I21-Resonant Inelastic X-ray Scattering (RIXS)
|
S.
Agrestini
,
F.
Borgatti
,
P.
Florio
,
J.
Frassineti
,
D.
Fiore Mosca
,
Q.
Faure
,
B.
Detlefs
,
C. j.
Sahle
,
S.
Francoual
,
J.
Choi
,
Mirian
Garcia-Fernandez
,
K.-J.
Zhou
,
V. f.
Mitrović
,
P. m.
Woodward
,
G.
Ghiringhelli
,
C.
Franchini
,
F.
Boscherini
,
S.
Sanna
,
M.
Moretti Sala
Open Access
Abstract: A supposedly nonmagnetic 5𝑑1 double perovskite oxide is investigated by a combination of spectroscopic and theoretical methods, namely, resonant inelastic x-ray scattering, x-ray absorption spectroscopy, magnetic circular dichroism, and multiplet ligand-field calculations. We found that the large spin-orbit coupling admixes the 5𝑑 𝑡2𝑔 and 𝑒𝑔 orbitals, covalency raises the 5𝑑 population well above the nominal value, and the local symmetry is lower than 𝑂ℎ. The obtained electronic interactions account for the finite magnetic moment of Os in this compound and, in general, of 5𝑑1 ions. Our results provide direct evidence of elusive Jahn-Teller distortions, hinting at a strong electron-lattice coupling.
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Aug 2024
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Leonardo
Martinelli
,
Krzysztof
Wohlfeld
,
Jonathan
Pelliciari
,
Riccardo
Arpaia
,
Nicholas B.
Brookes
,
Daniele
Di Castro
,
Mirian
Garcia-Fernandez
,
Mingu
Kang
,
Yoshiharu
Krockenberger
,
Kurt
Kummer
,
Daniel E.
Mcnally
,
Eugenio
Paris
,
Thorsten
Schmitt
,
Hideki
Yamamoto
,
Andrew
Walters
,
Ke-Jin
Zhou
,
Lucio
Braicovich
,
Riccardo
Comin
,
Marco
Moretti Sala
,
Thomas P.
Devereaux
,
Maria
Daghofer
,
Giacomo
Ghiringhelli
Diamond Proposal Number(s):
[20690]
Abstract: We have investigated the
3
d
orbital excitations in
CaCuO
2
(CCO),
Nd
2
CuO
4
(NCO), and
La
2
CuO
4
(LCO) using high-resolution resonant inelastic x-ray scattering. In LCO they behave as well-localized excitations, similarly to several other cuprates. On the contrary, in CCO and NCO the
d
x
y
orbital clearly disperses, pointing to a collective character of this excitation (orbiton) in compounds without apical oxygen. We ascribe the origin of the dispersion as stemming from a substantial next-nearest-neighbor (NNN) orbital superexchange. Such an exchange leads to the liberation of the orbiton from its coupling to magnons, which is associated with the orbiton hopping between nearest neighbor copper sites. Finally, we show that the exceptionally large NNN orbital superexchange can be traced back to the absence of apical oxygens suppressing the charge transfer energy.
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Feb 2024
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
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)
|
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)
|
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.
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May 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)
|
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.
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May 2021
|
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Roberto
Fumagalli
,
Abhishek
Nag
,
Stefano
Agrestini
,
Mirian
Garcia-Fernandez
,
Andrew C.
Walters
,
Davide
Betto
,
Nicholas B.
Brookes
,
Lucio
Braicovich
,
Ke-Jin
Zhou
,
Giacomo
Ghiringhelli
,
Marco Moretti
Sala
Diamond Proposal Number(s):
[23423]
Abstract: Motivated by the recent synthesis of Ba
CuO
(BCO), a high temperature superconducting cuprate with putative
ground state symmetry, we investigated its electronic structure by means of Cu
x-ray absorption (XAS) and resonant inelastic x-ray scattering (RIXS) at the Cu
edge on a polycrystalline sample. We show that the XAS profile of BCO is characterised by two peaks associated to inequivalent Cu sites, and that its RIXS response features a single, sharp peak associated to crystal-field excitations. We argue that these observations are only partially compatible with the previously proposed crystal structure of BCO. Based on our spectroscopic results and on previously published powder diffraction measurements, we propose a crystalline structure characterized by two inequivalent Cu sites located at alternated planes along the
axis: nominally trivalent Cu(1) belonging to very short Cu-O chains, and divalent Cu(2) in the oxygen deficient CuO
planes. We also analyze the low-energy region of the RIXS spectra to estimate the magnitude of the magnetic interactions in BCO and find that in-plane nearest neighbor superexchange exceeds 120 meV, similarly to that of other layered cuprates. Although these results do not support the pure
ground state scenario, they hint at a significant departure from the common quasi-2D electronic structure of superconducting cuprates of pure
symmetry.
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Dec 2020
|
|
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Abstract: We present experimental results on resonant inelastic x-ray scattering (RIXS) in perpendicular geometry excited with circularly polarized x rays at the Co L3,2 edges in Co ferrite (CoFe2O4) and Co metal and at the Fe L3,2 edges in Fe metal. In this geometry with magnetic samples the incident x-ray beam is perpendicular to the magnetization and the magnetic dichroism is only present in RIXS. We study the 3s-RIXS channel terminating in an inner shell 3s hole and extra 3d electron (2p63dn→2p53dn+1→2p63s13dn+1). The work is based on the measurement of the spectra vs incident photon energy and integrated over the scattered photon energy. We present data resolved in linear polarization of the scattered beam for scattering at 45° and data summed over the outgoing polarizations and taken vs the scattering angle φ. The results show common features in both metals and ionic system: the dichroism scales as sin2φ while the spectral shape remains constant. The dichroism is maximum when the outgoing linear polarization is in the scattering plane and zero when the outgoing linear polarization is perpendicular to the scattering plane. The presence of the dichroism is due to the breaking of the mirror symmetry of the geometry consisting of the helicity vector of the incident radiation, the sample magnetization, and the linear polarization of the scattered beam. This is expected, in general, when the scattering occurs without rearrangement in the intermediate state. It is noteworthy that this occurs also in the metallic systems, where the scattering takes place with rearrangement due to a spin-dependent screening of the intermediate state core hole. This shows that this rearrangement does not require a more complex vector system in its description. The results show the relation between the selection of the scattering angle and the measurement of the polarization of the scattered radiation. We also present results from a geometry where the dichroism is absent in the emission integrated over outgoing polarization but where it is observed when this polarization is selected.
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May 2007
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