Spectral Properties Of Strongly Correlated Multi-Impurity Models In The Kondo Insulator Regime: Emergent Coherence, Metallic Surface States, And Quantum Phase Transitions

We investigate the real-space spectral properties of strongly correlated multi-impurity arrays in the Kondo insulator regime. Employing a recently developed mapping onto an effective correlated cluster problem makes the problem accessible to the numerical renormalization group. The evolution of the spectrum as a function of cluster size and cluster site is studied. We applied the extended Lieb-Mattis theorem to predict whether the spectral function must vanish at the Fermi energy developing a true pseudogap or whether the spectral function remains finite at omega = 0. Our numerical renormalization group spectra confirm the predictions of the theorem and shows a metallic behavior at the surface of a cluster prevailing in arbitrary spatial dimensions. We present a conventional minimal extension of a particle-hole symmetric Anderson lattice model at U = 0 that leads to a gapped bulk band but a surface band with mainly f-orbital character for weak and moderate hybridization strength. The change in the site-dependent spectra upon introducing a Kondo hole in the center of the cluster is presented as a function of the hole-orbital energy. In particular, the spectral signatures across the KosterlitzThouless-type quantum phase transition from a singlet to a local moment fixed point are discussed.