London penetration depth for

Here, kab and kc are the London penetration depths for a magnetic field in the c-direction and parallel to the afo-plane, respectively. Bc2(c) and Bc2(ab) are approximate upper critical fields aligned in the c-direction and parallel to the afo-plane, respectively and ab are the coherence lengths in c-dtrecfion and in the ab plane, respectively. Considerably different values have been reported for the parameters listed in Table 4.2-28. This is tme in particular for Hq2 and also for which is usually... 

First we review some typical materials parameters obtained from measurements on randomly oriented ceramics (6-7). Since the YBaCuO structure (5) and electronic properties 81 are highly anisotropic, the orientationally-averaged values obtained from studies of ceramics are only an initial indication until more complete experimental results on single crystals and oriented films and ceramics become available. For material with a resistivity just above the transition of 400 /xficm, a Hall carrier density of 4xl021cm , and dHc2/dT of 2 T/K (6-7). one deduces a BCS coherence length (0) of 1-4 nm, a London penetration depth A(0) of 200 nm, a mean free path t of 1.2 nm, a thermodynamic critical field Hc(0) of 1 T (10000 Oe) and an upper critical... 

Further results from TF-p,SR studies on UPd2Al3 concern superconducting properties that are outside this review. We mention the approximately isotropic London penetration depth ( 5000A) and the ratio %/T 10 (T being the Fermi tenqierature) which is one order of magnitude larger than that for simple metallic BCS superconductors (W.D. Wu et al. 1994b). 

Measurements of the London penetration depth A(T) point to the existence of aniostropic superconducting phases in UBejj (Einzel et al. 1986) and CeCu2Si2 (Gross et al. 1988), as well. Figure 76 demonstrates for the former system clear deviations from the temperature dependence expected for an ordinary, isotropic superconductor. As an explanation, it has been proposed (Gross et al. 1986, Millis 1987) to use the standard connection between the condensate velocity and the electromagnetic potentials,... 

Table k.2-28 Maximum Ti and a compilation of several values of the coherence lengths, London penetration depths and upper critical fields at T = 0 K for superconducting compounds of the Bi—Sr—Ca—Cu—O system, cont. 

It should be noted that the Miessner effect does not completely repel H that is, the field is able to penetrate the surface of the superconductor to a depth known as the London penetration depth, X. For most superconductors, X is on the order of 100 nm decaying exponentially beyond this region toward the bulk of the superconductor structure. 

The factor that determines whether a material will by a type-I or type-II superconductor is the ratio of the London penetration depth to the coherence length. If A/ <0.71, the material will be type-I if A/ > 0.71, it will be a type-II. (The reason for this will be discussed later.) Both penetration depth and coherence length are influenced by the addition of impurities which disrupt the regularity of the lattice. The penetration depth increases according to... 

A. Chattopadhyay and E. London, Parallax method for direct measurement of membrane penetration depth utilizing fluorescence quenching by spin-labeled phospholipids, Biochemistry 26, 39-45 (1987). 

In the classical model of superconductivity, the London equations (London and London 1935) are equivalent to Ohm s law j = o-E for a normal electric conductor. The first of the London equations [Eq. (E.l)] represents a conductor with R = 0, while the second [Eq. (E.2)] is equivalent to the Meissner-Ochsenfeld effect (Figure E.l), and describes the decay of a magnetic field within a thin surface layer characterized by the penetration depth,... 

Figure 11.11 Penetration depth (h) as a function of chlorosulphonic acid treatment time at room temperature for LDPE ( X HOPE (O) and PP ( ). After Kalnins, Conde Braha and Gedde (1992) with permission from Elsevier Applied Science, London.

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