Susceptibility of the transverse field Ising model on the square lattice
  Susceptibility of the transverse field Ising model on the square lattice is calculated numerically in the paramagnetic phase in a wide range of temperatures and transverse fields. An expression with one constant $\pi$, that determines both the critical exponent $\gamma$ and the critical transverse field, compellingly represents the data asymptotically near the quantum critical point, except for a narrow classical region close to the phase transition line, and shows two crossovers as temperature varies. 
A. Kashuba
cond-mat.mes-hall cond-mat.str-el