From exact solution of Mixed-Valence Impurity to Mixed-Valence Insulators

Several years ago, it was discovered through Wilson renormalization group cal culations [1] and bosonization methods [2] that isolated mixed valence impu rities, unlike Kondo impurities, have a singularity in the limit of zero energy. The excitations in that case can be expressed as a localized Majorana and a propagating Majorana. While a metallic mixed valence lattice does not have the symmetries to allow such excitations, the insulating lattice state may have protection so that such excitations may exist and give rise at low temperatures to specific heat singularity and magneto-oscillations with a large Fermi-surface. The theory for the lattice [3] is approximate and motivated by recent exper iments together with some predictions for future experiments which may add confidence to the ideas or rule them out. 

[1] I. Perakis, C.M. Varma and A.E. Ruckenstein, Phys. Rev. Letters 70, 2478 (1994). 

C. Sire, C.M. Varma, A.E. Ruckenstein and T. Giamarchi, Phys. Rev. Letters 72, 2478 (1994). 

C.M. Varma, Phys. Rev. B 102, 155145 (2020).