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1.
The upper critical field of clean MgB2 is investigated
using the two-band layered Ginzburg--Landau (GL) theory. The
calculated results are fitted to the experimental data of clean
MgB2 crystal very well in a broad temperature range. Based
on the GL theory for clean superconductors, a phenomenological
theory for dirty superconductor is proposed. Selecting appropriate
parameters, two-band layered GL theory is successfully applied to
the crystal of Mg(B1-xCx)2 and the neutron
irradiation samples of MgB2. 相似文献
2.
K. Takanaka 《Solid State Communications》1982,42(2):123-128
The upper critical field of anisotropic superconductors described by the effective mass model is calculated in the general direction of the applied magnetic field. 相似文献
3.
A. Changjan P. Udomsamuthirun 《Physica C: Superconductivity and its Applications》2011,471(1-2):23-25
The upper critical field, the lower critical field and the critical magnetic field ratio of anisotropic magnetic superconductors are calculated by Ginzburg–Landau theory analytically. The effect of the Ginzburg–Landau parameter (κ0), magnetic susceptibility (χ) and magnetic-to-anisotropic parameter ratio (θ) on the critical field ratio are considered. We find that the value of critical field ratio increases with increasing κ0 and θ, and decreases with increasing χ. The highest and the lowest value of critical field ratio is found in the diamagnetic superconductors and the ferromagnetic superconductors, respectively. 相似文献
4.
P. Udomsamuthirun R. Peamsuwan C. Kumvongsa 《Physica C: Superconductivity and its Applications》2009,469(13):736-739
The effect of anisotropic order parameter on the specific heat of anisotropic two-band superconductors in BCS weak-coupling limit is investigated. An analytical specific heat jump and the numerical specific heat are shown by using anisotropic order parameters, and the electron–phonon interaction and non-electron–phonon interaction. The two models of anisotropic order parameters are used for numerical calculation that we find little effect on the numerical results. The specific heat jump of MgB2, Lu2Fe3Si5 and Nb3Sn superconductors can fit well with both of them. By comparing the experimental data with overall range of temperature, the best fit is Nb3Sn, MgB2, and Lu2Fe3Si5 superconductors. 相似文献
5.
We propose that a new state with a fully gapless Fermi surface appears in quasi-2D multiband superconductors in magnetic field applied parallel to the plane. It is characterized by a paramagnetic moment caused by a finite density of states on the open Fermi surface. We calculate thermodynamic and magnetic properties of the gapless state for both s-wave and d-wave cases, and discuss the details of the first order metamagnetic phase transition that accompanies the appearance of the new phase in s-wave superconductors. We suggest possible experiments to detect this state both in the s-wave (2-H NbSe2) and d-wave (CeCoIn5) superconductors. 相似文献
6.
NMR line shape has been constructed for anisotropic type-II superconductors in tilted magnetic fields, with inclusion of vortex-lattice
magnetic-field nonuniformities and of the skin effect near the superconductor surface. The NMR line shape parameters are shown
to change considerably when the external magnetic field changes direction. This makes it possible to obtain more detailed
information about the characteristics of a superconductor, in particular, its anisotropy parameter.
Fiz. Tverd. Tela (St. Petersburg) 40, 993–997 (June 1998) 相似文献
7.
8.
Fermi surface topology and the upper critical field in two-band superconductors: application to MgB2
Recent measurements of the anisotropy of the upper critical field B(c2) on MgB2 single crystals have shown a puzzling strong temperature dependence. Here, we present a calculation of the upper critical field based on a detailed modeling of band structure calculations that takes into account both the unusual Fermi surface topology and the two gap nature of the superconducting order parameter. Our results show that the strong temperature dependence of the B(c2) anisotropy can be understood as an interplay of the dominating gap on the sigma band, which possesses a small c-axis component of the Fermi velocity, with the induced superconductivity on the pi-band possessing a large c-axis component of the Fermi velocity. We provide analytic formulas for the anisotropy ratio at T=0 and T=T(c) and quantitatively predict the distortion of the vortex lattice based on our calculations. 相似文献
9.
采用二带Ginziburg-Landau(G-L)理论模型计算了各向异性超导体的上临界磁场,发现上临界磁场Hc2的解析式中包含序参量的各向异性和有效质量的各向异性;上临界磁场ab-面内分量Hc|2|ab、c-轴方向分量Hc|2|ab与实验数据符合;上临界磁场比率在实验许可范围之内。 相似文献
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13.
A. I. Posazhennikova M. V. Sadovskii 《Journal of Experimental and Theoretical Physics》1997,85(6):1162-1167
We carry out the Ginzburg-Landau expansion for superconductors with anisotropic s and d pairing in the presence of anisotropic normal-impurity scattering, which enhances the stability of d pairing with respect to disordering. We find that the slope of the curve of the upper critical field, |dH
c2/dT|T
c, in superconductors with d pairing behaves nonlinearly as disorder grows: at low scattering anisotropy the slope rapidly decreases with increasing impurity
concentration, then gradually but nonlinearly increases with concentration, reaches its maximum, and then rapidly decreases,
vanishing at the critical impurity concentration. In superconductors with anisotropic s pairing, |dH
c2/dT|T
c always increases with impurity concentration, finally reaching the familiar asymptotic value characteristic of the isotropic
case, irrespective of whether there is anisotropic impurity scattering.
Zh. éksp. Teor. Fiz. 112, 2124–2133 (December 1997) 相似文献
14.
Richard A. Klemm 《Solid State Communications》1983,46(9):705-708
We propose a model for the layered superconductors with electronically isolated magnetic intercalates in which the electrons propagate freely in the dirty superconducting layers with arbitrarily strong spin-orbit scattering, and spin-flip scatter off the magnetic ions during interlayer tunneling. We calculate the upper critical field Hc2 including demagnetization effects. In a parallel field below the dimensional-crossover temperature T1, a new type of spin ordering is predicted. 相似文献
15.
The ultrasonic attenuation coefficient for longitudinal waves is formulated for two-band superconductors. The resulting expression differs from that previously obtained by Fal'ko. 相似文献
16.
Y. Tanaka P.M. ShirageA. Iyo 《Physica C: Superconductivity and its Applications》2010,470(22):2023-2026
Competition between an interband Josephson interaction and a biquadratic interband interaction can break time-reversal symmetry when the interband interactions are very weak compared with the intraband interaction. We demonstrate this using the phenomenological Ginzburg–Landau free energy, taking into account terms essential for this phenomenon. This time-reversal symmetry-breaking state peels away a sheet of an interband phase difference soliton wall. This sheet is the domain wall between two different chiral states. The peeling reduces the formation energy of the domain wall. The domain wall can simultaneously erase the Meissner effect and the specific heat jump when the entropy invokes many domain walls, and its life time is prolonged by a pinning owing to an inhomogeneity such as surface roughness. 相似文献
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18.
A theory of the proximity effects in the inhomogeneous dirty superconductors has been developed. The critical magnetic field as a function of temperature and of the length of the inhomogeneity has been investigated. The angular dependence has been obtained. 相似文献
19.
Recent observation of unusual vortex patterns in MgB(2) single crystals raised speculations about possible "type-1.5" superconductivity in two-band materials, mixing the properties of both type-I and type-II superconductors. However, the strict application of the standard two-band Ginzburg-Landau (GL) theory results in simply proportional order parameters of the two bands-and does not support the "type-1.5" behavior. Here we derive the extended GL formalism (accounting all terms of the next order over the small τ=1-T/T(c) parameter) for a two-band clean s-wave superconductor and show that the two condensates generally have different spatial scales, with the difference disappearing only in the limit T→T(c). The extended version of the two-band GL formalism improves the validity of GL theory below T(c) and suggests revisiting the earlier calculations based on the standard model. 相似文献
20.
用两带Ginzburg-Landau(GL)理论分析了Lu2Fe3Si5的表面临界磁场,当超导体的表面与任一主晶面重合,且外磁场平行于超导体的表面时,比值Hc3/Hc2(HC2是Lu2Fe3Si5的上临界磁场)强烈依赖于温度. 当超导体的表面是bc平面,且
关键词:
两带超导体
GL理论
2Fe3Si5')" href="#">Lu2Fe3Si5
表面临界磁场 相似文献