I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Zubia
Hasan
,
Grace A.
Pan
,
Harrison
Labollita
,
Austin
Kaczmarek
,
Suk Hyun
Sung
,
Shekhar
Sharma
,
Purnima P.
Balakrishnan
,
Edward
Mercer
,
Vivek
Bhartiya
,
Alpha T.
N'Diaye
,
Zaher
Salman
,
Thomas
Prokscha
,
Andreas
Suter
,
Alexander J.
Grutter
,
Mirian
Garcia-Fernandez
,
Ke-Jin
Zhou
,
Jonathan
Pelliciari
,
Valentina
Bisogni
,
Ismail
El Baggari
,
Darrell G.
Schlom
,
Matthew R.
Barone
,
Charles M.
Brooks
,
Katja C.
Nowack
,
Antia S.
Botana
,
Brendan D.
Faeth
,
Alberto
De La Torre
,
Julia A.
Mundy
Open Access
Abstract: Geometrically frustrated lattices can display a range of correlated phenomena, ranging from spin frustration and charge order to dispersionless flat bands due to quantum interference. One particularly compelling family of such materials is the half-valence spinel LiB2O4 materials. On the B-site frustrated pyrochlore sublattice, the interplay of correlated metallic behavior and charge frustration leads to a superconducting state in LiTi2O4 and heavy fermion behavior in LiV2O4. To date, however, LiTi2O4 has primarily been understood as a conventional BCS superconductor despite a lattice structure that could host more exotic ground states. Here, we present a multimodal investigation of LiTi2O4, combining ARPES, RIXS, proximate magnetic probes, and ab-initio many-body theoretical calculations. Our data reveals a novel mobile polaronic ground state with spectroscopic signatures that underlie co-dominant electron-phonon coupling and electron-electron correlations also found in the lightly doped cuprates. The cooperation between the two interaction scales distinguishes LiTi2O4 from other superconducting titanates, suggesting an unconventional origin to superconductivity in LiTi2O4. Our work deepens our understanding of the rare interplay of electron-electron correlations and electron-phonon coupling in unconventional superconducting systems. In particular, our work identifies the geometrically frustrated, mixed-valence spinel family as an under-explored platform for discovering unconventional, correlated ground states.
|
Jan 2026
|
|
Optics
|
Arindam
Majhi
,
Wadwan
Singhapong
,
Wai Jue
Tan
,
Andrey
Sokolov
,
Stefano
Agrestini
,
Mirian
Garcia-Fernandez
,
Ke-Jin
Zhou
,
Andrew C.
Walters
,
Chris
Bowen
,
Alexander J. G.
Lunt
,
Hongchang
Wang
,
Kawal J.
Sawhney
Open Access
Abstract: Laterally graded multilayer optics play an important role in advanced X-ray applications, enabling precise control of beam properties for spectroscopic and focusing techniques. The Multilayer Deposition System (MDS) at Diamond Light Source (DLS) has demonstrated its ability to fabricate highly precise laterally graded X-ray optics. Developing such optics is challenging due to stringent requirements for precise lateral thickness variations and sagittal uniformity, achieved through optimized substrate speed profiles and advanced mask design. This study presents a comprehensive investigation into the design, fabrication, and characterization of laterally graded multilayers. An adjustable mask design improves sagittal uniformity and reduces optimization times. The structural and optical performance of the multilayers is evaluated, confirming their suitability for synchrotron applications. Two types of laterally graded multilayers were developed: one with a constant lateral gradient (0.005 nm/mm) for O-K edge polarizers, achieving sagittal thickness variations of approximately 0.3–0.4% across an 80 mm substrate, and another featuring a strong variable gradient from 0.037 to 0.112 nm/mm, designed to match the elliptical periodicity profile. The constant gradient multilayer polarizer has been successfully implemented on the state-of-the-art I21 beamline at DLS, highlighting the MDS's role in producing next-generation X-ray optics that meet the stringent demands of synchrotron beamlines.
|
Jan 2026
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Diamond Proposal Number(s):
[36210]
Open Access
Abstract: Quasiparticles describe collective excitations in many-body systems, and their symmetry classification is of fundamental importance for physical processes such as excited states, transport phenomena, and phase transitions. Recent studies have introduced chirality as an additional degree of freedom in condensed matter physics, leading to a range of novel phenomena. Among these, chiral phonons are of special interest because they carry angular momentum and therefore intrinsically break time reversal symmetry, which non-trivially bridges the spin system with the lattice. Here, we directly prove the presence of chiral phonons in a prototypical polar LiNbO3 crystal. Our demonstration of chiral phonons in a ferroelectric enables in-situ electrical control of momentum-dependent “magnetic” polarization with the reversible phonon handedness. This ferroic control of phonon chirality has substantial potential in the emerging field of chiral phononics, particularly along the associated control of its phonon angular momentum.
|
Dec 2025
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Open Access
Abstract: Oxygen redox (OR) in Li1.2Ni0.13Co0.13Mn0.54O2 (LRNMC) and Na0.67Mg0.28Mn0.72O2 (NMMO) has been associated with the formation of embedded molecular O2 due to the appearance of their distinctive features in RIXS, while it is unclear whether OR also affects the oxygen left in the lattice. Here we use high-resolution oxygen K-edge resonant inelastic X-ray scattering (RIXS) at threshold excitation (527.5 – 529.5 eV) revealing lattice responses due to OR. We find that both cathodes show pronounced multiphonon progressions, which are either altered or activated upon charging. The first progression, with a fundamental energy loss ∼67-74 meV, matches the A1g lattice-oxygen mode observed by Raman spectroscopy, confirming its bulk origin. The second progression that exhibits a fundamental loss of ∼98 meV appears only at the highest state of charge and is resonant with the new pre-edge states at 527.5 eV. The latter mode emerges concurrently with the characteristic trapped-O2 RIXS signal and is strongly coupled to an occupied electronic band near the Fermi level, indicating that OR may not only contribute to the formation of molecular O2, but also perturbs lattice oxygen states, likely via polaron-forming oxidized lattice oxygen.
|
Dec 2025
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
D.
Takegami
,
T.
Aoyama
,
T.
Okauchi
,
T.
Yamaguchi
,
S.
Tippireddy
,
S.
Agrestini
,
Mirian
Garcia-Fernandez
,
T.
Mizokawa
,
K.
Ohgushi
,
Ke-Jin
Zhou
,
J.
Chaloupka
,
J.
Kuneš
,
A.
Hariki
,
H.
Suzuki
Diamond Proposal Number(s):
[35709]
Open Access
Abstract: X-ray magnetic circular dichroism provides a means to identify ferromagnetic, chiral, and altermagnetic orders via their time-reversal-symmetry (𝒯) breaking. However, the symmetry properties that govern circular dichroism (CD) in resonant inelastic x-ray scattering (RIXS) remain poorly understood. We show that, due to the inherent irreversibility of the RIXS process, RIXS-CD does not require 𝒯 breaking to be present, but reflects the change in unitary symmetries associated with magnetic ordering. Using the altermagnetic MnTe as a model system, we observe an azimuthal-angle dependent RIXS-CD signal in the magnon excitations. Our findings highlight the sensitivity of RIXS-CD to the relativistic symmetry in magnetic systems and its potential application as a probe of magnetic domains.
|
Nov 2025
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
L.
Martinelli
,
I.
Biało
,
X.
Hong
,
J.
Oppliger
,
C.
Lin
,
T,
Schaller
,
J.
Küspert
,
M. H.
Fischer
,
T.
Kurosawa
,
N.
Momono
,
M.
Oda
,
D. V.
Novikov
,
A.
Khadiev
,
E.
Weschke
,
J.
Choi
,
S.
Agrestini
,
Mirian
Garcia-Fernandez
,
Ke-Jin
Zhou
,
Q.
Wang
,
J.
Chang
Diamond Proposal Number(s):
[33512]
Open Access
Abstract: We use uniaxial strain in combination with ultra-high-resolution resonant inelastic x-ray scattering (RIXS) at the oxygen-𝐾 and copper-𝐿3 edges to study the excitations stemming from the charge ordering wave vector in La1.875Sr0.125CuO4. By detwinning stripe ordering, we demonstrate that the optical phonon anomalies do not show any stripe anisotropy. The low-energy charge excitations also retain an in-plane fourfold symmetry. As such, we find that both phonon and charge excitations are decoupled entirely from the strength of static charge ordering. The almost isotropic character of charge excitations is indicative of a quantum critical behavior and remains a possible source for the strange metal properties found in the normal state of cuprate superconductors.
|
Jul 2025
|
|
I15-1-X-ray Pair Distribution Function (XPDF)
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Diamond Proposal Number(s):
[35064, 39285, 40912]
Open Access
Abstract: Li-rich disordered rocksalts are promising next-generation cathode materials for Li-ion batteries. Recent reports have shown it is also possible to obtain Na-rich disordered rocksalts, however, it is currently poorly understood how the knowledge of the structural and redox chemistry translates from the Li-rich to the Na-rich analogs. Here, the properties of Li2MnO2F and Na2MnO2F are compared, which have different ion sizes (Li+ = 0.76 vs Na+ = 1.02 Å) but the same disordered rocksalt structure and stoichiometry. It is found that Na2MnO2F exhibits lower voltage Mn- and O-redox couples, opening access to a wider compositional range within the same voltage limits. Furthermore, the intercalation mechanism switches from predominantly single-phase solid solution behavior in Li2MnO2F to a two-phase transition in Na2MnO2F, accompanied by a greater decrease in the average Mn─O/F bond length. Li2MnO2F retains its long-range disordered rocksalt structure throughout the first cycle. In contrast, Na2MnO2F becomes completely amorphous during charge and develops a local structure characteristic of a post-spinel. This amorphization is partially reversible on discharge. The results show how the ion intercalation behavior of disordered rocksalts differs dramatically when changing from Li- to Na-ions and offers routes to control the electrochemical properties of these high-energy-density cathodes.
|
May 2025
|
|
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.
|
May 2025
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Karin
Von Arx
,
Pascal
Rothenbühler
,
Qisi
Wang
,
Leonardo
Martinelli
,
Jaewon
Choi
,
Mirian
Garcia-Fernandez
,
Stefano
Agrestini
,
Ke-Jin
Zhou
,
Antonio
Vecchione
,
Rosalba
Fittipaldi
,
Yasmine
Sassa
,
Mario
Cuoco
,
Filomena
Forte
,
Johan
Chang
Diamond Proposal Number(s):
[27638]
Open Access
Abstract: Multi-band Mott insulators with moderate spin-orbit and Hund’s coupling are key reference points for theoretical concept developments of correlated electron systems. The ruthenate Mott insulator Ca2RuO4 has therefore been intensively studied by spectroscopic probes. However, it has been challenging to resolve the fundamental excitations emerging from the hierarchy of electronic energy scales. Here we apply high resolution resonant inelastic x-ray scattering to probe deeper into the low-energy electronic excitations found in Ca2RuO4. In this fashion, we probe a series of spin-orbital excitations. By taking advantage of enhanced energy resolution, we probe a 40 meV mode through the oxygen K-edge. The polarization dependence of this low-energy excitations exposes a distinct orbital nature, originating from the interplay of spin-orbit coupling and octahedral rotations. Additionally, we discuss the role of magnetic correlations to describe the occurrence of excitations with amplitudes which are multiple of a given energy. Such direct determination of relevant electronic energy scales sharpens the target for theory developments of Mott insulators’ orbital degree of freedom.
|
May 2025
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Sophia F. R.
Tenhuisen
,
Grace A.
Pan
,
Qi
Song
,
Denitsa R.
Baykusheva
,
Dan
Ferenc Segedin
,
Berit H.
Goodge
,
Hanjong
Paik
,
Jonathan
Pelliciari
,
Valentina
Bisogni
,
Yanhong
Gu
,
Stefano
Agrestini
,
Abhishek
Nag
,
Mirian
Garcia-Fernandez
,
Ke-Jin
Zhou
,
Lena F.
Kourkoutis
,
Charles M.
Brooks
,
Julia E. A.
Mundy
,
Mark P. M.
Dean
,
Matteo
Mitrano
Diamond Proposal Number(s):
[27484]
Abstract: Magnetic interactions are thought to play a key role in the properties of many unconventional superconductors, including cuprates, iron pnictides, and square-planar nickelates. Superconductivity was also recently observed in the bilayer and trilayer Ruddlesden-Popper nickelates, the electronic structure of which is expected to differ from that of cuprates and square-planar nickelates. Here we study how electronic structure and magnetic interactions evolve with the number of layers, 𝑛, in thin film Ruddlesden-Popper nickelates Nd𝑛+1Ni𝑛O3𝑛+1 with 𝑛=1,3, and 5 using resonant inelastic x-ray scattering (RIXS). The RIXS spectra are consistent with a high-spin |3𝑑8
𝐿
̲
⟩ electronic configuration, resembling that of La2−𝑥Sr𝑥NiO4 and the parent perovskite, NdNiO3. The magnetic excitations soften to lower energy in the structurally self-doped, higher-𝑛 films. Our observations confirm that structural tuning is an effective route for altering electronic properties, such as magnetic superexchange, in this prominent family of materials.
|
Apr 2025
|
|
