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Phase fluctuations of s-wave superconductors on a lattice
Based on an attractive Hubbard model on a lattice with up to second
neighbor hopping we derive an effective Hamiltonian for phase fluctuations. The
superconducting gap is assumed to have s-wave symmetry. The effective
Hamiltonian we finally arrive at is of the extended XY type. While it correctly
reduces to a simple XY in the continuum limit, in the general case, it contains
higher neighbor interaction in spin space. An important feature of our
Hamiltonian is that it gives a much larger fluctuation region between the
Berezinskii-Kosterlitz-Thouless transition temperature identified with
for superconducting and the mean field transition temperature identified with
the pseudogap temperature.Comment: 3 figure
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