Finite-size effects on the phase diagram of difermion condensates in   two-dimensional four-fermion interaction models
  We investigate finite-size effects on the phase structure of chiral and difermion condensates at finite temperature and density in the framework of the two-dimensional large-$N$ Nambu-Jona-Lasinio model. We take into account size-dependent effects by making use of $zeta$-function and compactification methods. The thermodynamic potential and the gap equations for the chiral and difermion condensed phases are then derived in the mean-field approximation. Size-dependent critical lines separating the different phases are obtained considering anti-periodic boundary conditions for the spatial coordinate. 
L.M. Abreu, A.P.C. Malbouisson, J.M.C. Malbouisson
hep-th cond-mat.stat-mech hep-ph