Mechanical Engineering
|
Open Access
Abstract: A common procurement strategy is to produce a fully optimised reference design that makes assumptions about the manufacturing process and supplier capability. This approach can restrict the opportunities for some companies to include their own specialist manufacturing capability to provide a more effective and cost efficient solution. A new approach is suggested following the recent experience at Diamond Light Source. The manufacture of high stiffness welded fabrications up to 13m in length for the I21 RIXS Spectrometer is used as an example. The I21 RIXS Spectrometer design was optimised for stiffness and control of vibration. The use of Finite Element Analysis enabled different design options and compromises to be explored utilising the supplier's capabilities. The final design was tested during manufacture to verify the FEA model. With the I21 RIXS Spectrometer commissioned the data collected shows the final stability performance of the system including detector stability over full experiment durations has met the scientific goals of the design.
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Dec 2018
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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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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Abstract: Resonant inelastic soft X-ray scattering (RIXS) [1, 2] is a powerful bulk-sensitive photon-in / photonout
spectroscopic and scattering probe of the electronic structure of condensed matter with elemental
sensitivity. It is a unique tool for studying low energy excitations in complex correlated systems, being
sensitive to charge-, orbital-, spin-, and lattice-degrees of freedom [3-7]. Dedicated instrumentation
for soft X-ray RIXS with ultra-high resolution in energy and momentum spaces has become available
thereby enabling characterization of collective excitations such as magnons and phonons. In this presentation
I will give a brief introduction of the I21-RIXS beamline which is currently under construction at
Diamond Light Source in the UK. Details of the key beamline performance, the optical design and the
mechanical designs are to be presented.
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Nov 2015
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Soonmin
Kang
,
Kangwon
Kim
,
Beom Hyun
Kim
,
Jonghyeon
Kim
,
Kyung Ik
Sim
,
Jae-ung
Lee
,
Sungmin
Lee
,
Kisoo
Park
,
Seokhwan
Yun
,
Taehun
Kim
,
Abhishek
Nag
,
Andrew
Walters
,
Mirian
Garcia-fernandez
,
Jiemin
Li
,
Laurent
Chapon
,
Ke-jin
Zhou
,
Young-woo
Son
,
Jae Hoon
Kim
,
Hyeonsik
Cheong
,
Je-geun
Park
Diamond Proposal Number(s):
[18503, 18906]
Abstract: An exciton is the bosonic quasiparticle of electron–hole pairs bound by the Coulomb interaction. Bose–Einstein condensation of this exciton state has long been the subject of speculation in various model systems and examples have been found more recently in optical lattices and two-dimensional materials. Unlike these conventional excitons formed from extended Bloch states, excitonic bound states from intrinsically many-body localized states are rare. Here we show that a spin–orbit-entangled exciton state appears below the Néel temperature of 150 kelvin in NiPS3, an antiferromagnetic van der Waals material. It arises intrinsically from the archetypal many-body states of the Zhang–Rice singlet, and reaches a coherent state assisted by the antiferromagnetic order. Using configuration-interaction theory, we determine the origin of the coherent excitonic excitation to be a transition from a Zhang–Rice triplet to a Zhang–Rice singlet. We combine three spectroscopic tools—resonant inelastic X-ray scattering, photoluminescence and optical absorption—to characterize the exciton and to demonstrate an extremely narrow excitonic linewidth below 50 kelvin. The discovery of the spin–orbit-entangled exciton in antiferromagnetic NiPS3 introduces van der Waals magnets as a platform to study coherent many-body excitons.
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Jul 2020
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Roberto
Fumagalli
,
Abhishek
Nag
,
Stefano
Agrestini
,
Mirian
Garcia-Fernandez
,
Andrew C.
Walters
,
Davide
Betto
,
Nicholas B.
Brookes
,
Lucio
Braicovich
,
Ke-Jin
Zhou
,
Giacomo
Ghiringhelli
,
Marco Moretti
Sala
Diamond Proposal Number(s):
[23423]
Abstract: Motivated by the recent synthesis of Ba
CuO
(BCO), a high temperature superconducting cuprate with putative
ground state symmetry, we investigated its electronic structure by means of Cu
x-ray absorption (XAS) and resonant inelastic x-ray scattering (RIXS) at the Cu
edge on a polycrystalline sample. We show that the XAS profile of BCO is characterised by two peaks associated to inequivalent Cu sites, and that its RIXS response features a single, sharp peak associated to crystal-field excitations. We argue that these observations are only partially compatible with the previously proposed crystal structure of BCO. Based on our spectroscopic results and on previously published powder diffraction measurements, we propose a crystalline structure characterized by two inequivalent Cu sites located at alternated planes along the
axis: nominally trivalent Cu(1) belonging to very short Cu-O chains, and divalent Cu(2) in the oxygen deficient CuO
planes. We also analyze the low-energy region of the RIXS spectra to estimate the magnitude of the magnetic interactions in BCO and find that in-plane nearest neighbor superexchange exceeds 120 meV, similarly to that of other layered cuprates. Although these results do not support the pure
ground state scenario, they hint at a significant departure from the common quasi-2D electronic structure of superconducting cuprates of pure
symmetry.
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Dec 2020
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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A.
Nag
,
M.
Zhu
,
M.
Bejas
,
J.
Li
,
H. C.
Robarts
,
H.
Yamase
,
A. N.
Petsch
,
D.
Song
,
H.
Eisaki
,
A. C.
Walters
,
M.
Garcia-Fernandez
,
A.
Greco
,
S. M.
Hayden
,
K.
Zhou
Diamond Proposal Number(s):
[24587]
Open Access
Abstract: High
T
c
superconductors show a rich variety of phases associated with their charge degrees of freedom. Valence charges can give rise to charge ordering or acoustic plasmons in these layered cuprate superconductors. While charge ordering has been observed for both hole- and electron-doped cuprates, acoustic plasmons have only been found in electron-doped materials. Here, we use resonant inelastic x-ray scattering to observe the presence of acoustic plasmons in two families of hole-doped cuprate superconductors (
La
1.84
Sr
0.16
CuO
4
and
Bi
2
Sr
1.6
La
0.4
CuO
6
+
δ
), crucially completing the picture. Interestingly, in contrast to the quasistatic charge ordering which manifests at both Cu and O sites, the observed acoustic plasmons are predominantly associated with the O sites, revealing a unique dichotomy in the behavior of valence charges in hole-doped cuprates.
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Dec 2020
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Jiaqi
Lin
,
Jie
Yuan
,
Kui
Jin
,
Zhiping
Yin
,
Gang
Li
,
Ke-jin
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)
|
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
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Diamond Proposal Number(s):
[23889]
Abstract: Li-rich cathode materials are potential candidates for next-generation Li-ion batteries. However, they exhibit a large voltage hysteresis on the first charge/discharge cycle, which involves a substantial (up to 1 V) loss of voltage and therefore energy density. For Na cathodes, for example Na0.75[Li0.25Mn0.75]O2, voltage hysteresis can be explained by the formation of molecular O2 trapped in voids within the particles. Here we show that this is also the case for Li1.2Ni0.13Co0.13Mn0.54O2. Resonant inelastic X-ray scattering and 17O magic angle spinning NMR spectroscopy show that molecular O2, rather than O22−, forms within the particles on the oxidation of O2− at 4.6 V versus Li+/Li on charge. These O2 molecules are reduced back to O2− on discharge, but at the lower voltage of 3.75 V, which explains the voltage hysteresis in Li-rich cathodes. 17O magic angle spinning NMR spectroscopy indicates a quantity of bulk O2 consistent with the O-redox charge capacity minus the small quantity of O2 loss from the surface. The implication is that O2, trapped in the bulk and lost from the surface, can explain O-redox.
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Sep 2020
|
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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.
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Dec 2019
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