I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Marli R.
Cantarino
,
Rafael M. P.
Teixeira
,
Kevin R.
Pakuszewski
,
Wagner R.
Da Silva Neto
,
Juliana G.
De Abrantes
,
Mirian
Garcia-Fernandez
,
Pascoal G.
Pagliuso
,
Cris
Adriano
,
Claude
Monney
,
Thorsten
Schmitt
,
Eric C.
Andrade
,
Fernando A.
Garcia
Diamond Proposal Number(s):
[33194]
Open Access
Abstract: In doped Hund's metals, such as the iron-based superconductors, effects like charge doping and chemical pressure are often considered the dominant factors. Partial chemical substitution, however, inevitably introduces disorder. Here, we investigate spin excitations in Ba(Fe1−𝑥Cr𝑥)2As2 (CrBFA) by high-resolution resonant inelastic x-ray scattering for samples with 𝑥=0,0.035, and 0.085. In CrBFA, Cr acts as a hole dopant, but also introduces localized spins that compete with Fe-derived magnetic excitations. We found that the Fe-derived magnetic excitations are softened and damped, becoming overdamped for 𝑥=0.085. At this doping level, complementary angle-resolved photoemission spectroscopy measurements show increased electronic localization and a suppression of the nematic 𝑑𝑥𝑧/𝑑𝑦𝑧 band splitting present in the parent compound. We thus propose a localized spin model that explicitly incorporates substitutional disorder and Cr local moments, successfully reproducing our key observations. Our findings reveal a case where disorder dominates over charge doping in the case of a Hund's metal.
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Feb 2026
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I09-Surface and Interface Structural Analysis
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Trung-Phuc
Vo
,
Olena
Tkach
,
Aki
Pulkkinen
,
Didier
Sébilleau
,
Aimo
Winkelmann
,
Olena
Fedchenko
,
Yaryna
Lytvynenko
,
Dmitry
Vasilyev
,
Hans-Joachim
Elmers
,
Gerd
Schoenhense
,
Jan
Minar
Diamond Proposal Number(s):
[33765]
Open Access
Abstract: The intricate fine structure of Kikuchi diffraction plays a vital role in probing phase transformations and strain distributions in functional materials, particularly in electron microscopy. Beyond these applications, it also proves essential in photoemission spectroscopy (PES) at high photon energies, aiding in the disentanglement of complex angle-resolved PES data and enabling emitter-site-specific studies. However, the detection and analysis of these rich faint structures in photoelectron diffraction, especially in the hard x-ray regime, remain highly challenging, with only a limited number of simulations successfully reproducing these patterns. The strong energy dependence of Kikuchi patterns further complicates their interpretation, necessitating advanced theoretical approaches. To enhance structural analysis, we present a comprehensive theoretical study of fine diffraction patterns and their evolution with energy by simulating core-level emissions from Ge(100) and Si(100). Using multiple-scattering theory and the fully relativistic one-step photoemission model, we simulate faint pattern networks for various core levels across different kinetic energies (106–4174 eV), avoiding cluster size convergence issues inherent in cluster-based methods. Broadening in patterns is discussed via the inelastic scattering treatment. For the first time, circular dichroism has been observed and successfully reproduced in the angular distribution of Si(100) 1𝑠, revealing detailed features and asymmetries up to 31%. Notably, we successfully replicate experimental bulk and more “surface-sensitivity” diffraction features, further validating the robustness of our simulations. The results show remarkable agreement with the experimental data obtained using circularly polarized radiations, demonstrating the potential of this methodology for advancing high-energy PES investigations.
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Feb 2026
|
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I19-Small Molecule Single Crystal Diffraction
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S.
Chicco
,
E.
Garlatti
,
A.
Mavromagoulos
,
A. B.
Canaj
,
P.
Bonfà
,
A.
Piovano
,
S.
Dey
,
H.
Little
,
A.
Chiesa
,
A. S.
Ivanov
,
I. J.
Onuorah
,
S.
Parsons
,
G.
Rajaraman
,
Tatiana
Guidi
,
M.
Murrie
,
S.
Carretta
Diamond Proposal Number(s):
[16139]
Open Access
Abstract: Molecular nanomagnets have garnered significant attention in recent years thanks to their unique potential in quantum information processing as molecular qudits and in high-density memory encoding as single-molecule magnets. However, fully unlocking the potential of these systems requires a comprehensive understanding of the interplay between the various mechanisms that govern their relaxation dynamics, which remains a noncompletely understood phenomenon. In this work, we employ a cost-effective semi-ab initio approach to model the magnetization relaxation dynamics in a testbed Dy-based single-molecule magnet and determine the effects of applied external pressure on the interplay between various mechanisms, such as coupling with molecular vibrations and quantum tunneling. Ab initio phonon calculations are validated by direct comparison with inelastic neutron scattering experiments, which are used for the first time to investigate pressure-induced modifications of phonons and vibrations in a molecular nanomagnet. The combination of our theoretical approach with different experimental techniques allows us to predict an overall acceleration of the relaxation dynamics under pressure, disentangling the role of different ingredients, such as crystal field axiality and phonons.
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Jan 2026
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|
|
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B.
Decrausaz
,
M.
Pikulski
,
O.
Ivashko
,
N. B.
Christensen
,
J.
Choi
,
L.
Udby
,
K.
Lefmann
,
H. M.
Ronnow
,
J.
Mesot
,
J.
Ollivier
,
T.
Kurosawa
,
N.
Momono
,
M.
Oda
,
J.
Chang
,
D. G.
Mazzone
,
C.
Niedermayer
Open Access
Abstract: Quantum matter phases may coexist microscopically even when they display competing tendencies. A fundamental question is whether such a competition can be avoided through the elimination of one phase while the other one condenses into the ground state. Here, we present a high-resolution neutron spectroscopy study of the low-energy spin excitations in the high-temperature superconductor La1.855Sr0.145CuO4. In the normal state, we find low-energy magnetic fluctuations at incommensurate reciprocal lattice positions where spin-density-wave order emerges at lower Sr concentration or at high magnetic fields. While these spin excitations are largely suppressed by the emergence of the superconducting spin gap, some low-energy magnetic fluctuations persist deep inside the superconducting state. We interpret this result in terms of a dynamic competition between superconductivity and magnetism, where superconductivity impedes the condensation of low-energy magnetic fluctuations through the formation of magnetically mediated Cooper pairs.
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May 2025
|
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Diamond Proposal Number(s):
[26777]
Open Access
Abstract: Resonant inelastic x-ray scattering (RIXS) has become a prominent technique to study quasiparticle excitations. With advances in polarization analysis capabilities at different facilities, RIXS offers exceptional potential for investigating symmetry-broken quasiparticles such as chiral phonons and magnons. At optical wavelengths, birefringence can severely affect polarization states in low-symmetry systems. Here we show its importance for soft x-ray resonances. Given the growing interest in circular dichroism (CD) in RIXS, it is important to evaluate how birefringence may affect the RIXS spectra of anisotropic systems. We investigate CuO, a well-known anisotropic material, using Cu 𝐿3-edge RIXS and detect significant CD in both magnetic and orbital excitations in the collinear antiferromagnetic phase. We demonstrate that the CD can be modeled by a proper treatment of RIXS scattering amplitudes derived from single-ion calculations with birefringence. Recognizing these effects is crucial for unambiguous identification of subtle dichroic effects induced by symmetry-broken quasiparticles. Furthermore, the combined sensitivity of RIXS and birefringence to local symmetry presents an opportunity to study microscopic changes driven by external perturbations.
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May 2025
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I13-2-Diamond Manchester Imaging
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Diamond Proposal Number(s):
[17971]
Open Access
Abstract: We propose an imaging system and methodology for mapping soft-tissue samples in three dimensions, with micron-scale and isotropic spatial resolution, with low-concentrations as well as in the absence of heavy metal staining. We used hard x-ray phase-contrast imaging for the x-ray ability to nondestructively probe the internal structure of opaque specimens and for enhanced contrast obtained by exploiting phase effects, even in cases with reduced or absent staining agents. To demonstrate its applicability to soft-tissue specimens, we built a compact system that is easily deployable in a laboratory setting. The imaging system is based on a conventional rotating anode x-ray tube and a state-of-the-art custom-made radiation detector. The systems performance is quantitatively assessed on a calibration standard. Its potential for soft-tissue microscopy is demonstrated on two biological specimens and benchmarked against gold-standard synchrotron data. We believe that the approach proposed here can be valuable as a bridging imaging modality for intravital correlative light and electron microscopy and be applied across disciplines where the three-dimensional morphology of pristine-condition soft tissues is a key element of the investigation.
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Jan 2025
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
A.
Nag
,
L.
Zinni
,
J.
Choi
,
J.
Li
,
S.
Tu
,
A. C.
Walters
,
S.
Agrestini
,
S. M.
Hayden
,
Matías
Bejas
,
Z.
Lin
,
H.
Yamase
,
K.
Jin
,
M.
Garcia-Fernandez
,
J.
Fink
,
Andrés
Greco
,
Ke-Jin
Zhou
Diamond Proposal Number(s):
[27872]
Open Access
Abstract: Estimating many-body effects that deviate from an independent particle approach has long been a key research interest in condensed matter physics. Layered cuprates are prototypical systems, where electron-electron interactions are found to strongly affect the dynamics of single-particle excitations. It is, however, still unclear how the electron correlations influence charge excitations, such as plasmons, which have been variously treated with either weak or strong correlation models. In this work, we demonstrate the hybridized nature of collective valence charge fluctuations leading to dispersing acoustic-like plasmons in hole-doped La1.84Sr0.16CuO4 and electron-doped La1.84Ce0.16CuO4 using the two-particle probe, resonant inelastic x-ray scattering. We then describe the plasmon dispersions in both systems, within both the weak-coupling mean-field random phase approximation (RPA) and strong-coupling 𝑡−𝐽−𝑉 model in a large-𝑁 scheme. The 𝑡−𝐽−𝑉 model, which includes the correlation effects implicitly, accurately describes the plasmon dispersions as resonant excitations outside the single-particle intraband continuum. In comparison, a quantitative description of the plasmon dispersion in the RPA approach is obtained only upon explicit consideration of renormalized electronic band parameters. Our comparative analysis shows that electron correlations significantly impact the low-energy plasmon excitations across the cuprate doping phase diagram, even at long wavelengths. Thus, complementary information on the evolution of electron correlations, influenced by the rich electronic phases in condensed matter systems, can be extracted through the study of two-particle charge response.
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Nov 2024
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I10-Beamline for Advanced Dichroism - scattering
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M. T.
Littlehales
,
S. H.
Moody
,
P. J.
Bereciartua
,
D. A.
Mayoh
,
Z. B.
Parkin
,
T. J.
Blundell
,
E.
Unsworth
,
S.
Francoual
,
G.
Balakrishnan
,
D.
Alba Venero
,
P. D.
Hatton
Diamond Proposal Number(s):
[34192]
Open Access
Abstract: The Eu(Ga1−𝑥Al𝑥)4 series is composed of centrosymmetric structures which exhibit a wide range of rich topological phenomena, including some members hosting magnetic skyrmions. In this letter, we investigate the previously unreported intermediate compound EuGa2.4Al1.6, which hosts two distinct phase transitions under zero applied magnetic field. We have used resonant elastic x-ray scattering with full linear polarization analysis to unambiguously determine the zero-field magnetic structures, which consist of a transition between a basal plane transverse spin density wave at higher temperatures into a noncollinear helical ground state. Furthermore, we demonstrate a phase coexistence regime below the transition and reveal an elliptically modulated helical magnetic structure emerging from wavevector splitting.
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Jul 2024
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I05-ARPES
|
Open Access
Abstract: We report on the interplay between a van Hove singularity and a charge density wave state in
2
H
−
TaSe
2
. We use angle-resolved photoemission spectroscopy to investigate changes in the Fermi surface of this material under surface doping with potassium. At high doping, we observe modifications which imply the disappearance of the
(
3
×
3
)
charge density wave and formation of a different correlated state. Using a tight-binding-based approach as well as an effective model, we explain our observations as a consequence of coupling between the single-particle Lifshitz transition during which the Fermi level passes a van Hove singularity and the charge density order. In this scenario, the high electronic density of states associated with the van Hove singularity induces a change in the periodicity of the charge density wave from the known
(
3
×
3
)
to a new
(
2
×
2
)
superlattice.
|
Jan 2024
|
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I11-High Resolution Powder Diffraction
|
H.
Lane
,
P. M.
Sarte
,
K.
Guratinder
,
A. M.
Arevalo-Lopez
,
R. S.
Perry
,
E. C.
Hunter
,
T.
Weber
,
B.
Roessli
,
A.
Stunault
,
Y.
Su
,
R. A.
Ewings
,
S. D.
Wilson
,
P.
Böni
,
J. P.
Attfield
,
C.
Stock
Open Access
Abstract: MgV
2
O
4
is a spinel based on magnetic
V
3
+
ions, which host both spin
(
S
=
1
)
and orbital
(
l
eff
=
1
)
moments. Owing to the underlying pyrochlore coordination of the magnetic sites, the spins in
MgV
2
O
4
only antiferromagnetically order once the frustrating interactions imposed by the
F
d
¯
3
m
lattice are broken through an orbitally-driven structural distortion at
T
S
≃
60
K. Consequently, a Néel transition occurs at
T
N
≃
40
K. Low-temperature spatial ordering of the electronic orbitals is fundamental to both the structural and magnetic properties; however, considerable discussion on whether it can be described by complex or real orbital ordering is ambiguous. We apply neutron spectroscopy to resolve the nature of the orbital ground state and characterize hysteretic spin-orbital correlations using x-ray and neutron diffraction. Neutron spectroscopy finds multiple excitation bands and we parametrize these in terms of a multilevel (or excitonic) theory based on the orbitally degenerate ground state. Meaningful for the orbital ground state, we report an “optical-like” mode at high energies that we attribute to a crystal-field-like excitation from the spin-orbital
j
eff
=
2
ground-state manifold to an excited
j
eff
=
1
energy level. We parametrize the magnetic excitations in terms of a Hamiltonian with spin-orbit coupling and local crystalline electric field distortions resulting from deviations from perfect octahedra surrounding the
V
3
+
ions. We suggest that this provides compelling evidence for complex orbital order in
MgV
2
O
4
. We then apply the consequences of this model to understand hysteretic effects in the magnetic diffuse scattering where we propose that
MgV
2
O
4
displays a high-temperature orbital memory of the low-temperature spin order.
|
Nov 2023
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