I05-ARPES
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Niels B. M.
Schröter
,
Ding
Pei
,
Maia G.
Vergniory
,
Yan
Sun
,
Kaustuv
Manna
,
Fernando
De Juan
,
Jonas A.
Krieger
,
Vicky
Süss
,
Marcus
Schmidt
,
Pavel
Dudin
,
Barry
Bradlyn
,
Timur K.
Kim
,
Thorsten
Schmitt
,
Cephise
Cacho
,
Claudia
Felser
,
Vladimir N.
Strocov
,
Yulin
Chen
Diamond Proposal Number(s):
[19883, 21400]
Abstract: Topological semimetals in crystals with a chiral structure (which possess a handedness due to a lack of mirror and inversion symmetries) are expected to display numerous exotic physical phenomena, including fermionic excitations with large topological charge1, long Fermi arc surface states2,3, unusual magnetotransport4 and lattice dynamics5, as well as a quantized response to circularly polarized light6. So far, all experimentally confirmed topological semimetals exist in crystals that contain mirror operations, meaning that these properties do not appear. Here, we show that AlPt is a structurally chiral topological semimetal that hosts new four-fold and six-fold fermions, which can be viewed as a higher spin generalization of Weyl fermions without equivalence in elementary particle physics. These multifold fermions are located at high symmetry points and have Chern numbers larger than those in Weyl semimetals, thus resulting in multiple Fermi arcs that span the full diagonal of the surface Brillouin zone. By imaging these long Fermi arcs, we experimentally determine the magnitude and sign of their Chern number, allowing us to relate their dispersion to the handedness of their host crystal.
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May 2019
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I05-ARPES
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S. V.
Borisenko
,
D. V.
Evtushinsky
,
Z. H
Liu
,
I.
Morozov
,
R.
Kappenberger
,
S.
Wurmehl
,
B.
Büchner
,
A. N.
Yaresko
,
T. K.
Kim
,
M.
Hoesch
,
T.
Wolf
,
N. D.
Zhigadlo
Diamond Proposal Number(s):
[10372, 11643]
Abstract: Spin–orbit coupling is a fundamental interaction in solids that can induce a broad range of unusual physical properties, from topologically non-trivial insulating states to unconventional pairing in superconductors1, 2, 3, 4, 5, 6, 7. In iron-based superconductors its role has, so far, not been considered of primary importance, with models based on spin- or orbital fluctuations pairing being used most widely8, 9, 10. Using angle-resolved photoemission spectroscopy, we directly observe a sizeable spin–orbit splitting in all the main members of the iron-based superconductors. We demonstrate that its impact on the low-energy electronic structure and details of the Fermi surface topology is stronger than that of possible nematic ordering11, 12, 13. The largest pairing gap is supported exactly by spin–orbit-coupling-induced Fermi surfaces, implying a direct relation between this interaction and the mechanism of high-temperature superconductivity.
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Dec 2015
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I05-ARPES
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L. X.
Yang
,
Z. K.
Liu
,
Y.
Sun
,
H.
Peng
,
H. F.
Yang
,
T.
Zhang
,
Binbin
Zhou
,
Y
Zhang
,
Y. F.
Guo
,
Marein
Rahn
,
D.
Prabhakaran
,
Z.
Hussain
,
S. K.
Mo
,
C.
Felser
,
B.
Yan
,
Y. L.
Chen
Diamond Proposal Number(s):
[13177]
Abstract: Three-dimensional (3D) topologicalWeyl semimetals (TWSs) represent a state of quantum matter with unusual electronic structures that resemble both a ‘3D graphene’ and a topological insulator. Their electronic structure displays pairs of Weyl points (through which the electronic bands disperse linearly along all three momentum directions) connected by topological surface states, forming a unique arc-like Fermi surface (FS). Each Weyl point is chiral and contains half the degrees of freedom of a Dirac point, and can be viewed as a magnetic monopole in momentum space. By performing angle-resolved photoemission spectroscopy on the non-centrosymmetric compound TaAs, here we report its complete band structure, including the unique Fermi-arc FS and linear bulk band dispersion across the Weyl points, in agreement with the theoretical calculations1, 2. This discovery not only confirms TaAs as a 3DTWS, but also provides an ideal platform for realizing exotic physical phenomena (for example, negative magnetoresistance, chiral magnetic effects and the quantum anomalous Hall effect) which may also lead to novel future applications.
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Aug 2015
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I05-ARPES
|
Su-yang
Xu
,
Nasser
Alidoust
,
Ilya
Belopolski
,
Zhujun
Yuan
,
Guang
Bian
,
Tay-rong
Chang
,
Hao
Zheng
,
Vladimir N.
Strocov
,
Daniel
Sanchez
,
Guoqing
Chang
,
Chenglong
Zhang
,
Daixiang
Mou
,
Yun
Wu
,
Lunan
Huang
,
Chi-cheng
Lee
,
Shin-ming
Huang
,
Baokai
Wang
,
Arun
Bansil
,
Horng-tay
Jeng
,
Titus
Neupert
,
Adam
Kaminski
,
Hsin
Lin
,
Shuang
Jia
,
M.
Zahid Hasan
Diamond Proposal Number(s):
[10074]
Abstract: Three types of fermions play a fundamental role in our understanding of nature: Dirac, Majorana and Weyl. Whereas Dirac fermions have been known for decades, the latter two have not been observed as any fundamental particle in high-energy physics, and have emerged as a much-sought-out treasure in condensed matter physics. A Weyl semimetal is a novel crystal whose low-energy electronic excitations behave as Weyl fermions. It has received worldwide interest and is believed to open the next era of condensed matter physics after graphene and three-dimensional topological insulators. However, experimental research has been held back because Weyl semimetals are extremely rare in nature. Here, we present the experimental discovery of the Weyl semimetal state in an inversion-symmetry-breaking single-crystalline solid, niobium arsenide (NbAs). Utilizing the combination of soft X-ray and ultraviolet photoemission spectroscopy, we systematically study both the surface and bulk electronic structure of NbAs. We experimentally observe both the Weyl cones in the bulk and the Fermi arcs on the surface of this system. Our ARPES data, in agreement with our theoretical band structure calculations, identify the Weyl semimetal state in NbAs, which provides a real platform to test the potential of Weyltronics.
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Aug 2015
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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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I05-ARPES
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Jonathon
Riley
,
F.
Mazzola
,
Maciej
Dendzik
,
M.
Michiardi
,
T.
Takayama
,
Lewis
Bawden
,
C.
Granerød
,
M.
Leandersson
,
T.
Balasubramanian
,
Moritz
Hoesch
,
Timur
Kim
,
H.
Takagi
,
Worawat
Meevasana
,
Ph.
Hoffmann
,
M. s.
Bahramy
,
Justin
Wells
,
Philip
King
Diamond Proposal Number(s):
[9427, 9500]
Abstract: Methods to generate spin-polarized electronic states in non-magnetic solids are strongly desired to enable all-electrical manipulation of electron spins for new quantum devices1. This is generally accepted to require breaking global structural inversion symmetry1, 2, 3, 4, 5. In contrast, here we report the observation from spin- and angle-resolved photoemission spectroscopy of spin-polarized bulk states in the centrosymmetric transition-metal dichalcogenide WSe2. Mediated by a lack of inversion symmetry in constituent structural units of the bulk crystal where the electronic states are localized6, we show how spin splittings up to ∼0.5 eV result, with a spin texture that is strongly modulated in both real and momentum space. Through this, our study provides direct experimental evidence for a putative locking of the spin with the layer and valley pseudospins in transition-metal dichalcogenides7, 8, of key importance for using these compounds in proposed valleytronic devices.
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Oct 2014
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I16-Materials and Magnetism
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Abstract: Magnetismthe spontaneous alignment of atomic moments in a materialis driven by quantum mechanical exchange interactions that operate over interatomic distances. Some magnetic interactions cause1, 2, or are caused by3, 4, a twisting of arrangements of atoms. This can lead to the magnetoelectric effect, predicted to play a prominent role in future technology, and to the phenomenon of weak ferromagnetism, governed by the so-called DzyaloshinskiiMoriya interaction5, 6, 7, 8. Here we determine the sign of the latter interaction in iron borate (FeBO3) by using synchrotron radiation. We present a novel experimental technique based on the interference between two X-ray scattering processes, where one acts as a reference wave. Our experimental results are validated by state-of-the-art ab initio calculations. Together, our experimental and theoretical approaches are expected to open up new possibilities for exploring, modelling and exploiting novel magnetic and magnetoelectric materials.
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Feb 2014
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