2016/06/24 by Rok Žitko, Michele Fabrizio
Physics and Astronomy · #Condensed matter physics #Fermi liquid theory #Ground state #Pairing #Physics #Physics of Superconductivity and Magnetism #Quantum and electron transport phenomena #Quantum mechanics #Rare-earth and actinide compounds #Superconductivity #cond-mat.str-el
paper · pdf · doi:10.1103/physrevb.95.085121
published as Phys. Rev. B 95, 085121 (2017) · 5 pages, 4 figures
arxiv created 2016/06/24 · openalex publication_date 2017/02/16 · arxiv updated 2017/10/02 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We study how the non-Fermi-liquid nature of the overscreened multichannel Kondo impurity model affects the response to a BCS pairing term that, in the absence of the impurity, opens a gap \mathrm\ensuremathΔ. We find that the low-energy spectrum in the limit \mathrm\ensuremathΔ\ensuremath→0 actually does not correspond to the spectrum strictly at \mathrm\ensuremathΔ=0. In particular, in the two-channel Kondo model, the \mathrm\ensuremathΔ\ensuremath→0 ground state is an orbitally degenerate spin singlet, while it is an orbital singlet with a residual spin degeneracy at \mathrm\ensuremathΔ=0. In addition, there are fractionalized spin-1/2 subgap excitations whose energy in units of \mathrm\ensuremathΔ tends toward a finite and universal value when \mathrm\ensuremathΔ\ensuremath→0, as if the universality of the anomalous power-law exponents that characterize the overscreened Kondo effect turned into universal energy ratios when the scale invariance is broken by \mathrm\ensuremathΔ\ensuremath≠0. This intriguing phenomenon can be explained by the renormalization flow toward the overscreened fixed point and the gap cutting off the orthogonality catastrophe singularities. We also find other non-Fermi-liquid features at finite \mathrm\ensuremathΔ: the local density of states lacks coherence peaks, the states in the continuum above the gap are unconventional, and the boundary entropy is a nonmonotonic function of temperature. The persistent subgap excitations are characteristic of the non-Fermi-liquid fixed point of the model, and thus depend on the impurity spin and the number of screening channels.