Density Induced Phase Transitions in the Schwinger Model: A Study with   Matrix Product States
  We numerically study the zero temperature phase structure of the multiflavor Schwinger model at nonzero chemical potential. Using matrix product states, we reproduce analytical results for the phase structure for two flavors in the massless case and extend the computation to the massive case, where no analytical predictions are available. Our calculations allow us to locate phase transitions in the mass-chemical potential plane with great precision and provide a concrete example of tensor networks overcoming the sign problem in a lattice gauge theory calculation. 
Mari Carmen Ba\~nuls, Krzysztof Cichy, J. Ignacio Cirac, Karl Jansen,   Stefan K\"uhn
hep-lat cond-mat.str-el quant-ph