Thermofield transfer-matrix method and its applications to quantum spin systems

Abstract
The thermofield transfer-matrix method is formulated in detail and applied to one-dimensional quantum spin systems. The convergence properties of the thermofield transfer matrix are examined in detail by use of the numerically exact method. It is shown that this method is a unification of the quantum transfer-matrix method and projector method, and provides a very powerful means to study a variety of quantum systems.