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)
|
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)
|
Qisi
Wang
,
Karin
Von Arx
,
Masafumi
Horio
,
Deepak John
Mukkattukavil
,
Julia
Kuespert
,
Yasmine
Sassa
,
Thorsten
Schmitt
,
Abhishek
Nag
,
Sunseng
Pyon
,
Tomohiro
Takayama
,
Hidenori
Takagi
,
Mirian
Garcia-Fernandez
,
Ke-Jin
Zhou
,
Johan
Chang
Diamond Proposal Number(s):
[24481]
Open Access
Abstract: Charge order is universal to all hole-doped cuprates. Yet, the driving interactions remain an unsolved problem. Electron-electron interaction is widely believed to be essential, whereas the role of electron-phonon interaction is unclear. We report an ultrahigh-resolution resonant inelastic x-ray scattering (RIXS) study of the in-plane bond-stretching phonon mode in stripe-ordered cuprate La1.675Eu0.2Sr0.125CuO4. Phonon softening and lifetime shortening are found around the charge ordering wave vector. In addition to these self-energy effects, the electron-phonon coupling is probed by its proportionality to the RIXS cross section. We find an enhancement of the electron-phonon coupling around the charge-stripe ordering wave vector upon cooling into the low-temperature tetragonal structure phase. These results suggest that, in addition to electronic correlations, electron-phonon coupling contributes substantially to the emergence of long-range charge-stripe order in cuprates.
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Jun 2021
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|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Nimrod
Bachar
,
Kacper
Koteras
,
Jakub
Gawraczynski
,
Waldemar
Trzciński
,
Józef
Paszula
,
Riccardo
Piombo
,
Paolo
Barone
,
Zoran
Mazej
,
Giacomo
Ghiringhelli
,
Abhishek
Nag
,
Ke-Jin
Zhou
,
José
Lorenzana
,
Dirk
Van Der Marel
,
Wojciech
Grochala
Diamond Proposal Number(s):
[24869]
Open Access
Abstract: Charge-transfer insulators are the parent phase of a large group of today's unconventional high-temperature superconductors. Here we study experimentally and theoretically the interband excitations of the charge-transfer insulator silver fluoride
AgF
2
, which has been proposed as an excellent analog of oxocuprates. Optical conductivity and resonant inelastic x-ray scattering on
AgF
2
polycrystalline sample show a close similarity with that measured on undoped
La
2
CuO
4
. While the former shows a charge-transfer gap
∼
3.4
eV, larger than in the cuprate,
d
d
excitations are nearly at the same energy in the two materials. Density functional theory and exact diagonalization cluster computations of the multiplet spectra show that
AgF
2
is more covalent than the cuprate, in spite of the larger fundamental gap. Furthermore, we show that
AgF
2
is at the verge of a charge-transfer instability. The overall resemblance of our data on
AgF
2
to those published previously on
La
2
CuO
4
suggests that the underlying charge-transfer insulator physics is the same, while
AgF
2
could also benefit from a proximity to a charge density wave phase as in
BaBiO
3
. Therefore, our work provides a compelling support to the future use of fluoroargentates for materials' engineering of novel high-temperature superconductors.
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May 2022
|
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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.
|
Jul 2020
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Diamond Proposal Number(s):
[25589]
Open Access
Abstract: Layered Li-rich transition metal oxides undergo O-redox, involving the oxidation of the O2− ions charge compensated by extraction of Li+ ions. Recent results have shown that for 3d transition metal oxides the oxidized O2− forms molecular O2 trapped in the bulk particles. Other forms of oxidised O2− such as O22− or (O–O)n− with long bonds have been proposed, based especially on work on 4 and 5d transition metal oxides, where TM–O bonding is more covalent. Here, we show, using high resolution RIXS that molecular O2 is formed in the bulk particles on O2‒ oxidation in the archetypal Li-rich ruthenates and iridate compounds, Li2RuO3, Li2Ru0.5Sn0.5O3 and Li2Ir0.5Sn0.5O3. The results indicate that O-redox occurs across 3, 4, and 5d transition metal oxides, forming O2, i.e. the greater covalency of the 4d and 5d compounds still favours O2. RIXS and XAS data for Li2IrO3 are consistent with a charge compensation mechanism associated primarily with Ir redox up to and beyond the 5+ oxidation state, with no evidence of O–O dimerization.
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May 2021
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
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.
|
Dec 2020
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
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.
|
Dec 2020
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Diamond Proposal Number(s):
[25589]
Open Access
Abstract: Oxidation and reduction of the oxide ions in the bulk of cathode materials is a potential route towards increasing the energy density of Li-ion batteries. Here, we present neutron PDF data which demonstrates the presence of short 1.2 Å O–O distances in a charged O-redox cathode material, corresponding to the bond length of molecular O2. This was achieved by collecting our data close to absolute zero (2 K), suppressing thermal motion which may have obscured detection by PDF previously. This direct detection of molecular O2 trapped in the material by diffraction complements the X-ray spectroscopy studies by e.g. RIXS while avoiding issues of possible beam damage as well as being a bulk average technique.
|
Dec 2021
|
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