I20-Scanning-X-ray spectroscopy (XAS/XES)
|
Maryia
Zinouyeva
,
Martina
Fracchia
,
Giulia
Maranini
,
Davide
Impelluso
,
Nicholas B.
Brookes
,
Lorenzo
Grilli
,
Kurt
Kummer
,
Francesco
Rosa
,
Matteo
Aramini
,
Giacomo
Ghiringhelli
,
Paolo
Ghigna
,
Marco
Moretti Sala
,
Mauro
Coduri
Open Access
Abstract: We employ several X-ray based techniques, including X-ray diffraction, X-ray absorption spectroscopy and resonant inelastic X-ray scattering, to disentangle the contributions of individual chemical species to the structural, electronic and magnetic properties of high-entropy oxides. In the benchmark compound Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O and related systems, we unambiguously resolve a sizable Jahn–Teller distortion at the Cu sites, more pronounced in the absence of Ni2+ and Mg2+, suggesting that these ions promote positional order, whereas Cu2+ ions act to destabilize it. Moreover, we detect magnetic excitations and estimate the strength of the interactions between pairs of different magnetic elements. Our results provide valuable insights into the role of various chemical species in shaping the physical properties of high-entropy oxides.
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Nov 2025
|
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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)
|
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)
|
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.
|
Mar 2024
|
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
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.
|
Feb 2024
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
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.
|
Feb 2024
|
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
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
.
|
Mar 2023
|
|
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
|
|
I05-ARPES
|
Georg
Poelchen
,
Igor P.
Rusinov
,
Susanne
Schulz
,
Monika
Guttler
,
Max
Mende
,
Alexander
Generalov
,
Dmitry Yu.
Usachov
,
Steffen
Danzenbacher
,
Johannes
Hellwig
,
Marius
Peters
,
Kristin
Kliemt
,
Yuri
Kucherenko
,
Victor N.
Antonov
,
Clemens
Laubschat
,
Evgueni V.
Chulkov
,
Arthur
Ernst
,
Kurt
Kummer
,
Cornelius
Krellner
,
Denis V.
Vyalikh
Diamond Proposal Number(s):
[24339]
Abstract: The f-driven temperature scales at the surfaces of strongly correlated materials have increasingly come into the focus of research efforts. Here, we unveil the emergence of a two-dimensional Ce Kondo lattice, which couples ferromagnetically to the ordered Co lattice below the P-terminated surface of the antiferromagnet CeCo2P2. In its bulk, Ce is passive and behaves tetravalently. However, because of symmetry breaking and an effective magnetic field caused by an uncompensated ferromagnetic Co layer, the Ce 4f states become partially occupied and spin-polarized near the surface. The momentum-resolved photoemission measurements indicate a strong admixture of the Ce 4f states to the itinerant bands near the Fermi level including surface states that are split by exchange interaction with Co. The temperature-dependent measurements reveal strong changes of the 4f intensity at the Fermi level in accordance with the Kondo scenario. Our findings show how rich and diverse the f-driven properties can be at the surface of materials without f-physics in the bulk.
|
Feb 2022
|
|
|
|
Open Access
Abstract: Hall effect and quantum oscillation measurements on high temperature cuprate superconductors show that underdoped compositions have small Fermi surface pockets whereas when heavily overdoped, a single much larger pocket is found. The origin of this change in electronic structure has been unclear, but may be related to the high temperature superconductivity. Here we show that the clean overdoped single-layer cuprate Tl2Ba2CuO6+δ (Tl2201) displays CDW order with a remarkably long correlation length ξ ≈ 200 Å which disappears above a hole doping of pCDW ≈ 0.265. We show that the evolution of the electronic properties of Tl2201 as the doping is lowered may be explained by a Fermi surface reconstruction which accompanies the emergence of the CDW below pCDW. Our results demonstrate importance of CDW correlations in understanding the electronic properties of overdoped cuprates.
|
Jan 2022
|
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