Quasiparticle and Josephson tunneling of overdoped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} single crystals
Journal Article
·
· Physical Review. B, Condensed Matter and Materials Physics
- Science and Technology Center for Superconductivity and Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
- Naval Research Laboratory, Washington, DC 20375 (United States)
The point contact tunneling technique is used to examine quasiparticle and Josephson currents in overdoped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi-2212) single crystals with bulk T{sub c} values ranging from 82 K down to 62 K. Superconductor-insulator-normal-metal (SIN) tunnel junctions are formed between Bi-2212 crystals and a Au tip, which display well-resolved quasiparticle gap features including sharp conductance peaks. Reproducible superconductor-insulator-superconductor (SIS) tunnel junctions are also obtained between two pieces of the Bi-2212 crystals, resulting in simultaneous quasiparticle and Josephson currents. The dynamic conductances of both SIN and SIS junctions are qualitatively similar to those found on optimally doped Bi-2212, but with reduced gap values, e.g., {delta}=15-20 meV for T{sub c}=62 K. Fits to the conductance data in the gap region are obtained using a model with d{sub x{sup 2}-y{sup 2}} symmetry, and it is shown that this provides a better fit than s-wave symmetry. Both SIN and SIS tunneling conductances also display dip and hump features at high bias voltages similar to those found on optimal and underdoped crystals, indicating that these are intrinsic properties of the quasiparticles. The SIS data indicate that these features appear to be part of a larger spectrum that extends out to 300-400 mV. The Josephson current has been measured for 13 SIS junctions on the 62 K crystals with resistances varying over two decades. It is found that the maximum value depends on junction resistance in a manner consistent with Ambegaokar-Baratoff theory, but with a reduced I{sub c}R{sub n} product. (c) 2000 The American Physical Society.
- Research Organization:
- Argonne National Laboratory (ANL), Argonne, IL
- OSTI ID:
- 20215336
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Journal Name: Physical Review. B, Condensed Matter and Materials Physics Journal Issue: 5 Vol. 61; ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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