Finite wave vector pairing in doped two-leg ladders
  We consider the effects of Umklapp processes in doped two-leg fermionic ladders. These may emerge either at special band fillings or as a result of the presence of external periodic potentials. We show that such Umklapp processes can lead to profound changes of physical properties and in particular stabilize pair-density wave phases. 
N. J. Robinson, F. H. L. Essler, E. Jeckelmann, A. M. Tsvelik
cond-mat.str-el cond-mat.supr-con