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Journal of the Korean Physical Society

Analysis of spin-polaron formation in hund lattices

Y. Arredondo, Oracio Navarro, Emmanuel Vallejo, M. Avignon

Published May 1, 2013• 0 citations
Publisher

Abstract

We consider a one-dimensional Hund lattice model where a conducting band is coupled with localized spins s = 1/2 interacting antiferromagnetically, with coupling constant J , and investigate the ground state phase diagram as a function of both the exchange coupling J and the band filling, n . From spin structure factor measurements we found different evolving magnetic orderings in the ground state related to the particle distribution in the systems, although no charge density waves are formed, as found from density-density correlation function measurements. We study the quasiparticle formation and phase separation using the density-matrix renormalization group method, which is a highly efficient method to investigate quasi-one-dimensional strongly correlated systems.

DOI
10.3938/jkps.62.1504

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We consider a one-dimensional Hund lattice model where a conducting band is coupled with localized spins s = 1/2 interacting antiferromagnetically, with coupling constant J , and investigate the ground state phase diagram as a function of both the exchange coupling J and the band filling, n . From spin structure factor measurements we found different evolving magnetic orderings in the ground state related to the particle distribution in the systems, although no charge density waves are formed, as found from density-density correlation function measurements. We study the quasiparticle formation and phase separation using the density-matrix renormalization group method, which is a highly efficient method to investigate quasi-one-dimensional strongly correlated systems.
Even though realistic one-dimensional experiments in the field of half-metallic semiconductors are not at hand yet, we are interested in the underlying fundamental physics. In this regard we study a one-dimensional ferromagnetic Kondo lattice model, a model in which a conduction band is coupled ferromagnetically to a background of localized d moments with coupling constant J(H), and investigate the T = 0 phase diagram as a function of the antiferromagnetic interaction J between the localized moments and the band-filling n, since it has been observed that doping of the compounds has led to formation of magnetic domains. We explore the spin-polaron formation by looking at the nearest-neighbour correlation functions in the spin and charge regimes for which we use the density matrix renormalization group method, which is a highly efficient method to investigate quasi-one-dimensional strongly correlated systems.
We study the spectral properties of the one-dimensional Kondo lattice model as a function of the exchange coupling, the band filling, and the quasimomentum in the ferromagnetic and paramagnetic phases. Using the density-matrix renormalization group method, we compute the dispersion relation of the quasiparticles, their lifetimes, and the ZZZ factor. Sigrist et al. [Phys. Rev. Lett. 67, 2211 (1991)] provided the exact ground state and the quasiparticle-dispersion relation of the Kondo lattice model with one conduction electron. The quasiparticle could be identified as the spin polaron. Our calculations of the dispersion relation for partial band fillings give a result similar to the one-electron case, which suggests that the quasiparticle in both cases is the spin polaron. We find that the quasiparticle lifetime differs by orders of magnitude between the ferromagnetic and paramagnetic phases and depends strongly on the quasimomentum.
We study numerically the one-dimensional Kondo and Hund lattices consisting of localized spins interacting antiferromagnetically or ferromagnetically with the itinerant electrons, respectively. Using the density-matrix renormalization group we find, for both models and in the small coupling regime, the existence of new magnetic phases where the local spins order forming ferromagnetic islands coupled antiferromagnetically. Furthermore, by increasing the interaction parameter |J| we find that this order evolves toward the ferromagnetic regime through a spiral-like phase with longer characteristic wavelengths. These results shed new light on the zero temperature magnetic phase diagram for these models.
Charge and spin orderings are studied on the simplest one-dimensional (1D) and the two-dimensional (2D) square lattices within the generalized Falicov-Kimball model with Hund coupling between localized and itinerant electrons. Using the restricted phase diagram method (RPDM), a number of simple rules of formation of various sorts of ground-state phases have been detected. In particular, relationships between density of current carriers (electrons or holes) and type of charge and magnetic arrangement have been determined. In two dimensions in the mixed-valence regime, only axial stripes (vertical or horizontal) have been found for intermediate values of the coupling constants. They are composed of ferromagnetic or antiferromagnetic chains interchanged with nonmagnetic ones. For band fillings close to the half filling, stripe phases oriented along one of the main diagonal direction are formed. The results suggest the possibility of tuning modulations of charge and magnetic superstructures with a change in doping.
We study the spin ordering of localized quantum spins interacting with itinerant electrons via antiferromagnetic (Kondo model) or ferromagnetic (Hund coupling) exchange interactions in the one‐dimensional lattice models. In the case of ferromagnetic coupling we also include a super‐exchange interaction between the localized spins. Using the Density Matrix Renormalization Group (DMRG) we show, for both models, the existence of new magnetic phases with spin ordering consisting of ferromagnetic islands coupled antiferromagnetically.
We map out the phase diagram of the one-dimensional Anderson lattice by studying the ground-state magnetization as a function of band filling using the density matrix renormalization group technique. For strong coupling, we find that the quarter-filled system has an S=0 ground state with strong antiferromagnetic correlations. As additional electrons are put in, we find first a ferromagnetic phase, as reported by M\"oller and W\"olfle, and then a phase in which the ground state has total spin S=0. Within this S=0 phase, we find Ruderman-Kittel-Kasuya-Yosida oscillations in the spin-spin correlation functions. \textcopyright{} 1996 The American Physical Society.