Threshold Field Properties of Some Superconductors

Maxwell, E.; Lutes, O. S.

doi:10.1103/physrev.95.333

Cited by 47 publications

(9 citation statements)

References 6 publications

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“…To obtain (Op/'OT)To we use OT ~to O-T rrTc hn~-8~,m 2 h~,sgn (11) and for Op/Otz* we use OKn,,,/O~ * = -zrTc (12) Results for these quantities along with 0 2 Tc/Olz*2 are tabulated in Table I, together with the cutoff ~oc that was used on the Matsubara sums, and the corresponding value of tz* adjusted to get the measured To This/x* value differs from the tunneling value "for two reasons. First, it depends on the cutoff we, and second, a sharp cutoff on the imaginary axis does not correspond to a sharp cutoff on the real axis, as is discussed by Leavens and Fenton 7 and Vidberg and Serene.…”

Section: Tc and Its Functional Derivativesmentioning

confidence: 99%

Thermodynamics of strong coupling superconductors including the effect of anisotropy

1981

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The thermodynamics of several elemental superconductors is computed from isotropic Eliashberg theory formulated on the imaginary frequency axis. A symmary of the available experimental literature is presented and a comparison with theory is given. The small disagreements that are found are all in the direction expected from anisotropy effects. We calculate the effect of a small amount of model anisotropy on the critical temperature, critical field, and high-temperature specific heat from an exact solution of the anisotropic Eliashberg equations. These are the first such results below the critical temperature ; unlike previous analytical work, we include retardation, anisotropy in the mass enhancement, and the effect of the Coulomb repulsion in enhancing anisotropy, all of which are significant. We derive a new formula independent of any model anisotropy for the rate of decrease with impurity lifetime of the critical temperature. Finally we demonstrate how the commonly used formulas of Markowitz and Kadanoff and of Clem may give entirely misleading estimates of the gap anisotropy when used to interpret certain experiments.

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Section: Tc and Its Functional Derivativesmentioning

confidence: 99%

Thermodynamics of strong coupling superconductors including the effect of anisotropy

1981

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“…Our results exhibit a universal relation Tc = cJns for all families, where c ∼ 1, J is the in plane Heisenberg exchange, and ns is the carrier density. This relates cuprate superconductivity to magnetism in the same sense that phonon mediated superconductivity is related to atomic mass.The critical temperature for superconductivity T c in metallic superconductors varies with isotope substitution [1]. This observation, known as the isotope effect, played a key role in exposing their mechanism for superconductivity.…”

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confidence: 99%

“…The critical temperature for superconductivity T c in metallic superconductors varies with isotope substitution [1]. This observation, known as the isotope effect, played a key role in exposing their mechanism for superconductivity.…”

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confidence: 99%

Magnetic analog of the isotope effect in cuprates

et al. 2006

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We present extensive magnetic measurements of the (CaxLa1−x)(Ba1.75−xLa0.25+x)Cu3Oy system with its four different families (x) having a T max c (x) variation of 28% and minimal structural changes. For each family, we measured the Néel temperature, the anisotropies of the magnetic interactions, and the spin glass temperature. Our results exhibit a universal relation Tc = cJns for all families, where c ∼ 1, J is the in plane Heisenberg exchange, and ns is the carrier density. This relates cuprate superconductivity to magnetism in the same sense that phonon mediated superconductivity is related to atomic mass.The critical temperature for superconductivity T c in metallic superconductors varies with isotope substitution [1]. This observation, known as the isotope effect, played a key role in exposing their mechanism for superconductivity. In contrast, the mechanism for superconductivity in the cuprate is still elusive, but is believed to be of magnetic origin [2]. Verifying this belief would require an experiment similar to the isotope effect, namely, a measurement of T c versus the magnetic interaction strength J, with no other structural changes in the compounds under investigation. Here we present such an experiment using the (Ca x La 1−x )(Ba 1.75−x La 0.25+x )Cu 3 O y (CLBLCO) system with its four different superconducting families, for which maximum T c (T max c ) varies by 28%. This is a large change compared to Sn, which has the strongest isotope effect in nature where T c varies only by 4%. For each family, we measured the Néel Temperature T N and the anisotropies of the magnetic interactions. This allows us to obtain the Heisenberg coupling J. In addition, we determine the spin glass temperature T g of underdoped samples. J, T g and T c allow us to generate a unified phase diagram for magnetism and superconductivity from no doping to over doping. We combine this result with a previous determination of the superconducting carrier density n s [3], and demonstrate experimentally a magnetic analog of the isotope effect.

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“…It is known that strongly coupled systems yield positive deviations, while weakly coupled systems yield negative ones. 29 Such positive deviations for the present samples are shown in Figure 3, with the data fitted to the following expression:…”

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confidence: 70%