Switching between one- and two-dimensional conductance: Coupled chains in the monolayer of Pb on Si(5 5 7)

Four-point conductance measurements of a high temperature annealed monolayer of Pb on Si(5 5 7) are combined with tunneling microscopy (STM) and LEED for structural investigations. We found extremely high surface state conductance which becomes quasi-one-dimensional below a critical temperature of Tc = 78 K. The change from low to extremely high conductance anisotropy is associated with a reversible order-disorder phase transition with a temperature dependence ∝1/T + const. along the chains below the phase transition. Below the phase transition order is found simultaneously in the lateral separation between Pb chains and along the chains. There a 10-fold superperiodicity appears. We suggest that strong two-dimensional coupling, leading to electronic stabilization of terraces with a width of 423 lattice constants, results in perfect nesting normal to the chains at EF (below Tc), which is the origin of this switching to one-dimensional behavior. Therefore, no metal-insulator transition is expected at low temperature.