Structural distortion as prerequisite for superconductivity in LiFeAs
  The nonadiabatic Heisenberg model predicts a structural distortion in LiFeAs below a temperature higher than (or at least equal to) the superconducting transition temperature. Within this group-theoretical model, the reduction of the symmetry caused by the distortion is a prerequisite for the superconducting state in this compound and can be realized by a mere displacement of the iron atoms from their positions in the space group P4/nmm. 
Ekkehard Kr\"uger, Horst P. Strunk
cond-mat.supr-con cond-mat.str-el