Depinning transitions between adsorbate chains coupled by Friedel oscillations

The low coverage phase transitions of the p(8×1) and the p(5 ×1) chain structures of the Sr/Mo(112) system have been investigated with low-energy electron diffraction (LEED) at constant coverages. It turns out that both structures show similar physics. They first undergo depinning phase transitions at temperatures just below 100 K into striped domain wall structures. The domain wall lattice shows continuous melting at temperatures between 197 and 218 K. Coupling between the adsorbate chains can be described by the potential created by adsorbate-induced charge density waves involving surface states. Within this model domain wall formation appears as thermal excitation of stacking faults on a discrete lattice. For the p(5×1) structure, domain wall formation energies of approximately 65 and 38 meV have been derived for heavy and light walls, respectively, from a fit to the experimental data of depinning.