I10-Beamline for Advanced Dichroism
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Xiaoqian
Zhang
,
Qiangsheng
Lu
,
Wenqing
Liu
,
Wei
Niu
,
Jiabao
Sun
,
Jacob
Cook
,
Mitchel
Vaninger
,
Paul F.
Miceli
,
David J.
Singh
,
Shang-Wei
Lian
,
Tay-Rong
Chang
,
Xiaoqing
He
,
Jun
Du
,
Liang
He
,
Rong
Zhang
,
Guang
Bian
,
Yongbing
Xu
Diamond Proposal Number(s):
[22532]
Open Access
Abstract: While the discovery of two-dimensional (2D) magnets opens the door for fundamental physics and next-generation spintronics, it is technically challenging to achieve the room-temperature ferromagnetic (FM) order in a way compatible with potential device applications. Here, we report the growth and properties of single- and few-layer CrTe2, a van der Waals (vdW) material, on bilayer graphene by molecular beam epitaxy (MBE). Intrinsic ferromagnetism with a Curie temperature (TC) up to 300 K, an atomic magnetic moment of ~0.21 𝜇B
μ
B
/Cr and perpendicular magnetic anisotropy (PMA) constant (Ku) of 4.89 × 105 erg/cm3 at room temperature in these few-monolayer films have been unambiguously evidenced by superconducting quantum interference device and X-ray magnetic circular dichroism. This intrinsic ferromagnetism has also been identified by the splitting of majority and minority band dispersions with ~0.2 eV at Г point using angle-resolved photoemission spectroscopy. The FM order is preserved with the film thickness down to a monolayer (TC ~ 200 K), benefiting from the strong PMA and weak interlayer coupling. The successful MBE growth of 2D FM CrTe2 films with room-temperature ferromagnetism opens a new avenue for developing large-scale 2D magnet-based spintronics devices.
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May 2021
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I05-ARPES
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Jia-Xin
Yin
,
Wenlong
Ma
,
Tyler A.
Cochran
,
Xitong
Xu
,
Songtian S.
Zhang
,
Hung-Ju
Tien
,
Nana
Shumiya
,
Guangming
Cheng
,
Kun
Jiang
,
Biao
Lian
,
Zhida
Song
,
Guoqing
Chang
,
Ilya
Belopolski
,
Daniel
Multer
,
Maksim
Litskevich
,
Zi-Jia
Cheng
,
Xian P.
Yang
,
Bianca
Swidler
,
Huibin
Zhou
,
Hsin
Lin
,
Titus
Neupert
,
Ziqiang
Wang
,
Nan
Yao
,
Tay-Rong
Chang
,
Shuang
Jia
,
M.
Zahid Hasan
Diamond Proposal Number(s):
[22332]
Abstract: The quantum-level interplay between geometry, topology and correlation is at the forefront of fundamental physics. Kagome magnets are predicted to support intrinsic Chern quantum phases owing to their unusual lattice geometry and breaking of time-reversal symmetry. However, quantum materials hosting ideal spin–orbit-coupled kagome lattices with strong out-of-plane magnetization are lacking. Here, using scanning tunnelling microscopy, we identify a new topological kagome magnet, TbMn6Sn6, that is close to satisfying these criteria. We visualize its effectively defect-free, purely manganese-based ferromagnetic kagome lattice with atomic resolution. Remarkably, its electronic state shows distinct Landau quantization on application of a magnetic field, and the quantized Landau fan structure features spin-polarized Dirac dispersion with a large Chern gap. We further demonstrate the bulk–boundary correspondence between the Chern gap and the topological edge state, as well as the Berry curvature field correspondence of Chern gapped Dirac fermions. Our results point to the realization of a quantum-limit Chern phase in TbMn6Sn6, and may enable the observation of topological quantum phenomena in the RMn6Sn6 (where R is a rare earth element) family with a variety of magnetic structures. Our visualization of the magnetic bulk–boundary–Berry correspondence covering real space and momentum space demonstrates a proof-of-principle method for revealing topological magnets.
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Jul 2020
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I05-ARPES
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Su-Yang
Xu
,
Nasser
Alidoust
,
Guoqing
Chang
,
Hong
Lu
,
Bahadur
Singh
,
Ilya
Belopolski
,
Daniel S.
Sanchez
,
Xiao
Zhang
,
Guang
Bian
,
Hao
Zheng
,
Marious-Adrian
Husanu
,
Yi
Bian
,
Shin-Ming
Huang
,
Chuang-Han
Hsu
,
Tay-Rong
Chang
,
Horng-Tay
Jeng
,
Arun
Bansil
,
Titus
Neupert
,
Vladimir N.
Strocov
,
Hsin
Lin
,
Shuang
Jia
,
M. Zahid
Hasan
Open Access
Abstract: In quantum field theory, Weyl fermions are relativistic particles that travel at the speed of light and strictly obey the celebrated Lorentz symmetry. Their low-energy condensed matter analogs are Weyl semimetals, which are conductors whose electronic excitations mimic the Weyl fermion equation of motion. Although the traditional (type I) emergent Weyl fermions observed in TaAs still approximately respect Lorentz symmetry, recently, the so-called type II Weyl semimetal has been proposed, where the emergent Weyl quasiparticles break the Lorentz symmetry so strongly that they cannot be smoothly connected to Lorentz symmetric Weyl particles. Despite some evidence of nontrivial surface states, the direct observation of the type II bulk Weyl fermions remains elusive. We present the direct observation of the type II Weyl fermions in crystalline solid lanthanum aluminum germanide (LaAlGe) based on our photoemission data alone, without reliance on band structure calculations. Moreover, our systematic data agree with the theoretical calculations, providing further support on our experimental results.
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Jun 2017
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I05-ARPES
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D.
Sutter
,
C. G.
Fatuzzo
,
S.
Moser
,
M.
Kim
,
R.
Fittipaldi
,
A.
Vecchione
,
V.
Granata
,
Y.
Sassa
,
F.
Cossalter
,
G.
Gatti
,
M.
Grioni
,
H. M.
Rønnow
,
N. C.
Plumb
,
C. E.
Matt
,
M.
Shi
,
M.
Hoesch
,
T. K.
Kim
,
T.-R.
Chang
,
H.-T.
Jeng
,
C.
Jozwiak
,
A.
Bostwick
,
E.
Rotenberg
,
A.
Georges
,
T.
Neupert
,
J.
Chang
Diamond Proposal Number(s):
[14617, 12926]
Open Access
Abstract: A paradigmatic case of multi-band Mott physics including spin-orbit and Hund’s coupling is realized in Ca2RuO4. Progress in understanding the nature of this Mott insulating phase has been impeded by the lack of knowledge about the low-energy electronic structure. Here we provide—using angle-resolved photoemission electron spectroscopy—the band structure of the paramagnetic insulating phase of Ca2RuO4 and show how it features several distinct energy scales. Comparison to a simple analysis of atomic multiplets provides a quantitative estimate of the Hund’s coupling J=0.4 eV. Furthermore, the experimental spectra are in good agreement with electronic structure calculations performed with Dynamical Mean-Field Theory. The crystal field stabilization of the dxy orbital due to c-axis contraction is shown to be essential to explain the insulating phase. These results underscore the importance of multi-band physics, Coulomb interaction and Hund’s coupling that together generate the Mott insulating state of Ca2RuO4.
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May 2017
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I05-ARPES
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Ilya
Belopolski
,
Su-Yang
Xu
,
Yukiaki
Ishida
,
Xingchen
Pan
,
Peng
Yu
,
Daniel S.
Sanchez
,
Hao
Zheng
,
Madhab
Neupane
,
Nasser
Alidoust
,
Guoqing
Chang
,
Tay-Rong
Chang
,
Yun
Wu
,
Guang
Bian
,
Shin-Ming
Huang
,
Chi-Cheng
Lee
,
Daixiang
Mou
,
Lunan
Huang
,
You
Song
,
Baigeng
Wang
,
Guanghou
Wang
,
Yao-Wen
Yeh
,
Nan
Yao
,
Julien E.
Rault
,
Patrick
Le Fèvre
,
François
Bertran
,
Horng-Tay
Jeng
,
Takeshi
Kondo
,
Adam
Kaminski
,
Hsin
Lin
,
Zheng
Liu
,
Fengqi
Song
,
Shik
Shin
,
M. Zahid
Hasan
Diamond Proposal Number(s):
[13653]
Abstract: It has recently been proposed that electronic band structures in crystals can give rise to a previously overlooked type of Weyl fermion, which violates Lorentz invariance and, consequently, is forbidden in particle physics. It was further predicted that MoxW1−xTe2 may realize such a type-II Weyl fermion. Here, we first show theoretically that it is crucial to access the band structure above the Fermi level ɛF to show a Weyl semimetal in MoxW1−xTe2. Then, we study MoxW1−xTe2 by pump-probe ARPES and we directly access the band structure >0.2 eV above ɛF in experiment. By comparing our results with ab initio calculations, we conclude that we directly observe the surface state containing the topological Fermi arc. We propose that a future study of MoxW1−xTe2 by pump-probe ARPES may directly pinpoint the Fermi arc. Our work sets the stage for the experimental discovery of the first type-II Weyl semimetal in MoxW1−xTe2.
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Aug 2016
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I05-ARPES
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Cheng-Long
Zhang
,
Su-Yang
Xu
,
Ilya
Belopolski
,
Zhujun
Yuan
,
Ziquan
Lin
,
Bingbing
Tong
,
Guang
Bian
,
Nasser
Alidoust
,
Chi-Cheng
Lee
,
Shin-Ming
Huang
,
Tay-Rong
Chang
,
Guoqing
Chang
,
Chuang-Han
Hsu
,
Horng-Tay
Jeng
,
Madhab
Neupane
,
Daniel
Sanchez
,
Hao
Zheng
,
Junfeng
Wang
,
Hsin
Lin
,
Chi
Zhang
,
Hai-Zhou
Lu
,
Shun-Qing
Shen
,
Titus
Neupert
,
M.
Zahid Hasan
,
Shuang
Jia
Open Access
Abstract: Weyl semimetals provide the realization of Weyl fermions in solid-state physics. Among all the physical phenomena that are enabled by Weyl semimetals, the chiral anomaly is the most unusual one. Here, we report signatures of the chiral anomaly in the magneto-transport measurements on the first Weyl semimetal TaAs. We show negative magnetoresistance under parallel electric and magnetic fields, that is, unlike most metals whose resistivity increases under an external magnetic field, we observe that our high mobility TaAs samples become more conductive as a magnetic field is applied along the direction of the current for certain ranges of the field strength. We present systematically detailed data and careful analyses, which allow us to exclude other possible origins of the observed negative magnetoresistance. Our transport data, corroborated by photoemission measurements, first-principles calculations and theoretical analyses, collectively demonstrate signatures of the Weyl fermion chiral anomaly in the magneto-transport of TaAs.
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Feb 2016
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I05-ARPES
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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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