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.
|
Nov 2022
|
|
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.
|
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
|
|
I05-ARPES
|
C. h. p.
Wen
,
H. c.
Xu
,
Q.
Yao
,
R.
Peng
,
X. h.
Niu
,
Q. y.
Chen
,
Z. t.
Liu
,
D. w.
Shen
,
Q.
Song
,
X.
Lou
,
Y. f.
Fang
,
X. s.
Liu
,
Y. h.
Song
,
Y. j.
Jiao
,
T. f.
Duan
,
H. h.
Wen
,
P.
Dudin
,
G.
Kotliar
,
Z. p.
Yin
,
D. l.
Feng
Diamond Proposal Number(s):
[14737, 16345, 20697]
Abstract: The mechanism of high superconducting transition temperatures (Tc) in bismuthates remains under debate despite more than 30 years of extensive research. Our angle-resolved photoemission spectroscopy studies on Ba0.51K0.49BiO3 reveal an unexpectedly 34% larger bandwidth than in conventional density functional theory calculations. This can be reproduced by calculations that fully account for long-range Coulomb interactions—the first direct demonstration of bandwidth expansion due to the Fock exchange term, a long-accepted and yet uncorroborated fundamental effect in many body physics.Furthermore, we observe an isotropic superconducting gap with 2Δ0/kBTc=3.51±0.05, and strong electron-phonon interactions with a coupling constant λ∼1.3±0.2. These findings solve a long-standing mystery—Ba0.51K0.49BiO3 is an extraordinary Bardeen-Cooper-Schrieffer superconductor, where long-range Coulomb interactions expand the bandwidth, enhance electron-phonon coupling, and generate the high Tc. Such effects will also be critical for finding new superconductors.
|
Sep 2018
|
|
I05-ARPES
|
Q.
Yao
,
D. W.
Shen
,
C. H. P.
Wen
,
C. Q.
Hua
,
L. Q.
Zhang
,
N. Z.
Wang
,
X. H.
Niu
,
Q. Y.
Chen
,
P.
Dudin
,
Y. H.
Lu
,
Y.
Zheng
,
X. H.
Chen
,
X. G.
Wan
,
D. l.
Feng
Diamond Proposal Number(s):
[14737]
Abstract: van der Waals heterostructures (vdWHs) exhibit rich properties and thus potential for applications, and charge transfer between different layers in a heterostructure often dominates its properties and device performance. It is thus critical to reveal and understand the charge transfer effects in vdWHs, for which electronic structure measurements have proven to be effective. Using angle-resolved photoemission spectroscopy, we studied the electronic structures of (PbSe)1.16(TiSe2)m (m = 1, 2), which are naturally occurring vdWHs, and discovered several striking charge transfer effects, which may widely exist in vdWHs. When the thickness of the TiSe2 lay- ers is halved from m = 2 to m = 1, the amount of charge transfered increases unexpectedly by more than 250 %. This is accompanied by a dramatic drop in the electron-phonon interaction strength far beyond the prediction by first-principles calculations and, consequently, superconductivity only exists in the m = 2 compound with strong electron-phonon interaction, albeit with lower carrier density. Furthermore, we found that the amount of charge transfered in both compounds is nearly halved when warmed from below 10 K to room temperature, due to the different thermal expansion coefficients of the constituent layers of these misfit compounds. These un- precedentedly large charge transfer effects provide important insights for further understanding and application of devices based on vdWHs.
|
Mar 2018
|
|
I05-ARPES
|
Q. y.
Chen
,
D. f.
Xu
,
X. H.
Niu
,
R.
Peng
,
H. c.
Xu
,
C. h. p.
Wen
,
X.
Liu
,
L.
Shu
,
S. y.
Tan
,
X. c.
Lai
,
Y. j.
Zhang
,
H.
Lee
,
V. n.
Strocov
,
F.
Bisti
,
P.
Dudin
,
J.-X.
Zhu
,
H. q.
Yuan
,
S.
Kirchner
,
D. l.
Feng
Diamond Proposal Number(s):
[11914]
Abstract: A key issue in heavy fermion research is how subtle changes in the hybridization between the 4f (5f) and conduction electrons can result in fundamentally different ground states. CeRhIn5 stands out as a particularly notable example: when replacing Rh with either Co or Ir, antiferromagnetism gives way to superconductivity. In this photoemission study of CeRhIn5, we demonstrate that the use of resonant angle-resolved photoemission spectroscopy with polarized light allows us to extract detailed information on the 4f crystal field states and details on the 4f and conduction electron hybridization, which together determine the ground state. We directly observe weakly dispersive Kondo resonances of f electrons and identify two of the three Ce 4f
1
5/2 crystal-electric-field levels and band-dependent hybridization, which signals that the hybridization occurs primarily between the Ce 4f states in the CeIn3 layer and two more three-dimensional bands composed of the Rh 4d and In 5p orbitals in the RhIn2 layer. Our results allow us to connect the properties observed at elevated temperatures with the unusual low-temperature properties of this enigmatic heavy fermion compound.
|
Feb 2018
|
|
