Phase transitions driven by competing interactions in low-dimensional systems

Variable-temperature scanning tunnelling microscopy is used to study an orderorder phase transition in a virtually defect-free quasi-one-dimensional surface system. The phase transition is driven by competing electronic interactions. The phase diagram is captured by a modified Landau formalism containing a coupling term between two different subsystems. The extra term has the effect of a spontaneously generated field which drives the phase transition. The proposed formalism applies to a variety of problems, where competing interactions produce sometimes counter-intuitive ordering phenomena.