60 research outputs found
Orbital-dependent singlet dimers and orbital-selective Peierls transitions in transition metal compounds
We show that in transition metal compounds containing structural metal dimers
there may exist in the presence of different orbitals a special state with
partial formation of singlets by electrons on one orbital, while others are
effectively decoupled and may give e.g. long-range magnetic order or stay
paramagnetic. Similar situation can be realized in dimers spontaneously formed
at structural phase transitions, which can be called orbital-selective Peierls
transition. This can occur in case of strongly nonuniform hopping integrals for
different orbitals and small intra-atomic Hund's rule coupling JH. Yet another
consequence of this picture is that for odd number of electrons per dimer there
exist competition between double exchange mechanism of ferromagnetism, and the
formation of singlet dimer by electron on one orbital, with remaining electrons
giving a net spin of a dimer. The first case is realized for strong Hund's rule
coupling, typical for 3d compounds, whereas the second is more plausible for
4d-5d compounds. We discuss some implications of these phenomena, and consider
examples of real systems, in which orbital-selective phase seems to be
realized.Comment: to be published in PRB Rapid Co
Coulomb interaction and stability of CE-type structure in half-doped manganites, reply
In his Comment (cond-mat/0104353), Shen points out that the on-site Coulomb
interaction, that can cause charge order in half-doped manganites, also
destabilizes the magnetic CE-phase observed in these systems. This is a valid
observation, but it is not a priori clear whether in the relevant parameter
regime the C-phase is indeed lower in energy then the CE-phase within our
model. We conclude that the proposed model, which correctly captures the
interplay of spin, charge and orbital degrees of freedom in the half-doped
manganites and gives a reasonable description of their electronic structure, is
by itself not sufficient for the precise determination of the regions of
stabilities of different phases. For this several other factors should be taken
into account.Comment: 1 page, to appear in Phys. Rev. Let
Suppression of Magnetism in Ba\u3csub\u3e5\u3c/sub\u3eAlIr\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e11\u3c/sub\u3e: Interplay of Hund\u27s Coupling, Molecular Orbitals, and Spin-Orbit Interaction
The electronic and magnetic properties of Ba5AlIr2O11 containing Ir-Ir dimers are investigated using the generalized gradient approximation (GGA) and GGA + spin-orbit coupling (SOC) calculations. We found that the strong suppression of the magnetic moment in this compound recently found by Terzic et al. [Phys. Rev. B 91, 235147 (2015)] is not due to charge ordering but is related to the joint effect of the spin-orbit interaction and strong covalency, resulting in the formation of metal-metal bonds. They conspire and act against the intraatomic Hund\u27s rule exchange interaction to reduce total magnetic moment of the dimer. We argue that the same mechanism could be relevant for other 4d and 5d dimerized transition metal compounds
A valence bond liquid on the honeycomb lattice
The honeycomb lattice material Li2RuO3 undergoes a dimerization of Ru4+
cations on cooling below 270C, where the magnetic susceptibility vanishes. We
use density functional theory calculations to show that this reflects the
formation of a 'valence bond crystal', with a strong bond disproportionation.
On warming, x-ray diffraction shows that discrete three-fold symmetry is
regained on average, and the dimerization apparently disappears. In contrast,
local structural measurements using high-energy x-rays, show that disordered
dimers survive at the nanoscale up to at least 650C. The high temperature phase
of Li2RuO3 is thus an example of a valence bond liquid, where thermal
fluctuations drive resonance between different dimer coverages, a classic
analogue of the resonating valence bond state often discussed in connection
with high T cuprates.Comment: 5 pages, 4 figures, References correcte
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