Characteristic features of the temperature dependence of the surface impedance in polycrystalline $\chem{MgB_2}$ samples

Yu. A. Nefyodov; M. R. Trunin; A. F. Shevchun; D. V. Shovkun; N. N. Kolesnikov; M. P. Kulakov; A. Agliolo Gallitto; S. Fricano

doi:doi:10.1209/epl/i2002-00656-8

DOI: 10.1209/epl/i2002-00656-8

Europhys. Lett., 58 (3) , pp. 422-428 (2002)

Characteristic features of the temperature dependence of the surface impedance in polycrystalline $\chem{MgB_2}$ samples

Yu. A. Nefyodov¹, M. R. Trunin¹, A. F. Shevchun¹, D. V. Shovkun¹, N. N. Kolesnikov¹, M. P. Kulakov¹, A. Agliolo Gallitto² and S. Fricano²

¹ Institute of Solid State Physics - 142432 Chernogolovka, Moscow district, Russia
² INFM, Unità di Palermo and Dipartimento di Scienze Fisiche e Astronomiche Via Archirafi 36, I-90123 Palermo, Italy

(Received 13 November 2001; accepted in final form 4 February 2002)

Abstract
The real $R_{\ab{s}}(T)$ and imaginary $X_{\ab{s}}(T)$ parts of the surface impedance $Z_{\ab{s}}(T)=R_{\ab{s}}(T)+iX_{\ab{s}}(T)$ in polycrystalline $\chem{MgB_2}$ samples of different density with the critical temperature $T_{\ab{c}}\approx 38$ $\un{K}$ are measured at the frequency of 9.4 $\un{GHz}$ and in the temperature range $5\le T<200$ $\un{K}$ . The normal skin-effect condition $R_{\ab{s}}(T)=X_{\ab{s}}(T)$ at $T\ge T_{\ab{c}}$ holds only for the samples of the highest density with roughness sizes not more than 0.1 $\un{\mu m}$ . For such samples extrapolation $T\rightarrow 0$ of the linear at $T<T_{\ab{c}}/2$ temperature dependences $\lambda_{\ab{L}}(T)=X_{\ab{s}}(T)/\omega\mu_0$ and $R_{\ab{s}}(T)$ results in values of the London penetration depth $\lambda_{\ab{L}}(0)\approx 600$ $\un{\AA}$ and residual surface resistance $R_{\ab{res}}\approx 0.8$ $\un{m\Omega}$ . In the entire temperature range the dependences $R_{\ab{s}}(T)$ and $X_{\ab{s}}(T)$ are well described by the modified two-fluid model.

PACS
74.25.Nf - Response to electromagnetic fields (nuclear magnetic resonance, surface impedance, etc.).
74.70.Ad - Metals; alloys and binary compounds (including A15, Laves phases, etc.).

© EDP Sciences 2002

Characteristic features of the temperature dependence of the surface impedance in polycrystalline samples

Characteristic features of the temperature dependence of the surface impedance in polycrystalline $\chem{MgB_2}$ samples