I05-ARPES
|
Diamond Proposal Number(s):
[26631]
Open Access
Abstract: Interaction between electrons and phonons in solids is a key effect defining the physical properties of materials, such as electrical and thermal conductivity. In transition metal dichalcogenides (TMDCs), the electron–phonon coupling results in the formation of polarons, quasiparticles that manifest themselves as discrete features in the electronic spectral function. In this study, we report the formation of polarons at the alkali-dosed MoSe2 surface, where Rashba-like spin splitting of the conduction band states is caused by an inversion-symmetry breaking electric field. In addition, we observed a crossover from phonon-like to plasmon-like polaronic spectral features at the MoSe2 surface with increasing doping. Our findings support the concept of electron–phonon coupling-mediated superconductivity in electron-doped layered TMDC materials, as observed using ionic liquid gating technology. Furthermore, the discovered spin-splitting at the Fermi level could offer crucial experimental validation for theoretical models of Ising-type superconductivity in these materials.
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Nov 2024
|
|
I05-ARPES
|
T. K.
Kim
,
K. S.
Pervakov
,
D. V.
Evtushinsky
,
S. W.
Jung
,
G.
Poelchen
,
K.
Kummer
,
V. A.
Vlasenko
,
A. V.
Sadakov
,
A. S.
Usoltsev
,
V. M.
Pudalov
,
D.
Roditchev
,
V. S.
Stolyarov
,
D. V.
Vyalikh
,
V.
Borisov
,
R.
Valentí
,
A.
Ernst
,
S. V.
Eremeev
,
E. V.
Chulkov
Diamond Proposal Number(s):
[19041, 22192]
Open Access
Abstract: In the novel stoichiometric iron-based material
RbEuFe
4
As
4
, superconductivity coexists with a peculiar long-range magnetic order of Eu 4f states. Using angle-resolved photoemission spectroscopy, we reveal a complex three-dimensional electronic structure and compare it with density functional theory calculations. Multiple superconducting gaps were measured on various sheets of the Fermi surface. High-resolution resonant photoemission spectroscopy reveals magnetic order of the Eu 4f states deep into the superconducting phase. Both the absolute values and the anisotropy of the superconducting gaps are remarkably similar to the sibling compound without Eu, indicating that Eu magnetism does not affect the pairing of electrons. A complete decoupling between Fe- and Eu-derived states was established from their evolution with temperature, thus unambiguously demonstrating that superconducting and a long-range magnetic orders exist independently from each other. The established electronic structure of
RbEuFe
4
As
4
opens opportunities for the future studies of the highly unorthodox electron pairing and phase competition in this family of iron-based superconductors with doping.
|
May 2021
|
|
I05-ARPES
|
Y. W.
Li
,
H. J.
Zheng
,
Y. Q.
Fang
,
D. Q.
Zhang
,
Y. J.
Chen
,
C.
Chen
,
A. J.
Liang
,
W. J.
Shi
,
D.
Pei
,
L. X.
Xu
,
S.
Liu
,
J.
Pan
,
D. H.
Lu
,
M.
Hashimoto
,
A.
Barinov
,
S. W.
Jung
,
Cephise
Cacho
,
M. X.
Wang
,
Y.
He
,
L.
Fu
,
H. J.
Zhang
,
F. Q.
Huang
,
L. X.
Yang
,
Z. K.
Liu
,
Y. L.
Chen
Diamond Proposal Number(s):
[125135]
Open Access
Abstract: Topological superconductors (TSCs) are unconventional superconductors with bulk superconducting gap and in-gap Majorana states on the boundary that may be used as topological qubits for quantum computation. Despite their importance in both fundamental research and applications, natural TSCs are very rare. Here, combining state of the art synchrotron and laser-based angle-resolved photoemission spectroscopy, we investigated a stoichiometric transition metal dichalcogenide (TMD), 2M-WS2 with a superconducting transition temperature of 8.8 K (the highest among all TMDs in the natural form up to date) and observed distinctive topological surface states (TSSs). Furthermore, in the superconducting state, we found that the TSSs acquired a nodeless superconducting gap with similar magnitude as that of the bulk states. These discoveries not only evidence 2M-WS2 as an intrinsic TSC without the need of sensitive composition tuning or sophisticated heterostructures fabrication, but also provide an ideal platform for device applications thanks to its van der Waals layered structure.
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May 2021
|
|
I05-ARPES
|
R. C.
Vidal
,
H.
Bentmann
,
J. i.
Facio
,
T.
Heider
,
P.
Kagerer
,
C. I.
Fornari
,
T. R. F.
Peixoto
,
T.
Figgemeier
,
S.
Jung
,
Cephise
Cacho
,
B.
Büchner
,
J.
Van Den Brink
,
C. M.
Schneider
,
L.
Plucinski
,
E. F.
Schwier
,
K.
Shimada
,
M.
Richter
,
A.
Isaeva
,
F.
Reinert
Diamond Proposal Number(s):
[22468]
Abstract: Using angle-resolved photoelectron spectroscopy (ARPES), we investigate the surface electronic structure of the magnetic van der Waals compounds
MnBi
4
Te
7
and
MnBi
6
Te
10
, the
n
=
1
and 2 members of a modular
(
Bi
2
Te
3
)
n
(
MnBi
2
Te
4
)
series, which have attracted recent interest as intrinsic magnetic topological insulators. Combining circular dichroic, spin-resolved and photon-energy-dependent ARPES measurements with calculations based on density functional theory, we unveil complex momentum-dependent orbital and spin textures in the surface electronic structure and disentangle topological from trivial surface bands. We find that the Dirac-cone dispersion of the topologial surface state is strongly perturbed by hybridization with valence-band states for
Bi
2
Te
3
-terminated surfaces but remains preserved for
MnBi
2
Te
4
-terminated surfaces. Our results firmly establish the topologically nontrivial nature of these magnetic van der Waals materials and indicate that the possibility of realizing a quantized anomalous Hall conductivity depends on surface termination.
|
Apr 2021
|
|
I05-ARPES
|
Diamond Proposal Number(s):
[26443]
Open Access
Abstract: We investigate the electronic structure of the
2
H
and
3
R
polytypes of
Nb
S
2
. The Fermi surfaces measured by angle-resolved photoemission spectroscopy show a remarkable difference in size, reflecting a significantly increased band filling in
3
R
−
Nb
1
+
x
S
2
compared to
2
H
−
Nb
S
2
, which we attribute to the presence of additional interstitial Nb, which act as electron donors. Thus, we find that the stoichiometry, rather than the stacking arrangement, is the most important factor in the difference in electronic and physical properties of the two phases. Our high resolution data on the
2
H
phase shows kinks in the spectral function that are fingerprints of the electron-phonon coupling. However, the strength of the coupling is found to be much larger for the the sections of bands with Nb
4
d
x
2
−
y
2
,
x
y
character than for the Nb
4
d
3
z
2
−
r
2
. Our results provide an experimental framework for interpreting the two-gap superconductivity and latent charge density wave in
2
H
−
Nb
S
2
.
|
Apr 2021
|
|
I05-ARPES
|
Saumya
Mukherjee
,
Sung Won
Jung
,
Sophie F.
Weber
,
Chunqiang
Xu
,
Dong
Qian
,
Xiaofeng
Xu
,
Pabitra K.
Biswas
,
Timur K.
Kim
,
Laurent C.
Chapon
,
Matthew D.
Watson
,
Jeffrey B.
Neaton
,
Cephise
Cacho
Diamond Proposal Number(s):
[21591]
Open Access
Abstract: Transition-metal dichalcogenides (TMDs) offer an ideal platform to experimentally realize Dirac fermions. However, typically these exotic quasiparticles are located far away from the Fermi level, limiting the contribution of Dirac-like carriers to the transport properties. Here we show that NiTe2 hosts both bulk Type-II Dirac points and topological surface states. The underlying mechanism is shared with other TMDs and based on the generic topological character of the Te p-orbital manifold. However, unique to NiTe2, a significant contribution of Ni d orbital states shifts the energy of the Type-II Dirac point close to the Fermi level. In addition, one of the topological surface states intersects the Fermi energy and exhibits a remarkably large spin splitting of 120 meV. Our results establish NiTe2 as an exciting candidate for next-generation spintronics devices.
|
Jul 2020
|
|
I05-ARPES
I06-Nanoscience (XPEEM)
|
Sung Won
Jung
,
Sangyeon
Pak
,
Sanghyo
Lee
,
Sonka
Reimers
,
Saumya
Mukherjee
,
Pavel
Dudin
,
Timur K.
Kim
,
Mattia
Cattelan
,
Neil
Fox
,
Sarnjeet S.
Dhesi
,
Cephise
Cacho
,
Seungnam
Cha
Diamond Proposal Number(s):
[24367, 22901]
Abstract: The recent rise of van der Waals (vdW) crystals has opened new prospects for studying versatile and exotic fundamental physics with future device applications such as twistronics. Even though the recent development on Angle-resolved photoemission spectroscopy (ARPES) with Nano-focusing optics, making clean surfaces and interfaces of chemically transferred crystals have been challenging to obtain high-resolution ARPES spectra. Here, we show that by employing nano-ARPES with submicron sized beam and polystyrene-assisted transfer followed by annealing process in ultra-high vacuum environment, remarkably clear ARPES spectral features such as spin-orbit splitting and band renormalization of CVD-grown, monolayered MoS2 can be measured. Our finding paves a way to exploit chemically transferred crystals for measuring high-resolution ARPES spectra to observe exotic quasi-particles in vdW heterostructures.
|
Jul 2020
|
|
I05-ARPES
|
Lixuan
Xu
,
Yuanhao
Mao
,
Hongyuan
Wang
,
Jiaheng
Li
,
Yujie
Chen
,
Yunyouyou
Xia
,
Yiwei
Li
,
Ding
Pei
,
Jing
Zhang
,
Huijun
Zheng
,
Kui
Huang
,
Chaofan
Zhang
,
Shengtao
Cui
,
Aiji
Liang
,
Wei
Xia
,
Hao
Su
,
Sungwon
Jung
,
Cephise
Cacho
,
Meixiao
Wang
,
Gang
Li
,
Yong
Xu
,
Yanfeng
Guo
,
Lexian
Yang
,
Zhongkai
Liu
,
Yulin
Chen
,
Mianheng
Jiang
Diamond Proposal Number(s):
[23648, 24827]
Abstract: Magnetic topological quantum materials (TQMs) provide a fertile ground for the emergence of fascinating topological magneto-electric effects. Recently, the discovery of intrinsic antiferromagnetic (AFM) topological insulator MnBi2Te4 that could realize quantized anomalous Hall effect and axion insulator phase ignited intensive study on this family of TQM compounds. Here, we investigated the AFM compound MnBi4Te7 where Bi2Te3 and MnBi2Te4 layers alternate to form a superlattice. Using spatial- and angle-resolved photoemission spectroscopy, we identified ubiquitous (albeit termination dependent) topological electronic structures from both Bi2Te3 and MnBi2Te4 terminations. Unexpectedly, while the bulk bands show strong temperature dependence correlated with the AFM transition, the topological surface states with a diminishing gap show negligible temperature dependence across the AFM transition. Together with the results of its sister compound MnBi2Te4, we illustrate important aspects of electronic structures and the effect of magnetic ordering in this family of magnetic TQMs.
|
Jul 2020
|
|
I05-ARPES
|
Zakariae
El Youbi
,
Sungwon
Jung
,
Saumya
Mukherjee
,
Mauro
Fanciulli
,
Jakub
Schusser
,
Olivier
Heckmann
,
Christine
Richter
,
Jan
Minar
,
Karol
Hricovini
,
Matthew D.
Watson
,
Cephise
Cacho
Diamond Proposal Number(s):
[24921]
Open Access
Abstract: The dosing of layered materials with alkali metals has become a commonly used strategy in ARPES experiments. However, precisely what occurs under such conditions, both structurally and electronically, has remained a matter of debate. Here we perform a systematic study of 1T-
HfTe
2
, a prototypical semimetal of the transition metal dichalcogenide family. By utilizing photon energy-dependent angle-resolved photoemission spectroscopy (ARPES), we have investigated the electronic structure of this material as a function of potassium (K) deposition. From the
k
z
maps, we observe the appearance of 2D dispersive bands after electron dosing, with an increasing sharpness of the bands, consistent with the wave-function confinement at the topmost layer. In our highest-dosing cases, a monolayerlike electronic structure emerges, presumably as a result of intercalation of the alkali metal. Here, by bringing the topmost valence band below
E
F
, we can directly measure a band overlap of
∼
0.2
eV. However, 3D bulklike states still contribute to the spectra even after considerable dosing. Our work provides a reference point for the increasingly popular studies of the alkali metal dosing of semimetals using ARPES.
|
Jun 2020
|
|
I05-ARPES
|
Hiroaki
Tanaka
,
Yuita
Fujisawa
,
Kenta
Kuroda
,
Ryo
Noguchi
,
Shunsuke
Sakuragi
,
Cedric
Bareille
,
Barnaby
Smith
,
Cephise
Cacho
,
Sung Won
Jung
,
Takayuki
Muro
,
Yoshinori
Okada
,
Takeshi
Kondo
Diamond Proposal Number(s):
[24488]
Abstract: A large anomalous Hall effect (AHE) has been observed in ferromagnetic
Fe
3
Sn
2
with breathing kagome bilayers. To understand the underlying mechanism for this, we investigate the electronic structure of
Fe
3
Sn
2
by angle-resolved photoemission spectroscopy (ARPES). In particular, we use both vacuum ultraviolet light (VUV) and soft x ray (SX), which allow surface-sensitive and relatively bulk-sensitive measurements, respectively, and distinguish bulk states from surface states, which should be unlikely related to the AHE. While VUV-ARPES observes two-dimensional bands mostly due to surface states, SX-ARPES reveals three-dimensional band dispersions with a periodicity of the rhombohedral unit cell in the bulk. Our data show a good consistency with a theoretical calculation based on density functional theory, suggesting a possibility that
Fe
3
Sn
2
is a magnetic Weyl semimetal.
|
Apr 2020
|
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