1997/07/22 by E. Otnes, Otnes, E., Asle Sudbø +2
Physics and Astronomy · #Advanced Chemical Physics Studies #FOS: Physical sciences #Physics of Superconductivity and Magnetism #Rare-earth and actinide compounds #Superconductivity (cond-mat.supr-con) #cond-mat.supr-con
paper · pdf · doi:10.48550/arxiv.cond-mat/9707225
RevTex, 18 pages including 10 EPS figures; amstex, epsfig, subfigure required
arxiv created 1997/07/22 · openalex publication_date 1997/07/22 · arxiv updated 2009/11/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We consider the Cooper-problem on a lattice model including onsite and near-neighbor interactions. Expanding the interaction in basis functions for the irreducible representation for the point group C4v yields a classification of the symmetry of the Cooper-pair wave function, which we calculate in real-space. A change of symmetry upon doping, from s-wave at low filling fractions, to dx2-y2 at higher filling fractions, is found. Fermi-surface details are thus important for the symmetry of the superconducting wave function. Symmetry forbids mixing of s-wave and d-wave symmetry in the Cooper-pair wavefunction on a square lattice, unless accidental degeneracies occur. This conclusion also holds for the selfconsistent treatment of the many-body problem, at the critical temperature Tc. Below Tc, we find temperatures which are not critical points, where new superconducting channels open up in the order parameter due to bifurcations in the solutions of the nonlinear gap-equation. We calculate the free energy, entropy, coherence length, critical magnetic fields, and Ginzburg-Landau parameter κ. The model is of the extreme type-II variety. At the temperatures where subdominant channels condense, we find cusps in the internal energy and entropy, as well as as BCS-like discontinuities in the specific heat. The specific heat anomalies are however weaker than at the true superconducting critical point, and argued to be of a different nature.