Angular Dependence Of Hc2 Research Articles

Superconductivity in Noncentrosymmetric LaNiZn Single Crystal

In this study, we observed bulk superconductivity in LaNiZn below Tc = 1.5 K, as confirmed by its electrical transport and specific heat capacity (ΔCel/γTc = 1.41). The upper critical fields along the hexagonal crystallographic c-axis and in the basal plane at 30 mK were found to be 0.36 and 0.24 T, respectively, suggesting mainly an orbital mechanism for field-induced depairing and a negligible spin triplet component in the superconducting order parameter. The angular dependence of Hc2 is explained by an effective mass model with an oblate-shaped effective Fermi surface. Our experimental and band calculation under local density approximation results suggested that LaNiZn is a Bardeen–Cooper–Schrieffer s-wave-type superconductor in the dirty limit, possibly involving multiple bands.

In-Plane Anisotropy of Upper Critical Field and Flux-Flow Resistivity in Layered Organic Superconductor β′′-(ET)2SF5CH2CF2SO3

We report the in-plane anisotropy of the upper critical field (Hc2) and the flux-flow resistivity (FFR) for a layered organic superconductor β′′-(ET)2SF5CH2CF2SO3 with the incoherent nature of the interlayer transport. The in-plane angular dependence of Hc2 showed a fourfold oscillation with maxima in the directions around H || b and a axes. This result is compatible with a \(d_{x^{2} - y^{2}}\) order parameter. The determined nodal structure is consistent with theoretical predictions of superconductivity mediated by charge fluctuations. Moreover, the dependence of the FFR on in-plane field-orientation showed a fourfold symmetry with cusp-like minima in the directions around H || b and a axes, which is very similar to the FFR for κ-(ET)2Cu(NCS)2 with d-wave pairing symmetry. From these results, we claim that the vortex dynamics is strongly affected by the superconducting gap structure for highly two-dimensional superconductors with d-wave pairing symmetry.

ANISOTROPIC SUPERCONDUCTING PROPERTIES OF CaAlSi AND CaGaSi

Anisotropic superconducting properties of new layered intermetallic compounds CaAlSi and CaGaSi with AlB 2 structure are studied. These superconductors show moderate anisotropy with anisotropy parameter [Formula: see text] determined by both magnetic and transport measurements. Despite the small value of γ, angular dependence of Hc2 in CaAlSi shows cusp-like feature for fields parallel to the superconducting plane, suggesting the presence of two-dimensional superconducting units. By contrast, Hc2(θ) in CaGaSi can be reasonably well explained by the anisotropic GL-model. X-ray diffraction measurements reveal the presence of superstructure along the c-axis in CaAlSi but not in CaGaSi . These findings suggest a close relationship between the anomalous angular dependence of Hc2 and the superstructure. Possible origins of the two-dimensional superconducting units in CaAlSi are discussed.

Two-band Effects in the Critical Fields of MgB2

The influence of the two-gap/two-band superconductivity on the anisotropy properties of MgB2 is discussed. It is shown that due to the different anisotropies and different field sensitivities of both bands the lower critical field Hc1 and the upper critical one Hc2 reveal very different and temperature-dependent anisotropies. The deviations of the angular dependence of Hc2(Θ) from the classical form is discussed in the framework of the two-band model.

In-Plane Fourfold Symmetry of the Upper Critical Field Observed in La(Sr)214 Single Crystals

In order to establish the existence of in-plane anisotropy of the upper critical field H c2 (θ), the out-of-plane resistivity ρ c measurements were performed on La(Sr)214 single crystals with rectangular and cylindrical shape under rotating magnetic field applied within the ab-plane. Although observed ρ c shows non-sinusoidal twofold symmetry, clear fourfold symmetry was obtained after subtracting twofold sinusoidal component in ρ c which is due to the unavoidable misalignment of the magnetic field with respect to ab-plane. H c2 (θ) is estimated from the extracted fourfold component of ρ c with the flux flow theory. Angular dependence of H c2 (θ) was well fitted by cos(4θ). Since the fourfold component of H c2 (θ) was largest at θ = nπ/2, which corresponds to the a-axis direction, the present results strongly suggest the $$d_{x^2 - y^2 } $$ type symmetry in La(Sr)214. In addition, the difference in fourfold component of H c2 at θ = nπ/2 and nπ/2+π/4 was found to increase with decreasing temperature.

Preferential position of order parameter and angular dependence of upper critical fields in Nb/NbZr multilayers

The Nb/NbZr multilayer, which is composed of two superconductors with the same critical temperature and the different electron diffusion constant, is a typical system to exhibit the anomalous upturn inT-dependence of upper critical fieldHc2II parallcl to the film surface. For the angular dependence ofHc2, we have observed a minimum on the tilt of θ (as θ=0o forH⊥ film). This is interpreted as the dimensional crossover of the localized order parameter at Open image in new window (as θ=0o forH ⊥ film). This mechanism has been also confirmed in the variation ofI-V characteristics withH-direction to the film, where the samples were located at the specific configuration in the field.

Upper critical field of aD-wave superconductor stabilized by antiferromagnetic fluctuations

We have derived microscopic equations for the upper critical magnetic field of aD-wave superconductor stabilized by antiferromagnetic spin fluctuations. We present numerical results for the reduced fieldh c2(t) as a function of reduced temperaturet when the magnetic field is along thez axis and also zero-order results when it is along thex ory axis. Two differentD-wave models are considered. The angular dependence ofH c2 forT nearT c is given as a function of polar angleϑ in thez−x orz−y plane.

Anomalous upper critical fields of superconducting N b/ N bo.5 Z ro.5 multilayers

Abstract Upper critical fields have been studied for N b/ N bo.5 Z ro.5 multilayers grown onto the substrates of 300°C by magnetron sputtering. The multilayers are constituted from two superconducting materials with different electronic diffusion constants and nearly equal critical temperatures. For the samples with period of 360-, 400- and 500-A, the upturn features at lower temperature in addition to dimensional crossover were observed in parallel upper critical field Hc2. Noticeable changes were also found in the transition width ΔHc2I (T) and the angular dependence of HC2 in the region of temperature which the upturn took place. The positive curvatures of H... had a tendency to depend upon N b layer thicknesses.

Anisotropic critical fields of NbCu in situ formed composites

We have measured the upper critical field of NbCu in situ formed tape composites and found it anisotropic. The angular dependence of Hc2 is in good agreement with the predictions of the anisotropic Ginzburg-Landau model.

Anisotropy of the Ginzburg-Landau parameter κ in NbSe2

On small single crystals of 2H NbSe 2 we have measured the temperature and angular dependence ofH c2 as well as the temperature dependence ofH c1 close toT c. Using an effective mass approach to the Ginzburg-Landau equations we have analyzed our data in terms of an anisotropic κ and obtained values for the coherence distances and penetration depths parallel and perpendicular to the layers. The connection between these parameters and normal-state properties is discussed and shown to be more complex than in the isotropic case.