On the Thermodynamical Relation between Rotating Charged BTZ Black Holes   and Effective String Theory
  In this paper we study the first law of thermodynamics for the (2+1) dimensional rotating charged BTZ black hole considering a pair of thermodinamical systems constructed with the two horizons of this solution. We show that these two systems are similar to the right and left movers of string theory and that the temperature associated with the black hole is the harmonic mean of the temperatures associated with these two systems. 
Alexis Larranaga