I21-Resonant Inelastic X-ray Scattering (RIXS)
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Eleanor
Lawrence Bright
,
Lei
Xu
,
Lottie
Harding
,
Ross
Springell
,
Andrew
Walters
,
Martin
Sundermann
,
Mirian
Garcia-Fernandez
,
Stefano
Agrestini
,
Roberto
Caciuffo
,
Gerrit
Van Der Laan
,
Gerry H.
Lander
Diamond Proposal Number(s):
[29274]
Abstract: Resonant inelastic x-ray scattering (RIXS) using an incident energy tuned to the uranium N4,5 absorption edges is reported from epitaxial films of α-U3O8 and UN. Theory shows that for U3O8 the multiplets associated with a 5f1 configuration with a ground state of 2F5/2 and the excited state of 2F7/2 are observed. However, the strong transition predicted at a transfer energy of 1.67 eV is not observed. We assume this is a consequence of the intermediate state lifetime broadening due to interaction with continuum states when the transferred energy exceeds the onset of the continuum in the presence of the core hole. This hypothesis is supported by the results obtained for the 5f-itinerant system UN, where no sharp transitions have been observed, although the broad scattering response centered at ∼ 1 eV is considered a signature of a predominantly 5f3 configuration in this band-like semi-metallic system. These experiments and theory add important information on these materials, both of which have been investigated since the 1960s, as well as whether RIXS at the uranium N edge can become a valuable tool for actinide research.
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Feb 2023
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Optics
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Open Access
Abstract: Angle-resolved photoemission spectroscopy (ARPES) is a powerful method for measuring the electronic band structure of solids. Diamond Light Source is planning to build a multibend-achromat (MBA) synchrotron – Diamond-II - which will provide an almost diffraction-limited photon source in the vacuum-ultraviolet photon energy range. The improved emittance and higher coherence of MBA synchrotrons means that samples with features smaller than 1 µm can be readily studied using ARPES, provided the beamline is designed to take full advantage of the new photon source. We have developed an analytical method for optimising the optical design of a future Nano-ARPES beamline for Diamond-II. Our method enables one to explore large regions of parameter space for a beamline design in an unbiased and systematic way, with minimal requirements on computing power. We believe that the analytical method presented here will be a useful tool for synchrotron beamline designers, as it allows many beamline characteristics to be simulated quickly while working within any practical limitations.
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Dec 2022
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Abhishek
Nag
,
Yiran
Peng
,
Jiemin
Li
,
Stefano
Agrestini
,
Hannah C.
Robarts
,
Mirian
Garcia-Fernandez
,
Andrew C.
Walters
,
Qi
Wang
,
Qiangwei
Yin
,
Hechang
Lei
,
Zhiping
Yin
,
Ke-Jin
Zhou
Diamond Proposal Number(s):
[27905]
Open Access
Abstract: Among condensed matter systems, Mott insulators exhibit diverse properties that emerge from electronic correlations. In itinerant metals, correlations are usually weak, but can also be enhanced via geometrical confinement of electrons, that manifest as ‘flat’ dispersionless electronic bands. In the fast developing field of topological materials, which includes Dirac and Weyl semimetals, flat bands are one of the important components that can result in unusual magnetic and transport behaviour. To date, characterisation of flat bands and their magnetism is scarce, hindering the design of novel materials. Here, we investigate the ferromagnetic Kagomé semimetal Co3Sn2S2 using resonant inelastic X-ray scattering. Remarkably, nearly non-dispersive Stoner spin excitation peaks are observed, sharply contrasting with the featureless Stoner continuum expected in conventional ferromagnetic metals. Our band structure and dynamic spin susceptibility calculations, and thermal evolution of the excitations, confirm the nearly non-dispersive Stoner excitations as unique signatures of correlations and spin-polarized electronic flat bands in Co3Sn2S2. These observations serve as a cornerstone for further exploration of band-induced symmetry-breaking orders in topological materials.
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Nov 2022
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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U.
Kumar
,
A.
Nag
,
J.
Li
,
H. C.
Robarts
,
A. C.
Walters
,
M.
Garcia-Fernandez
,
R.
Saint-Martin
,
A.
Revcolevschi
,
J.
Schlappa
,
T.
Schmitt
,
Steven
Johnston
,
K.-J.
Zhou
Diamond Proposal Number(s):
[21184]
Abstract: Resonant inelastic x-ray scattering (RIXS) is an evolving tool for investigating the spin dynamics of strongly correlated materials, which complements inelastic neutron scattering. In isotropic spin-
1
2
Heisenberg antiferromagnetic (HAFM) spin chains, both techniques have observed non-spin-conserving (NSC) excitations confined to the two-spinon phase space. However, a recent O
K
-edge RIXS study of the one-dimensional HAFM
Sr
2
CuO
3
observed spin-conserving (SC) four-spinon excitations outside the two-spinon phase space. Here, we demonstrate that analogous four-spinon excitations can also be accessed at the Cu
L
3
edge in the related material
SrCuO
2
. Through detailed modeling, we establish that these excitations appear in both the SC and NSC channels of the Cu
L
3
edge, and are only captured by higher-order terms in the ultrashort core-hole lifetime expansion. Since these terms encode information about spin-spin correlations extending beyond nearest neighbors, our results offer different possibilities for studying nonlocal spin correlations in quantum magnets.
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Aug 2022
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Diamond Proposal Number(s):
[24593]
Open Access
Abstract: The microscopic origins of emergent behaviours in condensed matter systems are encoded in their excitations. In ordinary magnetic materials, single spin-flips give rise to collective dipolar magnetic excitations called magnons. Likewise, multiple spin-flips can give rise to multipolar magnetic excitations in magnetic materials with spin S ≥ 1. Unfortunately, since most experimental probes are governed by dipolar selection rules, collective multipolar excitations have generally remained elusive. For instance, only dipolar magnetic excitations have been observed in isotropic S = 1 Haldane spin systems. Here, we unveil a hidden quadrupolar constituent of the spin dynamics in antiferromagnetic S = 1 Haldane chain material Y2BaNiO5 using Ni L3-edge resonant inelastic x-ray scattering. Our results demonstrate that pure quadrupolar magnetic excitations can be probed without direct interactions with dipolar excitations or anisotropic perturbations. Originating from on-site double spin-flip processes, the quadrupolar magnetic excitations in Y2BaNiO5 show a remarkable dual nature of collective dispersion. While one component propagates as non-interacting entities, the other behaves as a bound quadrupolar magnetic wave. This result highlights the rich and largely unexplored physics of higher-order magnetic excitations.
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Apr 2022
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Yingying
Peng
,
Leonardo
Martinelli
,
Qizhi
Li
,
Matteo
Rossi
,
Matteo
Mitrano
,
Riccardo
Arpaia
,
Marco
Moretti Sala
,
Qiang
Gao
,
Xuefei
Guo
,
Gabriella Maria
De Luca
,
Andrew
Walters
,
Abhishek
Nag
,
Andi
Barbour
,
Genda
Gu
,
Jonathan
Pelliciari
,
Nicholas B.
Brookes
,
Peter
Abbamonte
,
Marco
Salluzzo
,
Xingjiang
Zhou
,
Ke-Jin
Zhou
,
Valentina
Bisogni
,
Lucio
Braicovich
,
Steven
Johnston
,
Giacomo
Ghiringhelli
Diamond Proposal Number(s):
[20012]
Abstract: While electron-phonon coupling (EPC) is crucial for Cooper pairing in conventional superconductors, its role in high-
T
c
superconducting cuprates is debated. Using resonant inelastic x-ray scattering at the oxygen
K
edge, we study the EPC in
Bi
2
Sr
2
Ca
Cu
2
O
8
+
δ
(Bi2212) and
Nd
1
+
x
Ba
2
−
x
Cu
3
O
7
−
δ
(NBCO) at different doping levels ranging from heavily underdoped (
p
=
0.07
) to overdoped (
p
=
0.21
). We analyze the data with a localized Lang-Firsov model that allows for the coherent excitations of two phonon modes. While electronic band dispersion effects are non-negligible, we are able to perform a study of the relative values of EPC matrix elements in these cuprate families. In the case of NBCO, the choice of the excitation energy allows us to disentangle modes related to the CuO chains and the
Cu
O
2
planes. Combining the results from the two families, we find the EPC strength decreases with doping at
q
∥
=
(
−
0.25
,
0
)
r.l.u., but has a nonmonotonic trend as a function of doping at smaller momenta. This behavior is attributed to the screening effect of charge carriers. We also find that the phonon intensity is enhanced in the vicinity of the charge-density-wave excitations while the extracted EPC strength appears to be less sensitive to their proximity. By performing a comparative study of two cuprate families, we are able to identify general trends in the EPC for the cuprates and provide experimental input to theories invoking a synergistic role for this interaction in
d
-wave pairing.
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Mar 2022
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Ke-Jin
Zhou
,
Andrew
Walters
,
Mirian
Garcia-Fernandez
,
Thomas
Rice
,
Matthew
Hand
,
Abhishek
Nag
,
Jiemin
Li
,
Stefano
Agrestini
,
Peter
Garland
,
Hongchang
Wang
,
Simon
Alcock
,
Ioana
Nistea
,
Brian
Nutter
,
Nicholas
Rubies
,
Giles
Knap
,
Martin
Gaughran
,
Fajin
Yuan
,
Peter
Chang
,
John
Emmins
,
George
Howell
Open Access
Abstract: The I21 beamline at Diamond Light Source is dedicated to advanced resonant inelastic X-ray scattering (RIXS) for probing charge, orbital, spin and lattice excitations in materials across condensed matter physics, applied sciences and chemistry. Both the beamline and the RIXS spectrometer employ divergent variable-line-spacing gratings covering a broad energy range of 280–3000 eV. A combined energy resolution of ∼35 meV (16 meV) is readily achieved at 930 eV (530 eV) owing to the optimized optics and the mechanics. Considerable efforts have been paid to the design of the entire beamline, particularly the implementation of the collection mirrors, to maximize the X-ray photon throughput. The continuous rotation of the spectrometer over 150° under ultra high vacuum and a cryogenic manipulator with six degrees of freedom allow accurate mappings of low-energy excitations from solid state materials in momentum space. Most importantly, the facility features a unique combination of the high energy resolution and the high photon throughput vital for advanced RIXS applications. Together with its stability and user friendliness, I21 has become one of the most sought after RIXS beamlines in the world.
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Mar 2022
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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C. D.
Dashwood
,
A.
Geondzhian
,
J. G.
Vale
,
A. C.
Pakpour-Tabrizi
,
C. A.
Howard
,
Q.
Faure
,
L. S. I.
Veiga
,
D.
Meyers
,
G. S.
Chiuzbaian
,
A.
Nicolaou
,
N.
Jaouen
,
R. B.
Jackman
,
A.
Nag
,
M.
Garcia-Fernandez
,
Ke-Jin
Zhou
,
A. C.
Walters
,
K.
Gilmore
,
D. F.
Mcmorrow
,
M. P. M.
Dean
Diamond Proposal Number(s):
[22695]
Open Access
Abstract: Interactions between electrons and lattice vibrations are responsible for a wide range of material properties and applications. Recently, there has been considerable interest in the development of resonant inelastic x-ray scattering (RIXS) as a tool for measuring electron-phonon (
e
-ph) interactions. Here, we demonstrate the ability of RIXS to probe the interaction between phonons and specific electronic states both near to, and away from, the Fermi level. We perform carbon
K
-edge RIXS measurements on graphite, tuning the incident x-ray energy to separately probe the interactions of the
π
∗
and
σ
∗
electronic states. Our high-resolution data reveal detailed structure in the multiphonon RIXS features that directly encodes the momentum dependence of the
e
-ph interaction strength. We develop a Green’s-function method to model this structure, which naturally accounts for the phonon and interaction-strength dispersions, as well as the mixing of phonon momenta in the intermediate state. This model shows that the differences between the spectra can be fully explained by contrasting trends of the
e
-ph interaction through the Brillouin zone, being concentrated at the
Γ
and
K
points for the
π
∗
states while being significant at all momenta for the
σ
∗
states. Our results advance the interpretation of phonon excitations in RIXS and extend its applicability as a probe of
e
-ph interactions to a new range of out-of-equilibrium situations.
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Dec 2021
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Jung-Hwa
Kim
,
Darren C.
Peets
,
Manfred
Reehuis
,
Peter
Adler
,
Andrey
Maljuk
,
Tobias
Ritschel
,
Morgan C.
Allison
,
Jochen
Geck
,
Jose R. L.
Mardegan
,
Pablo J.
Bereciartua Perez
,
Sonia
Francoual
,
Andrew
Walters
,
Thomas
Keller
,
Paula M.
Abdala
,
Philip
Pattison
,
Pinder
Dosanjh
,
Bernhard
Keimer
Open Access
Abstract: Since the discovery of charge disproportionation in the
FeO
2
square-lattice compound
Sr
3
Fe
2
O
7
by Mössbauer spectroscopy more than fifty years ago, the spatial ordering pattern of the disproportionated charges has remained “hidden” to conventional diffraction probes, despite numerous x-ray and neutron scattering studies. We have used neutron Larmor diffraction and Fe
K
-edge resonant x-ray scattering to demonstrate checkerboard charge order in the
FeO
2
planes that vanishes at a sharp second-order phase transition upon heating above 332 K. Stacking disorder of the checkerboard pattern due to frustrated interlayer interactions broadens the corresponding superstructure reflections and greatly reduces their amplitude, thus explaining the difficulty of detecting them by conventional probes. We discuss the implications of these findings for research on “hidden order” in other materials.
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Aug 2021
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Diamond Proposal Number(s):
[18469]
Open Access
Abstract: Resonant inelastic x-ray scattering (RIXS) is a powerful probe of elementary excitations in solids. It is now widely applied to study magnetic excitations. However, its complex cross section means that RIXS has been more difficult to interpret than inelastic neutron scattering (INS). Here we report
∼
37
meV resolution RIXS measurements of the magnetic excitations in
La
2
CuO
4
, the antiferromagnetic parent of one system of high-temperature superconductors. At high energies (
∼
2
eV), the RIXS spectra show angular-dependent
d
d
orbital excitations in agreement with previous RIXS studies but show new structure. They are interpreted with single-site multiplet calculations. At low energies (
≲
0.3
eV), we model the wave-vector-dependent single magnon RIXS intensity as the product of the calculated single-ion spin-flip RIXS cross section and the dynamical structure factor
S
(
Q
,
ω
)
of the spin-wave excitations. When
S
(
Q
,
ω
)
is extracted from our data, the wave-vector-dependence of the single-magnon pole intensity shows a similar variation to that observed by INS. Our results confirm that suitably corrected RIXS data can yield the genuine wave-vector and energy dependence of
S
(
Q
,
ω
)
for a cuprate antiferromagnet. In addition to spin waves, our data show structured multimagnon excitations with dispersing peaks in the intensity at energies higher than the single-magnon excitations.
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Jun 2021
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