Specific Heat ofMg11B2: Evidence for a Second Energy Gap

Abstract

Measurements of the specific heat of Mg11B2 from 1 to 50 K, in magnetic fields to 9 T, give the Debye temperature, Theta = 1050 K, the coefficient of the normal-state electron contribution, gamma(n) = 2.6 mJ mol(-1) K-2, and a discontinuity in the zero-field specific heat of 133 mJ mol(-1) K-1 at T(c) = 38.7 K. The estimated value of the electron-phonon coupling parameter, lambda = 0.62, could account for the observed T(c) only if the important phonon frequencies are unusually high relative to Theta. At low T, there is a strongly field-dependent feature that suggests the existence of a second energy gap, about 4 times smaller than the major gap.

Angular-dependent upper critical field of overdoped Ba(Fe1−xNix)2Murphy1, Tanatar2, Graf3 et al. 2013Phys. Rev. B235150View full textAdd to dashboardCite

“…The importance of the Fermi surface topology for the anisotropy of the H c2 was brought to focus by the discovery of pronounced multi-band effects in superconductivity of MgB 2 . [22][23][24] The upper critical field of this layered material is anisotropic and can be varied significantly by carbon and aluminum doping, [25][26][27] controlling the mean free path of the carriers and changing the inter-band coupling. Theoretical modeling explicitly included these effects into consideration and produced the angular dependence of the H c2 (θ) which was virtually identical to the dependence of Eq.…”

Response of Critical Temperature of the Superconducting Transition and Energy Gaps of MgB$_2$ to the Hydrostatic Compression

“…Îбнаружение в 2001 году сверхпроводящего состояния в дибориде магния (MgB 2 ) с высокой критической температурой T c = 39 К [1] привело к экспериментальному доказательству существования но-вого явления -двухзонной сверхпроводимости [2][3][4][5]. Расчёты из первых принципов электронной структуры MgB 2 [6] показали сложную топологию его поверхности Ôерми.…”

Measurement of the magnetic penetration depth of a superconducting MgB2thin film with a large intraband diffusivity

“…This value is smaller than those previously obtained in polycrystalline MgB 2 by specific heat measurements 36 and the values reported in clean single crystals. 37,38 As discussed earlier, the superconducting properties in multiband superconductors are affected by the interactions among the bands. 37 We obtain ξ ab (0) = 5.7 nm using H c2 (0) = Φ 0 /2πξ 2 (0) and our experimental value H c c2 (0) = 10 T. We can then use the Ginzburg-Landau theory to estimate the thermodynamic critical field in the film, H c = Φ 0 /2 √ 2πλ(0)ξ(0) = 2100 ± 300 Oe.…”

“…37,38 As discussed earlier, the superconducting properties in multiband superconductors are affected by the interactions among the bands. 37 We obtain ξ ab (0) = 5.7 nm using H c2 (0) = Φ 0 /2πξ 2 (0) and our experimental value H c c2 (0) = 10 T. We can then use the Ginzburg-Landau theory to estimate the thermodynamic critical field in the film, H c = Φ 0 /2 √ 2πλ(0)ξ(0) = 2100 ± 300 Oe. This value is close to the calculated value of H c = 2000 Oe from the two band model.…”