Superconducting order parameters temperature dependence

Fig. 11.13. Experimental observations of (T = 4.2 K) as a function of misorientation angle from the results of several groups [11.1-11.3] show an exponential dependence. Where the results were reported at E = 77 K, the values at 4.2 K were extrapolated from the temperature dependence of Jq [11.45]. The grain boundary tunneling current calculated from eq. 11.2 using the grain boundary widths from Fig. 11.12 shows excellent quantitative agreement for a width defined by a copper(I) valence between 1.5 and 1.9. This copper valence corresponds to the copper(I) valence in bulk YBCO when it becomes non-superconducting. The predicted drop in due to the symmetry of the superconducting order parameter is insufficient by two orders of magnitude to account for the observed behavior.

Figure 1. Schematic temperature dependence of the superconducting order parameters, where L Is for the mixed (s+d)-state and for the pure d j T - a -...

As a possible explanation of this phenomenon the authors consider, in the case of non s-wave pairing, the coupling between the superconducting order parameter with an environment of different symmetry and propose that it may lead to two different Tc s dependent on the crystallographic direction. Thus, T, which changes with the chain oxygen, may be the transition temperature for c-axis superconductivity while Td, which seems rather independent of oxygen, may be the transition temperature for the superconductivity of the planes. 

Summary. On the basis of phenomenological Ginzburg-Landau approach we investigate the problem of order parameter nucleation in a ferromagnetic superconductor and hybrid superconductor - ferromagnetic (S/F) systems with a domain structure in an applied external magnetic field H. We study the interplay between the superconductivity localized at the domain walls and between the domain walls and show that such interplay determines a peculiar nonlinear temperature dependence of the upper critical field. For hybrid S/F systems we also study the possible oscillatory behavior of the critical temperature TC(H) similar to the Little-Parks effect. 

We defined the parameters of our model and made numerical calculations of temperature dependent of two gaps. It is a qualitative agreement with experiments. We proposed a two channel scenario of superconductivity first a conventional channel (intraband gi) whichis is connected with BCS mechanism in different zone and a unconventional channel (interband gi) which describes the tunneling of a Cooper pair between two bands. The tunneling of Cooper pair also stabilizes the order parameters of superconductivity [9-12] and increases the critical temperature of superconductivity. 

Findings (c) and (d) in particular rule out the formation of local moments on Th or the formation of large moments on U atoms close to an Th impurity atom. The temperature dependence of the electronic depolarization rate reflects the behavior of a magnetic order parameter following a second-order phase transition. Since this holds also for the superconducting phase, the two parameters are coupled, as already discussed for UPt3. The magnetic moments involved are estimated to be 3 10 /Tb per U ion. 

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