Transport properties governed by surface barriers in Bi2Sr2CaCu2O8

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Abstract

One of the most common investigation techniques of type-II superconductors is the transport measurement, in which an electrical current is applied to a sample and the corresponding resistance is measured as a function of temperature and magnetic field. At temperatures well below the critical temperature, Tc, the resistance of a superconductor is usually immeasurably low. But at elevated temperatures and fields, in the so-called vortex liquid phase, a substantial linear resistance is observed1. In this dissipative state, which in anisotropic high-temperature superconductors like Bi2Sr2CaCu2O8 may occupy most of the mixed-state phase diagram, the transport current is usually assumed to flow uniformly across the sample as in a normal metal. To test this assumption, we have devised a measurement approach which allows determination of the flow pattern of the transport current across the sample. The surprising result is that, in Bi2Sr2CaCu2O8 crystals, most of the current flows at the edges of the sample rather than in the bulk, even in the highly resistive state, due to the presence of strong surface barriers. This finding has significant implications for the interpretation of existing resistivity data and may be of importance for the development of high-temperature superconducting wires and tapes.

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Figure 1: Experimental set-up.
Figure 2: Schematic cross-section of the sample with the attached Hall sensors (left) and the corresponding field profiles Bac(x) at three temperatures (right).
Figure 3: Self-induced field Bac(x) generated by 4 mA a.c. current as a function of the temperature during cooling of the Bi2Sr2CaCu2O8 crystal in a field Hdc = 0.1 T.
Figure 4: Resistance of Bi2Sr2CaCu2O8 crystal as a function of temperature at the indicated applied fields (Iac = 10 mA)..

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Acknowledgements

We thank M. Konczykowski, R. Doyle, V. Kogan, M. McElfresh and A. Koshelev for discussions. This work was supported by the Israel Ministry of Science, the German-Israeli Foundation for Scientific Research and Development (GIF), the MINERVA foundation (Munich, Germany), the Alhadeff Research Award, and the Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture, Japan.

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Correspondence to Dan T. Fuchs.

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