1. Comparison of the low-temperature specific heat of Fe- and Co-dopedBi1.8Pb0.2Sr2Ca(Cu1−xMx)2O8(M=Fe or Co): Anomolously enhanced electronic contribution due to Fe doping
- Author
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Franck Jp and Yu Mk
- Subjects
Superconductivity ,Effective mass (solid-state physics) ,Materials science ,Condensed matter physics ,Dopant ,Formula unit ,Doping ,Analytical chemistry ,Electron ,Magnetic susceptibility ,Ion - Abstract
Specific-heat data of Fe-doped Bi{sub 1.8}Pb{sub 0.2}Sr{sub 2}Ca(Cu{sub 1{minus}{ital x}}Fe{sub {ital x}}){sub 2}O{sub 8} in the range 2{endash}20 K are presented for {ital x}=1, 2, 4, 6, and 8{percent}. The data are compared with our previous measurements on Co-doped bismuth-strontium-calcium-copper oxide superconductors of nominal composition Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} (BISCO 2212). Both Fe and Co are magnetic substitutions with effective moments close to their free-ion value. In the normal state the magnetic susceptibility increases by more than a factor 2 over the doping range due to effective-mass enhancement. In the superconducting state both ions act as magnetic pair breakers. For Co doping the normal-state linear term {gamma} is observed, enhanced due to the effective-mass increase. For Fe doping we observe a large anomalous contribution to the electronic specific heat starting near 15 K and leading at the lowest temperature to a linear term near {gamma}{sub 0}=72 mJ/moleK{sup 2} (1 mole=1 formula unit). The anomalous term is typical of heavy fermion behavior. Comparison with specific-heat data of Co-doped BISCO 2212 suggests that hybridization between 3{ital d} electrons of the dopant and the planar carriers is more effective for Fe doping than for Co doping. {copyright} {ital 1996 The American Physicalmore » Society.}« less
- Published
- 1996