3,045 research outputs found
Magnetic Collapse and the Behavior of Transition Metal Oxides at High Pressure
We report a detail theoretical study of the electronic structure and phase
stability of transition metal oxides MnO, FeO, CoO, and NiO in their
paramagnetic cubic B1 structure by employing dynamical mean-field theory of
correlated electrons combined with \emph{ab initio} band structure methods
(DFT+DMFT). Our calculations reveal that under pressure these materials exhibit
a Mott insulator-metal transition (IMT) which is accompanied by a simultaneous
collapse of local magnetic moments and lattice volume, implying a complex
interplay between chemical bonding and electronic correlations. Moreover, our
results for the transition pressure show a monotonous decrease from ~ 145 GPa
to 40 GPa, upon moving from MnO to CoO. In contrast to that, in NiO, magnetic
collapse is found to occur at remarkably higher pressure of ~ 429 GPa. We
provide a unified picture of such a behavior and suggest that it is primary a
localized to itinerant moment behavior transition at the IMT that gives rise to
magnetic collapse in transition metal oxides.Comment: 6 pages, 3 figure
Slave-rotor mean field theories of strongly correlated systems and the Mott transition in finite dimensions
The multiorbital Hubbard model is expressed in terms of quantum phase
variables (``slave rotors'') conjugate to the local charge, and of auxiliary
fermions, providing an economical representation of the Hilbert space of
strongly correlated systems. When the phase variables are treated in a local
mean-field manner, similar results to the dynamical mean-field theory are
obtained, namely a Brinkman-Rice transition at commensurate fillings together
with a ``preformed'' Mott gap in the single-particle density of states. The
slave- rotor formalism allows to go beyond the local description and take into
account spatial correlations, following an analogy to the superfluid-insulator
transition of bosonic systems. We find that the divergence of the effective
mass at the metal- insulator transition is suppressed by short range magnetic
correlations in finite-dimensional systems. Furthermore, the strict separation
of energy scales between the Fermi- liquid coherence scale and the Mott gap
found in the local picture, holds only approximately in finite dimensions, due
to the existence of low-energy collective modes related to zero-sound.Comment: 16 pages, 12 figure
Competing superfluid and density-wave ground-states of fermionic mixtures with mass imbalance in optical lattices
We study the effect of mass imbalance on the phase diagram of a two-component
fermionic mixture with attractive interactions in optical lattices. Using
static and dynamical mean-field theories, we show that the pure superfluid
phase is stable for all couplings when the mass imbalance is smaller than a
limiting value. For larger imbalance, phase separation between a superfluid and
a charge-density wave takes place when the coupling exceeds a critical
strength. The harmonic trap induces a spatial segregation of the two phases,
with a rapid variation of the density at the boundary.Comment: e.g.:4 pages, 3 figure
How Rotation Affects Masses and Ages of Classical Cepheids
Classical Cepheid variable stars are both sensitive astrophysical
laboratories and accurate cosmic distance tracers. We have recently
investigated how the evolutionary effects of rotation impact the properties of
these important stars and here provide an accessible overview of some key
elements as well as two important consequences. Firstly, rotation resolves the
long-standing Cepheid mass discrepancy problem. Second, rotation increases main
sequence lifetimes, i.e, Cepheids are approximately twice as old as previously
thought. Finally, we highlight the importance of the short-period ends of
Cepheid period distributions as indicators for model adequacy.Comment: 5 pages, 4 figures, proceedings of the 22nd Los Alamos Stellar
Pulsation Conference "Wide-field variability surveys: a 21st-century
perspective" held in San Pedro de Atacama, Chile, Nov. 28 - Dec. 2, 201
Dynamical singlets and correlation-assisted Peierls transition in VO2
A theory of the metal-insulator transition in vanadium dioxide from the
high-temperature rutile to the low- temperature monoclinic phase is proposed on
the basis of cluster dynamical mean field theory, in conjunction with the
density functional scheme. The interplay of strong electronic Coulomb
interactions and structural distortions, in particular the dimerization of
vanadium atoms in the low temperature phase, plays a crucial role. We find that
VO2 is not a conventional Mott insulator, but that the formation of dynamical
V-V singlet pairs due to strong Coulomb correlations is necessary to trigger
the opening of a Peierls gap.Comment: 5 page
Rotationally-invariant slave-boson formalism and momentum dependence of the quasiparticle weight
We generalize the rotationally-invariant formulation of the slave-boson
formalism to multiorbital models, with arbitrary interactions, crystal fields,
and multiplet structure. This allows for the study of multiplet effects on the
nature of low-energy quasiparticles. Non-diagonal components of the matrix of
quasiparticle weights can be calculated within this framework. When combined
with cluster extensions of dynamical mean-field theory, this method allows us
to address the effects of spatial correlations, such as the generation of the
superexchange and the momentum dependence of the quasiparticle weight. We
illustrate the method on a two-band Hubbard model, a Hubbard model made of two
coupled layers, and a two-dimensional single-band Hubbard model (within a
two-site cellular dynamical mean-field approximation).Comment: added figures, improved discussio
Mott transition and suppression of orbital fluctuations in orthorhombic 3 perovskites
Using Wannier-functions, a low-energy Hamiltonian is derived for
orthorhombic transition-metal oxides. Electronic correlations are
treated with a new implementation of dynamical mean-field theory for non-cubic
systems. Good agreement with photoemission data is obtained. The interplay of
correlation effects and cation covalency (GdFeO-type distortions) is
found to suppress orbital fluctuations in LaTiO and even more in
YTiO, and to favor the transition to the insulating state.Comment: 4 pages, 3 figures; revised manuscrip
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