Non-perturbative approaches to magnetism in strongly correlated electron systems

Vollhardt, D.; Blümer, N.; Held, Karsten; Kollar, Marcus; Schlipf, J.; Ulmke, M.

doi:10.1007/s002570050375

Cited by 86 publications

(115 citation statements)

References 47 publications

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“…Clearly, simple Stoner ferromagnetism is inconsistent with our DMFT results not only at the quantitative but also qualitative level as the Stoner criterion would predict ferromagnetism for both signs of t for sufficiently large, but finite, values of U. Stoner theory is known to overestimate ferromagnetic tendencies. 75,76 In the present case, it would predict ferromagnetism for t Ͻ 0 in contrast to the more sophisticated DMFT treatment. This difference can be attributed to the on-site dynamical correlation effects which strongly redistribute the spectral weight of the electrons and that are not taken into account in standard mean-field theories.…”

Section: Ferromagnetismmentioning

confidence: 62%

Ferromagnetism, paramagnetism, and a Curie-Weiss metal in an electron-doped Hubbard model on a triangular lattice

2006

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Motivated by the unconventional properties and rich phase diagram of Na x CoO 2 we consider the electronic and magnetic properties of a two-dimensional Hubbard model on an isotropic triangular lattice doped with electrons away from half-filling. Dynamical mean-field theory ͑DMFT͒ calculations predict that for negative intersite hopping amplitudes ͑t Ͻ 0͒ and an on-site Coulomb repulsion, U, comparable to the bandwidth, the system displays properties typical of a weakly correlated metal. In contrast, for t Ͼ 0 a large enhancement of the effective mass, itinerant ferromagnetism, and a metallic phase with a Curie-Weiss magnetic susceptibility are found in a broad electron doping range. The different behavior encountered is a consequence of the larger noninteracting density of states ͑DOS͒ at the Fermi level for t Ͼ 0 than for t Ͻ 0, which effectively enhances the mass and the scattering amplitude of the quasiparticles. The shape of the DOS is crucial for the occurrence of ferromagnetism as for t Ͼ 0 the energy cost of polarizing the system is much smaller than for t Ͻ 0. Our observation of Nagaoka ferromagnetism is consistent with the A-type antiferromagnetism ͑i.e., ferromagnetic layers stacked antiferromagnetically͒ observed in neutron scattering experiments on Na x CoO 2 . The transport and magnetic properties measured in Na x CoO 2 are consistent with DMFT predictions of a metal close to the Mott insulator and we discuss the role of Na ordering in driving the system towards the Mott transition. We propose that the "Curie-Weiss metal" phase observed in Na x CoO 2 is a consequence of the crossover from a "bad metal" with incoherent quasiparticles at temperatures T Ͼ T * and Fermi liquid behavior with enhanced parameters below T * , where T * is a low energy coherence scale induced by strong local Coulomb electron correlations. Our analysis also shows that the one band Hubbard model on a triangular lattice is not enough to describe the unusual properties of Na x CoO 2 and is used to identify the simplest relevant model that captures the essential physics in Na x CoO 2 . We propose a model which allows for the Na ordering phenomena observed in the system which, we propose, drives the system close to the Mott insulating phase even at large dopings.

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Section: Ferromagnetismmentioning

confidence: 62%

Ferromagnetism, paramagnetism, and a Curie-Weiss metal in an electron-doped Hubbard model on a triangular lattice

2006

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“…This way, we have through exact relations generated all local Feynman diagrams for the self energy which is nothing but the DMFT self energy. These local DMFT diagrams account for the major part of electronic correlations, which is, among others, responsible for quasiparticle renormalizations including kinks [43,44,45], Mott-Hubbard transitions [3], and magnetism [4,46,47] with related spin-polaron physics [48,49].…”

Section: Inclusion Of Dmft Diagrams and Non-local Correlations Beyondmentioning

confidence: 99%

Ab initio calculations with the dynamical vertex approximation

et al. 2011

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Key words dynamical mean field theory, ab initio calculations, many body theoryWe propose an approach for the ab initio calculation of materials with strong electronic correlations which is based on all local (fully irreducible) vertex corrections beyond the bare Coulomb interaction. It includes the so-called GW and dynamical mean field theory and important non-local correlations beyond, with a computational effort estimated to be still manageable.--

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“…Recently, Guerrero and Noack [2] listed several possible extensions of the Hubbard model that should enhance ferromagnetism: (i) the addition of frustrating hopping terms [3][4][5], (ii) the inclusion of more than one orbital per unit cell, and (iii) the addition of more general nearestneighbor interactions [3,6]. In fact, a number of frustrated models with more general interactions, such as the t − t ′ Hubbard model, and multiband models, such as the periodic Anderson model (PAM), have ferromagnetic ground states [2,6,7].…”

Section: Introductionmentioning

confidence: 99%

Ferromagnetism in the two-dimensional periodic Anderson model

2001

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Using the constrained-path Monte Carlo method, we studied the magnetic properties of the twodimensional periodic Anderson model for electron fillings between 1/4 and 1/2. We also derived two effective low energy theories to assist in interpreting the numerical results. For 1/4 filling we found that the system can be a Mott or a charge transfer insulator, depending on the relative values of the Coulomb interaction and the charge transfer gap between the two non-interacting bands. The insulator may be a paramagnet or antiferromagnet. We concentrated on the effect of electron doping on these insulating phases. Upon doping we obtained a partially saturated ferromagnetic phase for low concentrations of conduction electrons. If the system were a charge transfer insulator, we would find that the ferromagnetism is induced by the well-known RKKY interaction. However, we found a novel correlated hopping mechanism inducing the ferromagnetism in the region where the non-doped system is a Mott insulator. Our regions of ferromagnetism spanned a much smaller doping range than suggested by recent slave boson and dynamical mean field theory calculations, but they were consistent with that obtained by density matrix renormalization group calculations of the one-dimensional periodic Anderson model.

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Non-perturbative approaches to magnetism in strongly correlated electron systems

Cited by 86 publications

References 47 publications

Ferromagnetism, paramagnetism, and a Curie-Weiss metal in an electron-doped Hubbard model on a triangular lattice

Ferromagnetism, paramagnetism, and a Curie-Weiss metal in an electron-doped Hubbard model on a triangular lattice

Ab initio calculations with the dynamical vertex approximation

Ferromagnetism in the two-dimensional periodic Anderson model

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