I05-ARPES
|
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.
|
Jul 2020
|
|
I05-ARPES
|
D.
Sutter
,
M.
Kim
,
C. E.
Matt
,
M.
Horio
,
R.
Fittipaldi
,
A.
Vecchione
,
V.
Granata
,
K.
Hauser
,
Y.
Sassa
,
G.
Gatti
,
M.
Grioni
,
M.
Hoesch
,
T. K.
Kim
,
E.
Rienks
,
N. C.
Plumb
,
M.
Shi
,
T.
Neupert
,
A.
Georges
,
J.
Chang
Diamond Proposal Number(s):
[15296]
Abstract: We present a comprehensive angle-resolved photoemission spectroscopy study of
Ca
1.8
Sr
0.2
RuO
4
. Four distinct bands are revealed and along the Ru-O bond direction their orbital characters are identified through a light polarization analysis and comparison to dynamical mean-field theory calculations. Bands assigned to
d
x
z
,
d
y
z
orbitals display Fermi liquid behavior with fourfold quasiparticle mass renormalization. Extremely heavy fermions—associated with a predominantly
d
x
y
band character—are shown to display non-Fermi-liquid behavior. We thus demonstrate that
Ca
1.8
Sr
0.2
RuO
4
is a hybrid metal with an orbitally selective Fermi liquid quasiparticle breakdown.
|
Mar 2019
|
|
I05-ARPES
|
C. E.
Matt
,
D.
Sutter
,
A. M.
Cook
,
Y.
Sassa
,
Martin
Mansson
,
O.
Tjernberg
,
L.
Das
,
M.
Horio
,
D.
Destraz
,
C. G.
Fatuzzo
,
K.
Hauser
,
M.
Shi
,
M.
Kobayashi
,
V. N.
Strocov
,
T.
Schmitt
,
P.
Dudin
,
M.
Hoesch
,
S.
Pyon
,
T.
Takayama
,
H.
Takagi
,
O. J.
Lipscombe
,
S. M.
Hayden
,
T.
Kurosawa
,
N.
Momono
,
M.
Oda
,
T.
Neupert
,
J.
Chang
Diamond Proposal Number(s):
[10550]
Open Access
Abstract: The minimal ingredients to explain the essential physics of layered copper-oxide (cuprates) materials remains heavily debated. Effective low-energy single-band models of the copper–oxygen orbitals are widely used because there exists no strong experimental evidence supporting multi-band structures. Here, we report angle-resolved photoelectron spectroscopy experiments on La-based cuprates that provide direct observation of a two-band structure. This electronic structure, qualitatively consistent with density functional theory, is parametrised by a two-orbital (d x 2 −y 2
dx2-y2
and d z 2
dz2
) tight-binding model. We quantify the orbital hybridisation which provides an explanation for the Fermi surface topology and the proximity of the van-Hove singularity to the Fermi level. Our analysis leads to a unification of electronic hopping parameters for single-layer cuprates and we conclude that hybridisation, restraining d-wave pairing, is an important optimisation element for superconductivity.
|
Mar 2018
|
|
I05-ARPES
|
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.
|
Jun 2017
|
|
I05-ARPES
|
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.
|
May 2017
|
|
I05-ARPES
|
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.
|
Feb 2016
|
|
I05-ARPES
|
S. Y.
Xu
,
I.
Belopolski
,
D.
Sanchez
,
C.
Zhang
,
G.
Chang
,
C.
Guo
,
G.
Bian
,
Z.
Yuan
,
H.
Lu
,
T. R
Chang
,
P. P
Shibayev
,
Mykhaylo
Prokopovych
,
N.
Alidoust
,
H.
Zheng
,
C. C
Lee
,
S. M.
Huang
,
R.
Sankar
,
F.
Chou
,
C. H.
Hsu
,
H. T
Jeng
,
A.
Bansil
,
T.
Neupert
,
V. N.
Strocov
,
H.
Lin
,
S.
Jia
,
M. Z.
Hasan
Abstract: Weyl semimetals are expected to open up new horizons in physics and materials science because they provide the first realization of Weyl fermions and exhibit protected Fermi arc surface states. However, they had been found to be extremely rare in nature. Recently, a family of compounds, consisting of tantalum arsenide, tantalum phosphide (TaP), niobium arsenide, and niobium phosphide, was predicted as a Weyl semimetal candidates. We experimentally realize a Weyl semimetal state in TaP. Using photoemission spectroscopy, we directly observe the Weyl fermion cones and nodes in the bulk, and the Fermi arcs on the surface. Moreover, we find that the surface states show an unexpectedly rich structure, including both topological Fermi arcs and several topologically trivial closed contours in the vicinity of the Weyl points, which provides a promising platform to study the interplay between topological and trivial surface states on a Weyl semimetal’s surface. We directly demonstrate the bulk-boundary correspondence and establish the topologically nontrivial nature of the Weyl semimetal state in TaP, by resolving the net number of chiral edge modes on a closed path that encloses the Weyl node. This also provides, for the first time, an experimentally practical approach to demonstrating a bulk Weyl fermion from a surface state dispersion measured in photoemission.
|
Nov 2015
|
|
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.
|
Aug 2015
|
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