Tamm's surface states and Bose-Einstein condensation
  We calculate and discuss the effects on the thermodynamic properties of a 3D Bose gas caused by a gap $\Delta$ in the energy of the particles constituting the gas that without the gap behaves like an ideal Bose gas. Explicit formulae with arbitrary $\Delta$ values are discussed for: the critical temperature which increases as the gap grows; the condensate fraction; the internal energy; and the constant-volume specific heat found to possess a jump-discontinuity for any $\Delta$ different from zero. Three dimensional infinite ideal Bose gas results are recovered when we the energy gap goes to zero. 
M. A. Sol\'is
cond-mat.quant-gas