The valence fluctuations have attracted much attention as a key origin of electronic instabilities such as unconventional superconductivity and non-Fermi liquid criticalities observed in Ce- and Yb-based heavy fermion systems [1,2].
To clarify the nature of the quantum critical point of the valence transition, we applied the density-matrix renormalization group method to the periodic Anderson model with Coulomb repulsion between f and conduction electrons [3]. It is found that the first-order valence transition emerges with the quantum critical point and the crossover from the Kondo to the mixed-valence states is strongly stabilized by quantum fluctuation and electron correlation. A remarkable result is that the superconducting correlation is developed in the Kondo regime near the sharp valence increase. The origin of the superconductivity is clarified to the development of the coherent motion of electrons with enhanced valence fluctuation. This results in the enhancement of the charge velocity, but not the charge compressibility, which is quite different from ordinary mechanism [3].
[1] K. Miyake, O. Narikiyo and Y. Onishi: Physica B 259-261 (1999) 676.
[2] Y. Onishi and K. Miyake, J. Phys. Soc. Jpn. 69 (2000) 3955.
[3] S. Watanabe, M. Imada and K. Miyake: J. Phys. Soc. Jpn. 75 (2006) 043710.
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Last updated: May 15 2016