I05-ARPES
|
Hongyun
Zhang
,
Jinxi
Lu
,
Kai
Liu
,
Yijie
Wang
,
Size
Wu
,
Wanying
Chen
,
Xuanxi
Cai
,
Kenji
Watanabe
,
Takashi
Taniguchi
,
Jose
Avila
,
Pavel
Dudin
,
Matthew D.
Watson
,
Alex
Louat
,
Takafumi
Sato
,
Pu
Yu
,
Wenhui
Duan
,
Zhida
Song
,
Guorui
Chen
,
Shuyun
Zhou
Diamond Proposal Number(s):
[37939]
Abstract: The fractional quantum anomalous Hall effect (FQAHE) is a fascinating emergent quantum state characterized by fractionally charged excitations in the absence of a magnetic field. Recently, the FQAHE has been observed in aligned rhombohedral pentalayer graphene on BN (aligned R5G/BN)1 with moiré potential. Intriguingly, the FQAHE preferably emerges when carriers are displaced away from the moiré interface1,2,3, raising debates about the role of moiré potential4,5,6,7,8,9,10,11,12,13,14,15,16,17. Here, by performing nanospot angle-resolved photoemission spectroscopy, we directly visualize the topological flat band in both aligned and non-aligned R5G/BN. The moiré potential in the aligned sample generates moiré bands and enhances the topological flat band as compared to non-aligned sample. Combined with theoretical calculations, we propose that the moiré bands on the top surface arise through the interlayer Coulomb interaction with the moiré-modulated bottom layer. Our results provide direct experimental evidence for the role of moiré potential in aligned rhombohedral graphene, and establish a foundation for understanding its emergent quantum phenomena.
|
Nov 2025
|
|
I05-ARPES
|
Y.
Alexanian
,
A.
De La Torre
,
S.
Mckeown Walker
,
M.
Straub
,
G.
Gatti
,
A.
Hunter
,
S.
Mandloi
,
E.
Cappelli
,
S.
Riccò
,
F. Y.
Bruno
,
M.
Radovic
,
N. C.
Plumb
,
M.
Shi
,
J.
Osiecki
,
C.
Polley
,
T. K.
Kim
,
P.
Dudin
,
M.
Hoesch
,
R. S.
Perry
,
A.
Tamai
,
F.
Baumberger
Diamond Proposal Number(s):
[10348, 12404, 17381]
Open Access
Abstract: The fate of the Fermi surface in bulk electron-doped Sr2IrO4 remains elusive, as does the origin and extension of its pseudogap phase. Here, we use high-resolution angle-resolved photoelectron spectroscopy (ARPES) to investigate the electronic structure of Sr2−xLaxIrO4 up to x = 0.2, a factor of two higher than in previous work. We find that the antinodal pseudogap persists up to the highest doping level, and thus beyond the sharp increase in Hall carrier density to ≃ 1 + x recently observed above x* ≃ 0.161. This suggests that doped iridates host a unique phase of matter in which a large Hall density coexists with an anisotropic pseudogap, breaking up the Fermi surface into disconnected arcs. The temperature boundary of the pseudogap is T* ≃ 200 K for x = 0.2, comparable to cuprates and to the energy scale of short range antiferromagnetic correlations in cuprates and iridates.
|
Oct 2025
|
|
I05-ARPES
|
G.
Gatti
,
J.
Issing
,
L.
Rademaker
,
F.
Margot
,
T. A.
De Jong
,
S. J.
Van Der Molen
,
J.
Teyssier
,
T. K.
Kim
,
M. D.
Watson
,
C.
Cacho
,
P.
Dudin
,
J.
Avila
,
K.
Cordero-Edwards
,
P.
Paruch
,
N.
Ubrig
,
I.
Gutiérrez-Lezama
,
A. f.
Morpurgo
,
A.
Tamai
,
F.
Baumberger
Diamond Proposal Number(s):
[29021]
Abstract: The recent observation of correlated phases in transition metal dichalcogenide moiré systems at integer and fractional filling promises new insight into metal-insulator transitions and the unusual states of matter that can emerge near such transitions. Here, we combine real- and momentum-space mapping techniques to study moiré superlattice effects in 57.4° twisted
WSe
2
(
tWSe
2
). Our data reveal a split-off flat band that derives from the monolayer
Γ
states. Using advanced data analysis, we directly quantify the moiré potential from our data. We further demonstrate that the global valence band maximum in
tWSe
2
is close in energy to this flat band but derives from the monolayer
K
states which show weaker superlattice effects. These results constrain theoretical models and open the perspective that
Γ
-valley flat bands might be involved in the correlated physics of twisted
WSe
2
.
|
Jul 2023
|
|
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
|
|
I05-ARPES
|
D. F.
Liu
,
E. K.
Liu
,
Q. N.
Xu
,
J. L.
Shen
,
Y. W.
Li
,
D.
Pei
,
A. J.
Liang
,
P.
Dudin
,
T. K.
Kim
,
C.
Cacho
,
Y. F.
Xu
,
Y.
Sun
,
L. X.
Yang
,
Z. K.
Liu
,
C.
Felser
,
S. S. P.
Parkin
,
Y. L.
Chen
Open Access
Abstract: The spin–orbit coupling (SOC) lifts the band degeneracy that plays a vital role in the search for different topological states, such as topological insulators (TIs) and topological semimetals (TSMs). In TSMs, the SOC can partially gap a degenerate nodal line, leading to the formation of Dirac/Weyl semimetals (DSMs/WSMs). However, such SOC-induced gap structure along the nodal line in TSMs has not yet been systematically investigated experimentally. Here, we report a direct observation of such gap structure in a magnetic WSM Co3Sn2S2 using high-resolution angle-resolved photoemission spectroscopy. Our results not only reveal the existence and importance of the strong SOC effect in the formation of the WSM phase in Co3Sn2S2, but also provide insights for the understanding of its exotic physical properties.
|
Jan 2022
|
|
|
|
D. F.
Liu
,
Q. N.
Xu
,
E. K.
Liu
,
J. L.
Shen
,
C. C.
Le
,
Y. W.
Li
,
D.
Pei
,
A. J.
Liang
,
P.
Dudin
,
T. K.
Kim
,
C.
Cacho
,
Y. F.
Xu
,
Y.
Sun
,
L. X.
Yang
,
Z. K.
Liu
,
C.
Felser
,
S. S. P.
Parkin
,
Y. L.
Chen
Abstract: Topological Weyl semimetals (TWSs) are exotic crystals possessing emergent relativistic Weyl fermions connected by unique surface Fermi arcs (SFAs) in their electronic structures. To realize the TWS state, certain symmetries (such as the inversion or time reversal symmetry) must be broken, leading to a topological phase transition (TPT). Despite the great importance in understanding the formation of TWSs and their unusual properties, direct observation of such a TPT has been challenging. Here, using a recently discovered magnetic TWS
Co
3
Sn
2
S
2
, we were able to systematically study its TPT with detailed temperature dependence of the electronic structures by angle-resolved photoemission spectroscopy. The TPT with drastic band structure evolution was clearly observed across the Curie temperature
(
T
C
=
177
K
)
, including the disappearance of the characteristic SFAs and the recombination of the spin-split bands that leads to the annihilation of Weyl points with opposite chirality. These results not only reveal important insights on the interplay between the magnetism and band topology in TWSs, but also provide a method to control their exotic physical properties.
|
Nov 2021
|
|
I05-ARPES
|
D. F.
Liu
,
L. Y.
Wei
,
C. C.
Le
,
H. Y.
Wang
,
X.
Zhang
,
N.
Kumar
,
C.
Shekhar
,
N. B. M.
Schröter
,
Y. W.
Li
,
D.
Pei
,
L. X.
Xu
,
P.
Dudin
,
T. K.
Kim
,
C.
Cacho
,
J.
Fujii
,
I.
Vobornik
,
M. X.
Wang
,
L. X.
Yang
,
Z. K.
Liu
,
Y. F.
Guo
,
J. P.
Hu
,
C.
Felser
,
S. S. P.
Parkin
,
Y. L.
Chen
Diamond Proposal Number(s):
[18005]
Open Access
Abstract: Dirac semimetals are classified into different phases based on the types of Dirac fermions. Tuning the transition among different types of Dirac fermions in one system remains a challenge. Recently, KMgBi was predicted to be located at a critical state in which various types of Dirac fermions can be induced owing to the existence of a flatband. Here, we carried out systematic studies on the electronic structure of KMgBi single crystals by combining angle-resolve photoemission spectroscopy and scanning tunneling microscopy/spectroscopy. The flatband was clearly observed near the Fermi level. We also revealed a small bandgap of ∼20 meV between the flatband and the conduction band. These results demonstrate the critical states of KMgBi that transition among various types of Dirac fermions can be tuned in one system.
|
Jun 2021
|
|
I05-ARPES
|
Simone M.
Kevy
,
Henriette E.
Lund
,
Laura
Wollesen
,
Kirstine J.
Dalgaard
,
Yu-Te
Hsu
,
Steffen
Wiedmann
,
Marco
Bianchi
,
Ann Julie Utne
Holt
,
Davide
Curcio
,
Deepnarayan
Biswas
,
Alfred J. H.
Jones
,
Klara
Volckaert
,
Cephise
Cacho
,
Pavel
Dudin
,
Philip
Hofmann
,
Martin
Bremholm
Diamond Proposal Number(s):
[20218]
Abstract: The crystal structure, electronic structure, and transport properties of crystals with the nominal composition
Nb
0.25
Bi
2
Se
3
are investigated. X-ray diffraction reveals that the as-grown crystals display phase segregation and contain major contributions of BiSe and the superconducting misfit layer compound
(
Bi
Se
)
1.1
Nb
Se
2
. The inhomogeneous character of the samples is also reflected in the electronic structure and transport properties of different single crystals. Angle-resolved photoemission spectroscopy (ARPES) reveals an electronic structure that resembles poor-quality
Bi
2
Se
3
with an ill-defined topological surface state. High-quality topological surface states are instead observed when using a highly focused beam size, i.e., nanoARPES. While the superconducting transition temperature is found to vary between 2.5 and 3.5 K, the majority of the bulk single crystals does not exhibit a zero-resistance state suggesting filamentary superconductivity in the materials. Susceptibility measurements of the system together with the temperature dependence of the coherence length extracted from the upper critical field are consistent with conventional BCS superconductivity of a type II superconductor.
|
Feb 2021
|
|
I05-ARPES
|
Niels B. M.
Schroeter
,
Iñigo
Robredo
,
Sebastian
Klemenz
,
Robert J.
Kirby
,
Jonas A.
Krieger
,
Ding
Pei
,
Tianlun
Yu
,
Samuel
Stolz
,
Thorsten
Schmitt
,
Pavel
Dudin
,
Timur K.
Kim
,
Cephise
Cacho
,
Andreas
Schnyder
,
Aitor
Bergara
,
Vladimir N.
Strocov
,
Fernando
De Juan
,
Maia G.
Vergniory
,
Leslie M.
Schoop
Diamond Proposal Number(s):
[26098, 20617]
Open Access
Abstract: Magnetic Weyl semimetals are a newly discovered class of topological materials that may serve as a platform for exotic phenomena, such as axion insulators or the quantum anomalous Hall effect. Here, we use angle-resolved photoelectron spectroscopy and ab initio calculations to discover Weyl cones in CoS2, a ferromagnet with pyrite structure that has been long studied as a candidate for half-metallicity, which makes it an attractive material for spintronic devices. We directly observe the topological Fermi arc surface states that link the Weyl nodes, which will influence the performance of CoS2 as a spin injector by modifying its spin polarization at interfaces. In addition, we directly observe a minority-spin bulk electron pocket in the corner of the Brillouin zone, which proves that CoS2 cannot be a true half-metal.
|
Dec 2020
|
|
I05-ARPES
|
Davide
Curcio
,
Alfred J. H.
Jones
,
Ryan
Muzzio
,
Klara
Volckaert
,
Deepnarayan
Biswas
,
Charlotte E.
Sanders
,
Pavel
Dudin
,
Cephise
Cacho
,
Simranjeet
Singh
,
Kenji
Watanabe
,
Takashi
Taniguchi
,
Jill A.
Miwa
,
Jyoti
Katoch
,
Soeren
Ulstrup
,
Philip
Hofmann
Diamond Proposal Number(s):
[20218]
Abstract: The presence of an electrical transport current in a material is one of the simplest and most important realizations of nonequilibrium physics. The current density breaks the crystalline symmetry and can give rise to dramatic phenomena, such as sliding charge density waves, insulator-to-metal transitions, or gap openings in topologically protected states. Almost nothing is known about how a current influences the electron spectral function, which characterizes most of the solid’s electronic, optical, and chemical properties. Here we show that angle-resolved photoemission spectroscopy with a nanoscale light spot provides not only a wealth of information on local equilibrium properties, but also opens the possibility to access the local nonequilibrium spectral function in the presence of a transport current. Unifying spectroscopic and transport measurements in this way allows simultaneous noninvasive local measurements of the composition, structure, many-body effects, and carrier mobility in the presence of high current densities. In the particular case of our graphene-based device, we are able to correlate the presence of structural defects with locally reduced carrier lifetimes in the spectral function and a locally reduced mobility with a spatial resolution of 500 nm.
|
Dec 2020
|
|
