I21-Resonant Inelastic X-ray Scattering (RIXS)
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Teguh Citra
Asmara
,
Robert J.
Green
,
Andreas
Suter
,
Yuan
Wei
,
Wenliang
Zhang
,
Daniel
Knez
,
Grant
Harris
,
Yi
Tseng
,
Tianlun
Yu
,
Davide
Betto
,
Mirian
Garcia-Fernandez
,
Stefano
Agrestini
,
Yannick Maximilian
Klein
,
Neeraj
Kumar
,
Carlos W.
Galdino
,
Zaher
Salman
,
Thomas
Prokscha
,
Marisa
Medarde
,
Elisabeth
Müller
,
Yona
Soh
,
Nicholas B.
Brookes
,
Ke-Jin
Zhou
,
Milan
Radovic
,
Thorsten
Schmitt
Diamond Proposal Number(s):
[28665]
Open Access
Abstract: Strongly-correlated transition-metal oxides are widely known for their various exotic phenomena. This is exemplified by rare-earth nickelates such as LaNiO3, which possess intimate interconnections between their electronic, spin, and lattice degrees of freedom. Their properties can be further enhanced by pairing them in hybrid heterostructures, which can lead to hidden phases and emergent phenomena. An important example is the LaNiO3/LaTiO3 superlattice, where an interlayer electron transfer has been observed from LaTiO3 into LaNiO3 leading to a high-spin state. However, macroscopic emergence of magnetic order associated with this high-spin state has so far not been observed. Here, by using muon spin rotation, x-ray absorption, and resonant inelastic x-ray scattering, direct evidence of an emergent antiferromagnetic order with high magnon energy and exchange interactions at the LaNiO3/LaTiO3 interface is presented. As the magnetism is purely interfacial, a single LaNiO3/LaTiO3 interface can essentially behave as an atomically thin strongly-correlated quasi-2D antiferromagnet, potentially allowing its technological utilization in advanced spintronic devices. Furthermore, its strong quasi-2D magnetic correlations, orbitally-polarized planar ligand holes, and layered superlattice design make its electronic, magnetic, and lattice configurations resemble the precursor states of superconducting cuprates and nickelates, but with an S→1 spin state instead.
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Aug 2024
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Izabela
Bialo
,
Leonardo
Martinelli
,
Gabriele
De Luca
,
Paul
Worm
,
Annabella
Drewanowski
,
Simon
Jöhr
,
Jaewon
Choi
,
Mirian
Garcia-Fernandez
,
Stefano
Agrestini
,
Ke-Jin
Zhou
,
Kurt
Kummer
,
Nicholas B.
Brookes
,
Luo
Guo
,
Anthony
Edgeton
,
Chang B.
Eom
,
Jan M.
Tomczak
,
Karsten
Held
,
Marta
Gibert
,
Qisi
Wang
,
Johan
Chang
Diamond Proposal Number(s):
[30189]
Open Access
Abstract: Magnetic frustration is a route for novel ground states, including spin liquids and spin ices. Such frustration can be introduced through either lattice geometry or incompatible exchange interactions. Here, we find that epitaxial strain is an effective tool for tuning antiferromagnetic exchange interactions in a square-lattice system. By studying the magnon excitations in La2NiO4 films using resonant inelastic x-ray scattering, we show that the magnon displays substantial dispersion along the antiferromagnetic zone boundary, at energies that depend on the lattice of the film’s substrate. Using first principles simulations and an effective spin model, we demonstrate that the antiferromagnetic next-nearest neighbour coupling is a consequence of the two-orbital nature of La2NiO4. Altogether, we illustrate that compressive epitaxial strain enhances this coupling and, as a result, increases the level of incompatibility between exchange interactions within a model square-lattice system.
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Jul 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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K.
Scott
,
E.
Kisiel
,
F.
Yakhou
,
S.
Agrestini
,
Mirian
Garcia-Fernandez
,
K.
Kummer
,
J.
Choi
,
R. D.
Zhong
,
J. A.
Schneeloch
,
G. D.
Gu
,
Ke-Jin
Zhou
,
N. B.
Brookes
,
A. F.
Kemper
,
M.
Minola
,
F.
Boschini
,
A.
Frano
,
A.
Gozar
,
E. H.
Da Silva Neto
Diamond Proposal Number(s):
[28523, 30146]
Abstract: Recent improvements in the energy resolution of resonant inelastic x-ray scattering experiments (RIXS) at the Cu-
L
3
edge have enabled the study of lattice, spin, and charge excitations. Here, we report on the detection of a low-intensity signal at 140 meV, twice the energy of the bond-stretching (BS) phonon mode, in the cuprate superconductor
Bi
2
Sr
2
Ca
Cu
2
O
8
+
x
(Bi-2212). Ultrahigh-resolution polarimetric RIXS measurements allow us to resolve the outgoing polarization of the signal and identify this feature as a two-phonon excitation. Further, we study the connection between the two-phonon mode and the BS one-phonon mode by constructing a joint density of states toy model that reproduces the key features of the data.
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Mar 2024
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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X. T.
Li
,
S. J.
Tu
,
L.
Chaix
,
C.
Fawaz
,
M.
D’astuto
,
X.
Li
,
F.
Yakhou-Harris
,
K.
Kummer
,
N. B.
Brookes
,
Mirian
Garcia-Fernandez
,
K.-J.
Zhou
,
Z. F.
Lin
,
J.
Yuan
,
K.
Jin
,
M. P.
Dean
,
X.
Liu
Diamond Proposal Number(s):
[27478]
Abstract: We investigated the high energy spin excitations in electron-doped
La
2
−
x
Ce
x
CuO
4
, a cuprate superconductor, by resonant inelastic x-ray scattering (RIXS) measurements. Efforts were paid to disentangle the paramagnon signal from non-spin-flip spectral weight mixing in the RIXS spectrum at
Q
∥
=
(
0.6
π
,
0
)
and
(
0.9
π
,
0
)
along the (1 0) direction. Our results show that, for doping level
x
from 0.07 to 0.185, the variation of the paramagnon excitation energy is marginal. We discuss the implication of our results in connection with the evolution of the electron correlation strength in this system.
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Feb 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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Abstract: van der Waals materials provide a versatile toolbox for the emergence of new quantum phenomena and fabrication of functional heterostructures. Among them, the trihalide VI3 stands out for its unique magnetic and structural landscape. Here we investigate the spin and orbital magnetic degrees of freedom in the layered ferromagnet VI3 by means of temperature-dependent X-ray absorption spectroscopy and X-ray magnetic circular and linear dichroism. We detect localized electronic states and reduced magnetic dimensionality, due to electronic correlations. We furthermore provide experimental evidence of (a) an unquenched orbital magnetic moment (up to 0.66(7) μB/V atom) in the ferromagnetic state and (b) an instability of the orbital moment in the proximity of the spin reorientation transition. Our results support a coherent picture where electronic correlations give rise to a strong magnetic anisotropy and a large orbital moment and establish VI3 as a prime candidate for the study of orbital quantum effects.
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Jan 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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Open Access
Abstract: Polarization dependent x-ray absorption spectroscopy was used to study the magnetic ground state and the orbital occupation in bulk-phase VI3 van der Waals crystals below and above the ferromagnetic and structural transitions. X-ray natural linear dichroism and X-ray magnetic circular dichroism spectra acquired at the V L2,3 edges are compared against multiplet cluster calculations within the frame of the ligand field theory to quantify the intra-atomic electronic interactions at play and evaluate the effects of symmetry reduction occurring in a trigonally distorted VI6 unit. We observed a non zero linear dichroism proving the presence of an anisotropic charge density distribution around the V3+ ion due to the unbalanced hybridization between the Vanadium and the ligand states. Such hybridization acts as an effective trigonal crystal field, slightly lifting the degeneracy of the t22g ground state. However, the energy splitting associated to the distortion underestimates the experimental band gap, suggesting that the insulating ground state is stabilized by Mott correlation effects rather than via a Jahn-Teller mechanism. Our results clarify the role of the distortion in VI3 and establish a benchmark for the study of the spectroscopic properties of other van der Waals halides, including emerging 2D materials with mono and few-layers thickness, whose fundamental properties might be altered by reduced dimensions and interface proximity.
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Jun 2023
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Andrea
Amorese
,
Philipp
Hansmann
,
Andrea
Marino
,
Peter
Körner
,
Thomas
Willers
,
Andrew
Walters
,
Ke-Jin
Zhou
,
Kurt
Kummer
,
Nicholas B.
Brookes
,
Hong-Ji
Lin
,
Chien-Te
Chen
,
Pascal
Lejay
,
Maurits W.
Haverkort
,
Liu Hao
Tjeng
,
Andrea
Severing
Diamond Proposal Number(s):
[18447]
Open Access
Abstract: We investigated the electronic structure of the enigmatic
CeRh
3
B
2
using resonant inelastic scattering and x-ray absorption spectroscopy in combination with ab initio density functional calculations. We find that the
Rh
4
d
states are irrelevant for the high-temperature ferromagnetism and the Kondo effect. We also find that the
Ce
4
f
crystal-field strength is too small to explain the strong reduction of the Ce magnetic moment. The data revealed instead the presence of two different active
Ce
4
f
orbitals, with each coupling selectively to different bands in
CeRh
3
B
2
. The intersite hybridization of the
∣
∣
J
=
5
2
,
J
z
=
±
1
2
⟩
crystal-field state and
Ce
5
d
band combined with the intrasite
Ce
4
f
–
5
d
exchange creates the strong ferromagnetism, while hybridization between the
∣
∣
J
=
5
2
,
J
z
=
±
5
2
⟩
and the B
s
p
in the
a
b
-plane contributes to the Kondo interaction, which causes the moment reduction. This orbital selective coupling explains the unique and seemingly contradictory properties of
CeRh
3
B
2
.
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Mar 2023
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