ISSN:
1434-6036
Keywords:
PACS. 74.25.Nf Response to electromagnetic fields (nuclear magnetic resonance, surface impedance, etc.) - 74.20.De Phenomenological theories (two-fluid, Ginzburg-Landau, etc.) - 74.76.Bz High- films
Source:
Springer Online Journal Archives 1860-2000
Topics:
Physics
Notes:
Abstract: The temperature dependent surface impedance Z s ( T ) of single-crystalline YBa 2 Cu 3 O 7-x (YBCO) was analyzed within the two-fluid model in terms of the fraction of paired charge carriers, f s ( T ), and of the quasiparticle scattering time . The usual approach was extended by considering a temperature dependent effective quasiparticle mass m * ( T ), which results from a strong electron-phonon interaction. This effect must not be neglected in the description of high-temperature superconductors due to the large ratio of T c to the Debye temperature T D . The temperature dependence of the penetration depth, , of high-quality YBCO crystals and films could be described with an electron-phonon coupling constant , and using f s ( T ) = 1- ( T / T c ) 2.8 as an approximation of the BCS theory. Different trial phonon spectra were encountered in terms of their ability to reproduce the -data. The scattering time was described by the Bloch-Grüneisen formalism with T D =460 K. Assuming an Einstein spectrum with , a residual resistivity and a fraction of unpaired quasiparticles at T = 0 K yielded a surprisingly good agreement of the model with Z s ( T )-data measured at 87 GHz with a high-quality epitaxial YBCO film between T =4 K and T c . While an exact reproduction of the surface impedance asks for a rigorous theoretical computation, our analysis demonstrates that strong electron-phonon coupling is relevant for discussing the unconventional transport properties of YBCO.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s100510051068
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