Yuxing Wang

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

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 McMillans 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.

Unusual effects of anisotropy on the specific heat of ceramic and single crystal MgB2

Abstract The two-gap structure in the superconducting state of MgB 2 gives rise to unusual thermodynamic properties which depart markedly from the isotropic single-band BCS model, both in their temperature- and field dependence. We report and discuss measurements of the specific heat up to 16 T on ceramic, and up to 14 T on single crystal samples, which demonstrate these effects in the bulk. The behavior in zero field is described in terms of two characteristic temperatures, a crossover temperature T c,π ≅13 K, and a critical temperature T c = T c,σ ≅38 K, whereas the mixed-state specific heat requires three characteristic fields, an isotropic crossover field μ 0 H c2,π ≅0.35 T, and an anisotropic upper critical field with extreme values μ 0 H c2,σ, c ≅3.5 T and μ 0 H c2,σ, ab ≅19 T, where the indexes π and σ refer to the three-dimensional and two-dimensional sheets of the Fermi surface. Irradiation-induced interband scattering tends to move the gaps toward a common value, and increases the upper critical field up to ∼28 T when T c ≅30 K.

Specific heat of Nb 3 Sn: The case for a second energy gap

We present specific-heat data for

Specific heat of MgB2 after irradiation

{\mathrm{Nb}}_{3}\mathrm{Sn}

Specific heat and magnetocaloric effect measurements using commercial heat-flow sensors

, a well-known technically applied superconductor with a critical temperature

Specific heat and magnetization of a Zr B 12 single crystal: Characterization of a type-II/1 superconductor

{T}_{c}\ensuremath{\cong}18\phantom{\rule{0.3em}{0ex}}\mathrm{K}

Specific heat of MgB_2 after irradiation

, in the temperature range from

Origin of the magnetization peak effect in the Nb 3 Sn superconductor

1.2\phantom{\rule{0.5em}{0ex}}\text{to}\phantom{\rule{0.5em}{0ex}}200\phantom{\rule{0.3em}{0ex}}\mathrm{K}

Phonon density of states, anharmonicity, electron-phonon coupling, and possible multigap superconductivity in the clathrate superconductors Ba 8 Si 46 and Ba 24 Si 100 : Factors behind large difference in T c

in zero magnetic field, and from

Modulated-bath ac calorimetry using modified commercial Peltier elements

1.5\phantom{\rule{0.5em}{0ex}}\text{to}\phantom{\rule{0.5em}{0ex}}22\phantom{\rule{0.3em}{0ex}}\mathrm{K}