The phonon-plasmon mechanism of high T_c

Abstract

New results describing further developments of the phonon-plasmon mechanism of high Tc, proposed earlier by the authors, are discussed. According to our approach, high Tc in the oxides is due to the coexistence of strong electron-phonon coupling and the plasmon mechanism connected with the formation of the unusual low-lying acoustic plasmon branches of these layered systems. It is shown that the importance of the phonon-plasmon mechanism (PPM) is connected with uniquely small values of EF and VF. For the lattice dynamics we consider phonon anharmonicity and the effect of hybridization of acoustic and optical branches. In addition, the existence of double well potentials for certain modes is discussed. Both effects lead to strong electron-phonon coupling. We also comment on the isotope effect. The non-monotonic dependence of Tc on the carrier concentration is explained within our model. A novel method based on the special feature of electron loss spectroscopy is proposed, namely its temperature dependence, which allows the determination of the presence of the low frequency plasmon branch. © 1989.