Ising model on a hyperbolic plane with a boundary
  A hyperbolic plane can be modeled by a structure called the enhanced binary tree. We study the ferromagnetic Ising model on top of the enhanced binary tree using the renormalization-group analysis in combination with transfer-matrix calculations. We find a reasonable agreement with Monte Carlo calculations on the transition point, and the resulting critical exponents suggest the mean-field surface critical behavior. 
Seung Ki Baek, Harri M\"akel\"a, Petter Minnhagen and Beom Jun Kim
cond-mat.stat-mech