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Microwave complex resistivity in High-Tc Superconductors in the mixed state

Nicola Pompeo 1Romolo Marcon 1Luigi Muzzi 1Enrico Silva 1Stefano Sarti 2

1. Dipartimento di Fisica and Unita' INFM, Universita' Roma Tre, Via della Vasca Navale 84, Roma 00146, Italy
2. Dipartimento di Fisica and Unita' INFM, Universita' di Roma "La Sapienza", Piazzale Aldo Moro 2, Roma 00185, 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.

We express our thanks to M. Boffa, M. C. Cucolo, A.M. Cucolo (Dip. di Fisica and Unita' INFM, Universita' di Salerno, Italy) and C. Camerlingo (CNR - Istituto di Cibernetica, Napoli, Italy) for samples preparation.

Work on YBCO has been partially supported by Italian MIUR under the FIRB project "Strutture semiconduttore/superconduttore per l'elettronica integrata".


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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