Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:cond-mat/0501251 · Physical Review B

Ferromagnetic polarons in the one-dimensional ferromagnetic Kondo model with quantum mechanical S=3∕2 core spins

Danilo R. Neuber, Maria Daghofer, Hans Gerd Evertz, Wolfgang von der Linden, R. M. Noack

Published Jan 3, 2006• 20 citations
arXivHTMLPDF

Abstract

We present an extensive numerical study of the ferromagnetic Kondo lattice model with quantum mechanical $S=3∕2$ core spins. We treat one orbital per site in one dimension using the density-matrix renormalization group and include on-site Coulomb repulsion between the electrons. We examine parameters relevant to manganites, treating the range of low to intermediate doping, $0\ensuremath{\lesssim}x<0.5$. In particular, we investigate whether quantum fluctuations favor phase separation over the ferromagnetic polarons observed in a model with classical core spins. We obtain very good agreement of the quantum model with previous results for the classical model, finding separated polarons, which are repulsive at short distance for finite ${t}_{2g}$ superexchange ${J}^{\ensuremath{'}}$. Taking on-site Coulomb repulsion into account, we observe phase separation for small but finite superexchange ${J}^{\ensuremath{'}}$, whereas for larger ${J}^{\ensuremath{'}}$, polarons are favored in accordance with simple energy considerations previously applied to classical spins. We discuss the interpretation of compressibilities and present a phase diagram with respect to doping and the ${t}_{2g}$ superexchange parameter ${J}^{\ensuremath{'}}$ with and without Coulomb repulsion.

DOI
10.1103/physrevb.73.014401

Related papers

Orbital polarons versus itinerant eg electrons in doped manganites

Maria Daghofer, Andrzej M. Oleś, Wolfgang von der Linden

We study an effective one-dimensional (1-D) orbital $t\text{\ensuremath{-}}J$ model derived for strongly correlated ${e}_{g}$ electrons in doped manganites. The ferromagnetic spin order at half filling is supported by orbital superexchange $\ensuremath{\propto}J$ which stabilizes orbital order with alternating ${x}^{2}\ensuremath{-}{y}^{2}$ and $3{z}^{2}\ensuremath{-}{r}^{2}$ orbitals. In a doped system it competes with the kinetic energy $\ensuremath{\propto}t$. When a single hole is doped to a half-filled chain, its motion is hindered and a localized orbital polaron is formed. An increasing doping generates either separated polarons or phase separation into hole-rich and hole-poor regions, and eventually polarizes the orbitals and gives a metallic phase with occupied $3{z}^{2}\ensuremath{-}{r}^{2}$ orbitals. This crossover, investigated by exact diagonalization at zero temperature, is demonstrated both by the behavior of correlation functions and by spectral properties, showing that the orbital chain with Ising superexchange is more classical and thus radically different from the 1-D spin $t\text{\ensuremath{-}}J$ model. At finite temperature we derive and investigate an effective 1-D orbital model using a combination of exact diagonalization with classical Monte Carlo for spin correlations. A competition between the antiferromagnetic and ferromagnetic spin order was established at half filling, and localized polarons were found for antiferromagnetic interactions at low hole doping. Finally, we clarify that the Jahn-Teller alternating potential stabilizes the orbital order with staggered orbitals, inducing the ferromagnetic spin order, and enhancing the localized features in the excitation spectra. Implications of these findings for colossal magnetoresistance manganites are discussed.

arXiv:cond-mat/0501190•Physical Review B•Nov 23, 2004•48 citations

Influence of nearest-neighbor Coulomb interactions on the phase diagram of the ferromagnetic Kondo model

André Luiz Malvezzi, Seiji Yunoki, Elbio R. Dagotto

The influence of a nearest-neighbor Coulomb repulsion of strength V on the properties of the ferromagnetic Kondo model is analyzed using computational techniques. The Hamiltonian studied here is defined on a chain using localized $S=1/2$ spins, and one orbital per site. Special emphasis is given to the influence of the Coulomb repulsion on the regions of phase separation recently discovered in this family of models, as well as on the double-exchange-induced ferromagnetic ground state. When phase separation dominates at $V=0,$ the Coulomb interaction breaks the large domains of the two competing phases into small ``islands'' of one phase embedded into the other. This is in agreement with several experimental results, as discussed in the text. Vestiges of the original phase separation regime are found in the spin structure factor as incommensurate peaks, even at large values of V. In the ferromagnetic regime close to density $n=0.5,$ the Coulomb interaction induces tendencies to charge ordering without altering the fully polarized character of the state. This regime of ``charge-ordered ferromagnetism'' may be related with experimental observations of a similar phase by Chen and Cheong [Phys. Rev. Lett. 76, 4042 (1996)]. Our results reinforce the recently introduced notion [see, e.g., S. Yunoki et al., Phys. Rev. Lett. 80, 845 (1998)] that in realistic models for manganites analyzed with unbiased many-body techniques, the ground state properties arise from a competition between ferromagnetism and phase-separation--charge-ordering tendencies.

arXiv:cond-mat/9809281•Physical review. B, Condensed matter•Mar 1, 1999•35 citations

Itinerant magnetism and magnetic polarons in the triangular lattice Hubbard model

Ivan Morera, Eugene Demler

We use density matrix renormalization group to investigate the phase diagram of the Fermi Hubbard model on a triangular lattice with densities above half-filling, $1 \leq n < 2$. We discuss the important role of kinetic magnetism and magnetic polarons. For strong interactions and low doublon dopings, attractive interaction between polarons results in phase separation between the fully polarized state at finite doping and the commensurate spin-density wave state at half-filling. For intermediate interaction strength and small doping, competition between antiferromagnetic superexchange and kinetic magnetism gives rise to the incommensurate spin density wave (I-SDW) phase. Fully polarized ferromagnetic (FPF) phase for weak interactions is limited to dopings close to the van Hove singularity in the density of states. With increasing interactions the FPF phase expands to lower dopings. For strong interactions it reaches the low doping regime and is better understood as arising from proliferation of Nagaoka-type ferromagnetic polarons. Other phases that we find include a partially polarized phase, another type of I-SDW at high densities, and Müller-Hartmann ferromagnetism close to the band insulating regime.

arXiv:2402.14074•Feb 21, 2024•0 citations

Formation of spin-polarons in the ferromagnetic Kondo lattice model away from half-filling

Y. Arredondo, Emmanuel Vallejo, Oracio Navarro +1 more

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.

Journal of Physics Condensed Matter•Jul 27, 2012•2 citations

Phase separation in the large-spin t−J model

Antimo Angelucci, Sandro Sorella

We investigate the phase diagram of the two-dimensional $t\ensuremath{-}J$ model using a recently developed technique that allows one to solve the mean-field model Hamiltonian with a variational calculation. The accuracy of our estimate is controlled by means of a small parameter $\frac{1}{q}$, analogous to the inverse spin magnitude $\frac{1}{s}$ employed in studying quantum spin systems. The mathematical aspects of the method and its connection with other large-spin approaches are discussed in detail. In the large-$q$ limit the problem of strongly correlated electron systems turns into the minimization of a total-energy functional. We have performed this optimization numerically on a finite but large $L\ifmmode\times\else\texttimes\fi{}L$ lattice. For a single hole the static small-polaron solution is stable except for small values of $J$, where polarons of increasing sizes have lower energy. At finite doping we recover phase separation above a critical $J$ and for any electron density, showing that the Emery et al. picture represents the semiclassical behavior of the $t\ensuremath{-}J$ model. Quantum fluctuations are expected to be very important, especially in the small-$J$-small-doping region, where phase separation may also be suppressed.

arXiv:cond-mat/9301030•Physical review. B, Condensed matter•Apr 1, 1993•13 citations

Magnetism in the dilute Kondo lattice model

M. Gulácsi, Ian P. McCulloch, Aušrius Juozapavičius +1 more

The one-dimensional dilute Kondo lattice model is investigated by means of bosonization for different dilution patterns of the array of impurity spins. The physical picture is very different if a commensurate or incommensurate doping of the impurity spins is considered. For the commensurate case, the obtained phase diagram is vertified using a non-Abelian density-matrix renormalization-group algorithm. The paramagnetic phase widens at the expense of the ferromagnetic phase as the f spins are diluted. For the incommensurate case, short-range antiferromagnetic correlations are found to dominate at low doping, which distinguishes the dilute Kondo lattice model from the standard Kondo lattice model.

arXiv:cond-mat/0304351•Physical Review B•May 26, 2004•6 citations
We present an extensive numerical study of the ferromagnetic Kondo lattice model with quantum mechanical S=3∕2S=3∕2S=3∕2 core spins. We treat one orbital per site in one dimension using the density-matrix renormalization group and include on-site Coulomb repulsion between the electrons. We examine parameters relevant to manganites, treating the range of low to intermediate doping, 0\ensuremath≲x<0.50\ensuremath{\lesssim}x<0.50\ensuremath≲x<0.5. In particular, we investigate whether quantum fluctuations favor phase separation over the ferromagnetic polarons observed in a model with classical core spins. We obtain very good agreement of the quantum model with previous results for the classical model, finding separated polarons, which are repulsive at short distance for finite t2g{t}_{2g}t2g​ superexchange J\ensuremath′{J}^{\ensuremath{'}}J\ensuremath′. Taking on-site Coulomb repulsion into account, we observe phase separation for small but finite superexchange J\ensuremath′{J}^{\ensuremath{'}}J\ensuremath′, whereas for larger J\ensuremath′{J}^{\ensuremath{'}}J\ensuremath′, polarons are favored in accordance with simple energy considerations previously applied to classical spins. We discuss the interpretation of compressibilities and present a phase diagram with respect to doping and the t2g{t}_{2g}t2g​ superexchange parameter J\ensuremath′{J}^{\ensuremath{'}}J\ensuremath′ with and without Coulomb repulsion.
We study an effective one-dimensional (1-D) orbital $t\text{\ensuremath{-}}J$ model derived for strongly correlated eg{e}_{g}eg​ electrons in doped manganites. The ferromagnetic spin order at half filling is supported by orbital superexchange $\ensuremath{\propto}J$ which stabilizes orbital order with alternating ${x}^{2}\ensuremath{-}{y}^{2}$ and $3{z}^{2}\ensuremath{-}{r}^{2}$ orbitals. In a doped system it competes with the kinetic energy $\ensuremath{\propto}t$. When a single hole is doped to a half-filled chain, its motion is hindered and a localized orbital polaron is formed. An increasing doping generates either separated polarons or phase separation into hole-rich and hole-poor regions, and eventually polarizes the orbitals and gives a metallic phase with occupied $3{z}^{2}\ensuremath{-}{r}^{2}$ orbitals. This crossover, investigated by exact diagonalization at zero temperature, is demonstrated both by the behavior of correlation functions and by spectral properties, showing that the orbital chain with Ising superexchange is more classical and thus radically different from the 1-D spin $t\text{\ensuremath{-}}J$ model. At finite temperature we derive and investigate an effective 1-D orbital model using a combination of exact diagonalization with classical Monte Carlo for spin correlations. A competition between the antiferromagnetic and ferromagnetic spin order was established at half filling, and localized polarons were found for antiferromagnetic interactions at low hole doping. Finally, we clarify that the Jahn-Teller alternating potential stabilizes the orbital order with staggered orbitals, inducing the ferromagnetic spin order, and enhancing the localized features in the excitation spectra. Implications of these findings for colossal magnetoresistance manganites are discussed.
The influence of a nearest-neighbor Coulomb repulsion of strength V on the properties of the ferromagnetic Kondo model is analyzed using computational techniques. The Hamiltonian studied here is defined on a chain using localized S=1/2S=1/2S=1/2 spins, and one orbital per site. Special emphasis is given to the influence of the Coulomb repulsion on the regions of phase separation recently discovered in this family of models, as well as on the double-exchange-induced ferromagnetic ground state. When phase separation dominates at V=0,V=0,V=0, the Coulomb interaction breaks the large domains of the two competing phases into small ``islands'' of one phase embedded into the other. This is in agreement with several experimental results, as discussed in the text. Vestiges of the original phase separation regime are found in the spin structure factor as incommensurate peaks, even at large values of V. In the ferromagnetic regime close to density n=0.5,n=0.5,n=0.5, the Coulomb interaction induces tendencies to charge ordering without altering the fully polarized character of the state. This regime of ``charge-ordered ferromagnetism'' may be related with experimental observations of a similar phase by Chen and Cheong [Phys. Rev. Lett. 76, 4042 (1996)]. Our results reinforce the recently introduced notion [see, e.g., S. Yunoki et al., Phys. Rev. Lett. 80, 845 (1998)] that in realistic models for manganites analyzed with unbiased many-body techniques, the ground state properties arise from a competition between ferromagnetism and phase-separation--charge-ordering tendencies.
We use density matrix renormalization group to investigate the phase diagram of the Fermi Hubbard model on a triangular lattice with densities above half-filling, 1≤n<21 \leq n < 21≤n<2. We discuss the important role of kinetic magnetism and magnetic polarons. For strong interactions and low doublon dopings, attractive interaction between polarons results in phase separation between the fully polarized state at finite doping and the commensurate spin-density wave state at half-filling. For intermediate interaction strength and small doping, competition between antiferromagnetic superexchange and kinetic magnetism gives rise to the incommensurate spin density wave (I-SDW) phase. Fully polarized ferromagnetic (FPF) phase for weak interactions is limited to dopings close to the van Hove singularity in the density of states. With increasing interactions the FPF phase expands to lower dopings. For strong interactions it reaches the low doping regime and is better understood as arising from proliferation of Nagaoka-type ferromagnetic polarons. Other phases that we find include a partially polarized phase, another type of I-SDW at high densities, and Müller-Hartmann ferromagnetism close to the band insulating regime.
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 investigate the phase diagram of the two-dimensional $t\ensuremath{-}J$ model using a recently developed technique that allows one to solve the mean-field model Hamiltonian with a variational calculation. The accuracy of our estimate is controlled by means of a small parameter 1q\frac{1}{q}q1​, analogous to the inverse spin magnitude 1s\frac{1}{s}s1​ employed in studying quantum spin systems. The mathematical aspects of the method and its connection with other large-spin approaches are discussed in detail. In the large-qqq limit the problem of strongly correlated electron systems turns into the minimization of a total-energy functional. We have performed this optimization numerically on a finite but large $L\ifmmode\times\else\texttimes\fi{}L$ lattice. For a single hole the static small-polaron solution is stable except for small values of JJJ, where polarons of increasing sizes have lower energy. At finite doping we recover phase separation above a critical JJJ and for any electron density, showing that the Emery et al. picture represents the semiclassical behavior of the $t\ensuremath{-}J$ model. Quantum fluctuations are expected to be very important, especially in the small-JJJ-small-doping region, where phase separation may also be suppressed.
The one-dimensional dilute Kondo lattice model is investigated by means of bosonization for different dilution patterns of the array of impurity spins. The physical picture is very different if a commensurate or incommensurate doping of the impurity spins is considered. For the commensurate case, the obtained phase diagram is vertified using a non-Abelian density-matrix renormalization-group algorithm. The paramagnetic phase widens at the expense of the ferromagnetic phase as the f spins are diluted. For the incommensurate case, short-range antiferromagnetic correlations are found to dominate at low doping, which distinguishes the dilute Kondo lattice model from the standard Kondo lattice model.