Antiferromagnetic Ising spin glass competing with BCS pairing interaction in a transverse field |
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Authors: | S G Magalhães F M Zimmer C J Kipper E J Calegari |
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Institution: | (1) Laboratório de Mecanica Estatística e Teoria da Matéria Condensada (PPGFIS-Dep. Física) - UFSM, 97105-900 Santa Maria, RS, Brazil |
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Abstract: | The competition among spin glass (SG), antiferromagnetism (AF)
and local pairing superconductivity (PAIR) is studied in a two-sublattice fermionic Ising spin glass model with a local BCS
pairing interaction in the presence of an applied magnetic transverse field Γ. In the present approach, spins in different
sublattices interact with a Gaussian random coupling with an antiferromagnetic mean J0 and standard deviation J.
The problem is formulated in the path integral formalism in which spin operators are represented by
bilinear combinations of Grassmann variables. The saddle-point Grand Canonical potential
is obtained within the static approximation and the replica symmetric ansatz. The results are analysed in phase diagrams in
which the AF and the SG phases can occur for small g (g is the strength of the local superconductor coupling written in units
of J), while the PAIR phase appears as unique solution for large g. However, there is a complex line transition separating
the PAIR phase from the others. It is second order at high temperature that ends in a tricritical point. The quantum fluctuations
affect deeply the transition lines and the tricritical point due to the presence of Γ. |
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Keywords: | 05 50 +q Lattice theory and statistics 64 60 Cn Order-disorder transformations statistical mechanics of model systems |
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