Confined two-dimensional fermions at finite density
  We introduce the chemical potential in a system of two-dimensional massless fermions, confined to a finite region, by imposing twisted boundary conditions in the Euclidean time direction. We explore in this simple model the application of functional techniques which could be used in more complicated situations. 
M. De Francia, H. Falomir, M. Loewe and E. M. Santangelo