I05-ARPES
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Diamond Proposal Number(s):
[22375]
Abstract: Type-II topological Dirac semimetals are topological quantum materials hosting Lorentz-symmetry breaking type-II Dirac fermions, which are tilted Dirac cones with various exotic physical properties, such as anisotropic chiral anomalies and novel quantum oscillations. Until now, only limited material systems have been confirmed by theory and experiments with the type-II Dirac fermions. Here, we investigated the electronic structure of a new type-II Dirac semimetal VAl3 with angle-resolved photoelectron spectroscopy. The measured band dispersions are consistent with the theoretical prediction, which suggests the Dirac points are located close to (at about 100 meV above) the Fermi level. Our work demonstrates a new type-II Dirac semimetal candidate system with different Dirac node configurations and application potentials.
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Mar 2022
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I05-ARPES
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Na
Qin
,
Xian
Du
,
Yangyang
Lv
,
Lu
Kang
,
Zhongxu
Yin
,
Jingsong
Zhou
,
Xu
Gu
,
Qinqin
Zhang
,
Runzhe
Xu
,
Wenxuan
Zhao
,
Yidian
Li
,
Shuhua
Yao
,
Yanfeng
Chen
,
Zhongkai
Liu
,
Lexian
Yang
,
Yulin
Chen
Diamond Proposal Number(s):
[20683]
Abstract: Ternary transition metal chalcogenides provide a rich platform to search and study intriguing electronic properties. Using Angle-Resolved Photoemission Spectroscopy and ab initio calculation, we investigate the electronic structure of Cu2TlX2 (X = Se, Te), ternary transition metal chalcogenides with quasi-two-dimensional crystal structure. The band dispersions near the Fermi level are mainly contributed by the Te/Se p orbitals. According to our ab-initio calculation, the electronic structure changes from a semiconductor with indirect band gap in Cu2TlSe2 to a semimetal in Cu2TlTe2, suggesting a band-gap tunability with the composition of Se and Te. By comparing ARPES experimental data with the calculated results, we identify strong modulation of the band structure by spin-orbit coupling in the compounds. Our results provide a ternary platform to study and engineer the electronic properties of transition metal chalcogenides related to large spin-orbit coupling.
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Dec 2021
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I05-ARPES
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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.
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Jul 2020
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I05-ARPES
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Cheng
Chen
,
Meixiao
Wang
,
Jinxiong
Wu
,
Huixia
Fu
,
Haifeng
Yang
,
Zhen
Tian
,
Teng
Tu
,
Han
Peng
,
Yan
Sun
,
Xiang
Xu
,
Juan
Jiang
,
Niels B. M.
Schroeter
,
Yiwei
Li
,
Ding
Pei
,
Shuai
Liu
,
Sandy A.
Ekahana
,
Hongtao
Yuan
,
Jiamin
Xue
,
Gang
Li
,
Jinfeng
Jia
,
Zhongkai
Liu
,
Binghai
Yan
,
Hailin
Peng
,
Yulin
Chen
Diamond Proposal Number(s):
[18005]
Open Access
Abstract: Semiconductors are essential materials that affect our everyday life in the modern world. Two-dimensional semiconductors with high mobility and moderate bandgap are particularly attractive today because of their potential application in fast, low-power, and ultrasmall/thin electronic devices. We investigate the electronic structures of a new layered air-stable oxide semiconductor, Bi2O2Se, with ultrahigh mobility (~2.8 × 105 cm2/V⋅s at 2.0 K) and moderate bandgap (~0.8 eV). Combining angle-resolved photoemission spectroscopy and scanning tunneling microscopy, we mapped out the complete band structures of Bi2O2Se with key parameters (for example, effective mass, Fermi velocity, and bandgap). The unusual spatial uniformity of the bandgap without undesired in-gap states on the sample surface with up to ~50% defects makes Bi2O2Se an ideal semiconductor for future electronic applications. In addition, the structural compatibility between Bi2O2Se and interesting perovskite oxides (for example, cuprate high–transition temperature superconductors and commonly used substrate material SrTiO3) further makes heterostructures between Bi2O2Se and these oxides possible platforms for realizing novel physical phenomena, such as topological superconductivity, Josephson junction field-effect transistor, new superconducting optoelectronics, and novel lasers.
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Sep 2018
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I05-ARPES
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Guang-Hao
Hong
,
Cheng-Wei
Wang
,
Juan
Jiang
,
Cheng
Chen
,
Sheng-Tao
Cui
,
Hai-Feng
Yang
,
Ai-Ji
Liang
,
Shuai
Liu
,
Yang-Yang
Lv
,
Jian
Zhou
,
Yan-Bin
Chen
,
Shu-Hua
Yao
,
Ming-Hui
Lu
,
Yan-Feng
Chen
,
Mei-Xiao
Wang
,
Le-Xian
Yang
,
Zhong-Kai
Liu
,
Yu-Lin
Chen
Diamond Proposal Number(s):
[16846]
Abstract: Dirac semimetals are materials in which the conduction and the valence bands have robust crossing points protected by topology or symmetry. Recently, a new type of Dirac semimetals, so called the Dirac line-node semimetals (DLNSs), have attracted a lot of attention, as they host robust Dirac points along the one-dimensional (1D) lines in the Brillouin zone (BZ). In this work, using angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations, we systematically investigated the electronic structures of non-symmorphic ZrSiS crystal where we clearly distinguished the surface states from the bulk states. The photon-energy-dependent measurements further prove the existence of Dirac line node along the X–R direction. Remarkably, by in situ surface potassium doping, we clearly observed the different evolutions of the bulk and surface electronic states while proving the robustness of the Dirac line node. Our studies not only reveal the complete electronic structures of ZrSiS, but also demonstrate the method manipulating the electronic structure of the compound.
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Jan 2018
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I05-ARPES
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Yiwei
Li
,
Yunyouyou
Xia
,
Sandy Adhitia
Ekahana
,
Nitesh
Kumar
,
Juan
Jiang
,
Lexian
Yang
,
Cheng
Chen
,
Chaoxing
Liu
,
Binghai
Yan
,
Claudia
Felser
,
Gang
Li
,
Zhongkai
Liu
,
Yulin
Chen
Diamond Proposal Number(s):
[15364]
Abstract: Group VIII transition-metal dichalcogenides have recently been proposed to host type-II Dirac fermions. They are Lorentz-violating quasiparticles marked by a strongly tilted conic dispersion along a certain momentum direction and therefore have no analogs in the standard model. Using high-resolution angle-resolved photoemission spectroscopy, we systematically studied the electronic structure of PtSe2 in the full three-dimensional Brillouin zone. As predicted, a pair of type-II Dirac crossings is experimentally confirmed along the kz axis. Interestingly, we observed conic surface states around time-reversal-invariant momenta
¯¯¯
Γ and
¯¯¯¯
M points. The signatures of nontrivial topology are confirmed by the first-principles calculation, which shows an intricate parity inversion of bulk states. Our discoveries not only contribute to a better understanding of topological band structure in PtSe2 but also help further explore the exotic properties, as well as potential application, of group VIII transition-metal dichalcogenides.
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Dec 2017
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I05-ARPES
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Qihang
Zhang
,
Zhongkai
Liu
,
Yan
Sun
,
Haifeng
Yang
,
Juan
Jiang
,
Sung-Kwan
Mo
,
Zahid
Hussain
,
Xiaofeng
Qian
,
Liang
Fu
,
Shuhua
Yao
,
Minghui
Lu
,
Claudia
Felser
,
Binghai
Yan
,
Yulin
Chen
,
Lexian
Yang
Diamond Proposal Number(s):
[16846]
Abstract: Using high resolution angle-resolved photoemission spectroscopy, we systematically investigate the electronic structure of Td-WTe2, which has attracted substantial research attention due to its diverse and fascinating properties, especially the predicted type-II topological Weyl semimetal (TWS) phase. The observed significant lattice contraction and the fact that our ARPES measurements are well reproduced by our ab initio calculations under reduced lattice constants support the theoretical prediction of a type-II TWS phase in Td-WTe2 at temperatures below 10 K. We also investigate the evolution of the electronic structure of Td-WTe2 and realize two-stage Lifshitz transitions induced by temperature regulation and surface modification, respectively. Our results not only shed light on the understanding of the electronic structure of Td-WTe2, but also provide a promising method to manipulate the electronic structures and physical properties of the type-II TWS Td-XTe2.
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Oct 2017
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I05-ARPES
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Sandy Adhitia
Ekahana
,
Shu-Chun
Wu
,
Juan
Jiang
,
Kenjiro
Okawa
,
Dharmalingam
Prabhakaran
,
Chan-Cuk
Hwang
,
Sung-Kwan
Mo
,
Takao
Sasagawa
,
Claudia
Felser
,
Binghai
Yan
,
Zhongkai
Liu
,
Yulin
Chen
Open Access
Abstract: Topological Nodal Semimetal (TNS), characterised by its touching conduction and valence bands, is a newly discovered state of quantum matter which exhibits various exotic physical phenomena. Recently, a new type of TNS called Topological Nodal Line Semimetal (TNLS) is predicted where its conduction and valence band form a degenerate 1D line which is further protected by its crystal symmetry. In this work, we systematically investigated the bulk and surface electronic structure of the non-symmorphic, TNLS in InBi with strong spin-orbit coupling by using Angle Resolved Photoemission Spectroscopy (ARPES). By tracking the crossing points of the bulk bands at the Brillouin zone boundary, we discovered the nodal-line feature along the XRX line, in agreement with the ab-initio calculations and confirmed it to be a new compound in the TNLS family. Our discovery provides new material platform for the study of these exotic topological quantum phases and paves the way for possible future applications.
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Jun 2017
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Hongtao
Yuan
,
Zhongkai
Liu
,
Gang
Xu
,
Bo
Zhou
,
Sanfeng
Wu
,
Dumitru
Dumcenco
,
Kai
Yan
,
Yi
Zhang
,
Sung-Kwan
Mo
,
Pavel
Dudin
,
Victor
Kandyba
,
Mikhail
Yablonskikh
,
Alexei
Barinov
,
Zhixun
Shen
,
Shoucheng
Zhang
,
Yingsheng
Huang
,
Xiaodong
Xu
,
Zahid
Hussain
,
Harold Y.
Hwang
,
Yi
Cui
,
Yulin
Chen
Abstract: Layered transition metal chalcogenides with large spin orbit coupling have recently sparked much interest due to their potential applications for electronic, optoelectronic, spintronics, and valleytronics. However, most current understanding of the electronic structure near band valleys in momentum space is based on either theoretical investigations or optical measurements, leaving the detailed band structure elusive. For example, the exact position of the conduction band valley of bulk MoS2 remains controversial. Here, using angle-resolved photoemission spectroscopy with submicron spatial resolution (micro-ARPES), we systematically imaged the conduction/valence band structure evolution across representative chalcogenides MoS2, WS2, and WSe2, as well as the thickness dependent electronic structure from bulk to the monolayer limit. These results establish a solid basis to understand the underlying valley physics of these materials, and also provide a link between chalcogenide electronic band structure and their physical properties for potential valleytronics applications.
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Aug 2016
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I05-ARPES
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Chandra
Shekhar
,
Ajaya K.
Nayak
,
Yan
Sun
,
Marcus
Schmidt
,
Michael
Nicklas
,
Inge
Leermakers
,
Uli
Zeitler
,
Yurii
Skourski
,
Jochen
Wosnitza
,
Zhongkai
Liu
,
Yulin
Chen
,
Walter
Schnelle
,
Horst
Borrmann
,
Yuri
Grin
,
Claudia
Felser
,
Binghai
Yan
Diamond Proposal Number(s):
[13177]
Abstract: Recent experiments have revealed spectacular transport properties in semimetals, such as the large, non-saturating magnetoresistance exhibited by WTe2 (ref. 1). Topological semimetals with massless relativistic electrons have also been predicted2 as three-dimensional analogues of graphene3. These systems are known as Weyl semimetals, and are predicted to have a range of exotic transport properties and surface states4, 5, 6, 7, distinct from those of topological insulators8, 9. Here we examine the magneto-transport properties of NbP, a material the band structure of which has been predicted to combine the hallmarks of a Weyl semimetal10, 11 with those of a normal semimetal. We observe an extremely large magnetoresistance of 850,000% at 1.85 K (250% at room temperature) in a magnetic field of up to 9 T, without any signs of saturation, and an ultrahigh carrier mobility of 5 × 106 cm2 V−1 s−1 that accompanied by strong Shubnikov–de Haas (SdH) oscillations. NbP therefore presents a unique example of a material combining topological and conventional electronic phases, with intriguing physical properties resulting from their interplay.
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Jun 2015
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