Triplet superconductivity

Manifestation of Triplet Superconductivity in Superconductor-Ferromagnet Structures... 

In summary we showed experimental results and theoretical calculations on magnetization orientation dependence of superconductor critical temperature in F/S/F all-metallic structures. This effect is based on the emergence of a small admixture of spin-triplet superconductivity in the hybrid... 

At the same time, the in-plane superconductivity is caused mainly by the ordinary singlet component. Therefore the macroscopic superconductivity due to the Josephson coupling between the layers is an interesting combination of the singlet superconductivity within the layers and the odd triplet superconductivity in the transversal direction. 

We studied odd, s-wave, triplet superconductivity that may arise in S/F multilayered structures with a non-collinear orientation of magnetizations. It was assumed that the orientation of the magnetization is not affected by the superconductivity (e.g. the energy of the magnetic anisotropy is much larger than the superconducting energy). The analysis was carried out in the dirty limit (Jr -C 1) when the Usadel equation is applicable. 

In summary, we showed that near a FQCP, spin fluctuation exchange gives rise to a strong first order transition into a triplet superconducting state. As a result, Tc saturates at a nonzero value at criticality. The first order transition persists up to a finite distance from the FQCP, where it becomes second order. 

We now define new operators Oa(q), which are the Fourier components of operators characterizing the various ordered states of the interacting one-dimensional gas, namely a = CDW, SDW, or singlet, triplet superconductivity SS and TS, for example ... 

The existence of the triplet n junction was previously discussed in [16,68-79]. It was shown that contribution to 1 from the triplet superconducting component can be both negative and positive. A n contact appears as a result of superposition of oscillating contributions to and monotonically decaying on the scale triplet part of the critical current. In S-FNF-S junctions the n state appears as a result of the interaction between two spatially non-oscillating contributions to the critical current. Each contribution decreases at a length of about the coherent length of the normal metal. 

It would be futile to try to list the complete literature of bulk measurements here. Reviews to be consulted are given, for example, by Sauls (1994), von Lohneysen (1994) and Taillefer (1994). Ultrasound and uniaxial stress data can be found in Adenwalla et al. (1990) and Boukhny et al. (1994a,b,c). They indicate a triplet superconducting-order parameter. 

The detailed experimental investigations have, at least for CeCu2Si2 and UBej3, spoiled the original hope of finding triplet superconductivity in metals similar to the known case of superfluid He. Apparently the lower symmetry and the lower purity of crystals play an essential role for the superconducting states found in heavy-fermion compounds. We would like to recall a few key observations which underline this conclusion ... 

In these systems triplet superconductivity is possible with a parallel orientation of the electron spins in a pair with total spin 1 (superconductivity in HFS-systems is connected with Cooper pairs, formed by fermions with a very large effective mass (m /mo 100-1000, biq is the free-electron mass)). 

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