The Electron Mechanism of Superconductivity

Geilikman, B.T.

doi:10.1070/pu1966v009n01abeh002897

Cited by 41 publications

(33 citation statements)

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“…3 for the exact fitted values of the parameters). These results are consistent with constraints imposed by the general theory of two-gap superconductors: In the low-T limit C es is determined by the smaller gap [10]; ∆C(T c )/γ n T c must be less than the BCS value (the experimental value is 1.32 and the BCS value is 1.43); one gap must be larger than the BCS gap and one smaller [11]. The derived values of the parameters are in remarkably good agreement with band-structure calculations [13].…”

supporting

confidence: 78%

“…A comparison of the fitted parameters, shown in conductor, interband coupling ensures that both gaps open at the same T c [10]. If the electron-phonon coupling is weaker in one band than the other the two gaps are likely to have similar T dependences [11] but C es will be determined by the smaller gap at low T [10]. Qualitatively, the T dependence of C es is consistent with the expectations for such a two-gap superconductor.…”

supporting

confidence: 74%

“…This corresponds to the fact that the smaller gap, which determines C es , is much smaller than the BCS gap. A comparison of the fitted parameters, shown in conductor, interband coupling ensures that both gaps open at the same T c [10]. If the electron-phonon coupling is weaker in one band than the other the two gaps are likely to have similar T dependences [11] but C es will be determined by the smaller gap at low T [10].…”

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confidence: 99%

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SPECIFIC HEAT OF Mg¹¹B₂ IN MAGNETIC FIELDS: TWO ENERGY GAPS IN THE SUPERCONDUCTING STATE

Fisher

Bouquet

Phillips

et al. 2002

Physical Phenomena at High Magnetic Fields IV

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We present specific-heat measurements on Mg 11 B 2 in magnetic fields to 9 T. The anomaly at T c is rapidly broadened and attenuated in fields, as expected for an anisotropic, randomly oriented superconductor. At low temperature there is a strongly field-dependent feature that shows the existence of a second energy gap. The Sommerfeld constant, γ, increases rapidly and nonlinearly with magnetic field, which cannot be accounted for by anisotropy. It approaches γ n = 2.6 mJ K -2 mol -1 , the coefficient of the normal-state electron contribution, asymptotically for fields greater than 5 T. In zero magnetic field the data can be fitted with a phenomenological two-gap model, a generalization of a semi-empirical model for single-gap superconductors. Both of the gaps close at the same T c ; one is larger and one smaller than the BCS weak coupling limit, in the ratio ~ 4:1, and each accounts for ~ 50% of the normal-state electron density of states. The parameters characterizing the fit agree well with those from theory and are in approximate agreement with some spectroscopic measurements.Soon after the discovery of superconductivity in MgB 2 with T c ~ 40 K [1], it was shown that the specific heat, C, provides compelling evidence for the existence of two distinctly different energy gaps. In this paper we will describe briefly how specific-heat measurements in magnetic fields, H, can be used to identify and quantify these energy gaps [2][3][4].

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confidence: 78%

supporting

confidence: 74%

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confidence: 99%

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SPECIFIC HEAT OF Mg¹¹B₂ IN MAGNETIC FIELDS: TWO ENERGY GAPS IN THE SUPERCONDUCTING STATE

Fisher

Bouquet

Phillips

et al. 2002

Physical Phenomena at High Magnetic Fields IV

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“…Geilikman et al [15] have calcutated and tabulated g(t) which yields again a universal behaviour on t. Differently to scattering on imperfections, λ s e (t)/λ n e (T = T c ) in the BCS limit increases initially with decreasing values of t in spite of a rapid decrease of electronic excitations. A maximum occurs at t ≈ 0.28 with λ s e (t = 0.28)/λ n e (T = T c ) = 2.44.…”

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confidence: 99%

Thermal conductivity of superconducting MgB₂

Bauer

Paul

Berger

et al. 2001

J. Phys.: Condens. Matter

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Thermal conductivity of superconducting MgB 2 was studied in both the superconducting and the normal state region. The latter is almost equally determined by the electronic -and the lattice contribution to the total thermal conductivity. In the superconducting state, however, the lattice contribution is larger. The electronic thermal conductivity below T c was derived from the experimental data considering the Bardeen-Rickayzen-Tewordt theory together with the model of Geilikman. The analysis shows that electron scattering on static imperfections dominates.

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“…This conjecture is based on four assumptions: (1) the 3D free electron like band crosses the Fermi level in all superconducting GIC and is fully empty in all nonsuperconducting ones; (2) this band is not related to intercalant s or p states, but is formed by free electrons propagating in the interstitial space; (3) this band is much weaker coupled with the phonons than the other bands, and (4) such band stracture is advantageous for the excitonic "sandwich" mechanism [7] or for the acoustic plasmons mechanism [8].…”

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Intercalant-Driven Superconductivity inYbC6andCaC6

2005

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Recently deiscovered superconductivity in YbC6 and CaC6 at temperatures substantially higher than previously known for intercalated graphites, raised several new questions: (1) Is the mechanism considerably different from the previously known intercalated graphites? (2) If superconductivity is conventional, what are the relevant phonons? (3) Given extreme similarity between YbC6 and CaCa6, why their critical temperatures are so different? We address these questions on the basis of first-principles calculations and conclude that coupling with intercalant phonons is likely to be the main force for superconductivity in YbC6 and CaC6, but not in alkaline-intercalated compounds, and explain the difference in Tc by the "isotope effect" due to the difference in Yb and Ca atomic masses.

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The Electron Mechanism of Superconductivity

Cited by 41 publications

References 1 publication

SPECIFIC HEAT OF Mg¹¹B₂ IN MAGNETIC FIELDS: TWO ENERGY GAPS IN THE SUPERCONDUCTING STATE

SPECIFIC HEAT OF Mg¹¹B₂ IN MAGNETIC FIELDS: TWO ENERGY GAPS IN THE SUPERCONDUCTING STATE

Thermal conductivity of superconducting MgB₂

Intercalant-Driven Superconductivity inYbC6andCaC6

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The Electron Mechanism of Superconductivity

Cited by 41 publications

References 1 publication

SPECIFIC HEAT OF Mg11B2 IN MAGNETIC FIELDS: TWO ENERGY GAPS IN THE SUPERCONDUCTING STATE

SPECIFIC HEAT OF Mg11B2 IN MAGNETIC FIELDS: TWO ENERGY GAPS IN THE SUPERCONDUCTING STATE

Thermal conductivity of superconducting MgB2

Intercalant-Driven Superconductivity inYbC6andCaC6

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Product

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SPECIFIC HEAT OF Mg¹¹B₂ IN MAGNETIC FIELDS: TWO ENERGY GAPS IN THE SUPERCONDUCTING STATE

SPECIFIC HEAT OF Mg¹¹B₂ IN MAGNETIC FIELDS: TWO ENERGY GAPS IN THE SUPERCONDUCTING STATE

Thermal conductivity of superconducting MgB₂