Critical spin and charge fluctuations at Kondo-destruction quantum critical points

Motivated by experimental evidence for heavy-fermion quantum criticality in metals with inherent particle-hole (ph) asymmetry, we investigate critical spin and charge responses in a Bose-Fermi Anderson impurity model away from the limit of integer impurity valence. The model features a sub-ohmic bosonic bath and a flat fermionic density of states. It arises in extended dynamical mean-field treatments of critical Kondo destruction [1], the phenomenon believed to underlie the beyond-Landau quantum criticality observed in a number of heavy-fermion materials [1, 2, 3]. For zero or weak ph asymmetry, Kondo and Kondo-destroyed phases are separated by a continuous quantum phase transition (QPT) exhibiting critical spin fluctuations. For strong ph asymmetry, by contrast, the Kondo-destruction QPT is discontinuous and of level-crossing character. The change in nature of the QPT takes place at a quantum tricritical point, in the vicinity of which one finds an energy/temperature window of coexisting critical spin and charge fluctuations.

[1] Q. Si et al., Nature 413, 804 (2001).

[2] P. Coleman et al., J. Phys. Condens. Matt. 13, R723 (2001).

[3] S. Kirchner et al., Rev. Mod. Phys. 92, 011002 (2020).