7,110 research outputs found
Pressure-induced metal-insulator transition in LaMnO3 is not of Mott-Hubbard type
Calculations employing the local density approximation combined with static
and dynamical mean-field theories (LDA+U and LDA+DMFT) indicate that the
metal-insulator transition observed at 32 GPa in paramagnetic LaMnO3 at room
temperature is not a Mott-Hubbard transition, but is caused by orbital
splitting of the majority-spin eg bands. For LaMnO3 to be insulating at
pressures below 32 GPa, both on-site Coulomb repulsion and Jahn-Teller
distortion are needed.Comment: 4 pages, 3 figure
Half-metallicity and magnetism in the CoMnAl/CoMnVAl heterostructure
We present a study of the electronic structure and magnetism of CoMnAl,
CoMnVAl and their heterostructure. We employ a combination of
density-functional theory and dynamical mean-field theory (DFT+DMFT). We find
that CoMnAl is a half-metallic ferromagnet, whose electronic and magnetic
properties are not drastically changed by strong electronic correlations,
static or dynamic. Non-quasiparticle states are shown to appear in the minority
spin gap without affecting the spin-polarization at the Fermi level predicted
by standard DFT. We find that CoMnVAl is a semiconductor or a semi-metal,
depending on the employed computational approach. We then focus on the
electronic and magnetic properties of the CoMnAl/CoMnVAl heterostructure,
predicted by previous first principle calculations as a possible candidate for
spin-injecting devices. We find that two interfaces, Co-Co/V-Al and
Co-Mn/Mn-Al, preserve the half-metallic character, with and without including
electronic correlations. We also analyse the magnetic exchange interactions in
the bulk and at the interfaces. At the Co-Mn/Mn-Al interface, competing
magnetic interactions are likely to favor the formation of a non-collinear
magnetic order, which is detrimental for the spin-polarization.Comment: 15 pages, 16 figure
LDA+DMFT Spectral Functions and Effective Electron Mass Enhancement in Superconductor LaFePO
In this Letter we report the first LDA+DMFT results (method combining Local
Density Approximation with Dynamical Mean-Field Theory) for spectral properties
of superconductor LaFePO. Calculated {\bf k}-resolved spectral functions
reproduce recent angle-resolved photoemission spectroscopy (ARPES) data [D. H.
Lu {\it et al}., Nature {\bf 455}, 81 (2008)]. Obtained effective electron mass
enhancement values 1.9 -- 2.2 are in good agreement with
infrared and optical studies [M. M. Qazilbash {\it et al}., Nature Phys. {\bf
5}, 647 (2009)], de Haas--van Alphen, electrical resistivity, and electronic
specific heat measurements results, that unambiguously evidence for moderate
correlations strength in LaFePO. Similar values of were found in the
other Fe-based superconductors with substantially different superconducting
transition temperatures. Thus, the dynamical correlation effects are essential
in the Fe-based superconductors, but the strength of electronic correlations
does not determine the value of superconducting transition temperature.Comment: 4 pages, 3 figure
Comparative study of correlation effects in CaVO3 and SrVO3
We present parameter-free LDA+DMFT (local density approximation + dynamical
mean field theory) results for the many-body spectra of cubic SrVO3 and
orthorhombic CaVO3. Both systems are found to be strongly correlated metals,
but not on the verge of a metal-insulator transition. In spite of the
considerably smaller V-O-V bond angle in CaVO3 the LDA+DMFT spectra of the two
systems for energies E<E_F are very similar, their quasiparticle parts being
almost identical. The calculated spectrum for E>E_F shows more pronounced,
albeit still small, differences. This is in contrast to earlier theoretical and
experimental conclusions, but in good agreement with recent bulk-sensitive
photoemission and x-ray absorption experiments.Comment: 15 pages, 6 figure
Momentum-resolved spectral functions of SrVO calculated by LDA+DMFT
LDA+DMFT, the merger of density functional theory in the local density
approximation and dynamical mean-field theory, has been mostly employed to
calculate k-integrated spectra accessible by photoemission spectroscopy. In
this paper, we calculate k-resolved spectral functions by LDA+DMFT. To this
end, we employ the Nth order muffin-tin (NMTO) downfolding to set up an
effective low-energy Hamiltonian with three t_2g orbitals. This downfolded
Hamiltonian is solved by DMFT yielding k-dependent spectra. Our results show
renormalized quasiparticle bands over a broad energy range from -0.7 eV to +0.9
eV with small ``kinks'', discernible in the dispersion below the Fermi energy.Comment: 21 pages, 8 figure
The Cerium volume collapse: Results from the LDA+DMFT approach
The merger of density-functional theory in the local density approximation
(LDA) and many-body dynamical mean field theory (DMFT) allows for an ab initio
calculation of Ce including the inherent 4f electronic correlations. We solve
the DMFT equations by the quantum Monte Carlo (QMC) technique and calculate the
Ce energy, spectrum, and double occupancy as a function of volume. At low
temperatures, the correlation energy exhibits an anomalous region of negative
curvature which drives the system towards a thermodynamic instability, i.e.,
the -to- volume collapse, consistent with experiment. The
connection of the energetic with the spectral evolution shows that the physical
origin of the energy anomaly and, thus, the volume collapse is the appearance
of a quasiparticle resonance in the 4f-spectrum which is accompanied by a rapid
growth in the double occupancy.Comment: 4 pages, 3 figure
High-temperature optical spectral weight and Fermi liquid renormalization in Bi-based cuprates
The optical conductivity and the spectral weight W(T) of two superconducting
cuprates at optimum doping, Bi2Sr2-xLaxCuO6 and Bi2Sr2CaCu2O8, have been first
measured up to 500 K. Above 300 K, W(T) deviates from the usual T2 behavior in
both compounds, even though the zero-frequency extrapolation of the optical
conductivity remains larger than the Ioffe-Regel limit. The deviation is
surprisingly well described by the T4 term of the Sommerfeld expansion, but its
coefficients are enhanced by strong correlation. This renormalization is due to
strong correlation, as shown by the good agreement with dynamical mean field
calculations.Comment: 5 pages, 3 figures, Physical Review Letters in pres
Multiplet ligand-field theory using Wannier orbitals
We demonstrate how ab initio cluster calculations including the full Coulomb
vertex can be done in the basis of the localized, generalized Wannier orbitals
which describe the low-energy density functional (LDA) band structure of the
infinite crystal, e.g. the transition metal 3d and oxygen 2p orbitals. The
spatial extend of our 3d Wannier orbitals (orthonormalized Nth order muffin-tin
orbitals) is close to that found for atomic Hartree-Fock orbitals. We define
Ligand orbitals as those linear combinations of the O 2p Wannier orbitals which
couple to the 3d orbitals for the chosen cluster. The use of ligand orbitals
allows for a minimal Hilbert space in multiplet ligand-field theory
calculations, thus reducing the computational costs substantially. The result
is a fast and simple ab initio theory, which can provide useful information
about local properties of correlated insulators. We compare results for NiO,
MnO and SrTiO3 with x-ray absorption, inelastic x-ray scattering, and
photoemission experiments. The multiplet ligand field theory parameters found
by our ab initio method agree within ~10% to known experimental values
Turning a nickelate Fermi surface into a cuprate-like one through heterostructuring
Using the local density approximation and its combination with dynamical
mean-field theory, we show that electronic correlations induce a single-sheet,
cuprate-like Fermi surface for hole-doped 1/1 LaNiO3 /LaAlO3 heterostructures,
even though both eg orbitals contribute to it. The Ni 3d 3z^2-1 orbital plays
the role of the axial Cu 4s-like orbital in the cuprates. These two results
indicate that "orbital engineering" by means of heterostructuring should be
possible. As we also find strong antiferromagnetic correlations, the low-energy
electronic and spin excitations in nickelate heterostructures resemble those of
high-temperature cuprate superconductors.Comment: 4 pages, 3 figure
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