Realistic quantum critical point in one-dimensional two-impurity models

Abstract

We show that the two-impurity Anderson model exhibits an additional quantum critical point at infinitely many specific distances between both impurities for an inversion symmetric onedimensional dispersion. Unlike the quantum critical point previously established,it is robust against particle-hole or parity symmetry breaking. The quantum critical point separates a spin doublet from a spin singlet ground state and is, therefore, protected. A finite single-particle tunneling t or an applied uniform gate voltage will drive the system across the quantum critical point. The discriminative magnetic properties of the different phases cause a jump in the spectral functions at low temperature, which might be useful for future spintronics devices. A local parity conservation will prevent the spin-spin correlation function from decaying to its equilibrium value after spin manipulations.

Spectral properties of strongly correlated multi impurity models in the Kondo insulator regime: Emergent coherence, metallic surface states and quantum phase transitions

“…It is interesting to note that this N f = 3 − 1 = 2 effective Kondo-hole MIAM is identical to a two-impurity Anderson model with both impurities located on the same sub-lattice. For this case we have explicitly proven in a NRG calculation including the full energy dependency of the conduction band host that the LM fixed point is stable [40]. Therefore ρ f 2 (ω = 0) = 0, for N f = 3 as observed in Fig.…”

“…For N f = 2, we have a realization of a two-impurity model where the energy dependent density of states break the particle-hole symmetry in the even and the odd channels [39][40][41], which generates the finite size hopping between the two correlated sites [4,41]. We obtain two Kondo peaks, one in the even and one in the odd channel, that are shifted away equally and in opposite direction from the chemical potential as a consequence of a nonresonant scattering.…”

Equilibrium and real-time properties of the spin correlation function in the two-impurity Kondo model

“…A word is in order to justify the choice k F R/π = (n + 0.11) as generic distance. k F R/π = n leads to a different physics [31] for a linear dispersion in one dimension considered here for two reasons: At first, one of the two parity conduction bands develops a pseudogap DOS at low temperatures, as depicted in Fig. 1, and does not participate in the screening any more.…”

Effective low-energy description of the two-impurity Anderson model: RKKY interaction and quantum criticality

“…Since the odd conduction band decouples for R → 0 [12,25,47] , the level flow of H TIAM matches those of H + TIAM that is very different to the flow of the FEG. This FP is well understood: only one half of the local triplet state can be screened by the conduction electrons and the system remains in an underscreend Kondo fixed point [12,25,47,53].…”

“…Recently, however, it has been shown [53] that for certain dispersions and distances between the impurities the TIAM exhibits a QCP, separating two orthogonal ground states with different degeneracy. This QCP is of different nature and has been experimentally observed in PTCDA-Au complexes on an Au surface [12] and is driven by the additional direct tunneling term between the two neighboring molecular orbitals [12,53].…”