The nature of the valence transition and its fluctuations is studied by using the density-matrix renormalization group method and the mean-field theory. It is shown that the superconducting correlation is developed in the Kondo regime near the quantum critical point of the valence transition. The origin is ascribed to the enhancement of the coherence of electrons, but not to the enhanced charge compressibility, which is in striking contrast to ordinary mechanisms showing the phase separation. The underlying mechanism of these phenomena is that the order parameter of the valence transition is not a conserving quantity.
展开▼
