I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Xiaoyang
Chen
,
Wenliang
Zhang
,
Fei
Peng
,
Ting
Cui
,
Guangdi
Zhou
,
Zezhong
Li
,
Jaewon
Choi
,
Lizhi
Xu
,
Yiu-Fung
Chiu
,
Stefano
Agrestini
,
Sahil
Tippireddy
,
Haoliang
Huang
,
Heng
Wang
,
Xianfeng
Wu
,
Peng
Li
,
Jin-Feng
Jia
,
Mirian
Garcia-Fernandez
,
Yi
Lu
,
Er-Jia
Guo
,
Qi-Kun
Xue
,
Zhuoyu
Chen
,
Donglai
Feng
,
Ke-Jin
Zhou
Diamond Proposal Number(s):
[42637]
Open Access
Abstract: The recent discovery of Ruddlesden-Popper (RP) nickelate thin-film superconductors has opened a new frontier in unconventional superconductivity. Its realization requires both compressive epitaxial strain and highly oxidative growth conditions, yet the microscopic pathway from the parent phase to the superconducting phase remains elusive. Here, X-ray absorption spectra and resonant inelastic X-ray scattering are employed to track this evolution by independently tuning strain and oxygen content in (La,Pr)3Ni2O7 − δ thin films. We uncover a remarkable two-step narrative. First, signatures of delocalization emerge: Spectral weight transfers from a “Upper Hubbard”-like peak to the hole-like peak associated with O 2pz state, and in parallel, the initially localized Ni
orbital becomes more itinerant followed by the broadening and weakening of dd orbital excitations. Second, as itinerancy increases, long-range spin-density-wave (SDW) order is suppressed in both intensity and correlation length, indicating direct competition with superconductivity. Yet, short-range magnons persist: they become damped but their bandwidth stays unchanged. Our results paint a coherent picture that both strain and oxygenation drive the RP bilayer nickelates towards the superconducting instability, where the O 2pz and Ni
orbitals become delocalized. Concomitantly, the long-range magnetic order loses coherence and gets suppressed. These findings establish an orbital-selective route to RP nickelate superconductivity, in which the emergence and progressive delocalization of the interlayer
-2pz-
channel and the robust short-range magnons upon the melting of SDW order are prerequisites, providing strong constraints for theory and the roadmap for designing nickelate superconductors.
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Aug 2026
|
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I05-ARPES
|
Xingtian
Sun
,
Suppanut
Sangphet
,
Nan
Guo
,
Yu
Fan
,
Yutong
Chen
,
Minyinan
Lei
,
Xue
Ming
,
Xiyu
Zhu
,
Hai-Hu
Wen
,
Haichao
Xu
,
Rui
Peng
,
Donglai
Feng
Diamond Proposal Number(s):
[39544]
Abstract: The superconducting transition temperatures (𝑇c’s) of trilayer or quadruple-layer cuprates typically surpass those of single-layer or bilayer systems. However, the lack of direct electronic-structure and superconducting-gap measurements in optimal-𝑇c quadruple-layer cuprates has impeded a comprehensive understanding of the origin of the enhanced 𝑇c in multilayer systems. In this Letter, using angle-resolved photoemission spectroscopy, we investigate the quadruple-layer cuprate (Cu,C)Ba2Ca3Cu4O11+𝛿 (CuC-1234) with a high 𝑇c of 110 K, and resolved distinct superconducting-gap behaviors between the inner CuO2 planes and outer CuO2 planes, in contrast to that reported for trilayer cuprates. Outer CuO2 planes develop their own superconducting gap and superconducting coherence peak at a temperature much lower than the 𝑇c of the material, while the large pairing strength and phase coherence concurrently emerge at the underdoped inner CuO2 planes at 𝑇c. Our findings suggest that CuO2 planes free of apical oxygen can have significant contribution to superconductivity up to 110 K in multilayer cuprates, even at a doping level of 0.07 holes per Cu, a level that lies deep in the underdoped regime of single- and bilayer cuprates. These findings provide new insights into the origin of high 𝑇c in multilayer cuprates.
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May 2026
|
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I05-ARPES
|
Zhisheng
Zhao
,
Tongrui
Li
,
Peng
Li
,
Xueliang
Wu
,
Jianghao
Yao
,
Ziyuan
Chen
,
Yajun
Yan
,
Shengtao
Cui
,
Zhe
Sun
,
Yichen
Yang
,
Zhicheng
Jiang
,
Zhengtai
Liu
,
Alex
Louat
,
Timur
Kim
,
Cephise
Cacho
,
Aifeng
Wang
,
Yilin
Wang
,
Dawei
Shen
,
Juan
Jiang
,
Donglai
Feng
Diamond Proposal Number(s):
[32274]
Abstract: The kagome metal FeGe provides a rich platform for understanding the mechanisms behind competing orders, as it exhibits charge order (CO) emerging deep within the antiferromagnetic phase. To investigate the intrinsic origin of this behavior, we examine the evolution of the low-energy electronic structure across the phase transition in annealed FeGe samples using angle-resolved photoemission spectroscopy. We find no evidence supporting a conventional nesting mechanism, such as Fermi surface nesting or van Hove singularities. However, we observe two notable changes in the band structure: an electron-like band around the K point and another around the A point, both shifting upward in energy when CO forms. These findings are consistent with our density-functional theory calculations, which suggest that the charge order in FeGe is primarily driven by magnetic energy savings due to a lattice distortion involving Ge1-dimerization. Our results provide photoemission evidence supporting this novel mechanism for CO formation in FeGe, in contrast to the conventional nesting-driven mechanisms.
|
Jun 2025
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Xiaoyang
Chen
,
Jaewon
Choi
,
Zhicheng
Jiang
,
Jiong
Mei
,
Kun
Jiang
,
Jie
Li
,
Stefano
Agrestini
,
Mirian
Garcia-Fernandez
,
Hualei
Sun
,
Xing
Huang
,
Dawei
Shen
,
Meng
Wang
,
Jiangping
Hu
,
Yi
Lu
,
Ke-Jin
Zhou
,
Donglai
Feng
Diamond Proposal Number(s):
[35805]
Open Access
Abstract: High-temperature superconductivity was discovered in the pressurized nickelate La3Ni2O7 which has a unique bilayer structure and mixed valence state of nickel. The properties at ambient pressure contain crucial information of the fundamental interactions and bosons mediating superconducting pairing. Here, using X-ray absorption spectroscopy and resonant inelastic X-ray scattering, we identified that Ni 3, Ni 3, and ligand oxygen 2p orbitals dominate the low-energy physics with a small charge-transfer energy. Well-defined optical-like magnetic excitations soften into quasi-static spin-density-wave ordering, evidencing the strong electronic correlation and rich magnetic properties. Based on an effective Heisenberg spin model, we extract a much stronger inter-layer effective magnetic superexchange than the intra-layer ones and propose two viable magnetic structures. Our findings emphasize that the Ni 3 orbital bonding within the bilayer induces novel electronic and magnetic excitations, setting the stage for further exploration of La3Ni2O7 superconductor.
|
Nov 2024
|
|
I05-ARPES
|
T.
Yu
,
M.
Xu
,
W. T.
Yang
,
Y. H.
Song
,
C. H. P.
Wen
,
Q.
Yao
,
X.
Lou
,
T.
Zhang
,
W.
Li
,
X. Y.
Wei
,
J. K.
Bao
,
G. H.
Cao
,
P.
Dudin
,
J. D.
Denlinger
,
V. N.
Strocov
,
R.
Peng
,
H. C.
Xu
,
D. L.
Feng
Diamond Proposal Number(s):
[20697]
Open Access
Abstract: The interactions between electrons and antiferromagnetic magnons (AFMMs) are important for a large class of correlated materials. For example, they are the most plausible pairing glues in high-temperature superconductors, such as cuprates and iron-based superconductors. However, unlike electron-phonon interactions (EPIs), clear-cut observations regarding how electron-AFMM interactions (EAIs) affect the band structure are still lacking. Consequently, critical information on the EAIs, such as its strength and doping dependence, remains elusive. Here we directly observe that EAIs induce a kink structure in the band dispersion of Ba1−xKxMn2As2, and subsequently unveil several key characteristics of EAIs. We found that the coupling constant of EAIs can be as large as 5.4, and it shows strong doping dependence and temperature dependence, all in stark contrast to the behaviors of EPIs. The colossal renormalization of electron bands by EAIs enhances the density of states at Fermi energy, which is likely driving the emergent ferromagnetic state in Ba1−xKxMn2As2 through a Stoner-like mechanism with mixed itinerant-local character. Our results expand the current knowledge of EAIs, which may facilitate the further understanding of many correlated materials where EAIs play a critical role.
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Nov 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
|
|
I05-ARPES
|
X.
Lou
,
T. l.
Yu
,
Y. h.
Song
,
C. h. P.
Wen
,
W. z.
Wei
,
A.
Leithe-Jasper
,
Z. f.
Ding
,
L.
Shu
,
S.
Kirchner
,
H. C.
Xu
,
R.
Peng
,
D. L.
Feng
Diamond Proposal Number(s):
[22518]
Abstract: CeOs
4
Sb
12
(COS) and
PrOs
4
Sb
12
(POS) are two representative compounds that provide the ideal vantage point to systematically study the physics of multi-
f
-electron systems. COS with Ce
4
f
1
, and POS with Pr
4
f
2
configurations show distinct properties of Kondo insulating and heavy fermion superconductivity, respectively. We unveiled the underlying microscopic origin by angle-resolved photoemission spectroscopy studies. Their eV-scale band structure matches well, representing the common characters of conduction electrons in
R
Os
4
Sb
12
systems (
R
=
rare
earth
). However,
f
electrons interact differently with conduction electrons in COS and POS. Strong hybridization between conduction electrons and
f
electrons is observed in COS with band dependent hybridization gaps, and the development of a Kondo insulating state is directly revealed. Although the ground state of POS is a singlet, finite but incoherent hybridization exists, which can be explained by the Kondo scattering with the thermally excited triplet crystalline electric field state. Our results help us to understand the intriguing properties in COS and POS, and provide a clean demonstration of the microscopic differences in heavy fermion systems with
4
f
1
and
4
f
2
configurations.
|
Apr 2021
|
|
I05-ARPES
|
X.
Lou
,
H. C.
Xu
,
C. H. P.
Wen
,
T. L.
Yu
,
W. Z.
Wei
,
Q.
Yao
,
Y. H.
Song
,
E.
Emmanouilidou
,
B.
Shen
,
N.
Ni
,
P.
Dudin
,
Y. B.
Huang
,
J.
Denlinger
,
R.
Sutarto
,
W.
Li
,
R.
Peng
,
D. L.
Feng
Diamond Proposal Number(s):
[20697]
Abstract: BaAg
2
As
2
, a sibling compound of
BaFe
2
As
2
with a nonmagnetic phase transition around 150 K, is studied by the comprehensive measurements of angle-resolved photoemission spectroscopy, synchrotron x-ray diffraction, and resonant soft x-ray scattering. The Fermi surfaces and electronic structure of
BaAg
2
As
2
are revealed, with strong
k
z
dispersion, consistent with the strongly contracted
c
/
a
ratio in
BaAg
2
As
2
. Across the phase transition, splitting of [101] Bragg peak is observed, showing a structural distortion with the in-plane distortion magnitude
δ
=
|
a
−
b
|
/
(
a
+
b
)
=
0.0052
. Although the nesting condition is satisfied in some parallel Fermi-surface sectors, there is no signature of charge density wave order at the nesting wave vector. Moreover, neither a charge density wave gap opening nor band reconstruction are observed across the phase transition. Instead, an enhancement on the spectral weight of dispersive bands is observed across the structural phase transition, which can explain the sharp drop of resistivity below the phase transition temperature. These studies could enrich the understanding of the variable and common features of the structural transition in transition metal pnictide layered materials.
|
Feb 2020
|
|
I05-ARPES
|
Diamond Proposal Number(s):
[1914]
Abstract: The energy scales in rare-earth-based heavy-fermion compounds are relatively small, which can be easily tuned by applying pressure, magnetic field, or chemical doping. By substituting Yb for Ce on the rare-earth site, the ground state of superconductivity can be smoothly suppressed without the appearance of an apparent quantum critical point, and a number of remarkable phenomena have been observed. The slight changes in the electronic structure are supposed to dominate the underlying physics in these compounds. In the present study, we provide an electronic structure study of
Ce
0.85
Yb
0.15
CoIn
5
with a superconducting state but suppressed transition temperature by angle-resolved photoemission spectroscopy, and the results are compared with
CeCoIn
5
. We find that the
f
electrons in
Ce
0.85
Yb
0.15
CoIn
5
are itinerant, forming the weakly dispersive hybridized band at low temperature. More interestingly, the hybridization strength between the
f
electrons and conduction electrons in
Ce
0.85
Yb
0.15
CoIn
5
is comparable with
CeCoIn
5
. Further temperature-dependent measurements provide direct evidence of the localized-to-itinerant crossover behavior of the
4
f
electrons in this compound.
|
Jan 2020
|
|
I05-ARPES
|
Q.
Yao
,
D.
Kaczorowski
,
P.
Swatek
,
D.
Gnida
,
C. H. P.
Wen
,
X. H.
Niu
,
R.
Peng
,
H. C.
Xu
,
P.
Dudin
,
S.
Kirchner
,
Q. Y.
Chen
,
D. W.
Shen
,
D. L.
Feng
Diamond Proposal Number(s):
[16345]
Abstract: The localized-to-itinerant transition of f electrons lies at the heart of heavy-fermion physics, but has only been directly observed in single-layer Ce-based materials. Here, we report a comprehensive study on the electronic structure and nature of the Ce 4f electrons in the heavy-fermion superconductor Ce2PdIn8, a typical n=2 CenMmIn3n+2m compound, using high-resolution and 4d−4f resonant photoemission spectroscopies. The electronic structure of this material has been studied over a wide temperature range, and hybridization between f and conduction electrons can be clearly observed to form a Kondo resonance near the Fermi level at low temperatures. The characteristic temperature of the localized-to-itinerant transition is around 120 K, which is much higher than its coherence temperature Tcoh∼30K.
|
Feb 2019
|
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