STUDY ON GROUND-STATES OF QUANTUM SPIN SYSTEMS BY RESTRUCTURING METHOD

We present a new method to study the ground state of quantum spin syst ems using Monte Carlo techniques. Our idea is to obtain the coefficien ts in the expansion of the ground state, both their magnitudes and the ir relative signs, from measurements of the normalized frequencies of each state on the boundary in the Trotter direction. This knowledge Of the ground state helps us to calculate some complicated physical quan tities such as time correlation functions. As a concrete example we st udy spin ladder systems with antiferromagnetic intrachain nearest neig hbor interactions, whose ground states may be equivalent to that of th e spin 1 chain. For the ladder with ferromagnetic rungs, we show how t o determine the magnitudes and relative signs of the coefficients in t he expansion. We also demonstrate that we can calculate the time corre lation function using these Monte Carlo data and analytical techniques . When the ladder has antiferromagnetic rungs, we examine White's clai m that the diagonally situated pair of spins are mostly triplet states in the ground state. Our results strongly suggest that the system has hidden order which is constructed by the specially aligned triplet st ates of diagonal pairs.