Study of Quantum Spin 1/2 XY Model by Means of Extended Migdal Approximation
Abstract
The quantum spin 1/2 XY model in dimensions d = 1, 2 and 3is studied by means of the extended Migdal approximation for the scalefactor of the transformation b = 2. It is found, with the imposedconditions to get the recursion equations, that an unstable fixedpoint between a T = 0 fixed point and that of T = ∞ existsfor d > 1. However, alternate imposed conditions lead to an unusualbehavior that the T = 0 fixed point does not appear in any dimensionand that a stable fixed point appears at a lower temperature than thatof an unstable one for d > 2. The same model on the simple cubic and facecentered cubic lattices is also treated by the twostep decimation transformation.
 Publication:

Progress of Theoretical Physics
 Pub Date:
 February 1981
 DOI:
 10.1143/PTP.65.451
 Bibcode:
 1981PThPh..65..451T