engleski

Anisotropy in MgB2 thin film studied by magnetic field dependent complex microwave conductivity

There is a general agreement that coherence length in the recently discovered binary compound MgB$_2$ is anisotropic, but a controversy arised on the question whether this anisotropy is temperature dependent or not. We have performed field and temperature dependent microwave measurements on high quality MgB$_2$ thin film in order to put more light into this controversy. The complex microwave conductivity has been analyzed both in the mean-field (MF) regime and in the fluctuation regime. The MF coherence length has been determined much below the transition to the normal state when a vortex contains many Landau levels. In contrast, the Ginzburg-Landau (GL) coherence length was obtained at the transition using the lowest-Landau-level (LLL) scaling of both, the real and imaginary parts of the complex microwave conductivity. The analysis reveals the anisotropy ratio of MF coherence lengths $\gamma_{; ; MF}; ; =\xi_{; ; MF}; ; ^{; ; ab}; ; /\xi_{; ; MF}; ; ^c\approx 2$, and the anisotropy ratio of GL coherence lengths $\gamma_{; ; GL}; ; \approx 2.8$. Both anisotropy ratios have been found to be temperature independent.

microwave response; MgB2 film; mixed state; depinning; fluctuations

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