Spinless Fermionic ladders in a magnetic field: Phase Diagram
  The system of interacting spinless fermions hopping on a two-leg ladder exhibits a series of quantum phase transitions when subjected to an external magnetic field. At half filling, these are either U(1) Gaussian phase transitions between two phases with distinct types of long-range order or Berezinskii-Kosterlitz-Thouless transitions between ordered and gapless phases. 
Sam T. Carr, Boris N. Narozhny, Alexander A. Nersesyan