Reentrant superconductivity

Fig. 16 (a) Phase diagram of K-(hg-ET)2Cu[N(CN)2]Cl determined from conductivity and magnetic measurements [213, 217, 218], N1-N4 nonmetallic phase, M metallic phase, RN reentrant nonmetallic phase, I-SC-I, II incomplete superconducting phase, S-SC complete superconducting phase. N2 shows the low-dimensional AF fluctuation. N3 shows growth of three-dimensional AF ordered phase. N4 weak ferromagnetic phase, (b) Proposed phase diagram [211, 212]... 

Sushko YV, Ito H, Ishiguro T, Horiuchi S, Saito G (1993) Reentrant superconductivity in k-(BEDT-TTF)2Cu[N(CN)2]C1 and its pressure phase diagram. Solid State Commun 87 997-1000... 

Fig. 5. Reentrant superconductivity in NdojsThg 65RU2 (after Hiiser et al. 1983). Upon cooling, first, the real part of the ac susceptibility, x. becomes negative, indicating superconductivity. Then the material reenters the normal state (x > 0) and reentrance of superconductivity occurs at lower temperatures.

Fig. 6. Resistance-vs.-temperature curves of a GdMO(,Sg sample for different values of the applied magnetic field, indicating near-reentrant superconductivity i.e. reentrant behaviour at finite field only (nominal composition...

Fig. 38. (a) Resistivity vs. temperature measured at different magnetic fields H on a polycrystalline HoNi2B2C sample. Tc is the superconducting transition temperature at H = 0. A near-reentrant behaviour occurs around a temperature Tn. (b) Temperature dependence of the specific heat Cp of a HoNi2B2C single crystal (2 mm x 3 mm x 0.1 mm in size), measured at zero magnetic fiekL Above the main peak of Cp(T) at Tn. two additional features appear (marked by arrows). Samples prepared by I. Freudenberger. 

It is obvious that the commensurate antiferromagnetic structure of fig. 39a coexists with superconductivity in HoNi2B2C, similar as in DyNi2B2C. On the other hand, as can be seen in fig. 43(a and c) the superconductivity is suppressed in the small temperature range where the two incommensurate magnetic structures of fig. 39(b and c) occur. Now the question is which of these two structures is more relevant for the near-reentrant behaviour. In Y().i5Hoo.85Ni2B2C the situation is totally different (fig. 43(b and d)). Here the a ... 

Reentrant superconductivity is known from so-called ferromagnetic superconductors like ErRh4B4 where the ferromagnetic transition at lower temperatures actually destroys superconductivity [244]. However, the exact magnetic structure in k-(ET)2Cu[N(CN)2]C1 is still unknown and the origin of the peculiar behavior is at present subject of speculations only. 

Oscillations in the transition temperature of SF sandwiches as a function of F-layer thickness, <7f, including reentrant superconductivity [10, 11]. 

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