Europhys. Lett.
Volume 63, Number 4, August 2003
Page(s) 590 - 596
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 01 November 2003
DOI: 10.1209/epl/i2003-00554-7
Europhys. Lett., 63 (4) , pp. 590-596 (2003)

Enhancement of Josephson coupling in $\chem{La_{2}CuO_{4+\delta}}$ by doping of $\chem{CuO}$ vapor during sintering

C. C. Wang, X. Zheng and J. Zhu

Electron Microscopy Laboratory, School of Materials Science and Engineering Tsinghua University - Beijing 100084, PRC

(Received 13 November 2002; accepted in final form 12 June 2003)

The transport properties of $\chem{La_{2}CuO_{4+\delta}}$ prepared under ambient atmosphere, using $\chem{CuO}$ vapor as doping resource, have been investigated in this paper. Two distinct transition temperatures were found from the doped sample. The high-temperature one, occurring at about 35 $\un{K}$, comes from the known 32 $\un{K}$ phase. The other one appearing near 10 $\un{K}$ is regarded as the result of Josephson coupling. Compared to the doped sample, the undoped sample shows weak Josephson coupling. We argue that the enhancement of Josephson coupling results from denser and more compacted grain boundaries in the doped sample, while the undoped sample has larger fractions of pores, which are harmful to this coupling. An interesting phenomenon is also observed: when Josephson coupling disappears due to an applied magnetic field or time elapse, the resistance increases as a power law, T-1/2, in the low-temperature region.

74.50.+r - Tunneling phenomena; point contacts, weak links, Josephson effects.
74.25.-q - Properties of type I and type II superconductors.
74.72.-h - Cuprate superconductors (high- $T_{\ab{c}}$ and insulating parent compounds).

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