Bipolaron-SO(5) Non-Fermi Liquid in a Two-channel Anderson Model with Phonon-assisted Hybridizations

TL;DR

This paper investigates non-Fermi liquid behavior in a two-channel Anderson model with phonon-assisted hybridizations, revealing hidden SO(5) symmetries and how different operators dominate depending on Coulomb interaction strength.

Contribution

It identifies hidden SO(5) degrees of freedom in the model and analyzes the variation of irrelevant operators near NFL fixed points using boundary conformal field theory and numerical renormalization group.

Findings

NFL spectra match two-channel Kondo model predictions

Dominance of spin or SO(5) operators depends on Coulomb U

Impurity specific heat is linear in temperature with logarithmic divergence in bipolaron fluctuations

Abstract

We analyze non-Fermi liquid (NFL) properties along a line of critical points in a two-channel Anderson model with phonon-assisted hybridizations. We succeed in identifying hidden nonmagnetic SO(5) degrees of freedom for valence-fluctuation regime and analyze the model on the basis of boundary conformal field theory. We find that the NFL spectra along the critical line, which is the same as those in the two-channel Kondo model, can be alternatively derived by a fusion in the nonmagnetic SO(5) sector. The leading irrelevant operators near the NFL fixed points vary as a function of Coulomb repulsion U; operators in the spin sector dominate for large U, while those in the SO(5) sector do for small U, and we confirm this variation in our numerical renormalization group calculations. As a result, the thermodynamic singularity for small U differs from that of the conventional two-channel Kondo problem. Especially, the impurity contribution to specific heat is proportional to temperature and bipolaron fluctuations, which are coupled electron-phonon fluctuations, diverge logarithmically at low temperatures for small U.