A systematic theoretical treatment of the influence of barrier impurities with short‐range potentials on electron tunneling near resonance energy through insulating layers is presented in the realistic three‐dimensional case. The comparison with the usual one‐dimensional model exhibits differences with respect to the dependence on tunneling direction and the broadening of impurity states. In particular, an evaluation of the resonance tunneling contribution is given for barrier impurities described by a screened charge potential.
Near the superconducting transition temperature pairpotential behaviour and supercurrent in nonhomogeneous sandwich systems of SNS-and SINIS-types (S superconductor, N normal metal, I insulator) are theoretidlly investigated. The proximity effect is taken into account by using an extrapolation length which relates the order parameter value to its first derivative at interfaces. I n frame of the microscopic theory of superconductivity this extrapolation length follows with the help of an appropriate variational principle which haa been checked on system which allow exact solutions. The resulting supercurrent expressions are discukd in detail with respect to tamperature dependence and impurity influence.
Proximityeffekt und Jososephsonstrom in supraleitenden Sandwichsystemen nahe der UbergangstemperaturInhaltsubersicht. Das Verhalten dea Paarpotantials und Suprastromes in inhomogenen Sandwichsystemen vom Typ SNS und SINIS (S Supraleiter, N Normalmetall, I Isolator) wird nahe der Ubergangstemperatur theoretisch untersucht. Der Proximityeffekt wird dabei durch eine Extrapolationsliinge, die den supraleitenden Ordnungsparameter mit seiner ersten Ableitung an Grenzfliichen verkniipft, beriicksichtigt. Im Rahmen der mikroskopischen Theorie der Supraleitung folgt diese Extrapolationsliinge mit Hilfe eines geeigneten Variationsverfahrens, das an Hand exakt losbarer Modelle iiberpriift wurde. Die erhaltenen Ausdriicke fur den Suprastrom werden beziiglich der Temperaturabhiingigkeit und des Einflusses von Verunreinigungen ausfiihrlich diskutiert.
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