11,950 research outputs found
Charge fluctuations in the unconventional metallic state of Li0.9Mo6O17
Charge fluctuations in the quasi-one-dimensional material Li0.9Mo6O17 are
analyzed based on a multi orbital extended Hubbard model. A charge ordering
transition induced by Coulomb repulsion is found with a charge ordering pattern
different from a conventional charge density wave driven by Fermi surface
nesting. The metallic state displays a characteristic charge collective mode
which softens signalling the proximity to the transition. We argue that the
strong scattering between electrons generated by these charge order
fluctuations can lead to the unconventional metallic state observed above the
superconducting transition temperature in Li0.9Mo6O17.Comment: 5 pages, 4 figures, typos corrected and references adde
Dynamical reduction of the dimensionality of exchange interactions and the "spin-liquid" phase of -(BEDT-TTF)
We show that the anisotropy of the effective spin model for the dimer Mott
insulator phase of -(BEDT-TTF) salts is dramatically different
from that of the underlying tight-binding model. Intra-dimer quantum
interference results in a model of coupled spin chains, where frustrated
interchain interactions suppress long-range magnetic order. Thus, we argue, the
"spin liquid" phase observed in some of these materials is a remnant of the
Tomonaga-Luttinger physics of a single chain. This is consistent with previous
experiments and resolves some outstanding puzzles. An erratum [Phys. Rev. Lett.
120, 199901 (2018).] is added as an appendix.Comment: Accepted by PRL, 6 pages, 5 figure
Odderon-Pomeron Interference
We show that the asymmetry in the fractional energy of charm versus anticharm
jets produced in high energy diffractive photoproduction is sensitive to the
interference of the Odderon and Pomeron exchange amplitudes
in QCD. We predict the dynamical shape of the asymmetry in a simple model and
estimate its magnitude to be of the order 15% using an Odderon coupling to the
proton which saturates constraints from proton-proton vs. proton-antiproton
elastic scattering. Measurements of this asymmetry at HERA could provide firm
experimental evidence for the presence of Odderon exchange in the high energy
limit of strong interactions.Comment: 12 pages, 4 figures, Minor corrections, Main results unchanged,
Contribution from photon exchange added, Numerical estimates updated and
uncertainties clarified. To appear in Physics Letters
Role of surface states in STM spectroscopy of (111) metal surfaces with Kondo adsorbates
A nearly-free-electron (NFE) model to describe STM spectroscopy of (111)
metal surfaces with Kondo impurities is presented. Surface states are found to
play an important role giving a larger contribution to the conductance in the
case of Cu(111) and Au(111) than Ag(111) surfaces. This difference arises from
the farther extension of the Ag(111) surface state into the substrate. The
different line shapes observed when Co is adsorbed on different substrates can
be explained from the position of the surface band onset relative to the Fermi
energy. The lateral dependence of the line shape amplitude is found to be
bulk-like for R|| < 4 Amstrongs and surface-like at larger distances, in
agreement with experimental data.Comment: 4 pages, 3 eps figure
Spin liquid phase in a spatially anisotropic frustrated antiferromagnet
We explore the effect of the third nearest-neighbors on the magnetic
properties of the Heisenberg model on an anisotropic triangular lattice. We
obtain the phase diagram of the model using Schwinger-boson mean-field theory.
Competition between N\'eel, spiral and collinear magnetically ordered phases is
found as we vary the on the ratios of the nearest, J1, next-nearest, J2, and
third-nearest, J_3, neighbor exchange couplings. A spin liquid phase is
stabilized between the spiral and collinear ordered states when J2/J1 < 1.8 for
rather small J3/J1 < 0.1. The lowest energy two-spinon dispersions relevant to
neutron scattering experiments are analyzed and compared to semiclassical
magnon dispersions finding significant differences in the spiral and collinear
phases between the two approaches. The results are discussed in the context of
the anisotropic triangular materials: Cs2CuCl4 and Cs2CuBr4 and layered organic
materials, kappa-(BEDT-TTF)2X and Y[Pd(dmit)2]2.Comment: 11 pages, 9 figure
Spin liquid phase due to competing classical orders in the semiclassical theory of the Heisenberg model with ring exchange on an anisotropic triangular lattice
Linear spin wave theory shows that ring exchange induces a quantum disordered
region in the phase diagram of the title model. Spin wave spectra show that
this is a direct manifestation of competing classical orders. A spin liquid is
found in the `Goldilocks zone' of frustration, where the quantum fluctuations
are large enough to cause strong competition between different classical
orderings but not strong enough to stabilize spiral order. We note that the
spin liquid phases of -(BEDT-TTF) and [Pd(dmit)] are
found in this Goldilocks zone.Comment: 5 pages, 3 figure
Interplay of frustration, magnetism, charge ordering, and covalency in a model of Na0.5CoO2
We investigate an effective Hamiltonian for Na0.5CoO2 that includes the
electrostatic potential due to the ordered Na ions and strong electronic
correlations. This model displays a subtle interplay between metallic and
insulating phases and between charge and magnetic order. For realistic
parameters, the model predicts an insulating phase with similarities to a
covalent insulator. We show that this interpretation gives a consistent
explanation of experiments on Na0.5CoO2, including the small degree of charge
ordering, the small charge gap, the large moment, and the optical conductivity.Comment: 5 pages, 4 figures. Text revised making more emphasis on model
properties. Figures compacte
Effects of anisotropy in spin molecular-orbital coupling on effective spin models of trinuclear organometallic complexes
We consider layered decorated honeycomb lattices at two-thirds filling, as
realized in some trinuclear organometallic complexes. Localized moments
with a single-spin anisotropy emerge from the interplay of Coulomb repulsion
and spin molecular-orbit coupling (SMOC). Magnetic anisotropies with bond
dependent exchange couplings occur in the honeycomb layers when the direct
intracluster exchange and the spin molecular-orbital coupling are both present.
We find that the effective spin exchange model within the layers is an XXZ +
120 honeycomb quantum compass model. The intrinsic non-spherical
symmetry of the multinuclear complexes leads to very different transverse and
longitudinal spin molecular-orbital couplings, which greatly enhances the
single-spin and exchange coupling anisotropies. The interlayer coupling is
described by a XXZ model with anisotropic biquadratic terms. As the correlation
strength increases the systems becomes increasingly one-dimensional. Thus, if
the ratio of SMOC to the interlayer hopping is small this stabilizes the
Haldane phase. However, as the ratio increases there is a quantum phase
transition to the topologically trivial `-phase'. We also predict a quantum
phase transition from a Haldane phase to a magnetically ordered phase at
sufficiently strong external magnetic fields.Comment: 22 pages, 11 figures. Final version of paper to be published in PRB.
Important corrections to appendix
- …