Interplay of superconductivity and magnetism

After a short report on the discovery of the quaternary borocarbide superconductors in Section 1.1, for comparison a limited survey of other superconductors based on boron and/or carbon will be presented in Section 1.2 whereas the interplay of superconductivity and magnetism in other materials is discussed in Section 1.3. At the end of this section some special features of the RNi2B2C compounds and review articles in this field can be found in Section 1.4 as well as the further outline of this chapter. 

The interesting feature is that the series of borocarbides represent all combinations of Tc and 7n and that both superconductivity and magnetism coexist at the highest ever reported temperature. This class of compounds led to further detailed studies to understand the interplay of superconductivity and magnetism, in addition to identifying new superconducting materials. 

The above picture is in a good agreement with the theory of itinerant electron systems with interplay between superconductivity and magnetism [8], In that theory, an itinerant SDW gap may appear at the Fermi surface only before an SC gap, i.e. in the normal state. This SDW gap is highly anisotropic since it is only formed at symmetric parts of the Fermi surface [8] ( see, fig.2). Its width ASDW being unusually large for an SC gap, well conforms to that for an SDW gap because of inequality ASc < ASDW... 

We have considered here the influence of dispersion asymmetry and Zee-man splitting on the Josephson current through a superconductor/quantum wire/superconductor junction. We showed that the violation of chiral symmetry in a quantum wire results in qualitatively new effects in a weak superconductivity. In particularly, the interplay of Zeeman and Rashba interactions induces a Josephson current through the hybrid ID structure even in the absence of any phase difference between the superconductors. At low temperatures (T critical Josephson current. For a transparent junction with small or moderate dispersion asymmetry (characterized by the dimensionless parameter Aa = (vif — v2f)/(vif + V2f)) it appears, as a function of the Zeeman splitting Az, abruptly at Az hvp/L. In a low transparency (D Josephson current at special (resonance) conditions is of the order of yfD. In zero magnetic field the anomalous supercurrent disappears (as it should) since the spin-orbit interaction itself respects T-symmetry. However, the influence of the spin-orbit interaction on the critical Josephson current through a quasi-ID structure is still anomalous. Contrary to what holds... 

The open issues mentioned here should legitimate the assumption that this class of compounds will provide further substantial and general insight into mechanisms of superconductivity and its interplay with magnetism. 

Because they exhibit interplay of magnetic and superconducting properties, the formation and crystal chemistry of MRgMy4B4 compounds have been examined. Ternary rare-earth and actinide (Th, U, Pu)-transition metal borides of the approxi-... 

In passing, it would be worth mentioning the corresponding situation in condensed matter physics. Magnetism and superconductivity (SC) have been two major concepts in condensed matter physics and their interplay has been repeatedly discussed [14], Very recently some materials have been observed to exhibit the coexistence phase of FM and SC, which properties have not been fully understood yet itinerant electrons are responsible to both phenomena in these materials and one of the important features is both phases cease at the same critical pressure [15]. In our case we shall see somewhat different features, but the similar aspects as well. 

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