I05-ARPES
|
D.
Pei
,
Y.-Y.
Lv
,
Y. Y. Y.
Xia
,
Y. W.
Li
,
J. Y.
Liu
,
N. B. M.
Schröter
,
C.
Cacho
,
Z. K.
Liu
,
L. X.
Yang
,
G.
Li
,
Y. B.
Chen
,
Y.
Chen
Diamond Proposal Number(s):
[20617, 25135]
Abstract: We investigate transport properties and the electronic structure of BiCuSO, a thermoelectric material which was predicted as a possible parent compound for unconventional superconductivity. For the
p
-type BiCuSO samples studied in this paper, our transport measurements show metallic behavior down to 2 K, and we observe an increase of saturated magnetic moment around 4 K, which could be due to the reorientation of the magnetic easy axis. Using angle-resolved photoemission spectroscopy measurements, we acquired the comprehensive electronic structure of BiCuSO including the predicted flat band, and by carrying out photon polarization dependent measurements we further investigated the orbital characters of bands near the Fermi level. Compared with its sister compound, BiCuSeO, we find the flat band could be the origin of high figure of merit
(
Z
T
)
value in the
BiCu
C
h
O
(
C
h
=
S
,
Se
)
family.
|
Jun 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
|
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.
|
May 2021
|
|
I05-ARPES
|
S.
Liu
,
W.
Xia
,
K.
Huang
,
Ding
Pei
,
T.
Deng
,
A. J.
Liang
,
J.
Jiang
,
H. F.
Yang
,
J.
Zhang
,
H. J.
Zheng
,
Y. J.
Chen
,
L. X.
Yang
,
Y. F.
Guo
,
M. X.
Wang
,
Z. K.
Liu
,
Y. L.
Chen
Diamond Proposal Number(s):
[25135]
Abstract: Recently, layered copper chalcogenides
Cu
2
X
family
(
X
=
S
,
Se
,
Te
)
has attracted tremendous research interests due to their high thermoelectric performance, which is partly due to the superionic behavior of mobile Cu ions, making these compounds “phonon liquids.” Here, we systematically investigate the electronic structure and its temperature evolution of the less studied single crystal
Cu
2
−
x
Te
by the combination of angle resolved photoemission spectroscopy (ARPES) and scanning tunneling microscope/spectroscopy (STM/STS) experiments. While the band structure of the
Cu
2
−
x
Te
shows agreement with the calculations, we clearly observe a
2
×
2
surface reconstruction from both our low temperature ARPES and STM/STS experiments which survives up to room temperature. Interestingly, our low temperature STM experiments further reveal multiple types of reconstruction patterns, which suggests the origin of the surface reconstruction being the distributed deficiency of liquidlike Cu ions. Our findings reveal the electronic structure and impurity level of
Cu
2
Te
, which provides knowledge about its thermoelectric properties from the electronic degree of freedom.
|
Mar 2021
|
|
I05-ARPES
|
Wujun
Shi
,
Benjamin J.
Wieder
,
Holger L.
Meyerheim
,
Yan
Sun
,
Yang
Zhang
,
Yiwei
Li
,
Lei
Shen
,
Yanpeng
Qi
,
Lexian
Yang
,
Jagannath
Jena
,
Peter
Werner
,
Klaus
Koepernik
,
Stuart
Parkin
,
Yulin
Chen
,
Claudia
Felser
,
B. Andrei
Bernevig
,
Zhijun
Wang
Abstract: Topological physics and strong electron–electron correlations in quantum materials are typically studied independently. However, there have been rapid recent developments in quantum materials in which topological phase transitions emerge when the single-particle band structure is modified by strong interactions. Here we demonstrate that the room-temperature phase of (TaSe4)2I is a Weyl semimetal with 24 pairs of Weyl nodes. Owing to its quasi-one-dimensional structure, (TaSe4)2I also hosts an established charge-density wave instability just below room temperature. We show that the charge-density wave in (TaSe4)2I couples the bulk Weyl points and opens a bandgap. The correlation-driven topological phase transition in (TaSe4)2I provides a route towards observing condensed-matter realizations of axion electrodynamics in the gapped regime, topological chiral response effects in the semimetallic phase, and represents an avenue for exploring the interplay of correlations and topology in a solid-state material.
|
Jan 2021
|
|
I05-ARPES
|
L.
Kang
,
L.
Shen
,
Y. J.
Chen
,
S. C.
Sun
,
X.
Gu
,
H. J.
Zheng
,
Z. K.
Liu
,
J. X.
Wu
,
H. L.
Peng
,
F. W.
Zheng
,
P.
Zhang
,
L. X.
Yang
,
Y. L.
Chen
Diamond Proposal Number(s):
[23648, 24827]
Abstract: Using high-resolution angle-resolved photoemission spectroscopy, we systematically investigate the electronic structure of β-InSe, a van der Waals semiconductor with a direct band gap. Our measurements show a good agreement with ab initio calculations, which helps reveal the important impact of spin-orbit coupling on the electronic structure of β-InSe. Using surface potassium doping, we tune the chemical potential of the system and observe the unoccupied conduction band. The direct band gap is determined to be about 1.3 eV. Interestingly, we observe a global band shift when the sample is illuminated by a continuous-wave laser at 632.8 nm, which can be understood by an efficient surface photovoltaic effect. The surface photovoltaic can be tuned by in situ surface potassium doping. Our results not only provide important insights into the semiconducting properties of InSe, but also suggest a feasible method to study and engineer the surface photovoltaic effect in InSe-based devices.
|
Dec 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
|
Liheng
An
,
Xiangbin
Cai
,
Ding
Pei
,
Meizhen
Huang
,
Zefei
Wu
,
Zishu
Zhou
,
Jiangxiazi
Lin
,
Zhehan
Ying
,
Ziqing
Ye
,
Xuemeng
Feng
,
Ruiyan
Gao
,
Cephise
Cacho
,
Matthew
Watson
,
Yulin
Chen
,
Ning
Wang
Diamond Proposal Number(s):
[24366]
Abstract: Twisted bilayer graphene provides a new two-dimensional platform for studying electron interaction phenomena and flat band properties such as correlated insulator transition, superconductivity and ferromagnetism at certain magic angles. Here, we present experimental characterization of interaction effects and superconductivity signatures in p-type twisted double-bilayer WSe2. Enhanced interlayer interactions are observed when the twist angle decreases to a few degrees as reflected by the high-order satellites in the electron diffraction patterns taken from the reconstructed domains from a conventional moiré superlattice. In contrast to twisted bilayer graphene, there is no specific magic angle for twisted WSe2. Flat band properties are observable at twist angles ranging from 1 to 4 degrees. Our work has facilitated future study in the area of flat band related properties in twisted transition metal dichalcogenide layered structures.
|
Jul 2020
|
|
I05-ARPES
|
Shuo-Ying
Yang
,
Yaojia
Wang
,
Brenden R.
Ortiz
,
Defa
Liu
,
Jacob
Gayles
,
Elena
Derunova
,
Rafael
Gonzalez-Hernandez
,
Libor
Šmejkal
,
Yulin
Chen
,
Stuart S. P.
Parkin
,
Stephen D.
Wilson
,
Eric S.
Toberer
,
Tyrel
Mcqueen
,
Mazhar N.
Ali
Diamond Proposal Number(s):
[22367]
Open Access
Abstract: The anomalous Hall effect (AHE) is one of the most fundamental phenomena in physics. In the highly conductive regime, ferromagnetic metals have been the focus of past research. Here, we report a giant extrinsic AHE in KV3Sb5, an exfoliable, highly conductive semimetal with Dirac quasiparticles and a vanadium Kagome net. Even without report of long range magnetic order, the anomalous Hall conductivity reaches 15,507 Ω−1 cm−1 with an anomalous Hall ratio of ≈ 1.8%; an order of magnitude larger than Fe. Defying theoretical expectations, KV3Sb5 shows enhanced skew scattering that scales quadratically, not linearly, with the longitudinal conductivity, possibly arising from the combination of highly conductive Dirac quasiparticles with a frustrated magnetic sublattice. This allows the possibility of reaching an anomalous Hall angle of 90° in metals. This observation raises fundamental questions about AHEs and opens new frontiers for AHE and spin Hall effect exploration, particularly in metallic frustrated magnets.
|
Jul 2020
|
|
I05-ARPES
|
H. F.
Yang
,
L. X.
Yang
,
Z. K.
Liu
,
Y.
Sun
,
C.
Chen
,
H.
Peng
,
M.
Schmidt
,
D.
Prabhakaran
,
B. A.
Bernevig
,
C.
Felser
,
B. H.
Yan
,
Y. L.
Chen
Diamond Proposal Number(s):
[19310, 18005]
Open Access
Abstract: Surface Fermi arcs (SFAs), the unique open Fermi-surfaces (FSs) discovered recently in topological Weyl semimetals (TWSs), are unlike closed FSs in conventional materials and can give rise to many exotic phenomena, such as anomalous SFA-mediated quantum oscillations, chiral magnetic effects, three-dimensional quantum Hall effect, non-local voltage generation and anomalous electromagnetic wave transmission. Here, by using in-situ surface decoration, we demonstrate successful manipulation of the shape, size and even the connections of SFAs in a model TWS, NbAs, and observe their evolution that leads to an unusual topological Lifshitz transition not caused by the change of the carrier concentration. The phase transition teleports the SFAs between different parts of the surface Brillouin zone. Despite the dramatic surface evolution, the existence of SFAs is robust and each SFA remains tied to a pair of Weyl points of opposite chirality, as dictated by the bulk topology.
|
Aug 2019
|
|
