10 June 1996 Temperature dependence of the dielectric function of laser deposited YBCO thin films at 3392 nm
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We have excited surface plasmons in a YBCO thin film at different temperatures using attenuated total reflection of light. The 300 nm thick c-axis film was fabricated using pulsed laser deposition onto an MgO (100) substrate with 248 nm KrF excimer radiation. Critical temperature of the film was 89.6 K and its roughness, as shown by atomic force microscopy, 20 nm rms, without droplets over areas of 10 micrometer by 10 micrometer. The sample was mounted in Otto geometry on a cooled stage which allowed the temperature to be varied between 300 K and 70 K. An infrared HeNe laser at 3392 nm was used to excite the surface plasmons. The dielectric function of the film was determined between room temperature and 80 K. The imaginary part of the dielectric function decreased substantially with reduction in temperature. Results obtained were: (epsilon) r equals -24.1 plus 0.0013T and (epsilon) i equals 7.7 plus 0.067T where T is the temperature in Kelvin. The ratio (epsilon) i300/(epsilon) i80 at 2.13 is less than the resistance ratio R300/R80 at 2.81. An explanation is offered in terms of two temperature independent mechanisms operative at optical frequencies: enhanced Rayleigh scattering of surface plasmons at grain boundaries and intraband/interband transitions. The real part of the dielectric function, (epsilon) r, was found to be only slightly temperature dependent. It was, however, highly sample dependent when comparison was made with the results of other films, a feature attributed to surface and grain boundary contamination.
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D. George Walmsley, D. George Walmsley, T. Bade, T. Bade, Patrick G. McCafferty, Patrick G. McCafferty, Chris J. T. Rea, Chris J. T. Rea, Paul Dawson, Paul Dawson, R. J. Wallace, R. J. Wallace, Robert M. Bowman, Robert M. Bowman, } "Temperature dependence of the dielectric function of laser deposited YBCO thin films at 3392 nm", Proc. SPIE 2696, Spectroscopic Studies of Superconductors, (10 June 1996); doi: 10.1117/12.241791; https://doi.org/10.1117/12.241791

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