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Weak instability of frustated fermionic models

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Weak instability of frustated fermionic models

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Título Weak instability of frustated fermionic models
Autor Theumann, Alba Graciela Rivas de
Abstract We study the Almeida-Thouless instability of two fermionic models analogous to spin glasses that exhibit frustration and that were solved some time ago with a replica symmetric ansatz. In the first model (I) we consider only the anisotropic, Ising-like limit, while in the second model (II) we consider the isotropic, Heisenberg-like Hamiltonian. In both models the interactions are of the Sherrington-Kirkpatrick type and the spins are represented by bilinear combinations of fermionic fields. While model I is almost classical, exhibiting a negative entropy at low temperatures, we show in this paper that the eigenvalue lRS is positive at the critical temperature and becomes negative at a temperature below the transition point. Model II is more interesting because λRS is positive at the critical temperature TSG , vanishes at T1>TSG , and becomes positive again at T2>T1. Although the entropy remains positive all the way down to T50, it presents a break of monotonicity when λRS becomes negative, indicating a negative specific heat in part of the instability region T2>T>T1 . The two stability regions in the ordered phase for T>T2 and T1>T>TSG are characterized by the correct sign of the entropy and specific heat. This seems to indicate that replica symmetry stability is enhanced in frustrated fermionic spin models.
Contido em Physical review. B, Condensed matter. New York. Vol. 56, no. 9 (Sept. 1997), p. 5500-5503
Assunto Fermions
Fisica da materia condensada
Origem Estrangeiro
Tipo Artigo de periódico
URI http://hdl.handle.net/10183/104213
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