We have grown single crystals of Bi2Sr2-xRxCuOy with R = La, Sm and Eu for a wide range of R content x and measured resistivity and the thermopower. The relation between the value of thermopower at 290 K, S(290), and the superconducting transition temperature Tc determined simultaneously on the same single crystal clearly shows that Tc at the optimal doping Tcmax strongly depends on the R element. More importantly, we found that the range of S(290) values of samples with a non-zero Tc is narrower when the R element is changed to one with a smaller ionic radius. The narrowing of the range of S(290) values indicates that the range of carrier density where high-Tc superconductivity occurs in this system depends on the R element. We argue that these behaviors are a consequence of the difference in the transfer integrals in the CuO2 plane accompanied with the structural change caused by replacing the R element to one with a different ionic radius.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering