Superconductivity (SC) in K-doped molecular alloys of C60 and C70 are studied by means of the nonresonant microwave low-field signal (LFS) and conventional ESR, and a LFS-search for SC in KxC70 is performed. The critical temperature of Kx(C60/C70) determined at the onset of hysteretic LFS, decreases to Tc=16K (at about 10% C70), and Tc=10K (at about 25% C70), compared with Tc=19K in pure KxC60 suggesting the decrease of electron-phonon coupling. A strong multicomponent g=2 ESR signal appears and coexists with LFS at low T for SC composition of Kx(C60/C70) indicating presence of a non-SC metallic phase. At overdoping LFS disappears and a single ESR line is enormously broadened to Δ Hpp(300K) = 80G. In KxC70 doped under the same conditions the LFS is not detected, indicating absence of SC above 5K, while a narrow ESR single line appears.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering