Specific heat in the superconducting and normal state (2–300 K, 0–16 T), and magnetic susceptibility of the 38 K superconductor MgB2: evidence for a multicomponent gap
By Yuxing Wang, T. Plackowski, A. Junod. 2001
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Abstract The specific heat C of a sintered polycrystalline sample of MgB 2 with a bulk superconducting transition temperature T c =36.7 K is measured as a function of the temperature (2–300 K) and magnetic field (0–16 T), together with magnetic properties (normal-state susceptibility, superconducting-state magnetization, etc.). The Sommerfeld constant γ =0.89±0.05 mJ/K 2 /gat (2.7 mJ/K 2 /mol) is determined in the normal state above H c2 . The normal- and superconducting-state entropies are equal at T c . Several moments of the PDOS are obtained from the lattice specific heat. We report bulk values for: the thermodynamic critical field, B c (0)=0.26 T; the slope of the upper critical field, (d B c2 /d T ) T c =0.56 T/K; the Ginzburg–Landau parameter, κ =38; the coherence length, ξ ≅5 nm; the lower critical field, B c1 ≅0.018 T; the London penetration depth, λ (0)≅180 nm. These results characterize MgB 2 as a type-II superconductor. The nearly quadratic dependence of C ( T ) versus T at T ≪ T c , its non-linear field dependence, and the discrepancy between the electron–phonon coupling constant λ ep as determined by the renormalization of the electron density of states ( λ ep ≅0.6) and by McMillan's equation for isotropic superconductors ( λ ep ≅1.1), are inconsistent with a single isotropic gap. In addition to high phonon frequencies, anisotropy or two-band gap structure may explain why the critical temperature of this superconductor is high in spite of its low condensation energy, which does not exceed 1/16 of that of YBa 2 Cu 3 O 7 and 1/4 of that of Nb 3 Sn.
Subfields: Condensed Matter Physics, Electronic, Optical and Magnetic Materials
View Paper: https://www.semanticscholar.org/paper/dd69fd4a86472beb8815790f8a292cb9f86a93cb
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Citations in the corpus
- Two-band superconductor magnesium diboride (2008, background): “The existence of two gaps was quickly discovered and confirmed by many experiments, including the measurements of specific heat [23, 24], point-contact spectroscopy [25], Raman spectroscopy [26, 27], photoemission spectroscopy [28] and scanning tunneling microscopy (STM) [29].”