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
|
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. 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
|
|
I05-ARPES
|
Q. Y.
Chen
,
D. F.
Xu
,
X. H.
Niu
,
J.
Jiang
,
R.
Peng
,
H. C.
Xu
,
C. H. P.
Wen
,
Z. F.
Ding
,
K.
Huang
,
L.
Shu
,
Y. J.
Zhang
,
H.
Lee
,
V. N.
Strocov
,
M.
Shi
,
F.
Bisti
,
T.
Schmitt
,
Y. B.
Huang
,
P.
Dudin
,
X. C.
Lai
,
S.
Kirchner
,
H. Q.
Yuan
,
D. L.
Feng
Diamond Proposal Number(s):
[11914]
Abstract: Heavy-fermion systems share some of the strange metal phenomenology seen in other unconventional superconductors, providing a unique opportunity to set strange metals in a broader context. Central to understanding heavy-fermion systems is the interplay of localization and itinerancy. These materials acquire high electronic masses and a concomitant Fermi volume increase as the f electrons delocalize at low temperatures. However, despite the wide-spread acceptance of this view, a direct microscopic verification has been lacking. Here we report high-resolution angle-resolved photoemission measurements on CeCoIn5, a prototypical heavy-fermion compound, which spectroscopically resolve the development of band hybridization and the Fermi surface expansion over a wide temperature region. Unexpectedly, the localized-to-itinerant transition occurs at surprisingly high temperatures, yet f electrons are still largely localized even at the lowest temperature. These findings point to an unanticipated role played by crystal-field excitations in the strange metal behavior of CeCoIn5. Our results offer a comprehensive experimental picture of the heavy-fermion formation, setting the stage for understanding the emergent properties, including unconventional superconductivity, in this and related materials.
|
Jul 2017
|
|
I05-ARPES
|
H. C.
Xu
,
X. H.
Niu
,
D. F.
Xu
,
J.
Jiang
,
Q.
Yao
,
Q. Y.
Chen
,
Q.
Song
,
M.
Abdel-Hafiez
,
D. A.
Chareev
,
A. N.
Vasiliev
,
Q. S.
Wang
,
H. l.
Wo
,
J.
Zhao
,
R.
Peng
,
D. l.
Feng
Diamond Proposal Number(s):
[11914, 12849]
Abstract: FeSe exhibits a novel ground state in which superconductivity coexists with a nematic order in the absence of any long-range magnetic order. Here, we report on an angle-resolved photoemission study on the superconducting gap structure in the nematic state of FeSe0.93S0.07, without the complications caused by Fermi surface reconstruction induced by magnetic order. We find that the superconducting gap shows a pronounced twofold anisotropy around the elliptical hole pocket near Z (0, 0, π), with gap minima at the end points of its major axis, while no detectable gap is observed around Γ (0, 0, 0) and the zone corner (π, π, kz). The large anisotropy and nodal gap distribution demonstrate the substantial effects of the nematicity on the superconductivity and thus put strong constraints on current theories.
|
Oct 2016
|
|
I05-ARPES
|
Q.
Song
,
Y. J.
Yan
,
Z. R.
Ye
,
M. Q.
Ren
,
D. F.
Xu
,
S. Y.
Tan
,
X. H.
Niu
,
B. P.
Xie
,
T.
Zhang
,
R.
Peng
,
H. C.
Xu
,
J.
Jiang
,
D. L.
Feng
Diamond Proposal Number(s):
[12849]
Abstract: Ba0.95Na0.05Ti2Sb2O is a titanium-based oxypnictide superconductor with possible density wave order. We
have performed high-resolution angle-resolved photoemission spectroscopy and scanning tunneling microscopy
(STM) studies on Ba0.95Na0.05Ti2Sb2O. Our STM studies find a charge density wave (CDW) order with the wave
vector of (π, π). The electronic structure shows both multiorbital and three-dimensional nature, consistent with
the theoretical calculations. The observed Fermi surfaces are well nested along the (π, π) direction, which might
drive the CDW transition. Likely due to the weak strength of the CDW order, we do not observe a leading-edge
gap. Instead, we observe an overall spectral weight enhancement with decreasing temperature, but the rate of this
enhancement is abruptly reduced or diminished in the CDW state, suggesting the suppression of spectral weight
or opening of a partial CDW gap. Our results give a comprehensive picture of the electronic structure and direct
observation of the CDW order in Ba0.95Na0.05Ti2Sb2O.
|
Jan 2016
|
|
