Temperature-dependent anomalies in the structure of the (001) surface of LiCu2O2

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 Å as the surface was cooled down to 140 K. This raises the possibility that isolated one-dimensional magnetic ion arrays may be realized; if true, it qualifies the Li1 +Cu2 +O22 − surface as a candidate to study one-dimensional magnetism. The rising Cu2 + rows induce a thermally activated 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, consistent with the rise of the Cu2 + rows, obtained with the aid of inelastic HAS measurements combined with surface lattice dynamical calculations are also reported.