2,166 research outputs found
Determining the Electron-Phonon Coupling Strength in Correlated Electron Systems from Resonant Inelastic X-ray Scattering
We show that high resolution Resonant Inelastic X-ray Scattering (RIXS)
provides direct, element-specific and momentum-resolved information on the
electron-phonon (e-p) coupling strength. Our theoretical analysis demonstrates
that the e-p coupling can be extracted from RIXS spectra by determining the
differential phonon scattering cross section. An alternative, very direct
manner to extract the coupling is to use the one and two-phonon loss ratio,
which is governed by the e-p coupling strength and the core-hole life-time.
This allows measurement of the e-p coupling on an absolute energy scale.Comment: 4 pages, 3 figure
Mediated tunable coupling of flux qubits
It is sketched how a monostable rf- or dc-SQUID can mediate an inductive
coupling between two adjacent flux qubits. The nontrivial dependence of the
SQUID's susceptibility on external flux makes it possible to continuously tune
the induced coupling from antiferromagnetic (AF) to ferromagnetic (FM). In
particular, for suitable parameters, the induced FM coupling can be
sufficiently large to overcome any possible direct AF inductive coupling
between the qubits.
The main features follow from a classical analysis of the multi-qubit
potential. A fully quantum treatment yields similar results, but with a
modified expression for the SQUID susceptibility.
Since the latter is exact, it can also be used to evaluate the
susceptibility--or, equivalently, energy-level curvature--of an isolated
rf-SQUID for larger shielding and at degenerate flux bias, i.e., a (bistable)
qubit. The result is compared to the standard two-level (pseudospin) treatment
of the anticrossing, and the ensuing conclusions are verified numerically.Comment: REVTeX 4, 16 pp., 4 EPS figures. N.B.: "Alec" is my first, and
"Maassen van den Brink" my family name. v2: major expansion and rewriting,
new title and co-author; to appear in New Journal of Physics special issue
(R. Fazio, ed.
Orbital excitations in LaMnO
We study the recently observed orbital excitations, orbitons, and treat
electron-electron correlations and lattice dynamics on equal footing. It is
shown that the orbiton energy and dispersion are determined by both
correlations and lattice-vibrations. The electron-phonon coupling causes
satellite structures in the orbiton spectral function and the elementary
excitations of the system are mixed modes with both orbital and phonon
character. It is proposed that the satellite structures observed in recent
Raman-scattering experiments on LaMnO are actually orbiton derived
satellites in the phonon spectral function, caused by the phonon-orbiton
interaction.Comment: 4 pages, 3 figures embedde
Excitonic quasiparticles in a spin-orbit Mott insulator
In condensed matter systems, out of a large number of interacting degrees of
freedom emerge weakly coupled particles, in terms of which most physical
properties are described. For example, Landau quasiparticles (QP) determine all
electronic properties of a normal metal. The lack of identification of such QPs
is major barrier for understanding myriad exotic properties of correlated
electrons, such as unconventional superconductivity and non-Fermi liquid
behaviours. Here, we report the observation of a composite particle in a Mott
insulator Sr2IrO4---and exciton dressed with magnons---that propagates with the
canonical characteristics of a QP: a finite QP residue and a lifetime longer
than the hopping time scale. The dynamics of this charge-neutral bosonic
excitation mirrors the fundamental process of the analogous one-hole
propagation in the background of ordered spins, for which a well-defined QP has
never been observed. The much narrower linewidth of the exciton reveals the
same intrinsic dynamics that is obscured for the hole and is intimately related
to the mechanism of high temperature superconductivity.Comment: submitted versio
Reentrant metallic transition at a temperature above Tc at the breakdown of cooperative Jahn-Teller orbital order in perovskite manganites
We report an interesting reentrant metallic resistivity pattern beyond a
characteristic temperature T* which is higher than other such characteristic
transition temperatures like T(c)(Curie point), T(N) (Neel point), T(CO)
(charge order onset point) or T(OO) (orbital order onset point) in a range of
rare-erath perovskite manganites (RE(1-x)A(x)MnO(3); RE = La, Nd, Y; A = Sr,
Ca; x = 0.0-0.5). Such a behavior is normally observed in doped manganites with
doping level (x) higher than the critical doping level x(c) (= 0.17-0.22)
required for the metallic ground state to emerge and hence in a system where
cooperative Jahn-Teller orbital order has already undergone a breakdown.
However, the observation made in the La(1-x)Ca(x)MnO(3) (x = 0.0-0.5) series
turns out to be an exception to this general trend.Comment: 15 pages including 3 figures; pdf onl
Establishing the fundamental magnetic interactions in the chiral skyrmionic Mott insulator Cu2OSeO3 by terahertz electron spin resonance
The recent discovery of skyrmions in CuOSeO has established a new
platform to create and manipulate skyrmionic spin textures. We use high-field
electron spin resonance (ESR) spectroscopy combining a terahertz free electron
laser and pulsed magnetic fields up to 64 T to probe and quantify its
microscopic spin-spin interactions. Besides providing direct access to the
long-wavelength Goldstone mode, this technique probes also the high-energy part
of the excitation spectrum which is inaccessible by standard low-frequency ESR.
Fitting the behavior of the observed modes in magnetic field to a theoretical
framework establishes experimentally that the fundamental magnetic building
blocks of this skyrmionic magnet are rigid, highly entangled and weakly coupled
tetrahedra.Comment: 5 pages, 3 Figure
New light on magnetic excitations: indirect resonant inelastic X-ray scattering on magnons
Recent experiments show that indirect resonant inelastic X-ray scattering
(RIXS) is a new probe of spin dynamics. Here I derive the cross-section for
magnetic RIXS and determine the momentum dependent four-spin correlation
function that it measures. These results show that this technique offers
information on spin dynamics that is complementary to e.g. neutron scattering.
The RIXS spectrum of Heisenberg antiferromagnets is calculated. It turns out
that only scattering processes that involve at least two magnons are allowed.
Other selection rules imply that the scattering intensity vanishes for specific
transferred momenta , in particular for . The calculated
spectra agree very well with the experimental data.Comment: 4 pages, 3 figure
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