I09-Surface and Interface Structural Analysis
I21-Resonant Inelastic X-ray Scattering (RIXS)
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A. S.
Menon
,
B. J.
Johnston
,
S. G.
Booth
,
L.
Zhang
,
K.
Kress
,
B. E.
Murdock
,
G.
Paez Fajardo
,
N. N.
Anthonisamy
,
N.
Tapia-Ruiz
,
S.
Agrestini
,
M.
Garcia-Fernandez
,
K.
Zhou
,
P. K.
Thakur
,
T. L.
Lee
,
A. J.
Nedoma
,
S. A.
Cussen
,
L. F. J.
Piper
Diamond Proposal Number(s):
[29104, 29113]
Open Access
Abstract: The desire to increase the energy density of stoichiometric layered
Li
TM
O
2
(TM = 3d transition metal) cathode materials has promoted investigation into their properties at high states of charge. Although there is increasing evidence for pronounced oxygen participation in the charge compensation mechanism, questions remain whether this is true
O
-redox, as observed in
Li
-excess cathodes. Through a high-resolution
O
K-edge resonant inelastic x-ray spectroscopy (RIXS) study of the
Mn
-free
Ni
-rich layered oxide
Li
Ni
0.98
W
0.02
O
2
, we demonstrate that the same oxidized oxygen environment exists in both
Li
-excess and non-
Li
-excess systems. The observation of identical RIXS loss features in both classes of compounds is remarkable given the differences in their crystallographic structure and delithiation pathways. This lack of a specific structural motif reveals the importance of electron correlation in the charge compensation mechanism for these systems and indicates how a better description of charge compensation in layered oxides is required to understand anionic redox for energy storage.
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Mar 2023
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Xiang
Ding
,
Charles C.
Tam
,
Xuelei
Sui
,
Yan
Zhao
,
Minghui
Xu
,
Jaewon
Choi
,
Huaqian
Leng
,
Ji
Zhang
,
Mei
Wu
,
Haiyan
Xiao
,
Xiaotao
Zu
,
Mirian
Garcia-Fernandez
,
Stefano
Agrestini
,
Xiaoqiang
Wu
,
Qingyuan
Wang
,
Peng
Gao
,
Sean
Li
,
Bing
Huang
,
Ke-Jin
Zhou
,
Liang
Qiao
Diamond Proposal Number(s):
[30296]
Abstract: The newly discovered nickelate superconductors so far only exist in epitaxial thin films synthesized by a topotactic reaction with metal hydrides1. This method changes the nickelates from the perovskite to an infinite-layer structure by deintercalation of apical oxygens1,2,3. Such a chemical reaction may introduce hydrogen (H), influencing the physical properties of the end materials4,5,6,7,8,9. Unfortunately, H is insensitive to most characterization techniques and is difficult to detect because of its light weight. Here, in optimally Sr doped Nd0.8Sr0.2NiO2H epitaxial films, secondary-ion mass spectroscopy shows abundant H existing in the form of Nd0.8Sr0.2NiO2Hx (x ≅ 0.2–0.5). Zero resistivity is found within a very narrow H-doping window of 0.22 ≤ x ≤ 0.28, showing unequivocally the critical role of H in superconductivity. Resonant inelastic X-ray scattering demonstrates the existence of itinerant interstitial s (IIS) orbitals originating from apical oxygen deintercalation. Density functional theory calculations show that electronegative H– occupies the apical oxygen sites annihilating IIS orbitals, reducing the IIS–Ni 3d orbital hybridization. This leads the electronic structure of H-doped Nd0.8Sr0.2NiO2Hx to be more two-dimensional-like, which might be relevant for the observed superconductivity. We highlight that H is an important ingredient for superconductivity in epitaxial infinite-layer nickelates.
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Mar 2023
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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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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)
|
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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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.
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Aug 2022
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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.
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Aug 2022
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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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
.
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Jul 2022
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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.
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Jun 2022
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