Magnetic penetration depth, temperature

In contrast to the conventional s-wave superconductor picture above, Gasparov et al. (2006) report unusual temperature dependence of the magnetic penetration depth A.(T) and upper critical field Hc2(T) and propose that ZrBi2 has an unconventional two-gap superconductivity. 

Figure 2.34 illustrates these serious experimental problems. In the upper part (a) the magnetic penetration depth of k-(ET)2Cu(NCS)2 measured by ac susceptibility [220] and in the lower part (b) the same quantity obtained by dc magnetization [227] is shown. The clear discrepancy of the behavior of A(T) at low temperatures is obvious. In the ac-susceptibility experiment consistent with [221, 222, 223] a variation is found. This non-exponential non-BCS dependence can be explained with energy-gap nodes of several different topologies [222]. On the other hand, the data of [227] could very well be described by conventional weak-coupUng theory in the clean limit as shown... 

Fig. 2.34. Temperature dependence of the in-plane magnetic penetration depth extracted from (a) ac-susceptibility and (b) dc-magnetization measurements. The inset in (b) shows the low-T data in enlarged scale together with model curves for BCS (solid line) and for two triplet states, ti and t4 (broken curves). From [220] and [227]...

Fig. 4. The temperature dependence of the magnetic penetration depth of the paired holon superconductor (solid line) compared with the experimental data of YBa2Cu307 8. The data is from Cooper et al. (Ref. 14).

When Hj < Hcl, B = 0 in the interior of the superconducting cylinder as shown in Figure 1(b), but magnetic flux enters the walls for a distance A ( 1400 A for fields parallel to the a-b plane in YBajCujOy at low temperatures (23)). Provided the sample is of macroscopic size, the penetration depth is negligible, but it... 

From the value of the resonant frequency and its change with temperature or other external parameters the permittivity of a dielectric sample and its temperature or field dependence can be determined. In case of superconductors, the temperature dependence of the magnetic field penetration depth can be determined [8], Since the mode spectrum of a resonator is controlled both its physical dimensions and by the material properties, the physical dimensions of all resonator components have to be known with tight tolerances. Relative changes of permittivity or penetration depth can be determine with much higher accuracy than absolute values. 

Fig. 16.48 This residual density of states was pointed out theoretically to appear in the unitarity limit scattering by non-magnetic impurities in p- or d-wave superconductors in a heavy fermion study.49 From this result it became possible to explain the BCS-like temperature dependence of the penetration depth, A,50 which supported strongly the. 9-wave pairing model in high-7 , superconductors at an early stage, in terms of the d-wave + impurity model.51 53...

For in plane field (0 = tt/2) one has I Aid, (/>) = (l sin(/) - -1 cos( ) and Isid, Fourier components vary like cos 4(/> and cos 20, respectively, in accordance with the empirical expressions in eq. (121). However, the above equations really predicts cusps at 0 = ninfl) (fig. 65(c)) analogous to the situation in the borocaibides and not the smooth minima as seen in fig. 65(b). Therefore, the existence of cusps cannot be safely infered from the experimental results in fig. 65, this would necessitate measurements at lower temperatures. Also experiments with variation of the polar angle d have to be performed to check the possible existence of node points along [001]. Finally /u-SR experiments show indications of the presence of magnetic moments in the SC phase which is interpreted, similarly as in Ui xTh, Bei3 as evidence for a nonunitary triplet SC state (Aoki et al., 2003). This l s also been claimed from a recent penetration depth study (Chia et al., 2003). 

Soon after the experimental observations of the modulation of the transition temperature, de Gennes published a significant theoretical treatment of the proximity effect that explained these observations and related the transition temperature of a metal/superconductor sandwich to the electron-electron interaction in the normal metal [69]. In the simplest case, the assumptions made were that the electron-electron interactions in the normal metal (N) are negligible and that the magnetic field is zero (// = 0). Then the clean and dirty cases could be considered. In the clean case, the mean free path (/n) in the normal metal is large compared to the coherence length ( n) and the penetration depth The following expression was derived for this case ... 

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