I21-Resonant Inelastic X-ray Scattering (RIXS)
|
A.
Nag
,
H. C.
Robarts
,
F.
Wenzel
,
J.
Li
,
H.
Elnaggar
,
R.-p.
Wang
,
A.
Walters
,
M.
Garcia-fernandez
,
F. M. F.
De Groot
,
M. W.
Haverkort
,
K.
Zhou
Open Access
Abstract: Understanding many-body physics of elementary excitations has advanced our control over material properties. Here, we study spin-flip excitations in NiO using Ni
L3-edge resonant inelastic x-ray scattering (RIXS) and present a strikingly different resonant energy behavior between single and double spin-flip excitations. Comparing our results with single-site full-multiplet ligand field theory calculations we find that the spectral weight of the double-magnon excitations originates primarily from the double spin-flip transition of the quadrupolar RIXS process within a single magnetic site. Quadrupolar spin-flip processes are among the least studied excitations, despite being important for multiferroic or spin-nematic materials due to their difficult detection. We identify intermediate state multiplets and intra-atomic core-valence exchange interactions as the key many-body factors determining the fate of such excitations. RIXS resonant energy dependence can act as a convincing proof of existence of nondipolar higher-ranked magnetic orders in systems for which, only theoretical predictions are available.
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Feb 2020
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
M.
Hepting
,
D.
Li
,
C. J.
Jia
,
H.
Lu
,
E.
Paris
,
Y.
Tseng
,
X.
Feng
,
M.
Osada
,
E.
Been
,
Y.
Hikita
,
Y.-d.
Chuang
,
Z.
Hussain
,
K. J.
Zhou
,
A.
Nag
,
M.
Garcia-fernandez
,
M.
Rossi
,
H. Y.
Huang
,
D. J.
Huang
,
Z. X.
Shen
,
T.
Schmitt
,
H. Y.
Hwang
,
B.
Moritz
,
J.
Zaanen
,
T. P.
Devereaux
,
W. S.
Lee
Diamond Proposal Number(s):
[22009]
Abstract: The search continues for nickel oxide-based materials with electronic properties similar to cuprate high-temperature superconductors. The recent discovery of superconductivity in the doped infinite-layer nickelate NdNiO2 has strengthened these efforts. Here, we use X-ray spectroscopy and density functional theory to show that the electronic structure of LaNiO2 and NdNiO2, while similar to the cuprates, includes significant distinctions. Unlike cuprates, the rare-earth spacer layer in the infinite-layer nickelate supports a weakly interacting three-dimensional 5d metallic state, which hybridizes with a quasi-two-dimensional, strongly correlated state with
3
d
x
2
−
y
2
3dx2−y2
symmetry in the NiO2 layers. Thus, the infinite-layer nickelate can be regarded as a sibling of the rare-earth intermetallics, which are well known for heavy fermion behaviour, where the NiO2 correlated layers play an analogous role to the 4f states in rare-earth heavy fermion compounds. This Kondo- or Anderson-lattice-like ‘oxide-intermetallic’ replaces the Mott insulator as the reference state from which superconductivity emerges upon doping.
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Jan 2020
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Jiaqi
Lin
,
Jie
Yuan
,
Kui
Jin
,
Zhiping
Yin
,
Gang
Li
,
Kejin
Zhou
,
Xingye
Lu
,
Marcus
Dantz
,
Thorsten
Schmitt
,
Hong
Ding
,
Haizhong
Guo
,
Mark P. M.
Dean
,
Xuerong
Liu
Open Access
Abstract: Electron correlations play a dominant role in the charge dynamics of the cuprates. We use resonant inelastic X-ray scattering (RIXS) to track the doping dependence of the collective charge excitations in electron doped La
2−x
2−x
Ce
x
x
CuO
4
4
(LCCO). From the resonant energy dependence and the out-of-plane momentum dependence, the charge excitations are identified as three-dimensional (3D) plasmons, which reflect the nature of the electronic structure and Coulomb repulsion on both short and long lengthscales. With increasing electron doping, the plasmon excitations increase monotonically in energy, a consequence of the electron correlation effect on electron structure near the Fermi surface (FS). Importantly, the plasmon excitations evolve from a broad feature into a well-defined peak with much increased life time, revealing the evolution of the electrons from incoherent states to coherent quasi-particles near the FS. Such evolution marks the reduction of the short-range electronic correlation, and thus the softening of the Mottness of the system with increasing electron doping.
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Jan 2020
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Robert A.
House
,
Urmimala
Maitra
,
Miguel A.
Pérez-osorio
,
Juan G.
Lozano
,
Liyu
Jin
,
James W.
Somerville
,
Laurent C.
Duda
,
Abhishek
Nag
,
Andrew
Walters
,
Kejin
Zhou
,
Matthew R.
Roberts
,
Peter G.
Bruce
Abstract: Alkali-rich transition metal oxide intercalation cathodes can increase the energy density of Li and Na-ion batteries by storing charge on the oxide and transition metal (TM) ions1–10. The high voltage associated with oxidation of O2- on the first charge is not recovered on discharge, resulting in significantly reduced energy density11. Displacement of TM ions from the TM to alkali metal layers has been proposed to explain the first cycle voltage loss9,12–16. By comparing two closely related intercalation cathodes, Na0.75[Li0.25Mn0.75]O2 and Na0.6[Li0.2Mn0.8]O2, we show that the first cycle voltage hysteresis is determined by the superstructure, specifically the local ordering of Li/TM ions in the TM layers. The honeycomb superstructure of Na0.75[Li0.25Mn0.75]O2, present in almost all O-redox compounds, is lost on charging, driven, in part, by formation of molecular O2 inside the solid. The O2 molecules are cleaved on discharge reforming O2-, but the Mn ions have migrated in the plane changing the coordination around O2- significantly lowering the voltage on discharge (hysteresis). The ribbon superstructure in Na0.6[Li0.2Mn0.8]O2 inhibits Mn disorder and hence O2 formation, suppressing hysteresis and promoting stable electron holes on O2- which are revealed by XAS. The results show that voltage hysteresis can be avoided in O-redox cathodes by forming materials with a superstructure (cation ordering) in the TM layers that suppresses TM migration.
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Dec 2019
|
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Diamond Proposal Number(s):
[18469, 18512]
Abstract: We report high-resolution resonant inelastic x-ray scattering (RIXS) measurements of the collective spin fluctuations in three compositions of the superconducting cuprate system
La
2
−
x
Sr
x
CuO
4
. We have mapped out the excitations throughout much of the two-dimensional
(
h
,
k
)
Brillouin zone. The spin fluctuations in
La
2
−
x
Sr
x
CuO
4
are found to be fairly well described by a damped harmonic oscillator model, thus our data allows us to determine the full wave vector dependence of the damping parameter. This parameter increases with doping and is largest along the
(
h
,
h
) line, where it is peaked near
(
0.2
,
0.2
)
. We have used a new procedure to determine the absolute wave vector dependent susceptibility for the doped compositions
La
2
−
x
Sr
x
CuO
4
(
x
=
0.12
,
0.16
)
by normalizing our data to
La
2
CuO
4
measurements made with inelastic neutron scattering (INS). We find that the evolution with doping of the intensity of high-energy excitations measured by RIXS and INS is consistent. For the doped compositions, the wave vector dependent susceptibility is much larger at
(
1
4
,
1
4
)
than at
(
1
2
,
0
)
. It increases rapidly along the
(
h
,
h
)
line towards the antiferromagnetic wave vector of the parent compound
(
1
2
,
1
2
)
. Thus, the strongest magnetic excitations, and those predicted to favor superconductive pairing, occur towards the
(
1
2
,
1
2
)
position as observed by INS.
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Dec 2019
|
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
J. G.
Vale
,
C. D.
Dashwood
,
E.
Paris
,
L. S. I.
Veiga
,
Mirian
Garcia-fernandez
,
A.
Nag
,
A.
Walters
,
K.
Zhou
,
I.-m.
Pietsch
,
Anton
Jesche
,
P.
Gegenwart
,
R.
Coldea
,
T.
Schmitt
,
D. F.
Mcmorrow
Diamond Proposal Number(s):
[20569]
Abstract: The excitations in honeycomb
α
−
Li
2
IrO
3
have been investigated with high-resolution resonant inelastic x-ray scattering (RIXS) at the O
K
edge. The low-energy response is dominated by a fully resolved ladder of excitations, which we interpret as being due to multiphonon processes in the presence of strong electron-phonon coupling (EPC). At higher energies, the orbital excitations are shown to be dressed by phonons. The high quality of the data permits a quantitative test of the analytical model for the RIXS cross section, which has been proposed to describe EPC in transition-metal oxides (TMOs). We find that the magnitude of the EPC is comparable to that found for a range of
3
d
TMOs. This indicates that EPC may be of equal importance in determining the phenomenology displayed by corresponding
5
d
-based systems.
|
Dec 2019
|
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B21-High Throughput SAXS
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Diamond Proposal Number(s):
[16028]
Abstract: Dihydrodipicolinate synthase (DHDPS) from Campylobacter jejuni is a natively homotetrameric enzyme that catalyzes the first unique reaction of (S)-lysine biosynthesis and is feedback-regulated by lysine through binding to an allosteric site. High-resolution structures of the DHDPS-lysine complex have revealed significant insights into the binding events. One key asparagine residue, N84, makes hydrogen bonds with both the carboxyl and the α-amino group of the bound lysine. We generated two mutants, N84A and N84D, to study the effects of these changes on the allosteric site properties. However, under normal assay conditions, N84A displayed notably lower catalytic activity, and N84D showed no activity. Here we show that these mutations disrupt the quaternary structure of DHDPS in a concentration-dependent fashion, as demonstrated by size-exclusion chromatography, multi-angle light scattering, dynamic light scattering, small-angle X-ray scattering (SAXS) and high-resolution protein crystallography.
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Oct 2019
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