Chemical Potential in the Gravity Dual of a 2+1 Dimensional System
  We study probe D5 branes in D3 brane AdS_5 and AdS_5-Schwarzschild backgrounds as a prototype dual description of strongly coupled 2+1 dimensional quasi-particles. We introduce a chemical potential through the U(1)_R symmetry group, U(1) baryon number and a U(1) of isospin in the multi-flavour case. We find the appropriate D5 embeddings in each case - the embeddings do not exhibit the spontaneous symmetry breaking that would be needed for a superconductor. The isospin chemical potential does induce the condensation of charged meson states. 
Nick Evans and Ed Threlfall