Conformal invariance and critical behavior of a quantum Hamiltonian with three-spin coupling in a longitudinal field

The critical behavior of a quantum spin chain with three-spin coupling in transverse and longitudinal fields is studied by finite-size scaling. The phase diagram and the thermal and magnetic critical exponents are obtained. Conformal invariance is used to extract the value of the central charge or conformal anomaly c. The results strongly suggest that for a finite longitudinal field the model belongs to the same universality class as the two-dimensional three-state Potts model.