Temperature dependence of the microwave surface impedance measured on different kinds of MgB$_2$ samples

Zhukov, A. A.; Cohen, L. F.; Purnell, A.; Bugoslavsky, Y.; Berenov, A.; MacManus-Driscoll, J. L.; Zhai, H. Y; Christen, Hans M.; Paranthaman, Mariappan P.; Lowndes, Douglas H.; Jo, M. A.; Blamire, M. C.; Hao, Ling; Gallop, J.

Temperature dependence of the microwave surface impedance measured on different kinds of MgB$_2$ samples

Authors

MacManus-Driscoll, J. L.

Zhai, H. Y

Christen, Hans M.

Paranthaman, Mariappan P.

Lowndes, Douglas H.

Description

In this paper we present the results of measurements of the microwave surface impedance of a powder sample and two films of MgB$_2$. One film has $T_c=30$ K and is not textured, the other is partially c-axis orientated with $T_c=38$ K. These samples show different types of temperature dependence of the field penetration depth: linear for the powder sample, exponential with $Δ/kT_c<1.76$ (film with $T_c=30$ K) and strong coupling behaviour with $Δ/kT_c\sim 2.25$ (film with $T_c=38$ K). The results are well described in terms of an anisotropic gap model or presence of a slightly deficient MgB$_2$ phase. The data set for all samples - taken as a whole cannot be fitted into a two gap scenario.
4 pages, 3 figures