Herman J. Fink | Searcharxiv

arXiv2011

High Tc Superconductivity: Doping Dependent Theory Confirmed by Experiment

A Hamiltonian H(Γ) applicable to cuprate HTS, with a doping dependent pairing interaction Γ(x) = V(x) + U(x), is linked to a Cu3d-O2p state probability model(SPM). A consequence of doping induced electron hopping, the SPM mandates that plaquettes with net charge and spin form in the CuO plane, establishing an effective spin-singlet exchange interaction U(x). The U(x) is determined from a set of probability functions that characterize the occupation of the single particle states. An exact treatment of the average static fluctuation part of H shows that diagonal matrix elements U_{k k} < 0 produce very effective pairing, with significant deviation from the mean field approximation, which also depends on a phonon-mediated interaction V. This deviation is primarily responsible for the diverse set of HTS properties. The SC phase transition boundary T_c(x), the SC gap Δ(x), and the pseudogap Δ_{pg}(x) are fundamentally related. Predictions are in excellent agreement with experiment, and a new class of HTS materials is proposed. Large static fluctuation results in extreme HTS and quantum criticality.

cond-mat.supr-con↗

arXiv2003

Surface Induced Anomalous Superconductivity

The Ginzburg-Landau (GL) theory is recast using a Hamiltonian involving the complete kinetic energy density which requires that the surface energy must contain a term \nabla |ψ|^2 to support superconducting (SC) states. The GL equations contain two temperature, t, dependent parameters α(t) and β(t), which are respectively the coefficients of the SC pair density \propto |ψ|^2, and the pair interaction term \propto |ψ|^4 in the free energy density. The sign of these parameters, which define distinct solution classes, and the ratio s(t) = \sqrt{|α|/|β|} are governed by the characteristics of the surface energy density. In addition to the conventional bulk superconducting states with (α< 0, β> 0), anomalous superconducting states exist for all other sign combinations, including cases with β< 0 which may exist only when surface pair interactions are significant. All possible solutions of our generalized nonlinear, one dimensional GL equations are found analytically and applied to a thin superconducting slab which manifests the possibility of states exhibiting enhanced, diminished, and pre-wetting superconductivity. Critical currents are determined as functions of s(t) and surface parameters. The results are applied to critical current experiments on SNS systems.

cond-mat.supr-con↗