I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Karin
Von Arx
,
Pascal
Rothenbühler
,
Qisi
Wang
,
Leonardo
Martinelli
,
Jaewon
Choi
,
Mirian
Garcia-Fernandez
,
Stefano
Agrestini
,
Ke-Jin
Zhou
,
Antonio
Vecchione
,
Rosalba
Fittipaldi
,
Yasmine
Sassa
,
Mario
Cuoco
,
Filomena
Forte
,
Johan
Chang
Diamond Proposal Number(s):
[27638]
Open Access
Abstract: Multi-band Mott insulators with moderate spin-orbit and Hund’s coupling are key reference points for theoretical concept developments of correlated electron systems. The ruthenate Mott insulator Ca2RuO4 has therefore been intensively studied by spectroscopic probes. However, it has been challenging to resolve the fundamental excitations emerging from the hierarchy of electronic energy scales. Here we apply high resolution resonant inelastic x-ray scattering to probe deeper into the low-energy electronic excitations found in Ca2RuO4. In this fashion, we probe a series of spin-orbital excitations. By taking advantage of enhanced energy resolution, we probe a 40 meV mode through the oxygen K-edge. The polarization dependence of this low-energy excitations exposes a distinct orbital nature, originating from the interplay of spin-orbit coupling and octahedral rotations. Additionally, we discuss the role of magnetic correlations to describe the occurrence of excitations with amplitudes which are multiple of a given energy. Such direct determination of relevant electronic energy scales sharpens the target for theory developments of Mott insulators’ orbital degree of freedom.
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May 2025
|
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I05-ARPES
|
Ola Kenji
Forslund
,
Xiaoxiong
Liu
,
Soohyeon
Shin
,
Chun
Lin
,
Masafumi
Horio
,
Qisi
Wang
,
Kevin
Kramer
,
Saumya
Mukherjee
,
Timur
Kim
,
Cephise
Cacho
,
Chennan
Wang
,
Tian
Shang
,
Victor
Ukleev
,
Jonathan S.
White
,
Pascal
Puphal
,
Yasmine
Sassa
,
Ekaterina
Pomjakushina
,
Titus
Neupert
,
Johan
Chang
Diamond Proposal Number(s):
[22091]
Abstract: The anomalous Hall effect (AHE) has emerged as a key indicator of time-reversal symmetry breaking (TRSB) and topological features in electronic band structures. Absent of a magnetic field, the AHE requires spontaneous TRSB but has proven hard to probe due to averaging over domains. The anomalous component of the Hall effect is thus frequently derived from extrapolating the magnetic field dependence of the Hall response. We show that discerning whether the AHE is an intrinsic property of the field-free system becomes intricate in the presence of strong magnetic fluctuations. As a study case, we use the Weyl semimetal PrAlGe, where TRSB can be toggled via a ferromagnetic transition, providing a transparent view of the AHE’s topological origin. Through a combination of thermodynamic, transport, and muon spin relaxation measurements, we contrast the behavior below the ferromagnetic transition temperature to that of strong magnetic fluctuations above. Our results on PrAlGe provide general insights into the interpretation of anomalous Hall signals in systems where TRSB is debated, such as families of kagome metals or certain transition metal dichalcogenides.
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Mar 2025
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
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)
|
Qiang
Gao
,
Shiyu
Fan
,
Qisi
Wang
,
Jiarui
Li
,
Xiaolin
Ren
,
Izabela
Bialo
,
Annabella
Drewanowski
,
Pascal
Rothenbühler
,
Jaewon
Choi
,
Ronny
Sutarto
,
Yao
Wang
,
Tao
Xiang
,
Jiangping
Hu
,
Ke-Jin
Zhou
,
Valentina
Bisogni
,
Riccardo
Comin
,
Johan
Chang
,
Jonathan
Pelliciari
,
Xingjiang
Zhou
,
Zhihai
Zhu
Diamond Proposal Number(s):
[30189]
Open Access
Abstract: Strongly correlated materials respond sensitively to external perturbations such as strain, pressure, and doping. In the recently discovered superconducting infinite-layer nickelates, the superconducting transition temperature can be enhanced via only ~ 1% compressive strain-tuning with the root of such enhancement still being elusive. Using resonant inelastic x-ray scattering (RIXS), we investigate the magnetic excitations in infinite-layer PrNiO2 thin films grown on two different substrates, namely SrTiO3 (STO) and (LaAlO3)0.3(Sr2TaAlO6)0.7 (LSAT) enforcing different strain on the nickelates films. The magnon bandwidth of PrNiO2 shows only marginal response to strain-tuning, in sharp contrast to the enhancement of the superconducting transition temperature Tc in the doped superconducting samples. These results suggest the bandwidth of spin excitations of the parent compounds is similar under strain while Tc in the doped ones is not, and thus provide important empirics for the understanding of superconductivity in infinite-layer nickelates.
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Jul 2024
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Paul
Worm
,
Qisi
Wang
,
Motoharu
Kitatani
,
Izabela
Bialo
,
Qiang
Gao
,
Xiaolin
Ren
,
Jaewon
Choi
,
Diana
Csontosová
,
Ke-Jin
Zhou
,
Xingjiang
Zhou
,
Zhihai
Zhu
,
Liang
Si
,
Johan
Chang
,
Jan M.
Tomczak
,
Karsten
Held
Diamond Proposal Number(s):
[30189]
Abstract: Infinite-layer nickelates show high-temperature superconductivity, and the experimental phase diagram agrees well with the one simulated within the dynamical vertex approximation (DΓA). Here, we compare the spin-fluctuation spectrum behind these calculations to resonant inelastic x-ray scattering experiments. The overall agreement is good. This independent cross validation of the strength of spin fluctuations strongly supports the scenario, advanced by DΓA, that spin fluctuations are the mediator of the superconductivity observed in nickelates.
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Jun 2024
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Jens
Oppliger
,
M. Michael
Denner
,
Julia
Kuespert
,
Ruggero
Frison
,
Qisi
Wang
,
Alexander
Morawietz
,
Oleh
Ivashko
,
Ann-Christin
Dippel
,
Martin
Von Zimmermann
,
Izabela
Bialo
,
Leonardo
Martinelli
,
Benoît
Fauqué
,
Jaewon
Choi
,
Mirian
Garcia-Fernandez
,
Ke-Jin
Zhou
,
Niels
Bech Christensen
,
Tohru
Kurosawa
,
Naoki
Momono
,
Migaku
Oda
,
Fabian D.
Natterer
,
Mark H.
Fischer
,
Titus
Neupert
,
Johan
Chang
Diamond Proposal Number(s):
[31819]
Open Access
Abstract: The removal or cancellation of noise has wide-spread applications in imaging and acoustics. In applications in everyday life, such as image restoration, denoising may even include generative aspects, which are unfaithful to the ground truth. For scientific use, however, denoising must reproduce the ground truth accurately. Denoising scientific data is further challenged by unknown noise profiles. In fact, such data will often include noise from multiple distinct sources, which substantially reduces the applicability of simulation-based approaches. Here we show how scientific data can be denoised by using a deep convolutional neural network such that weak signals appear with quantitative accuracy. In particular, we study X-ray diffraction and resonant X-ray scattering data recorded on crystalline materials. We demonstrate that weak signals stemming from charge ordering, insignificant in the noisy data, become visible and accurate in the denoised data. This success is enabled by supervised training of a deep neural network with pairs of measured low- and high-noise data. We additionally show that using artificial noise does not yield such quantitatively accurate results. Our approach thus illustrates a practical strategy for noise filtering that can be applied to challenging acquisition problems.
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Feb 2024
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I05-ARPES
|
Kevin P.
Kramer
,
Rina
Tazai
,
Karin
Von Arx
,
Masafumi
Horio
,
Julia
Küspert
,
Qisi
Wang
,
Yasmine
Sassa
,
Timur K.
Kim
,
Cephise
Cacho
,
Julien E.
Rault
,
Patrick
Le Fèvre
,
François
Bertran
,
Marc
Janoschek
,
Nicolas
Gauthier
,
Daniel
Mazzone
,
Ramzy
Daou
,
Johan
Chang
Open Access
Abstract: We present a resonant angle-resolved photoemission spectroscopy (ARPES) study of the electronic band structure and heavy fermion quasiparticles in CeRu2Si2. Using light polarization analysis, considerations of the crystal field environment and hybridization between conduction and f electronic states, we identify the d-electronic orbital character of conduction bands crossing the Fermi level. Resonant ARPES spectra suggest that the localized Ce f states hybridize with eg and t2g states around the zone center. In this fashion, we reveal the orbital structure of the heavy fermion quasiparticles in CeRu2Si2 and discuss its implications for metamagnetism and superconductivity in the related compound CeCu2Si2.
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Oct 2023
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I05-ARPES
|
C. E.
Matt
,
O.
Ivashko
,
M.
Horio
,
J.
Choi
,
Q.
Wang
,
D.
Sutter
,
N.
Dennler
,
M. H.
Fischer
,
S.
Katrych
,
L.
Forro
,
J.
Ma
,
B.
Fu
,
B. Q.
Lv
,
M. V.
Zimmermann
,
T. K.
Kim
,
N. C.
Plumb
,
N.
Xu
,
M.
Shi
,
Johan
Chang
Diamond Proposal Number(s):
[16104]
Open Access
Abstract: The interplay between structural and electronic phases in iron-based superconductors is a central theme in the search for the superconducting pairing mechanism. While electronic nematicity is competing with superconductivity, the effect of purely structural orthorhombic order is unexplored. Here, using x-ray diffraction and angle-resolved photoemission spectroscopy, we reveal a structural orthorhombic phase in the electron-doped iron-pnictide superconductor
Pr
4
Fe
2
As
2
Te
0.88
O
4
(
T
c
=
25
K), which is distinct from orthorhombicity in the nematic phase in underdoped pnictides. Despite the high electron doping we find an exceptionally high orthorhombic onset temperature (
T
ort
∼
250
K), no signatures of phase competition with superconductivity, and absence of electronic nematic order as the driving mechanism for orthorhombicity. Combined, our results establish a high-temperature phase in the phase diagram of iron-pnictide superconductors and impose strong constraints for the modeling of their superconducting pairing mechanism.
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Jun 2021
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Qisi
Wang
,
Karin
Von Arx
,
Masafumi
Horio
,
Deepak John
Mukkattukavil
,
Julia
Kuespert
,
Yasmine
Sassa
,
Thorsten
Schmitt
,
Abhishek
Nag
,
Sunseng
Pyon
,
Tomohiro
Takayama
,
Hidenori
Takagi
,
Mirian
Garcia-Fernandez
,
Ke-Jin
Zhou
,
Johan
Chang
Diamond Proposal Number(s):
[24481]
Open Access
Abstract: Charge order is universal to all hole-doped cuprates. Yet, the driving interactions remain an unsolved problem. Electron-electron interaction is widely believed to be essential, whereas the role of electron-phonon interaction is unclear. We report an ultrahigh-resolution resonant inelastic x-ray scattering (RIXS) study of the in-plane bond-stretching phonon mode in stripe-ordered cuprate La1.675Eu0.2Sr0.125CuO4. Phonon softening and lifetime shortening are found around the charge ordering wave vector. In addition to these self-energy effects, the electron-phonon coupling is probed by its proportionality to the RIXS cross section. We find an enhancement of the electron-phonon coupling around the charge-stripe ordering wave vector upon cooling into the low-temperature tetragonal structure phase. These results suggest that, in addition to electronic correlations, electron-phonon coupling contributes substantially to the emergence of long-range charge-stripe order in cuprates.
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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.
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May 2021
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