2001/07/12 by N. Klein, B. B. Jin, Klein, N. +13
Materials Science · Physics and Astronomy · #FOS: Physical sciences #Iron-based superconductors research #Physics of Superconductivity and Magnetism #Superconductivity (cond-mat.supr-con) #Superconductivity in MgB2 and Alloys
paper · pdf · doi:10.48550/arxiv.cond-mat/0107259
openalex publication_date 2001/07/12 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
We have measured the temperature dependence of the microwave surface impedance Zs = Rs + iΩμ0 of a MgB2 film at a frequency Ω/2Πof 18 GHz employing a dielectric resonator technique. We found that the temperature dependence of the magnetic field penetration depth \Lamda can be fitted by \Lamda(T)= \Lamda(0) [1-(T/Tc)2] ^(-1/2) with \Lamda(0)=(260 +/- 20)nm. The absolute value of \Lamda(0) was confirmed by direct measurements employing submillimeter wave transmission spectroscopy at 430 GHz. The analysis of the \Lamda(T) data below Tc/2 revealed significant deviations from the quadratic temperature dependence. In contrast, we found that an exponential temperature dependence fits the experimental data within the statistical measurement error for temperature changes of \Lamda of +/- 0.4 nm. This observation indicates thermal excitation of quasiparticles over a finite energy gap of (3.3 +/- 0.3) meV corresponding to Δ/kTc = 1.2 +/- 0.1. Our results strongly supports a multipgap or a strongly anisotropic gap and the absence of nodes in the gap function.