868 research outputs found
Deterministic quantum state transfer from an electronic charge qubit to a photonic polarization qubit
Building on an earlier proposal for the production of polarization-entangled
microwaves by means of intraband transitions in a pair of quantum dots, we show
how this device can be used to transfer an unknown single-qubit state from
electronic charge to photonic polarization degrees of freedom. No postselection
is required, meaning that the quantum state transfer happens deterministically.
Decoherence of the charge qubit causes a non-monotonic decay of the fidelity of
the transferred state with increasing decoherence rate.Comment: 3 pages, 3 figure
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
Ultrashort Lifetime Expansion for Indirect Resonant Inelastic X-ray Scattering
In indirect resonant inelastic X-ray scattering (RIXS) an intermediate state
is created with a core-hole that has a ultrashort lifetime. The core-hole
potential therefore acts as a femtosecond pulse on the valence electrons. We
show that this fact can be exploited to integrate out the intermediate states
from the expressions for the scattering cross section. By this we obtain an
effective scattering cross section that only contains the initial and final
scattering states. We derive in detail the effective cross section which turns
out to be a resonant scattering factor times a linear combination of the charge
response function and the dynamic longitudinal spin density
correlation function. This result is asymptotically exact for both strong and
weak local core-hole potentials and ultrashort lifetimes. The resonant
scattering pre-factor is shown to be weakly temperature dependent. We also
derive a sum-rule for the total scattering intensity and generalize the results
to multi-band systems. One of the remarkable outcomes is that one can change
the relative charge and spin contribution to the inelastic spectral weight by
varying the incident photon energy.Comment: 9 pages, 3 figures embedde
Resonant Inelastic X-ray Scattering on Spin-Orbit Coupled Insulating Iridates
We determine how the elementary excitations of iridium-oxide materials, which
are dominated by a strong relativistic spin-orbit coupling, appear in Resonant
Inelastic X-ray Scattering (RIXS). Whereas the RIXS spectral weight at the L2
x-ray edge vanishes, we find it to be strong at the L3-edge. Applying this to
Sr2IrO4, we observe that RIXS, besides being sensitive to local doublet to
quartet transitions, meticulously maps out the strongly dispersive delocalized
excitations of the low-lying spin-orbit doublets.Comment: 4 pages, 3 figure
Magnetic Excitations in La2CuO4 probed by Indirect Resonant Inelastic X-ray Scattering
Recent experiments on LaCuO suggest that indirect resonant inelastic
X-ray scattering (RIXS) might provide a probe for transversal spin dynamics. We
present in detail a systematic expansion of the relevant magnetic RIXS cross
section by using the ultrashort core-hole lifetime (UCL) approximation. We
compute the scattering intensity and its momentum dependence in leading order
of the UCL expansion. The scattering is due to two-magnon processes and is
calculated within a linear spin-wave expansion of the Heisenberg spin model for
this compound, including longer range and cyclic spin interactions. We observe
that the latter terms in the Hamiltonian enhance the first moment of the
spectrum if they strengthen the antiferromagnetic ordering. The theoretical
spectra agree very well with experimental data, including the observation that
scattering intensity vanishes for the transferred momenta and
. We show that at finite temperature there is an
additional single-magnon contribution to the scattering with a spectral weight
proportional to . We also compute the leading corrections to the UCL
approximation and find them to be small, putting the UCL results on a solid
basis. All this univocally points to the conclusion that the observed low
temperature RIXS intensity in LaCuO is due to two-magnon scattering.Comment: 11 pages, 13 figures, Phys. Rev. B 77, 134428 (2008) (v4: corrected
figs 7
Electrostatic attraction of nanoobjects - a versatile strategy towards mesostructured transition metal compounds
This highlight summarizes current challenges of mesostructuring and focuses on the scope and the potential of the ELAN – (electrostatic attraction of nanoobjects) strategy in mesostructuring of transition metal compounds. It discusses the limitations of this concept and highlights prominent examples. ELAN exploits the Coulomb attraction between inorganic precursors and polymeric templates in order to prevent macrophase separation. Essential requirements for ELAN are tailor-made, mesoscopic polyelectrolytic templates and charged molecular oligo-ions or stable colloids carrying a surface charge. The ELAN-strategy is highly reliable and opens the way to crystalline, mesoporous transition metal compounds with predefined polymorphism. It also provides the possibility to adjust wall chemistry and reactivity as well as the flexibility to synthesise different mesostructures (spheres, non-woven arrays or hexagonally ordered phases)
Bimagnon studies in cuprates with Resonant Inelastic X-ray Scattering at the O K edge. I - An assessment on La2CuO4 and a comparison with the excitation at Cu L3 and Cu K edges
We assess the capabilities of magnetic Resonant Inelastic X-ray Scattering
(RIXS) at the O edge in undoped cuprates by taking La_{2}CuO_{4} as a
benchmark case, based on a series of RIXS measurements that we present here. By
combining the experimental results with basic theory we point out the
fingerprints of bimagnon in the O edge RIXS spectra. These are a dominant
peak around 450 meV, the almost complete absence of dispersion both with
and polarization and the almost constant intensity vs. the transferred
momentum with polarization. This behavior is quite different from Cu
edge RIXS giving a strongly dispersing bimagnon tending to zero at the
center of the Brillouin zone. This is clearly shown by RIXS measurements at the
Cu edge that we present. The Cu bimagnon spectra and those at Cu
edge - both from the literature and from our data - however, have the same
shape. These similarities and differences are understood in terms of different
sampling of the bimagnon continuum. This panorama points out the unique
possibilities offered by O RIXS in the study of magnetic excitations in
cuprates near the center of the BZ
Momentum dependence of orbital excitations in Mott-insulating titanates
High-resolution resonant inelastic x-ray scattering has been used to
determine the momentum dependence of orbital excitations in Mott-insulating
LaTiO and YTiO over a wide range of the Brillouin zone. The data are
compared to calculations in the framework of lattice-driven and
superexchange-driven orbital ordering models. A superexchange model in which
the experimentally observed modes are attributed to two-orbiton excitations
yields the best description of the data.Comment: to appear in PR
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