Experimental observation of the breakdown by a magnetic field of the superconducting fluctuations in the normal state

Abstract

The effects induced on the magnetization by coherent fluctuating Cooper pairs in the normal state have been measured in Pb 1−x In x alloys up to high magnetic fields, of amplitudes above H C2 (0), the upper critical field extrapolated to T =0 K. Our results show that in dirty alloys these superconducting fluctuation effects are, in the entire H − T phase diagram above H C2 (T ), independent of the amount of impurities and that they vanish when H ∼ 1.1H C2 (0). These striking results are consistent with a phenomenological estimate that takes into account the limits imposed by the uncertainty principle to the shrinkage, when H increases, of the superconducting wave function.

Fluctuations aboveTcand the kinetic energy of Cooper pairs inLa1.9Sr0.1

“…For the high-T c compounds the kinetic energy evolves smoothly across the transition without any change, even in the first derivative with respect to the temperature, whereas, for Nb, it falls abruptly at the transition following standard BCS Ginzburg-Landau behavior. In this paper we find that the same features differentiate two other superconductors, a low-and a high-T c compound, namely, a Pb-In alloy, Pb 0.55 In 0.45 , 8 and La 1.9 Sr 0.1 CuO 4 ͑La-SrCuO͒. 9 Thus the smooth behavior of the kinetic energy along the transition found here, and before, 7 supports the view of vortex activity above the transition for the high-T c compounds.…”

In-plane and transverse superconducting fluctuation diamagnetism in the presence of charge-density waves in2H−NbSe2single crystals

“…This effect has been interpreted in terms of the shrinkage, induced by the magnetic field, of the superconducting wave-function to lengths of the order of the Cooper pairs size perpendicular to the applied field. 17,18 Due to the high H C2 (0) value (∼ 17 T) ∆M /H does not vanish even for the highest magnetic fields used in the experiments.…”

“…Nevertheless, these data show that the FD in both directions vanishes at H ≈ H ⊥, C2 , in agreement with the total energy cutoff prediction. 17,18 NbSe 2 Q ∼ 2k F ∼ 10 10 m −1 , 29 and since K ∼ 0.1, 30 the coupling can be treated perturbatively. The main correction is expected to happen for H ⊥ ab and it may be approached by renormalizing the reduced temperature as…”

“…The adequacy of the GGL theory to explain the FD of 2H-NbSe 2 when H ab, is typical of dirty metallic alloys like Pb 1−x In x with 0.08 ≥ x ≥ 0.45, 17,18,23,24 and of HTSC 25 which may also be considered as dirty materials. 26 This is consistent with the fact that for electric currents flowing in the c direction (which are induced when H ab) the electronic mean free path ℓ c is close to ξ c (0) (see Table I).…”

Out-of-plane fluctuation conductivity of layered superconductors in strong electric fields

“…(31), (32), (33), (34) and (35), valid for an arbitrary orientation of the electric field with respect to the layers, can be obtained in a simpler manner, without having to solve again the TDGL equation, by using a special scaling transformation of the coordinates and field components that reduces the problem to the isotropic case. 12,39 In the isotropic system, the coordinate axes can be in turn freely rotated so that the electric field acquires again only one non-zero component, for which the solution is already known.…”