Angular Dependent Critical Fields in NbTi-Ge Superlattices in the Weakly Localized Regime

1986 ◽  
Vol 77 ◽  
Author(s):  
Ben Y. Jin ◽  
J. B. Ketterson ◽  
J. E. Hilliard ◽  
E. J. McNiff ◽  
S. Foner ◽  
...  
Keyword(s):  
Diffusion Equation ◽  
Boundary Conditions ◽  
Angular Dependence ◽  
Critical Field ◽  
Upper Critical Field ◽  
Interaction Effects ◽  
Critical Fields ◽  
Gauge Invariant ◽  
Upper Critical Fields ◽  
Lowest Eigenvalue

ABSTRACTThe angular dependence of the upper critical fields, Hc(θ) for a set of NbTi-Ge superlattices were studied at various temperatures. The behavior of Hc(θ) at lower temperatures deviates from the Tinkham expression which is expected to be valid only in the Ginzberg-Landau regime close to Tc. We examine a model for calculating Hc(θ) involving the lowest eigenvalue of the gauge invariant diffusion equation (subject to boundary conditions appropriate to a slab) in the de Gennes expression for the upper critical field of a dirty superconductor at all temperatures. The disorder related localization and interaction effects as well, as the paramagnetic limiting effect, are also considered.

UPPER CRITICAL FIELD OF HIGH Tc SUPERCONDUCTING OXIDES

1987 ◽  
Vol 01 (02) ◽  
pp. 451-453
Author(s):  
Changgeng CUI ◽  
Shuquan GUO ◽  
Shanlin LI ◽  
Lie CHEN ◽  
Cheng DONG ◽  
...  
Keyword(s):  
Least Squares ◽  
Critical Field ◽  
High Field ◽  
Upper Critical Field ◽  
Critical Fields ◽  
High Tc ◽  
Dirty Limit ◽  
Straight Line ◽  
Upper Critical Fields ◽  
Superconducting Oxides

Upper critical fields Bc2(T) near Tc have been measured for the samples of Ba2YCu3Ox and Ba2GdCu3Ox. The upper critical field slope (dBc2dT)Tc and the upper critical field Bc2(O) have been calculated by using the least squares filling of straight line and using WHH expression in dirty limit respectively. The results show that Bc2(O) can be reach 114T and 127T for the samples of Ba2YCu3Ox and Ba2GdCu3Ox respectively. It is observed that there is a upwards curvature near Tc in the curves of B(T) vs.T. The main reason might be a proximity type effect in which a small amount of high Tc materials is able to raise the effective Tc of the samples, However such an effect could be suppressed at high field.

The effect of epitaxy on the upper critical fields of evaporated niobium films

1989 ◽  
Vol 4 (2) ◽  
pp. 283-287 ◽  
Author(s):  
Gin-ichiro Oya ◽  
Tetsuro Komukai ◽  
Yasuji Sawada
Keyword(s):  
Single Crystal ◽  
Critical Field ◽  
Surface Effect ◽  
Upper Critical Field ◽  
Critical Fields ◽  
Surface Nucleation ◽  
Single Crystal Films ◽  
Crystal Films ◽  
Upper Critical Fields ◽  
Niobium Suboxide

Two upper critical fields normal (Bc2⊥) and parallel (Bc2∥) to the surfaces of both single-crystal and polycrystalline Nb films are studied at 4.2 K in relation to the purity and morphology of the films, in order to make properties of the single-crystal films clear. High-quality single-crystal Nb films (with transition temperature Tc of ∼9.3 K and normal resistivity ρn of ∼0.2 μΩ · cm) are found to have magnetic properties characterized by Bc2⊥ of 0.31 T as low as Bc2 (bulk upper critical field) of bulk Nb, and Bc2∥/Bc2⊥ of ∼1.85 as high as Bc3/Bc2 (where Bc3 is the surface nucleation critical field) of pure Nb. These properties depend strongly on high purity and surface smoothness of the films, which is naturally accompanied by superconductivity. Polycrystalline Nb films have higher Bc2⊥ and lower Bc2∥/Bc2⊥, which result from a decrease in purity of the films and a presence of normal-conducting niobium-suboxide layers at the surfaces of the films, and thereby a decrease of the surface effect in the films.

scholarly journals Extremely high upper critical field in BiCh2-based (Ch: S and Se) layered superconductor LaO0.5F0.5BiS2−xSex (x = 0.22 and 0.69)

2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Kazuhisa Hoshi ◽  
Ryosuke Kurihara ◽  
Yosuke Goto ◽  
Masashi Tokunaga ◽  
Yoshikazu Mizuguchi
Keyword(s):  
Symmetry Breaking ◽  
Critical Field ◽  
Upper Critical Field ◽  
Layered Superconductor ◽  
Inversion Symmetry ◽  
Critical Fields ◽  
Local Inversion ◽  
Upper Critical Fields ◽  
Spin Polarisation ◽  
Inversion Asymmetry

AbstractCentrosymmetric compounds with local inversion symmetry breaking have tremendously interesting and intriguing physical properties. In this study, we focus on a BiCh2-based (Ch: S, Se) layered superconductor, as a system with local inversion asymmetry, because spin polarisation based on the Rashba–Dresselhaus-type spin–orbit coupling has been observed in centrosymmetric BiCh2-based LaOBiS2 systems, while the BiCh2 layer lacks local inversion symmetry. Herein, we report the existence of extremely high in-plane upper critical fields in the BiCh2-based system LaO0.5F0.5BiS2−xSex (x = 0.22 and 0.69). The superconducting states are not completely suppressed by the applied magnetic fields with strengths up to 55 T. Thus, we consider that the in-plane upper critical field is enhanced by the local inversion symmetry breaking and its layered structure. Our study will open a new pathway for the discovery of superconductors that exhibit a high upper critical field by focusing on the local inversion symmetry breaking.

On the angular dependence of the upper critical field in thin films

1966 ◽  
Vol 20 (2) ◽  
pp. 122-123 ◽  
Author(s):  
K. Yamafuji ◽  
T. Kawashima ◽  
F. Irie
Keyword(s):  
Thin Films ◽  
Angular Dependence ◽  
Critical Field ◽  
Upper Critical Field

UPPER CRITICAL FIELD OF UNCONVENTIONAL SUPERCONDUCTORS FROM CHEMICAL EQUILIBRIUM

1999 ◽  
Vol 13 (29n31) ◽  
pp. 3443-3448 ◽  
Author(s):  
A. KALLIO ◽  
J. HISSA ◽  
T. HÄYRYNEN ◽  
V. BRÄYSY
Keyword(s):  
Magnetic Field ◽  
Critical Field ◽  
Normal State ◽  
Chemical Equilibrium ◽  
Critical Density ◽  
Upper Critical Field ◽  
Universal Function ◽  
Zero Magnetic Field ◽  
Mathematical Treatment ◽  
Critical Fields

We have shown previously that many normal state properties of high Tc superconductors in zero magnetic field can be understood in terms of a single universal function f(t) in the scaled variable t=T/T*, where T* is connected with temperature independent gap 2Δ=2kBT*, which gives the binding energy of a pair in analogy with dissociation of molecules. The function f(t) determines the fraction of bosons (B++) and fermions (h+) at temperature T and it is obtained from the mathematical treatment of chemical equilibrium with respect to the reaction B++⇌ 2h+. Since for magnetic fields of reasonable strength the Zeeman energy is much smaller than the pseudo gap Δ~100K-800K, the function f(t) in the normal state is largely independent of magnetic field. The main effect of the magnetic field is to increase the tendency for bosons to localize. This means that the critical density nL for delocalization in the ab-plane direction and the critical density for superfluidity nc (≳ nL) both increase with magnetic field. This causes the corresponding temperatures TBL(H) and Tc(H) to go down with the field. Assuming a power law dependence nc(H)/nc(0)=1+AHμ, the upper critical fields for several heavy fermion compounds are shown to fall into a single curve. The purpose here is to show that the upper critical field Hc2(y) (y=Tc(H)/Tc(0)) can be expressed in a simple way in terms of f(t). We show that this theory predicts all the shapes of Hc2(y) observed in several unconventinal superconductors such as Tl 2 Ba 2 CuO 6+δ, with Tc=15 K.

Anisotropic Upper Critical Field of Single Crystal RNi2B2C (R = Y, Lu)

1998 ◽  
Vol 12 (29n31) ◽  
pp. 3264-3266 ◽  
Author(s):  
A. C. Du Mar ◽  
K. D. D. Rathnayaka ◽  
D. G. Naugle ◽  
P. C. Canfield
Keyword(s):  
Low Temperature ◽  
Single Crystal ◽  
Critical Field ◽  
Upper Critical Field ◽  
Critical Fields ◽  
Linear Behavior ◽  
Upward Curvature

Measurements of the anisotropic upper critical field curves have been extended for YNi 2B2C and LuNi2B2C (T c = 15.6 K and 16.1 K, respectively). Measurements of R(T, H) were taken along the crystallographic directions of <100> and <110>. The resulting critical fields show an upward curvature near T c and a linear behavior at low temperature, which continues to below 2 K with little, if any, sign of saturation.

The temperature and angular dependence of the upper critical field of YBa 2 Cu 3 O 7-δ crystals

1989 ◽  
Vol 162-164 ◽  
pp. 735-736 ◽  
Author(s):  
U. Welp ◽  
W.K. Kwok ◽  
G.W. Crabtree ◽  
K.G. Vandervoort ◽  
J.Z. Liu
Keyword(s):  
Angular Dependence ◽  
Critical Field ◽  
Upper Critical Field
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