I05-ARPES
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Diamond Proposal Number(s):
[36633]
Open Access
Abstract: The 4Hb polytype of TaS2 is a natural heterostructure of H and T-type layers. Intriguing recent evidence points towards a possibly chiral superconducting ground state, unlike the superconductivity found in other polytypes where the T layers are absent, requiring understanding of the possible contributions of electrons from the T layers. Here we use micro-focused angle resolved photoemission spectroscopy to reveal that the T termination of the 4Hb structure is metallic, but a subsurface T layer - seen below an H termination and thus more representative of the bulk case - is gapped. The results imply a complete charge transfer of 1 electron per 13 Ta from the T to adjacent H layers in the bulk, but an incomplete charge transfer at the T termination, yielding a metallic Fermi surface with a planar-chiral character. A similar metallic state is found in an anomalous region with likely T-H-H’ stacking at the surface. Our results exclude cluster Mott localisation in either the bulk or surface of 4Hb-TaS2 and point to a scenario of superconductivity arising from Josephson-like tunneling between the H layers.
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Jan 2026
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B23-Circular Dichroism
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Francesco
Furlan
,
Michal
Šámal
,
Jiří
Rybáček
,
Andrea
Taddeucci
,
Marta
Di Girolamo
,
Davide
Nodari
,
Giuliano
Siligardi
,
Jessica
Wade
,
Binghai
Yan
,
Irena G.
Stará
,
Nicola
Gasparini
,
Matthew J.
Fuchter
Diamond Proposal Number(s):
[32632]
Open Access
Abstract: The photon spin information encoded in circularly polarized (CP) light is of high interest for current and future technologies, including low-power displays, encrypted communications and high-performance quantum applications. Engineering organic light-emitting diodes (LED) to emit oppositely handed electroluminescent CP light typically requires access to left- and right-handed chiral molecules. In conjugated polymer LEDs, the handedness of CP electroluminescence also depends on the active-layer thickness or direction of current flow. For a given active-layer thickness, it remains unknown whether a single-handed chiral material can emit CP light with opposite handedness in the same LED architecture. Here we demonstrate organic LEDs in which the handedness of the emitted CP electroluminescence can be controlled electrically, solely by using specific interlayers with no change in the emissive material composition or thickness. We reveal that this occurs due to a change in mechanism for the generation of CP electroluminescence, as a function of the recombination zone position within the device. This result provides a paradigm shift in the realization of organic CP-LEDs with controllable spin angular momentum information and further contributes to ongoing discussions relating the fundamental physics of chiral optoelectronics.
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Nov 2025
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I05-ARPES
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Christopher
Broyles
,
Xiaohan
Wan
,
Wenting
Cheng
,
Dingsong
Wu
,
Hengxin
Tan
,
Qiaozhi
Xu
,
Shannon L.
Gould
,
Hasan
Siddiquee
,
Leyan
Xiao
,
Ryan
Chen
,
Wanyue
Lin
,
Yuchen
Wu
,
Prakash
Regmi
,
Yun Suk
Eo
,
Jieyi
Liu
,
Yulin
Chen
,
Binghai
Yan
,
Kai
Sun
,
Sheng
Ran
Diamond Proposal Number(s):
[36513]
Open Access
Abstract: The resurgence of interest in Kondo insulators has been driven by two major mysteries: the presence of metallic surface states and the observation of quantum oscillations. To further explore these mysteries, it is crucial to investigate another similar system beyond the two existing ones, SmB6 and YbB12. Here, we address this by reporting on a Kondo insulator, U3Bi4Ni3. Our transport measurements reveal that a surface state emerges below 250 kelvin and dominates transport properties below 150 kelvin, which is well above the temperature scale of SmB6 and YbB12. At low temperatures, the surface conductivity is about one order of magnitude higher than the bulk. The robustness of the surface state indicates that it is inherently protected. The similarities and differences between U3Bi4Ni3 and the other two Kondo insulators will provide valuable insights into the nature of metallic surface states in Kondo insulators and their interplay with strong electron correlations.
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Mar 2025
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I05-ARPES
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Diamond Proposal Number(s):
[15822]
Abstract: FeSe
0.45
Te
0.55
(FeSeTe) has recently emerged as a promising candidate to host topological superconductivity, with a Dirac surface state and signatures of Majorana bound states in vortex cores. However, correlations strongly renormalize the bands compared to electronic structure calculations, and there is no evidence for the expected bulk band inversion. We present here a comprehensive angle resolved photoemission (ARPES) study of FeSeTe as a function of photon energies ranging from 15–100 eV. We find that although the top of the bulk valence band shows essentially no
k
z
dispersion, its normalized intensity exhibits a periodic variation with
k
z
. We show, using ARPES selection rules, that the intensity oscillation is a signature of band inversion indicating a change in the parity going from
Γ
to
Z
. We also present a simple realistic tight-binding model which gives insight into ARPES observations. Thus we provide direct evidence for a topologically nontrivial bulk band structure that supports protected surface states.
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Jun 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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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
|
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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I05-ARPES
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Jinxiong
Wu
,
Hongtao
Yuan
,
Mengmeng
Meng
,
Cheng
Chen
,
Yan
Sun
,
Zhuoyu
Chen
,
Wenhui
Dang
,
Congwei
Tan
,
Yujing
Liu
,
Jianbo
Yin
,
Yubing
Zhou
,
Shaoyun
Huang
,
H. Q.
Xu
,
Yi
Cui
,
Harold Y.
Hwang
,
Zhongfan
Liu
,
Yulin
Chen
,
Binghai
Yan
,
Hailin
Peng
Diamond Proposal Number(s):
[14132]
Abstract: High-mobility semiconducting ultrathin films form the basis of modern electronics, and may lead to the scalable fabrication of highly performing devices. Because the ultrathin limit cannot be reached for traditional semiconductors, identifying new two-dimensional materials with both high carrier mobility and a large electronic bandgap is a pivotal goal of fundamental research1, 2, 3, 4, 5, 6, 7, 8, 9. However, air-stable ultrathin semiconducting materials with superior performances remain elusive at present10. Here, we report ultrathin films of non-encapsulated layered Bi2O2Se, grown by chemical vapour deposition, which demonstrate excellent air stability and high-mobility semiconducting behaviour. We observe bandgap values of ∼0.8 eV, which are strongly dependent on the film thickness due to quantum-confinement effects. An ultrahigh Hall mobility value of >20,000 cm2 V−1 s−1 is measured in as-grown Bi2O2Se nanoflakes at low temperatures. This value is comparable to what is observed in graphene grown by chemical vapour deposition11 and at the LaAlO3–SrTiO3 interface12, making the detection of Shubnikov–de Haas quantum oscillations possible. Top-gated field-effect transistors based on Bi2O2Se crystals down to the bilayer limit exhibit high Hall mobility values (up to 450 cm2 V−1 s−1), large current on/off ratios (>106) and near-ideal subthreshold swing values (∼65 mV dec–1) at room temperature. Our results make Bi2O2Se a promising candidate for future high-speed and low-power electronic applications.
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Apr 2017
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I05-ARPES
|
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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