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.
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Jul 2022
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Yingying
Peng
,
Leonardo
Martinelli
,
Qizhi
Li
,
Matteo
Rossi
,
Matteo
Mitrano
,
Riccardo
Arpaia
,
Marco
Moretti Sala
,
Qiang
Gao
,
Xuefei
Guo
,
Gabriella Maria
De Luca
,
Andrew
Walters
,
Abhishek
Nag
,
Andi
Barbour
,
Genda
Gu
,
Jonathan
Pelliciari
,
Nicholas B.
Brookes
,
Peter
Abbamonte
,
Marco
Salluzzo
,
Xingjiang
Zhou
,
Ke-Jin
Zhou
,
Valentina
Bisogni
,
Lucio
Braicovich
,
Steven
Johnston
,
Giacomo
Ghiringhelli
Diamond Proposal Number(s):
[20012]
Abstract: While electron-phonon coupling (EPC) is crucial for Cooper pairing in conventional superconductors, its role in high-
T
c
superconducting cuprates is debated. Using resonant inelastic x-ray scattering at the oxygen
K
edge, we study the EPC in
Bi
2
Sr
2
Ca
Cu
2
O
8
+
δ
(Bi2212) and
Nd
1
+
x
Ba
2
−
x
Cu
3
O
7
−
δ
(NBCO) at different doping levels ranging from heavily underdoped (
p
=
0.07
) to overdoped (
p
=
0.21
). We analyze the data with a localized Lang-Firsov model that allows for the coherent excitations of two phonon modes. While electronic band dispersion effects are non-negligible, we are able to perform a study of the relative values of EPC matrix elements in these cuprate families. In the case of NBCO, the choice of the excitation energy allows us to disentangle modes related to the CuO chains and the
Cu
O
2
planes. Combining the results from the two families, we find the EPC strength decreases with doping at
q
∥
=
(
−
0.25
,
0
)
r.l.u., but has a nonmonotonic trend as a function of doping at smaller momenta. This behavior is attributed to the screening effect of charge carriers. We also find that the phonon intensity is enhanced in the vicinity of the charge-density-wave excitations while the extracted EPC strength appears to be less sensitive to their proximity. By performing a comparative study of two cuprate families, we are able to identify general trends in the EPC for the cuprates and provide experimental input to theories invoking a synergistic role for this interaction in
d
-wave pairing.
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Mar 2022
|
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
M.
Rossi
,
H.
Lu
,
A.
Nag
,
D.
Li
,
M.
Osada
,
K.
Lee
,
B. Y.
Wang
,
S.
Agrestini
,
Mirian
Garcia-Fernandez
,
J. J.
Kas
,
Y.-D.
Chuang
,
Z. X.
Shen
,
H. Y.
Hwang
,
B.
Moritz
,
Ke-Jin
Zhou
,
T. P.
Devereaux
,
W. S.
Lee
Diamond Proposal Number(s):
[25165]
Abstract: The recent discovery of superconductivity in Nd1−xSrxNiO2 has drawn significant attention in the field. A key open question regards the evolution of the electronic structure with respect to hole doping. Here we exploit x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) to probe the doping-dependent electronic structure of Nd1−xSrxNiO. Upon doping, a high-energy feature in Ni L3-edge XAS develops in addition to the main absorption peak, while XAS at the O K-, Nd M3- and Nd M5-edge exhibits a much weaker response. This implies that doped holes are mainly introduced into Ni 3 d states. By comparing our data to atomic multiplet calculations including D4h crystal field, the doping-induced feature in Ni L3-edge XAS is consistent with a d 8 spin-singlet state in which doped holes reside in the 3dx2−y2 orbitals. This is further supported by the softening of RIXS orbital excitations due to doping, corroborating with the Fermi level shift associated with increasing holes in the Ni 3dx2−y2 orbital.
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Dec 2021
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
H.
Lu
,
M.
Rossi
,
A.
Nag
,
M.
Osada
,
D. F.
Li
,
K.
Lee
,
B. Y.
Wang
,
M.
Garcia-Fernandez
,
S.
Agrestini
,
Z. X.
Shen
,
E. M.
Been
,
B.
Moritz
,
T. P.
Devereaux
,
J.
Zaanen
,
H. Y.
Hwang
,
K.-J.
Zhou
,
W.-S.
Lee
Diamond Proposal Number(s):
[25165]
Abstract: The discovery of superconductivity in infinite-layer nickelates brings us tantalizingly close to a material class that mirrors the cuprate superconductors. We measured the magnetic excitations in these nickelates using resonant inelastic x-ray scattering at the Ni L3-edge. Undoped NdNiO2 possesses a branch of dispersive excitations with a bandwidth of approximately 200 milli–electron volts, which is reminiscent of the spin wave of strongly coupled, antiferromagnetically aligned spins on a square lattice. The substantial damping of these modes indicates the importance of coupling to rare-earth itinerant electrons. Upon doping, the spectral weight and energy decrease slightly, whereas the modes become overdamped. Our results highlight the role of Mottness in infinite-layer nickelates.
|
Jul 2021
|
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Haiyu
Lu
,
Matteo
Rossi
,
Jung-Ho
Kim
,
Hasan
Yavas
,
Ayman
Said
,
Abhishek
Nag
,
Mirian
Garcia-Fernandez
,
Stefano
Agrestini
,
Ke-Jin
Zhou
,
Chunjing
Jia
,
Brian
Moritz
,
Thomas P.
Devereaux
,
Zhi-Xun
Shen
,
Wei-Sheng
Lee
Diamond Proposal Number(s):
[25165]
Abstract: We utilized high-energy-resolution resonant inelastic x-ray scattering (RIXS) at both the Ta and Ni
L
3
edges to map out element-specific particle-hole excitations in
Ta
2
Ni
Se
5
across the phase transition. Our results reveal a momentum-dependent gaplike feature in the low-energy spectrum, which agrees well with the band gap in element-specific joint density of states calculations based on ab initio estimates of the electronic structure in both the low-temperature monoclinic and high-temperature orthorhombic structures. Below
T
c
, the RIXS energy-momentum map shows a minimal gap at the Brillouin zone center
(
∼
0.16
eV
)
, confirming that
Ta
2
Ni
Se
5
possesses a direct band gap in its low-temperature ground state. However, inside the gap, no signature of anticipated collective modes with an energy scale comparable to the gap size can be identified. Upon increasing the temperature to above
T
c
, whereas the gap at the zone center closes, the RIXS map at finite momenta still possesses the gross features of the low-temperature map, suggesting a substantial mixing between the Ta and Ni orbits in the conduction and valence bands, which does not change substantially across the phase transition. Our experimental observations and comparison to the theoretical calculations lend further support to the phase transition and the corresponding gap opening in
Ta
2
Ni
Se
5
being largely structural by nature, with a possible minor contribution from the putative exciton condensate.
|
Jun 2021
|
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Jonathan
Pelliciari
,
Seher
Karakuzu
,
Qi
Song
,
Riccardo
Arpaia
,
Abhishek
Nag
,
Matteo
Rossi
,
Jiemin
Li
,
Tianlun
Yu
,
Xiaoyang
Chen
,
Rui
Peng
,
Mirian
Garcia-Fernandez
,
Andrew C.
Walters
,
Qisi
Wang
,
Jun
Zhao
,
Giacomo
Ghiringhelli
,
Donglai
Feng
,
Thomas A.
Maier
,
Ke-Jin
Zhou
,
Steven
Johnston
,
Riccardo
Comin
Diamond Proposal Number(s):
[18883]
Open Access
Abstract: In ultrathin films of FeSe grown on SrTiO3 (FeSe/STO), the superconducting transition temperature Tc is increased by almost an order of magnitude, raising questions on the pairing mechanism. As in other superconductors, antiferromagnetic spin fluctuations have been proposed to mediate SC making it essential to study the evolution of the spin dynamics of FeSe from the bulk to the ultrathin limit. Here, we investigate the spin excitations in bulk and monolayer FeSe/STO using resonant inelastic x-ray scattering (RIXS) and quantum Monte Carlo (QMC) calculations. Despite the absence of long-range magnetic order, bulk FeSe displays dispersive magnetic excitations reminiscent of other Fe-pnictides. Conversely, the spin excitations in FeSe/STO are gapped, dispersionless, and significantly hardened relative to its bulk counterpart. By comparing our RIXS results with simulations of a bilayer Hubbard model, we connect the evolution of the spin excitations to the Fermiology of the two systems revealing a remarkable reconfiguration of spin excitations in FeSe/STO, essential to understand the role of spin fluctuations in the pairing mechanism.
|
May 2021
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
M.
Hepting
,
D.
Li
,
C. J.
Jia
,
H.
Lu
,
E.
Paris
,
Y.
Tseng
,
X.
Feng
,
M.
Osada
,
E.
Been
,
Y.
Hikita
,
Y.-D.
Chuang
,
Z.
Hussain
,
K. J.
Zhou
,
A.
Nag
,
M.
Garcia-Fernandez
,
M.
Rossi
,
H. Y.
Huang
,
D. J.
Huang
,
Z. X.
Shen
,
T.
Schmitt
,
H. Y.
Hwang
,
B.
Moritz
,
J.
Zaanen
,
T. P.
Devereaux
,
W. S.
Lee
Diamond Proposal Number(s):
[22009]
Abstract: The search continues for nickel oxide-based materials with electronic properties similar to cuprate high-temperature superconductors. The recent discovery of superconductivity in the doped infinite-layer nickelate NdNiO2 has strengthened these efforts. Here, we use X-ray spectroscopy and density functional theory to show that the electronic structure of LaNiO2 and NdNiO2, while similar to the cuprates, includes significant distinctions. Unlike cuprates, the rare-earth spacer layer in the infinite-layer nickelate supports a weakly interacting three-dimensional 5d metallic state, which hybridizes with a quasi-two-dimensional, strongly correlated state with
3
d
x
2
−
y
2
3dx2−y2
symmetry in the NiO2 layers. Thus, the infinite-layer nickelate can be regarded as a sibling of the rare-earth intermetallics, which are well known for heavy fermion behaviour, where the NiO2 correlated layers play an analogous role to the 4f states in rare-earth heavy fermion compounds. This Kondo- or Anderson-lattice-like ‘oxide-intermetallic’ replaces the Mott insulator as the reference state from which superconductivity emerges upon doping.
|
Jan 2020
|
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I11-High Resolution Powder Diffraction
|
Peter J. E. M.
Van Der Linden
,
Marco
Moretti Sala
,
Christian
Henriquet
,
Matteo
Rossi
,
Kenya
Ohgushi
,
François
Fauth
,
Laura
Simonelli
,
Carlo
Marini
,
Edmundo
Fraga
,
Claire
Murray
,
Jonathan
Potter
,
Michael
Krisch
Diamond Proposal Number(s):
[14463]
Abstract: We have developed a helium gas flow cryostat for use on synchrotron tender to hard X-ray beamlines. Very efficient sample cooling is achieved because the sample is placed directly in the cooling helium flow on a removable sample holder. The cryostat is compact and easy to operate; samples can be changed in less than 5 min at any temperature. The cryostat has a temperature range of 2.5–325 K with temperature stability better than 0.1 K. The very wide optical angle and the ability to operate in any orientation mean that the cryostat can easily be adapted for different X-ray techniques. It is already in use on different beamlines at the European Synchrotron Radiation Facility (ESRF), ALBA Synchrotron Light Facility (ALBA), and Diamond Light Source (DLS) for inelastic X-ray scattering, powder diffraction, and X-ray absorption spectroscopy. Results obtained at these beamlines are presented here.
|
Nov 2016
|
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