55 research outputs found
Role of the Ce valence in the coexistence of superconductivity and ferromagnetism of CeOFBiS revealed by Ce -edge x-ray absorption spectroscopy
We have performed Ce -edge x-ray absorption spectroscopy (XAS)
measurements on CeOFBiS, in which the superconductivity of the
BiS layer and the ferromagnetism of the CeOF layer are induced
by the F-doping, in order to investigate the impact of the F-doping on the
local electronic and lattice structures. The Ce -edge XAS spectrum of
CeOBiS exhibits coexistence of (Ce) and (Ce)
state transitions revealing Ce mixed valency in this system. The spectral
weight of the state decreases with the F-doping and completely
disappears for where the system shows the superconductivity and the
ferromagnetism. The results suggest that suppression of Ce-S-Bi coupling
channel by the F-doping appears to drive the system from the valence
fluctuation regime to the Kondo-like regime, leading to the coexistence of the
superconducting BiS layer and the ferromagnetic CeOF layer.Comment: 5 pages, 5 figure
Orbital-selective confinement effect of Ru orbitals in SrRuO ultrathin film
The electronic structure of SrRuO thin film with thickness from 50 to 1
unit cell (u.c.) is investigated via the resonant inelastic x-ray scattering
(RIXS) technique at the O K-edge to unravel the intriguing interplay of orbital
and charge degrees of freedom. We found that orbital-selective quantum
confinement effect (QCE) induces the splitting of Ru orbitals. At the same
time, we observed a clear suppression of the electron-hole continuum across the
metal-to-insulator transition (MIT) occurring at the 4 u.c. sample. From these
two clear observations we conclude that QCE gives rise to a Mott insulating
phase in ultrathin SrRuO films. Our interpretation of the RIXS spectra is
supported by the configuration interaction calculations of RuO clusters.Comment: 7 pages, 7 figure
Terahertz displacive excitation of a coherent Raman-active phonon in V2O3
Nonlinear processes involving frequency-mixing of light fields set the basis for ultrafast coherent spectroscopy of collective modes in solids. In certain semimetals and semiconductors, generation of coherent phonon modes can occur by a displacive force on the lattice at the difference-frequency mixing of a laser pulse excitation on the electronic system. Here, as a low-frequency counterpart of this process, we demonstrate that coherent phonon excitations can be induced by the sum-frequency components of an intense terahertz light field, coupled to intraband electronic transitions. This nonlinear process leads to charge-coupled coherent dynamics of Raman-active phonon modes in the strongly correlated metal VO. Our results show an alternative up-conversion pathway for the optical control of Raman-active modes in solids mediated by terahertz-driven electronic excitation
Strain-engineering of the charge and spin-orbital interactions in Sr2IrO4
In the high spin-orbit coupled Sr2IrO4, the high sensitivity of the ground
state to the details of the local lattice structure shows a large potential for
the manipulation of the functional properties by inducing local lattice
distortions. We use epitaxial strain to modify the Ir-O bond geometry in
Sr2IrO4 and perform momentum-dependent Resonant Inelastic X-ray Scattering
(RIXS) at the metal and at the ligand sites to unveil the response of the low
energy elementary excitations. We observe that the pseudospin-wave dispersion
for tensile-strained Sr2IrO4 films displays large softening along the [h,0]
direction, while along the [h,h] direction it shows hardening. This evolution
reveals a renormalization of the magnetic interactions caused by a
strain-driven crossover from anisotropic to isotropic interactions between the
magnetic moments. Moreover, we detect dispersive electron-hole pair excitations
which shift to lower (higher) energies upon compressive (tensile) strain,
manifesting a reduction (increase) in the size of the charge gap. This behavior
shows an intimate coupling between charge excitations and lattice distortions
in Sr2IrO4, originating from the modified hopping elements between the t2g
orbitals. Our work highlights the central role played by the lattice degrees of
freedom in determining both the pseudospin and charge excitations of Sr2IrO4
and provides valuable information towards the control of the ground state of
complex oxides in the presence of high spin-orbit coupling.Comment: Published in Proceedings of the National Academy of Sciences,
September 202
Collective nature of orbital excitations in layered cuprates in the absence of apical oxygens
We have investigated the 3d orbital excitations in CaCuO2 (CCO), Nd2CuO4
(NCO) and La2CuO4 (LCO) using high-resolution resonant inelastic x-ray
scattering. In LCO they behave as well-localized excitations, similarly to
several other cuprates. On the contrary, in CCO and NCO the dxy orbital clearly
disperse, pointing to a collective character of this excitation (orbiton) in
compounds without apical oxygen. We ascribe the origin of the dispersion as
stemming from a substantial next-nearest-neighbor (NNN) orbital superexchange.
Such an exchange leads to the liberation of orbiton from its coupling to
magnons, which is associated with the orbiton hopping between nearest neighbor
copper sites. We show that the exceptionally large NNN orbital superexchange
can be traced back to the absence of apical oxygens suppressing the charge
transfer energy.Comment: 18 pages, 7 figure
Differential cross sections and spin density matrix elements for the reaction gamma p -> p omega
High-statistics differential cross sections and spin density matrix elements
for the reaction gamma p -> p omega have been measured using the CLAS at
Jefferson Lab for center-of-mass (CM) energies from threshold up to 2.84 GeV.
Results are reported in 112 10-MeV wide CM energy bins, each subdivided into
cos(theta_CM) bins of width 0.1. These are the most precise and extensive omega
photoproduction measurements to date. A number of prominent structures are
clearly present in the data. Many of these have not previously been observed
due to limited statistics in earlier measurements
First measurement of direct photoproduction on the proton
We report on the results of the first measurement of exclusive
meson photoproduction on protons for GeV and GeV. Data were collected with the CLAS detector at the Thomas
Jefferson National Accelerator Facility. The resonance was detected via its
decay in the channel by performing a partial wave analysis of the
reaction . Clear evidence of the meson
was found in the interference between and waves at GeV. The -wave differential cross section integrated in the mass range of
the was found to be a factor of 50 smaller than the cross section
for the meson. This is the first time the meson has been
measured in a photoproduction experiment
Partial wave analysis of the reaction gamma p -> p omega$ and the search for nucleon resonances
An event-based partial wave analysis (PWA) of the reaction gamma p -> p omega
has been performed on a high-statistics dataset obtained using the CLAS at
Jefferson Lab for center-of-mass energies from threshold up to 2.4 GeV. This
analysis benefits from access to the world's first high precision spin density
matrix element measurements, available to the event-based PWA through the decay
distribution of omega-> pi+ pi - pi0. The data confirm the dominance of the
t-channel pi0 exchange amplitude in the forward direction. The dominant
resonance contributions are consistent with the previously identified states
F[15](1680) and D[13](1700) near threshold, as well as the G[17](2190) at
higher energies. Suggestive evidence for the presence of a J(P)=5/2(+) state
around 2 GeV, a "missing" state, has also been found. Evidence for other states
is inconclusive
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