Ground-state correlations and finite temperature properties of the transverse Ising model |
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Authors: | J W?Kim S J?Lee T W?Kang Email author" target="_blank">M L?RistigEmail author |
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Institution: | (1) Quantum-functional Semiconductor Research Center, Dongguk University, 100-715 Seoul, Korea;(2) Institut für Theoretische Physik, Universität zu Köln, Koeln, Germany |
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Abstract: | We present a semi-analytic study of Ising spins on a simple square or
cubic lattice coupled to a transverse
magnetic field of variable strength. The formal analysis employs
correlated basis functions (CBF) theory to
investigate the properties of the corresponding N-body ground and
excited states. For these states we discuss
two different ansaetze of correlated trial wave functions and associated
longitudinal and transverse excitation
modes. The formalism is then generalized to describe the spin system at
nonzero temperatures with the help of
a suitable functional approximating the Helmholtz free energy. To test
the quality of the functional in a first step
we perform numerical calculations within the extended formalism but
ignore spatial correlations. Numerical results are
reported on the energies of the longitudinal and the transverse
excitation modes at zero temperature, on critical
data at finite temperatures, and on the optimized spontaneous
magnetization as a function of temperature and
external field strength. |
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Keywords: | |
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