I21-Resonant Inelastic X-ray Scattering (RIXS)
|
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.
|
May 2023
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
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.
|
Feb 2023
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
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.
|
Nov 2022
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
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.
|
Oct 2022
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
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.
|
Aug 2022
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Charles C.
Tam
,
Jaewon
Choi
,
Xiang
Ding
,
Stefano
Agrestini
,
Abhishek
Nag
,
Mei
Wu
,
Bing
Huang
,
Huiqian
Luo
,
Peng
Gao
,
Mirian
Garcia-Fernandez
,
Liang
Qiao
,
Ke-Jin
Zhou
Diamond Proposal Number(s):
[30296]
Abstract: In materials science, much effort has been devoted to the reproduction of superconductivity in chemical compositions, analogous to cuprate superconductors since their discovery over 30 years ago. This approach was recently successful in realising superconductivity in infinite-layer nickelates1,2,3,4,5,6. Although differing from cuprates in electronic and magnetic properties, strong Coulomb interactions suggest that infinite-layer nickelates have a propensity towards various symmetry-breaking orders that populate cuprates7,8,9,10. Here we report the observation of charge density waves (CDWs) in infinite-layer NdNiO2 films using Ni L3 resonant X-ray scattering. Remarkably, CDWs form in Nd 5d and Ni 3d orbitals at the same commensurate wavevector (0.333, 0) reciprocal lattice units, with non-negligible out-of-plane dependence and an in-plane correlation length of up to ~60 Å. Spectroscopic studies reveal a strong connection between CDWs and Nd 5d–Ni 3d orbital hybridization. Upon entering the superconducting state at 20% Sr doping, the CDWs disappear. Our work demonstrates the existence of CDWs in infinite-layer nickelates with a multiorbital character distinct from cuprates, which establishes their low-energy physics.
|
Aug 2022
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
M.
Hepting
,
M.
Bejas
,
A.
Nag
,
H.
Yamase
,
N.
Coppola
,
D.
Betto
,
C.
Falter
,
Mirian
Garcia-Fernandez
,
S.
Agrestini
,
K.-J.
Zhou
,
M.
Minola
,
C.
Sacco
,
L.
Maritato
,
P.
Orgiani
,
H. I.
Wei
,
K. M.
Shen
,
D. G.
Schlom
,
A.
Galdi
,
A.
Greco
,
B.
Keimer
Diamond Proposal Number(s):
[23933]
Open Access
Abstract: We use resonant inelastic x-ray scattering to probe the propagation of plasmons in the electron-doped cuprate superconductor
Sr
0.9
La
0.1
CuO
2
. We detect a plasmon gap of
∼
120
meV
at the two-dimensional Brillouin zone center, indicating that low-energy plasmons in
Sr
0.9
La
0.1
CuO
2
are not strictly acoustic. The plasmon dispersion, including the gap, is accurately captured by layered
t
−
J
−
V
model calculations. A similar analysis performed on recent resonant inelastic x-ray scattering data from other cuprates suggests that the plasmon gap is generic and its size is related to the magnitude of the interlayer hopping
t
z
. Our work signifies the three dimensionality of the charge dynamics in layered cuprates and provides a new method to determine
t
z
.
|
Jul 2022
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Matteo
Rossi
,
Motoki
Osada
,
Jaewon
Choi
,
Stefano
Agrestini
,
Daniel
Jost
,
Yonghun
Lee
,
Haiyu
Lu
,
Bai Yang
Wang
,
Kyuho
Lee
,
Abhishek
Nag
,
Yi-De
Chuang
,
Cheng-Tai
Kuo
,
Sang-Jun
Lee
,
Brian
Moritz
,
Thomas P.
Devereaux
,
Zhi-Xun
Shen
,
Jun-Sik
Lee
,
Ke-Jin
Zhou
,
Harold Y.
Hwang
,
Wei-Sheng
Lee
Diamond Proposal Number(s):
[25598, 27558]
Abstract: A defining signature of strongly correlated electronic systems is a rich phase diagram, which consists of multiple broken symmetries, such as magnetism, superconductivity and charge order1,2. In the recently discovered nickelate superconductors3,4,5,6,7,8,9,10, a large antiferromagnetic exchange energy has been reported, which implies the existence of strong electronic correlations11. However, signatures of a broken-symmetry state other than superconductivity have not yet been observed. Here we observe charge ordering in infinite-layer nickelates La1−xSrxNiO2 using resonant X-ray scattering. The parent compound orders along the Ni–O bond direction with an incommensurate wavevector, distinct from the stripe order observed in other nickelates12,13,14 that propagates along a direction 45° to the Ni–O bond. The resonance profile we measure indicates that ordering originates from the nickelate layers and induces a parasitic charge modulation of lanthanum electrons. Upon doping, the charge order diminishes and its wavevector shifts towards commensurate, hinting that strong electronic correlations are likely to be responsible for the ordered state. Our results suggest that the existence of charge order and its potential interplay with antiferromagnetic fluctuations and superconductivity are important themes in nickel-based superconductors.
|
Jul 2022
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Diamond Proposal Number(s):
[21725]
Open Access
Abstract: Cuprate superconductors have the highest critical temperatures (Tc) at ambient pressure, yet a consensus on the superconducting mechanism remains to be established. Finding an empirical parameter that limits the highest reachable Tc can provide crucial insight into this outstanding problem. Here, in the first two Ruddlesden-Popper members of the model Hg-family of cuprates, which are chemically nearly identical and have the highest Tc among all cuprate families, we use inelastic photon scattering to reveal that the energy of magnetic fluctuations may play such a role. In particular, we observe the single-paramagnon spectra to be nearly identical between the two compounds, apart from an energy scale difference of ~30% which matches their difference in Tc. The empirical correlation between paramagnon energy and maximal Tc is further found to extend to other cuprate families with relatively high Tc’s, hinting at a fundamental connection between them.
|
Jun 2022
|
|
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.
|
May 2022
|
|
