I21-Resonant Inelastic X-ray Scattering (RIXS)
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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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I21-Resonant Inelastic X-ray Scattering (RIXS)
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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.
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Apr 2025
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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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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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Subhrangsu
Sarkar
,
Roxana
Capu
,
Yurii G
Pashkevich
,
Jonas
Knobel
,
Marli R.
Cantarino
,
Abhishek
Nag
,
Kurt
Kummer
,
Davide
Betto
,
Roberto
Sant
,
Christopher W.
Nicholson
,
Jarji
Khmaladze
,
Ke-Jin
Zhou
,
Nicholas B.
Brookes
,
Claude
Monney
,
Christian
Bernhard
Diamond Proposal Number(s):
[22149]
Open Access
Abstract: Heterostructures from complex oxides allow one to combine various electronic and magnetic orders as to induce new quantum states. A prominent example is the coupling between superconducting and magnetic orders in multilayers from high-Tc cuprates and manganites. A key role is played here by the interfacial CuO2 layer whose distinct properties remain to be fully understood. Here, we study with resonant inelastic X-ray scattering (RIXS) the magnon excitations of this interfacial CuO2 layer. In particular, we show that the underlying antiferromagnetic exchange interaction at the interface is strongly suppressed to J ≈ 70 meV, as compared to J ≈ 130 meV for the CuO2 layers away from the interface. Moreover, we observe an anomalous momentum dependence of the intensity of the interfacial magnon mode and show that it suggests that the antiferromagnetic order is accompanied by a particular kind of orbital order that yields a so-called altermagnetic state. Such a two-dimensional altermagnet has recently been predicted to enable new spintronic applications and superconducting proximity effects.
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Mar 2024
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Riccardo
Arpaia
,
Leonardo
Martinelli
,
Marco
Moretti Sala
,
Sergio
Caprara
,
Abhishek
Nag
,
Nicholas B.
Brookes
,
Pietro
Camisa
,
Qizhi
Li
,
Qiang
Gao
,
Xingjiang
Zhou
,
Mirian
Garcia-Fernandez
,
Ke-Jin
Zhou
,
Enrico
Schierle
,
Thilo
Bauch
,
Ying Ying
Peng
,
Carlo
Di Castro
,
Marco
Grilli
,
Floriana
Lombardi
,
Lucio
Braicovich
,
Giacomo
Ghiringhelli
Diamond Proposal Number(s):
[23880]
Open Access
Abstract: The universality of the strange metal phase in many quantum materials is often attributed to the presence of a quantum critical point (QCP), a zero-temperature phase transition ruled by quantum fluctuations. In cuprates, where superconductivity hinders direct QCP observation, indirect evidence comes from the identification of fluctuations compatible with the strange metal phase. Here we show that the recently discovered charge density fluctuations (CDF) possess the right properties to be associated to a quantum phase transition. Using resonant x-ray scattering, we studied the CDF in two families of cuprate superconductors across a wide doping range (up to p = 0.22). At p* ≈ 0.19, the putative QCP, the CDF intensity peaks, and the characteristic energy Δ is minimum, marking a wedge-shaped region in the phase diagram indicative of a quantum critical behavior, albeit with anomalies. These findings strengthen the role of charge order in explaining strange metal phenomenology and provide insights into high-temperature superconductivity.
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Nov 2023
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Jaewon
Choi
,
Jiemin
Li
,
Abhishek
Nag
,
Jonathan
Pelliciari
,
Hannah
Robarts
,
Charles C.
Tam
,
Andrew
Walters
,
Stefano
Agrestini
,
Mirian
Garcia-Fernandez
,
Dongjoon
Song
,
Hiroshi
Eisaki
,
Steve
Johnston
,
Riccardo
Comin
,
Hong
Ding
,
Ke-Jin
Zhou
Diamond Proposal Number(s):
[29623, 21277]
Open Access
Abstract: The omnipresence of charge density waves (CDWs) across almost all cuprate families underpins a common organizing principle. However, a longstanding debate of whether its spatial symmetry is stripe or checkerboard remains unresolved. While CDWs in lanthanum- and yttrium-based cuprates possess a stripe symmetry, distinguishing these two scenarios has been challenging for the short-range CDW in bismuth-based cuprates. Here, we employed high-resolution resonant inelastic x-ray scattering to uncover the spatial symmetry of the CDW in Bi
Sr
La
CuO
. Across a wide range of doping and temperature, anisotropic CDW peaks with elliptical shapes were found in reciprocal space. Based on Fourier transform analysis of real-space models, we interpret the results as evidence of unidirectional charge stripes, hosted by mutually 90
-rotated anisotropic domains. Our work paves the way for a unified symmetry and microscopic description of CDW order in cuprates.
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Oct 2023
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Open Access
Abstract: A photon carrying one unit of angular momentum can change the spin angular momentum of a magnetic system with one unit (ΔMs = ±1) at most. This implies that a two-photon scattering process can manipulate the spin angular momentum of the magnetic system with a maximum of two units. Herein we describe a triple-magnon excitation in α-Fe2O3, which contradicts this conventional wisdom that only 1- and 2-magnon excitations are possible in a resonant inelastic X-ray scattering experiment. We observe an excitation at exactly three times the magnon energy, along with additional excitations at four and five times the magnon energy, suggesting quadruple and quintuple-magnons as well. Guided by theoretical calculations, we reveal how a two-photon scattering process can create exotic higher-rank magnons and the relevance of these quasiparticles for magnon-based applications.
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May 2023
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Robert A.
House
,
Gregory J.
Rees
,
Kit
Mccoll
,
John-Joseph
Marie
,
Mirian
Garcia-Fernandez
,
Abhishek
Nag
,
Ke-Jin
Zhou
,
Simon
Cassidy
,
Benjamin J.
Morgan
,
M.
Saiful Islam
,
Peter G.
Bruce
Diamond Proposal Number(s):
[25589]
Abstract: Oxide ions in transition metal oxide cathodes can store charge at high voltage offering a route towards higher energy density batteries. However, upon charging these cathodes, the oxidized oxide ions condense to form molecular O2 trapped in the material. Consequently, the discharge voltage is much lower than charge, leading to undesirable voltage hysteresis. Here we capture the nature of the electron holes on O2− before O2 formation by exploiting the suppressed transition metal rearrangement in ribbon-ordered Na0.6[Li0.2Mn0.8]O2. We show that the electron holes formed are delocalized across the oxide ions coordinated to two Mn (O–Mn2) arranged in ribbons in the transition metal layers. Furthermore, we track these delocalized hole states as they gradually localize in the structure in the form of trapped molecular O2 over a period of days. Establishing the nature of hole states on oxide ions is important if truly reversible high-voltage O-redox cathodes are to be realized.
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Feb 2023
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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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Haiyu
Lu
,
Makoto
Hashimoto
,
Su-Di
Chen
,
Shigeyuki
Ishida
,
Dongjoon
Song
,
Hiroshi
Eisaki
,
Abhishek
Nag
,
Mirian
Garcia-Fernandez
,
Riccardo
Arpaia
,
Giacomo
Ghiringhelli
,
Lucio
Braicovich
,
Jan
Zaanen
,
Brian
Moritz
,
Kurt
Kummer
,
Nicholas B.
Brookes
,
Ke-Jin
Zhou
,
Zhi-Xun
Shen
,
Thomas P.
Devereaux
,
Wei-Sheng
Lee
Diamond Proposal Number(s):
[22009]
Abstract: Identifying quantum critical points (QCPs) and their associated fluctuations may hold the key to unraveling the unusual electronic phenomena observed in cuprate superconductors. Recently, signatures of quantum fluctuations associated with charge order (CO) have been inferred from the anomalous enhancement of CO excitations that accompany the reduction of the CO order parameter in the superconducting state. To gain more insight into the interplay between CO and superconductivity, here we investigate the doping dependence of this phenomenon throughout the Bi-2212 cuprate phase diagram using resonant inelastic x-ray scattering (RIXS) at the Cu
L
3
edge. As doping increases, the CO wave vector decreases, saturating near a commensurate value of 0.25 reciprocal lattice unit beyond a characteristic doping
p
c
, where the correlation length becomes shorter than the apparent periodicity (
4
a
0
). Such behavior is indicative of the fluctuating nature of the CO; the proliferation of CO excitations in the superconducting state also appears strongest at
p
c
, consistent with expected behavior at a CO QCP. Intriguingly,
p
c
appears to be near optimal doping, where the superconducting transition temperature
T
c
is maximal.
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Oct 2022
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