Effect of geometrical symmetry on the angular dependence of the critical magnetic field in superconductor/normal metal multilayers

Abstract

The angular dependence of the upper critical field, H c ͑⌰͒, for Nb/ Pd multilayers with different geometrical symmetries ͑i.e., with an even or an odd number of bilayers, N bil ͒ and thickness of Nb and Pd layers of the order of superconducting coherence length were investigated ͑the angle ⌰ is here defined from the plane parallel to the sample surface͒. The presence of an angular dimensional crossover at some temperature dependent angle ⌰ * ͑T͒ was established. At angles ⌰Ͻ⌰ * ͑T͒ the multilayers are in two-dimensional mode while at ⌰Ͼ⌰ * ͑T͒ they are in a three-dimensional one. In addition, the sample with odd N bil has a larger value of ⌰ * ͑T͒ with respect to the sample with even N bil . The experimental results have been qualitatively explained in the framework of the Ginzburg-Landau theory. It was shown that the main features of the H c ͑⌰͒ dependences in samples with even and odd N bil values are related to the different localizations of the superconducting order parameter.

Superconducting critical temperature and softening of the phonon spectrum in ultrathin nb- and nbn/graphene hybrids

“…films with a thickness of a few lattice constants, the softening of the phonon spectra obtained by depositing metal nanoparticles on the film surface has been demonstrated to cause an increase of T c [16][17][18][19]. On the contrary, the quality of the surface in ultrathin superconducting films can have a strong detrimental effect on the values of the critical temperature, as observed and theoretically explained in proximity-coupled superconductor/normal metal (S/N) hybrids [20][21][22][23][24].…”

“…In contrast, the quality of the surface in ultrathin superconducting films can have a strong detrimental effect on the values of the critical temperature, as observed and theoretically explained in proximity-coupled superconductor/normal metal (S/N) hybrids [20][21][22][23][24]. The Eliashberg function for Nb, measured by tunnel spectroscopy [25] and calculated with λ ≈ 1.24 and µ * ≈ 0.21 [11], reveals that the EPhI is significant in the frequency range 2-7 THz.…”

Influence of the FFLO-like state on the upper critical field of a superconductor/ferromagnet bilayer: Angular and temperature dependence

“…Since this vortex structure is related to that one of a layered superconductor (see Chap. VIII-A of the review of Blatter et al 48 ), this conclusion is supported by the investigations of Prischepa et al 92 , who found an angular dimensional cross-over of H c (θ) at fixed temperature for Nb/Pd multilayers. Samples of odd and even numbers of normal/superconducting (N/S) bilayers of Pd/Nb (9 and 10, respectively, plus a capping Pd layer) were measured in the temperature range T < T * < T c0 , where the square-root behavior of H c (T ) indicates a two-dimensional behavior (for T * < T < T c0 a linear temperature law of H c (T ) is observed, indicating threedimensionality).…”

“…The latter range is interpreted as an unusual three-dimensional mode, because the large angle tail can be described by the Lawrence-Doniach model. The physical interpretation proposed is that for small angles the superconducting nucleus is localized in one period of the S/N structure, but for large angles, it is spread over more than one period by the perpendicular component of the external magnetic field, resulting in an object with a three dimensional feature (for a detailed discussion see the work of Prischepa et al 92 ). It is argued that, nevertheless, the Lawrence-Doniach description is not applicable, because it was deduced in the approximation of the homogeneous infinite medium.…”

Superconducting Order Parameter Nucleation and Critical Currents in the Presence of Weak Stray Fields in Superconductor/Insulator/Ferromagnet Hybrids

“…Apart from this, the location (relative to the domain wall) and the shape of the superconducting nuclei was studied [38]. In the case of stripe domains, when the field close to the ferromagnet can be approximated by a step function, the nucleation in the S-film is similar to the case of S/N structures (N is a normal metal) [43][44][45].…”