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

Merino, J., Powell, B. J. and McKenzie, Ross H. (2006) Ferromagnetism, paramagnetism, and a Curie-Weiss metal in an electron-doped Hubbard model on a triangular lattice. Physical Review B, 73 23: 235107. doi:10.1103/PhysRevB.73.235107

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Author Merino, J.
Powell, B. J.
McKenzie, Ross H.
Title Ferromagnetism, paramagnetism, and a Curie-Weiss metal in an electron-doped Hubbard model on a triangular lattice
Journal name Physical Review B   Check publisher's open access policy
ISSN 1098-0121
Publication date 2006
Sub-type Critical review of research, literature review, critical commentary
DOI 10.1103/PhysRevB.73.235107
Open Access Status File (Publisher version)
Volume 73
Issue 23
Start page 235107
Total pages 22
Editor P. D. Adams
Place of publication College Pk
Publisher American Physical Society
Collection year 2006
Language eng
Subject C1
240203 Condensed Matter Physics - Electronic and Magnetic Properties; Superconductivity
780102 Physical sciences
Abstract Motivated by the unconventional properties and rich phase diagram of NaxCoO2 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 (DMFT) calculations predict that for negative intersite hopping amplitudes (t < 0) 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 > 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 (DOS) at the Fermi level for t > 0 than for t < 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 > 0 the energy cost of polarizing the system is much smaller than for t < 0. Our observation of Nagaoka ferromagnetism is consistent with the A-type antiferromagnetism (i.e., ferromagnetic layers stacked antiferromagnetically) observed in neutron scattering experiments on NaxCoO2. The transport and magnetic properties measured in NaxCoO2 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 NaxCoO2 is a consequence of the crossover from a bad metal with incoherent quasiparticles at temperatures T > 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 NaxCoO2 and is used to identify the simplest relevant model that captures the essential physics in NaxCoO2. 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.
Keyword Physics, Condensed Matter
Spin-1/2 Heisenberg-antiferromagnet
Geometrically Frustrated Magnets
Finite-temperature Properties
Strongly Correlated Metals
Mean-field Theory
Unconventional Superconductivity
Infinite Dimensions
Nagaoka Theorem
Q-Index Code C1

Document type: Journal Article
Sub-type: Critical review of research, literature review, critical commentary
Collections: Centre for Organic Photonics and Electronics
Excellence in Research Australia (ERA) - Collection
School of Physical Sciences Publications
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Citation counts: TR Web of Science Citation Count  Cited 49 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 47 times in Scopus Article | Citations
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Created: Mon, 13 Aug 2007, 16:20:07 EST