Regensburg 2004 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 8: Postersitzung I: Supraleitung
TT 8.33: Poster
Montag, 8. März 2004, 14:30–19:00, Poster A
Frequency dependence up to microwave frequencies of the ab-plane conductivity peak near Tc of YBa2Cu2O7−δ — •D. Görlitz and J. Kötzler — Institut f. Angewandte Physik, Univ. Hamburg, D-20355 Hamburg
The linear suceptibility χ′ − iχ″ of d=50-600 nm thin films has been measured between 30mHz and 22GHz in ac-fields perpendicular to the CuO2-planes. For frequencies up to 800 kHz mutual induction techniques were employed, while between 0.45 and 22 GHz the complex resonance frequency, fr=fr+iΔ f, of helical resonators and of cylindrical cavities was determined. The complex shifts δfr=fr(T)−fr(0) are proportional to the dynamic susceptibility χ(ω), and DC-susceptibilities were employed to calibrate δ fr. The ab-plane conductivity σ(ω)=σ′−iσ″ is determined from χ(ω) by means of an exact inversion routine [1]. The loss component σ′ shows a peak at a temperature Tω near Tc, and the peak temperatures Tω exhibit an Arrhenius behaviour. Using the inverse kinetic inductivity determined from σ″,(µ0 Lk(T))−1=ω σ″(T,ω), the Arrhenius barriers are related to the nucleation energy of vortex cores threading the film. These barriers are found to disappear at T0, which is distinctly above the true critical temperature Tc, also extracted from Lk−1(T)[2]. At the largest frequency, 21.3 GHz, the σ′-peak becomes strongly suppressed since Tω approaches T0.
[1] J. Kötzler et al., Phys.Rev. B 50, 3384 (1994)
[2] J. Kötzler et al., Phys.Rev.Lett. 87, 127005 (2001) and 89,149704 (2002)