47 research outputs found
Magnetic properties of the three-dimensional Hubbard model at half filling
We study the magnetic properties of the 3d Hubbard model at half-filling in
the TPSC formalism, previously developed for the 2d model. We focus on the
N\'eel transition approached from the disordered side and on the paramagnetic
phase. We find a very good quantitative agreement with Dynamical Mean-Field
results for the isotropic 3d model. Calculations on finite size lattices also
provide satisfactory comparisons with Monte Carlo results up to the
intermediate coupling regime. We point out a qualitative difference between the
isotropic 3d case, and the 2d or anisotropic 3d cases for the double occupation
factor. Even for this local correlation function, 2d or anisotropic 3d cases
are out of reach of DMF: this comes from the inability of DMF to account for
antiferromagnetic fluctuations, which are crucial.Comment: RevTex, 9 pages +10 figure
Crossover in the nature of the metallic phases in the perovskite-type RNiO_3
We have measured the photoemission spectra of NdSmNiO,
where the metal-insulator transition and the N\'{e}el ordering occur at the
same temperature for and the metal-insulator transition
temperature () is higher than the N\'{e}el temperature for . For , the spectral intensity at the Fermi level is high in the
metallic phase above and gradually decreases with cooling in the
insulating phase below while for it shows a pseudogap-like
behavior above and further diminishes below . The results
clearly establish that there is a sharp change in the nature of the electronic
correlations in the middle () of the metallic phase of the
NiO system.Comment: 4 pages, 4 figure, submitted to Phys. Rev.
Evidence for short range orbital order in paramagnetic insulating (Al,V)_2O_3
The local structure of (Al_0.06V_0.94)_2O_3 in the paramagnetic insulating
(PI) and antiferromagnetically ordered insulating (AFI) phase has been
investigated using hard and soft x-ray absorption techniques. It is shown that:
1) on a local scale, the symmetry of the vanadium sites in both the PI and the
AFI phase is the same; and 2) the vanadium 3d - oxygen 2p hybridization, as
gauged by the oxygen 1s absorption edge, is the same for both phases, but
distinctly different from the paramagnetic metallic phase of pure V_2O_3. These
findings can be understood in the context of a recently proposed model which
relates the long range monoclinic distortion of the antiferromagnetically
ordered state to orbital ordering, if orbital short range order in the PI phase
is assumed. The measured anisotropy of the x-ray absorption spectra is
discussed in relation to spin-polarized density functional calculations.Comment: 8 pages, 5 figure
Magnetic field and pressure effects on charge density wave, superconducting, and magnetic states in LuIrSi and ErIrSi
We have studied the charge-density-wave (CDW) state for the superconducting
LuIrSi and the antiferromagnetic ErIrSi as
variables of temperature, magnetic field, and hydrostatic pressure. For
LuIrSi, the application of pressure strongly suppresses the CDW
phase but weakly enhances the superconducting phase. For ErIrSi,
the incommensurate CDW state is pressure independent and the commensurate CDW
state strongly depends on the pressure, whereas the antiferromagnetic ordering
is slightly depressed by applying pressure. In addition, ErIrSi
shows negative magnetoresistance at low temperatures, compared with the
positive magnetoresistance of LuIrSi.Comment: 12 pages, including 6 figure
The Numerical Renormalization Group Method for correlated electrons
The Numerical Renormalization Group method (NRG) has been developed by Wilson
in the 1970's to investigate the Kondo problem. The NRG allows the
non-perturbative calculation of static and dynamic properties for a variety of
impurity models. In addition, this method has been recently generalized to
lattice models within the Dynamical Mean Field Theory. This paper gives a brief
historical overview of the development of the NRG and discusses its application
to the Hubbard model; in particular the results for the Mott metal-insulator
transition at low temperatures.Comment: 14 pages, 7 eps-figures include
Electronic structure of NiS_{1-x}Se_x
We investigate the electronic structure of the metallic NiSSe
system using various electron spectroscopic techniques. The band structure
results do not describe the details of the spectral features in the
experimental spectrum, even for this paramagnetic metallic phase. However, a
parameterized many-body multi-band model is found to be successful in
describing the Ni~2 core level and valence band, within the same model. The
asymmetric line shape as well as the weak intensity feature in the Ni~2 core
level spectrum has been ascribed to extrinsic loss processes in the system. The
presence of satellite features in the valence band spectrum shows the existence
of the lower Hubbard band, deep inside the metallic regime, consistent
with the predictions of the dynamical mean field theory.Comment: To be published in Physical Review B, 18 pages and 5 figure
Electromagnetic Response of Layered Superconductors with Broken Lattice Inversion Symmetry
We investigate the macroscopic effects of charge density waves (CDW) and
superconductivity in layered superconducting systems with broken lattice
inversion symmetry (allowing for piezoelectricity) such as two dimensional (2D)
transition metal dichalcogenides (TMD). We work with the low temperature time
dependent Ginzburg-Landau theory and study the coupling of lattice distortions
and low energy CDW collective modes to the superconducting order parameter in
the presence of electromagnetic fields. We show that superconductivity and
piezoelectricity can coexist in these singular metals. Furthermore, our study
indicates the nature of the quantum phase transition between a commensurate CDW
phase and the stripe phase that has been observed as a function of applied
pressure.Comment: 9 pages, 1 figure. Final version. Accepted in Phys.Rev.
Absence of lattice strain anomalies at the electronic topological transition in zinc at high pressure
High pressure structural distortions of the hexagonal close packed (hcp)
element zinc have been a subject of controversy. Earlier experimental results
and theory showed a large anomaly in lattice strain with compression in zinc at
about 10 GPa which was explained theoretically by a change in Fermi surface
topology. Later hydrostatic experiments showed no such anomaly, resulting in a
discrepancy between theory and experiment. We have computed the compression and
lattice strain of hcp zinc over a wide range of compressions using the
linearized augmented plane wave (LAPW) method paying special attention to
k-point convergence. We find that the behavior of the lattice strain is
strongly dependent on k-point sampling, and with large k-point sets the
previously computed anomaly in lattice parameters under compression disappears,
in agreement with recent experiments.Comment: 9 pages, 6 figures, Phys. Rev. B (in press