151Eu Mössbauer effect study of T′- and T*-phase superconductors

The (La,Eu(2CuO4 system shows superconductivity by dopingCe orSr. Carriers inT′-phase doped withCe are electrons and those inT*-phase doped withSr are holes. In this work,151Eu Mossbauer analysis is applied for theT′-phase(La1−xEux)2−yCeyCuO4 and theT*-phase(La1−xEux)2−ySryCuO4 in order to compare the electronic state and the lattice vibration ofEu in these superconductors. In addition, correlations betweenTc and Mossbauer parameters are examined. The isomer shift of151Eu is 0.784–0.840 mm/s in theT*-phase and 0.689–0.733 mm/s in theT′-phase, which shows that the lanthanide in these superconductors is tri-valent. The Debye temperature of151Eu is 180–208 K in theT*-phase and 160–192 K in theT′-phase. The difference of isomer shift between these two phases is explained by theEu−O distance. For(La1−xEux)2−yCeyCuO4, a light correlation betweenTc and the Debye temperature is observed, which means the importance of the lattice vibration in high-Tc superconductivity.