1,099 research outputs found
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
Quasiparticle interference in antiferromagnetic parent compounds of Fe-based superconductors
Recently reported quasiparticle interference imaging in underdoped
Ca(Fe{1-x}Co{x})_2As{2} shows pronounced C{2} asymmetry that is interpreted as
an indication of an electronic nematic phase with a unidirectional electron
band, dispersive predominantly along the -axis of this orthorhombic
material. On the other hand, even more recent transport measurements on
untwinned samples show near isotropy of the resistivity in the plane, with
slightly larger conductivity along a (and not b). We show that in fact both
sets of data are consistent with the calculated ab initio Fermi surfaces, which
has a decisively broken C_{4}, and yet similar Fermi velocity in both
directions. This reconciles completely the apparent contradiction between the
conclusions of the STM and the transport experiments.Comment: A version of this work was posted (arXiv:1005.1761) as a comment on a
Science paper entitled "Nematic Electronic Structure in the Parent State of
the Iron-Based Superconductor Ca(Fe1-xCox)2As2". The comment was rejected by
Science on account of it being posted on the ArXiv. This is a version
published in PRB as a research pape
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