Magnetic Properties of the Hubbard Model on Three-Dimensional Lattices: Fluctuation-Exchange and Two-Particle Self-Consistent Studies (original) (raw)
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Physical Review B, 2009
We use the dynamical vertex approximation (DΓA) with a Moriyaesque λ correction for studying the impact of antiferromagnetic fluctuations on the spectral function of the Hubbard model in two and three dimensions. Our results show the suppression of the quasiparticle weight in three dimensions and dramatically stronger impact of spin fluctuations in two dimensions where the pseudogap is formed at low enough temperatures. Even in the presence of the Hubbard subbands, the origin of the pseudogap at weak-to-intermediate coupling is in the splitting of the quasiparticle peak. At stronger coupling (closer to the insulating phase) the splitting of Hubbard subbands is expected instead. The k-dependence of the self energy appears to be also much more pronounced in two dimensions as can be observed in the k-resolved DΓA spectra, experimentally accessible by angular resolved photoemission spectroscopy in layered correlated systems.
Effect of interactions, disorder and magnetic field in the Hubbard model in two dimensions
Pramana, 2005
The effects of both interactions and Zeeman magnetic field in disordered electronic systems are explored in the Hubbard model on a square lattice. We investigate the thermodynamic (density, magnetization, density of states) and transport (conductivity) properties using determinantal quantum Monte Carlo and inhomogeneous Hartree Fock techniques. We find that at half filling there is a novel metallic phase at intermediate disorder that is sandwiched between a Mott insulator and an Anderson insulator. The metallic phase is highly inhomogeneous and coexists with antiferromagnetic long-range order. At quarter filling also the combined effects of disorder and interactions produce a conducting state which can be destroyed by applying a Zeeman field, resulting in a magnetic field-driven transition. We discuss the implication of our results for experiments.
Physical Review B, 1999
In order to identify the most favorable situation for superconductivity in the repulsive single-band Hubbard model, we have studied instabilities for d-wave pairing mediated by antiferromagnetic spin fluctuations and p-pairing mediated by ferromagnetic fluctuations with the fluctuation exchange approximation in both two dimensions and three dimensions. By systematically varying the band filling and band structure we have shown that (i) d-pairing is stronger in two dimensions than in three dimensions, and (ii) p-pairing is much weaker than the d-pairing.
Magnetic correlations of the Hubbard model on frustrated lattices
Journal of Magnetism and Magnetic Materials, 2007
In order to study the magnetic properties of frustrated metallic systems, we present quantum Monte Carlo data on the magnetic susceptibility of the Hubbard model on triangular and kagome´lattices. We show that the underlying lattice structure is important and determines the nature and the doping dependence of the magnetic fluctuations in these models.
Correlation effects on magnetic frustration in the triangular-lattice Hubbard model
Physical Review B, 2008
Evolution of the magnetic response function in the triangular-lattice Hubbard model is studied with interaction strength within a systematic inverse-degeneracy expansion scheme which incorporates self-energy and vertex corrections and explicitly preserves the spin-rotation symmetry. It is shown that at half filling the response function goes through a nearly dispersionless regime around K for intermediate coupling strength, before undergoing an inversion at strong coupling, resulting in maximum response at the K point, consistent with the expected 120^o AF instability. Effects of finite hole/electron doping on the magnetic response function are also examined.
Magnetic fluctuations in coupled inequivalent Hubbard layers as a model for
The European Physical Journal B, 1999
We investigate, within the fluctuation-exchange approximation, a correlated-electron model for Y2Ba4Cu7O15 represented by two inequivalent Hubbard layers coupled by an interlayer hopping t ⊥. An energy offset δ is introduced in order to produce a different charge carrier concentration in the two layers. We compare several single-particle and magnetic excitations, namely, the single particle scattering rate, the spectral function and the spin lattice as well as spin-spin relaxation times in the two layers as a function of δ. We show that the induced interlayer magnetic coupling produces a tendency to "equalization" of the magnetic properties in the two layers whereby antiferromagnetic fluctuations are suppressed in the less doped layer and enhanced in the heavily doped one. The strong antiferromagnetic bilayer coupling causes the charge carriers in the plane with larger doping concentration to behave similar to those of the underdoped layer, they are coupled to. This effect grows for decreasing temperature. For high temperatures or if both layers are optimally or overdoped, i.e. when the antiferromagnetic correlation length becomes of the order or smaller than one lattice site the charge carrier and magnetic dynamics of the two layers is disconnected and the equalization effect disappears. These results are in good agreement with NMR experiments on Y2Ba4Cu7O15 by Stern et al. Phys. Rev B 51, 15478 (1995). We also compare the results with calculations on bilayer systems with equivalent layers as models for the constituent compounds YBa2Cu3O7 and YBa2Cu4O8.
Density-of-states picture and stability of ferromagnetism in the highly correlated Hubbard model
Physical Review B, 2004
The problem of stability of saturated and non-saturated ferromagnetism in the Hubbard model is considered in terms of the one-particle Green's functions. Approximations by Edwards and Hertz and some versions of the self-consisten approximations based on the 1/z-expansion are considered. The account of longitudinal fluctuations turns out to be essential for description of the non-saturated state. The corresponding pictures of density of states are obtained. "Kondo" density-of-states singularities owing to spin-flip processes are analyzed. The critical electron concentrations for instabilities of saturated ferromagnetism and paramagnetic state are calculated for various lattices. Drawbacks of various approximations are discussed. A comparison with the results of previous works is performed. 71.10.Fd Lattice fermion models (Hubbard model, etc.), 71.28.+d Narrow-band systems; intermediate-valence solids,
Quantum antiferromagnetism in the d=3 Hubbard model --- a spin-fluctuation approach
1998
A self-consistent spin-fluctuation theory is developed to obtain TN vs. U for the half-filled Hubbard model in the whole U/t range. Good agreement is obtained in the strong coupling limit with the high-temperature series-expansion result for the equivalent Heisenberg model. Quantum spinfluctuation correction to the sublattice magnetization is also obtained for all U at the one-loop level. A spin picture is used throughout, and quantum effects are incorporated through transverse spin fluctuations, which are evaluated in the random phase approximation using a new method.
Journal of the Physical Society of Japan, 2000
We have systematically studied superconducting instabilities in the repulsive Hubbard model for d-wave and p-wave pairing in various 2D and 3D lattices. Using fluctuation exchange approximation, we consider 3D face centered cubic lattice, 3D body centered cubic lattice, 3D simple cubic lattice, 2D square lattice and 2D triangular lattice, where either strong ferro-or antiferromagnetic spin fluctuation is present. We show that (i) d-wave instability mediated by antiferromagnetic spin fluctuations is stronger than p-wave instability mediated by ferromagnetic spin fluctuations both in 2D and 3D, and (ii)d-wave instability in 2D is much stronger than that in 3D. These amount that the "best" situation is the antiferromagnetic-fluctuation mediated in 2D as far as the single-band Hubbard model on ordinary lattices are concerned.
Physica B: Condensed Matter, 2005
In order to explore how superconductivity arises when charge fluctuations and spin fluctuations coexist, we have obtained a phase diagram against the off-site repulsion V and band filling n for the extended, repulsive Hubbard model on the square lattice with the fluctuation exchange approximation. We have found the existence of (i) a transition between dxy and d x 2 −y 2 pairing symmetries, (ii) f-pairing in between the d x 2 −y 2 and CDW phases for intermediate 0.5 < n < 1.0 and large V , and (iii) for anisotropic cases the pairing symmetry changing, in agreement with a previously proposed "generic phase diagram", as d → f → s when V (hence the charge fluctuations) are increased. All these are consequences of the structure in the charge and spin susceptibilities, which have peaks habitating at common or segregated positions in k space.