measurements combined with surface lattice dynamical calculations are also reported.