Even-odd effect of a spin-S impurity coupled to a quantum critical system

Article

关键词: KONDO;    FIELD;    SUPERFLUID;    INSULATOR;   

DOI  :  10.1103/PhysRevB.100.094514

来源: SCIE

【 摘 要 】

We discuss an even-odd effect for an impurity with N-fold-degenerate internal states immersed in a two-dimensional superfluid-Mott-insulator quantum critical bath which is described by a spin-S XY Bose-Kondo impurity model with N = 2S + 1. Using a dimensional- and momentum-cutoff regularized renormalization group and unbiased large-scale Monte Carlo numerical simulations, we establish the phase diagram for the S = 1 impurity with all relevant terms included. We show that a threefold-degenerate S = 1 impurity coupled to a critical bath has a nondegenerate ground state with a quantized charge, in qualitative contrast to the spin-1/2 case where the impurity is partially screened. We then argue that all impurities with odd-2S degeneracy share the same universal physics as the spin-1/2 case and all impurities with even-2S degeneracy are the same as the spin-1 case. We validate our conjecture with unbiased Monte Carlo simulations up to S = 2. A physical consequence of this even-odd effect is that two spin-1/2 impurities in the critical bath form a long-range entangled state at a low temperature, which can be realized in ultracold atoms in an optical lattice.

【 授权许可】

Free