Kondo lattice model: from local to nonlocal descriptions
Abstract
In this paper, we study the influence of spatial fluctuations in a twodimentional KondoLattice model (KLM) with antiferromagnetic couplings. To accomplish this, we first present an implementation of the dualfermion (DF) approach based on the hybridization expansion continuoustime quantum Monte Carlo impurity solver (CTHYB), which allows us to consistently compare the local and nonlocal descriptions of this model. We find that, the inclusion of nonlocality restores the selfenergy dispersion of the conduction electrons, {\it i.e.} the $\vec{k}$ dependence of $\Sigma(\vec{k}, i\omega_{n})$. The antiferromagnetic correlations result in an additional symmetry in $\Sigma(\vec{k}, i\omega_{n})$, which is well described by the Néel antiferromagnetic wavevector. A "metal""antiferromagnetic insulator""Kondo insulator" transition is observed at finite temperatures, which is driven by the competition of the effective RKKY interaction (at the weak coupling regime) and the Kondo singlet formation mechanism (at the strong coupling regime). Away from halffilling, the antiferromagnetic phase becomes unstable against hole doping. The system tends to develop a ferromagnetic phase with the spin susceptibility $\chi_{s}(Q)$ peaking at $Q=\Gamma$. However, for small $J/t$, no divergence of $\chi_{s}(\Gamma)$ is really observed, thus, we find no sign of longrange ferromagnetism in the holedoped twodimension KLM. The ferromagnetism is found to be stable at larger $J/t$ regime. Interestingly, we find the local approximation employed in this work, {\it i.e.} the dynamical meanfield theory (DMFT), is still a very good description of the KLM, especially in the holedoped case. However, at halffilling, the nonlocal fluctuation effect is indeed pronounced. We observe a strong reduction of the critical coupling strength for the onset of the Kondo insulating phase.
 Publication:

arXiv eprints
 Pub Date:
 August 2013
 arXiv:
 arXiv:1309.0156
 Bibcode:
 2013arXiv1309.0156L
 Keywords:

 Condensed Matter  Strongly Correlated Electrons
 EPrint:
 12 pages and 10 figures. Report on missing references are highly appreciated