52 research outputs found
t-J model of coupled CuO ladders in SrCaCuO
Starting from the proper charge transfer model for CuO coupled
ladders in SrCaCuO we derive the low energy
Hamiltonian for this system. It occurs that the widely used ladder t-J model is
not sufficient and has to be supplemented by the Coulomb repulsion term between
holes in the neighboring ladders. Furthermore, we show how a simple mean-field
solution of the derived t-J model may explain the onset of the charge density
wave with the odd period in SrCaCuO.Comment: 8 pages, 4 figures, 2 table
Quantum walk versus classical wave: Distinguishing ground states of quantum magnets by spacetime dynamics
We investigate wave packet spreading after a single spin flip in prototypical two-dimensional ferromagnetic and antiferromagnetic quantum spin systems. We find characteristic spatial magnon density profiles: While the ferromagnet shows a square-shaped pattern reflecting the underlying lattice structure, as exhibited by quantum walkers, the antiferromagnet shows a circular-shaped pattern which hides the lattice structure and instead resembles a classical wave pattern. We trace these fundamentally different behaviors back to the distinctly different magnon energy-momentum dispersion relations and also provide a real-space interpretation. Our findings point to opportunities for real-time, real-space imaging of quantum magnets both in materials science and in quantum simulators
Dispersion of orbital excitations in 2D quantum antiferromagnets
We map the problem of the orbital excitation (orbiton) in a 2D
antiferromagnetic and ferroorbital ground state onto a problem of a hole in 2D
antiferromagnet. The orbiton turns out to be coupled to magnons and can only be
mobile on a strongly renormalized scale by dressing with magnetic excitations.
We show that this leads to a dispersion relation reflecting the two-site unit
cell of the antiferromagnetic background, in contrast to the predictions based
on a mean-field approximation and linear orbital-wave theory.Comment: 4 pages, 2 figures, submitted to SCES 2011 conference proceeding
Possibility to realize spin-orbit-induced correlated physics in iridium fluorides
Recent theoretical predictions of "unprecedented proximity" of the electronic
ground state of iridium fluorides to the SU(2) symmetric
limit, relevant for superconductivity in iridates, motivated us to investigate
their crystal and electronic structure. To this aim, we performed
high-resolution x-ray powder diffraction, Ir L-edge resonant inelastic
x-ray scattering, and quantum chemical calculations on Rb[IrF] and
other iridium fluorides. Our results are consistent with the Mott insulating
scenario predicted by Birol and Haule [Phys. Rev. Lett. 114, 096403 (2015)],
but we observe a sizable deviation of the state from the
SU(2) symmetric limit. Interactions beyond the first coordination shell of
iridium are negligible, hence the iridium fluorides do not show any magnetic
ordering down to at least 20 K. A larger spin-orbit coupling in iridium
fluorides compared to oxides is ascribed to a reduction of the degree of
covalency, with consequences on the possibility to realize spin-orbit-induced
strongly correlated physics in iridium fluorides
Absence of Hole Confinement in Transition Metal Oxides with Orbital Degeneracy
We investigate the spectral properties of a hole moving in a two-dimensional
Hubbard model for strongly correlated t_2g electrons. Although superexchange
interactions are Ising-like, a quasi-one-dimensional coherent hole motion
arises due to effective three-site terms. This mechanism is fundamentally
different from the hole motion via quantum fluctuations in the conventional
spin model with SU(2) symmetry. The orbital model describes also propagation of
a hole in some e_g compounds, and we argue that orbital degeneracy alone does
not lead to hole self-localization.Comment: 4 pages, 5 figure
Directly characterizing the relative strength and momentum dependence of electron-phonon coupling using resonant inelastic x-ray scattering
The coupling between lattice and charge degrees of freedom in condensed
matter materials is ubiquitous and can often result in interesting properties
and ordered phases, including conventional superconductivity, charge density
wave order, and metal-insulator transitions. Angle-resolved photoemission
spectroscopy and both neutron and non-resonant x-ray scattering serve as
effective probes for determining the behavior of appropriate, individual
degrees of freedom -- the electronic structure and lattice excitation, or
phonon dispersion, respectively. However, each provides less direct information
about the mutual coupling between the degrees of freedom, usual through
self-energy effects, which tend to renormalize and broaden spectral features
precisely where the coupling is strong, impacting ones ability to quantitively
characterize the coupling. Here we demonstrate that resonant inelastic x-ray
scattering, or RIXS, can be an effective tool to directly determine the
relative strength and momentum dependence of the electron-phonon coupling in
condensed matter systems. Using a diagrammatic approach for an 8-band model of
copper oxides, we study the contributions from the lowest order diagrams to the
full RIXS intensity for a realistic scattering geometry, accounting for matrix
element effects in the scattering cross-section as well as the momentum
dependence of the electron-phonon coupling vertex. A detailed examination of
these maps offers a unique perspective into the characteristics of
electron-phonon coupling, which complements both neutron and non-resonant x-ray
scattering, as well as Raman and infrared conductivity.Comment: 10 pages, 10 figure
Micro integration of optical components for the fabrication of active optical cables
Optical interconnects have become very interesting for short reach data transfer. We examine a new concept for integration and miniaturization of such systems based on recent experiments. The application of these designs is an active optical cable. The advantages of the concept and the employed technologies are presented
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