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Microwave complex resistivity in High-Tc Superconductors in the mixed state
|Nicola Pompeo 1, Romolo Marcon 1, Luigi Muzzi 1, Enrico Silva 1, Stefano Sarti 2
1. Dipartimento di Fisica and Unita' INFM, Universita' Roma Tre, Via della Vasca Navale 84, Roma 00146, Italy
The microwave response of high-Tc superconductors in the vortex state is determined by superfluid and normal fluid together with the motion of flux lines. The mixing of these contributions makes difficult to isolate the contributions due to the charge carriers. At high enough frequencies, the vortex motion reduces to the simple flux flow. Thus, it can be isolated from the oveall response, allowing for the separate determination of the field dependent superfluid fraction ns(T,B). We have measured the (a,b) plane complex resistivity at 48 GHz in several highly oriented cuprate superconducting thin films, placed in the end-wall configuration in a resonating cavity, for temperatures from 65 K to Tc and magnetic fields up to 0.8 T (applied along the c axis). By preliminarly identificating the vortex contribution, we obtain the vortex viscosity. We compare our results with data from the literature. Having isolated the vortex motion contribution, we determine the field dependence of the superfluid fraction. We find that it follows a sublinear law (ns(T,B)=ns(T,0)-A B1/2), up to temperatures very close to Tc. This behaviour, which is a common feature of all the ReBCO (Re=Y, Sm) and Bi2212 samples investigated, is in agreement with the predictions for a superconductor with lines of nodes in the gap. Moreover, the extension of this field dependence in nearly the full temperature range explored (T>65 K) and up to temperatures close to Tc indicates that such pairing is not smeared out by the high operating temperatures.
Presentation: poster at E-MRS Fall Meeting 2004, Symposium E, by Nicola Pompeo
See On-line Journal of E-MRS Fall Meeting 2004
Submitted: 2004-04-30 14:14 Revised: 2009-06-08 12:55