Reflection of two-gap nature in penetration depth measurements of MgB$_2$ film

Details Reflection of two-gap nature in penetration depth measurements of MgB$_2$ film Reflection of two-gap nature in penetration depth measurements of MgB$_2$ film

2002-01-30

arxiv.org/abs/cond-mat/0201550v3

Phys. Rev. B 66, 064511 (2002)

Physics

Condensed Matter

Superconductivity

8 pages, 5 figures

Scientific paper

10.1103/PhysRevB.66.064511

The magnetic penetration depth, $\lambda^{-2}(T)$, in the basal plane of a magnesium diboride (MgB$_2$) film was measured using a two-coil mutual inductance technique at 50 kHz. This film has $T_c\simeq 38$ K, $\Delta T_c \leq 1$ K, and $\lambda(0)\sim 1500$ \AA. At low temperatures, $\lambda^{-2}(T)$ shows a clear exponential temperature dependence, indicating s-wave superconducting order parameter symmetry. However, the data are not quantitatively well described by theory assuming a single gap. From the data fit by the full BCS calculation assuming a double gap, the values of the two distinct gaps were obtained: $\Delta_S(0)=2.61\pm0.41$ meV and $\Delta_L(0)=6.50\pm0.33$ meV. The contributions of the small and the large gaps to the total superfluid density at T=0 were estimated to be 21% and 79%, respectively. Finally, we consider the effect of gap anisotropy on the penetration depth measurements, and find that the anisotropy does not play a significant role in determining the temperature dependence of the penetration depth.

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