194 research outputs found
Covalency and the metal-insulator transition in titanate and vanadate perovskites
A combination of density functional and dynamical mean-field theory is
applied to the perovskites SrVO, LaTiO and LaVO. We show that
DFT+DMFT in conjunction with the standard fully localized-limit (FLL)
double-counting predicts that LaTiO and LaVO are metals even though
experimentally they are correlation-driven ("Mott") insulators. In addition,
the FLL double counting implies a splitting between oxygen and transition
metal levels which differs from experiment. Introducing into the theory an
\textit{ad hoc} double counting correction which reproduces the experimentally
measured insulating gap leads also to a - splitting consistent with
experiment if the on-site interaction is chosen in a relatively narrow
range ( eV). The results indicate that these early transition
metal oxides will serve as critical test for the formulation of a general
\textit{ab initio} theory of correlated electron metals.Comment: 5 pages, 3 figure
Electronic correlations, magnetism and Hund's rule coupling in the ruthenium perovskites SrRuO and CaRuO
A comparative density functional plus dynamical mean field theory study of
the pseudocubic ruthenate materials CaRuO and SrRuO is presented. Phase
diagrams are determined for both materials as a function of Hubbard repulsion
and Hund's rule coupling . Metallic and insulating phases are found, as
are ferromagnetic and paramagnetic states. The locations of the relevant phase
boundaries are determined. Based on the computed phase diagrams, Mott-dominated
and Hund's dominated regimes of strong correlation are distinguished.
Comparison of calculated properties to experiments indicates that the actual
materials are in the Hund's coupling dominated region of the phase diagram so
can be characterized as Hund's metals, in common with other members of the
ruthenate family. Comparison of the phase diagrams for the two materials
reveals the role played by rotational and tilt (GdFeO-type) distortions of
the ideal perovskite structure. The presence of magnetism in SrRuO and its
absence in CaRuO despite the larger mass and larger tilt/rotational
distortion amplitude of CaRuO can be understood in terms of density of
states effects in the presence of strong Hund's coupling. Comparison of the
calculated low- properties of CaRuO to those of SrRuO provides
insight into the effects of magnetic order on the properties of a Hund's metal.
The study provides a simultaneous description of magnetism and correlations and
explicates the roles played by band theory and Hubbard and Hund's interactions
Band Structure and Terahertz Optical Conductivity of Transition Metal Oxides: Theory and Application to CaRuO
Density functional plus dynamical mean field calculations are used to show
that in transition metal oxides, rotational and tilting (GdFeO-type)
distortions of the ideal cubic perovskite structure produce a multiplicity of
low-energy optical transitions which affect the conductivity down to
frequencies of the order of or ~mV (terahertz regime), mimicking
non-Fermi-liquid effects even in systems with a strictly Fermi-liquid
self-energy. For CaRuO, a material whose measured electromagnetic response
in the terahertz frequency regime has been interpreted as evidence for
non-Fermi-liquid physics, the combination of these band structure effects and a
renormalized Fermi-liquid self-energy accounts for the low frequency optical
response which had previously been regarded as a signature of exotic physics.
Signatures of deviations from Fermi-liquid behavior at higher frequencies
(~meV) are discussed
Mott transition in the triangular lattice Hubbard model: a dynamical cluster approximation study
Based on dynamical cluster approximation (DCA) quantum Monte Carlo
simulations, we study the interaction-driven Mott metal-insulator transition
(MIT) in the half-filled Hubbard model on the anisotropic two-dimensional
triangular lattice, where the degree of frustration is varied between the
unfrustrated case and the fully frustrated, isotropic triangular lattice. Upon
increasing the DCA cluster size, we analyze the evolution of the MIT phase
boundary as a function of frustration in the phase diagram spanned by the
interaction strength and temperature, and provide a quantitative description of
the MIT phase boundary in the triangular lattice Hubbard model. Qualitative
differences in the phase boundary between the unfrustrated and fully frustrated
cases are exhibited. In particular, a change in the sign of the phase boundary
slope is observed, which via an impurity cluster eigenstate analysis, may be
related to a change in the nature of the insulating state. We discuss our
findings within the scenario that the triangular lattice electron system might
exhibit a quantum critical Mott MIT with a possible quantum spin liquid
insulating state, such as considered for the organic charge transfer salts
-(BEDT-TTF)Cu(CN) and
EtMeSb[Pd(dmit)]
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