I05-ARPES
|
Takafumi
Sato
,
Zhiwei
Wang
,
Daichi
Takane
,
Seigo
Souma
,
Chaoxi
Cui
,
Yongkai
Li
,
Kosuke
Nakayama
,
Tappei
Kawakami
,
Yuya
Kubota
,
Cephise
Cacho
,
Timur
Kim
,
Arian
Arab
,
Vladimir N.
Strocov
,
Yugui
Yao
,
Takashi
Takahashi
Diamond Proposal Number(s):
[23799]
Open Access
Abstract: We have performed angle-resolved photoemission spectroscopy on
EuIn
2
As
2
which is predicted to be an axion insulator in the antiferromagnetic state. By utilizing soft-x-ray and vacuum-ultraviolet photons, we revealed a three-dimensional hole pocket centered at the
Γ
point of the bulk Brillouin zone together with a heavily hole-doped surface state in the paramagnetic phase. Upon entering the antiferromagnetic phase, the band structure exhibits a marked reconstruction characterized by the emergence of an “M”-shaped bulk band near the Fermi level. The qualitative agreement with first-principles band-structure calculations suggests the occurrence of bulk-band inversion at the
Γ
point in the antiferromagnetic phase. We suggest that
EuIn
2
As
2
provides a good opportunity to study the exotic quantum phases associated with a possible axion-insulator phase.
|
Sep 2020
|
|
I05-ARPES
|
So
Kunisada
,
Shunsuke
Isono
,
Yoshimitsu
Kohama
,
Shiro
Sakai
,
Cédric
Bareille
,
Shunsuke
Sakuragi
,
Ryo
Noguchi
,
Kifu
Kurokawa
,
Kenta
Kuroda
,
Yukiaki
Ishida
,
Shintaro
Adachi
,
Ryotaro
Sekine
,
Timur K.
Kim
,
Cephise
Cacho
,
Shik
Shin
,
Takami
Tohyama
,
Kazuyasu
Tokiwa
,
Takeshi
Kondo
Diamond Proposal Number(s):
[20445, 20446]
Abstract: In cuprate superconductors with high critical transition temperature (Tc), light hole-doping to the parent compound, which is an antiferromagnetic Mott insulator, has been predicted to lead to the formation of small Fermi pockets. These pockets, however, have not been observed. Here, we investigate the electronic structure of the five-layered Ba2Ca4Cu5O10(F,O)2, which has inner copper oxide (CuO2) planes with extremely low disorder, and find small Fermi pockets centered at (π/2, π/2) of the Brillouin zone by angle-resolved photoemission spectroscopy and quantum oscillation measurements. The d-wave superconducting gap opens along the pocket, revealing the coexistence between superconductivity and antiferromagnetic ordering in the same CuO2 sheet. These data further indicate that superconductivity can occur without contribution from the antinodal region around (π, 0), which is shared by other competing excitations.
|
Aug 2020
|
|
I05-ARPES
|
Niels B. M.
Schroeter
,
Samuel
Stolz
,
Kaustuv
Manna
,
Fernando
De Juan
,
Maia G.
Vergniory
,
Jonas A.
Krieger
,
Ding
Pei
,
Thorsten
Schmitt
,
Pavel
Dudin
,
Timur K.
Kim
,
Cephise
Cacho
,
Barry
Bradlyn
,
Horst
Borrmann
,
Marcus
Schmidt
,
Roland
Widmer
,
Vladimir N.
Strocov
,
Claudia
Felser
Diamond Proposal Number(s):
[24703, 20617]
Open Access
Abstract: Topological semimetals feature protected nodal band degeneracies characterized by a topological invariant known as the Chern number (C). Nodal band crossings with linear dispersion are expected to have at most |C|=4
|
C
|
=
4
, which sets an upper limit to the magnitude of many topological phenomena in these materials. Here, we show that the chiral crystal palladium gallium (PdGa) displays multifold band crossings, which are connected by exactly four surface Fermi arcs, thus proving that they carry the maximal Chern number magnitude of 4. By comparing two enantiomers, we observe a reversal of their Fermi-arc velocities, which demonstrates that the handedness of chiral crystals can be used to control the sign of their Chern numbers.
|
Jul 2020
|
|
I05-ARPES
|
Paolo
Sessi
,
Feng-ren
Fan
,
Felix
Küster
,
Kaustuv
Manna
,
Niels B. M.
Schroeter
,
Jing-rong
Ji
,
Samuel
Stolz
,
Jonas A.
Krieger
,
Ding
Pei
,
Timur K.
Kim
,
Pavel
Dudin
,
Cephise
Cacho
,
Remo N.
Widmer
,
Horst
Borrmann
,
Wujun
Shi
,
Kai
Chang
,
Yan
Sun
,
Claudia
Felser
,
Stuart S. P.
Parkin
Diamond Proposal Number(s):
[2470, 20617]
Open Access
Abstract: It has recently been proposed that combining chirality with topological band theory results in a totally new class of fermions. Understanding how these unconventional quasiparticles propagate and interact remains largely unexplored so far. Here, we use scanning tunneling microscopy to visualize the electronic properties of the prototypical chiral topological semimetal PdGa. We reveal chiral quantum interference patterns of opposite spiraling directions for the two PdGa enantiomers, a direct manifestation of the change of sign of their Chern number. Additionally, we demonstrate that PdGa remains topologically non-trivial over a large energy range, experimentally detecting Fermi arcs in an energy window of more than 1.6 eV that is symmetrically centered around the Fermi level. These results are a consequence of the deep connection between chirality in real and reciprocal space in this class of materials, and, thereby, establish PdGa as an ideal topological chiral semimetal.
|
Jul 2020
|
|
I05-ARPES
|
Saumya
Mukherjee
,
Sung Won
Jung
,
Sophie F.
Weber
,
Chunqiang
Xu
,
Dong
Qian
,
Xiaofeng
Xu
,
Pabitra K.
Biswas
,
Timur K.
Kim
,
Laurent C.
Chapon
,
Matthew D.
Watson
,
Jeffrey B.
Neaton
,
Cephise
Cacho
Diamond Proposal Number(s):
[21591]
Open Access
Abstract: Transition-metal dichalcogenides (TMDs) offer an ideal platform to experimentally realize Dirac fermions. However, typically these exotic quasiparticles are located far away from the Fermi level, limiting the contribution of Dirac-like carriers to the transport properties. Here we show that NiTe2 hosts both bulk Type-II Dirac points and topological surface states. The underlying mechanism is shared with other TMDs and based on the generic topological character of the Te p-orbital manifold. However, unique to NiTe2, a significant contribution of Ni d orbital states shifts the energy of the Type-II Dirac point close to the Fermi level. In addition, one of the topological surface states intersects the Fermi energy and exhibits a remarkably large spin splitting of 120 meV. Our results establish NiTe2 as an exciting candidate for next-generation spintronics devices.
|
Jul 2020
|
|
I05-ARPES
|
Kosuke
Nakayama
,
Zhiwei
Wang
,
Daichi
Takane
,
Seigo
Souma
,
Yuya
Kubota
,
Yuki
Nakata
,
Cephise
Cacho
,
Timur
Kim
,
Sandy Adhitia
Ekahana
,
Ming
Shi
,
Miho
Kitamura
,
Koji
Horiba
,
Hiroshi
Kumigashira
,
Takashi
Takahashi
,
Yoichi
Ando
,
Takafumi
Sato
Diamond Proposal Number(s):
[23799]
Abstract: We have performed high-resolution angle-resolved photoemission spectroscopy of the ternary pnictide CaAuAs, which is predicted to be a three-dimensional topological Dirac semimetal (TDS). By accurately determining the bulk-band structure, we have revealed the coexistence of three-dimensional and quasi-two-dimensional Fermi surfaces with dominant hole carriers. The band structure around the Brillouin-zone center is characterized by an energy overlap between the hole and electron pockets, in excellent agreement with first-principles band-structure calculations. This indicates the occurrence of bulk-band inversion, supporting the TDS state in CaAuAs. Because of the high tunability in the chemical composition besides the TDS nature, CaAuAs provides a precious opportunity for investigating the quantum phase transition from TDS to other exotic topological phases.
|
Jul 2020
|
|
I05-ARPES
I06-Nanoscience
|
Sung Won
Jung
,
Sangyeon
Pak
,
Sanghyo
Lee
,
Sonka
Reimers
,
Saumya
Mukherjee
,
Pavel
Dudin
,
Timur K.
Kim
,
Mattia
Cattelan
,
Neil
Fox
,
Sarnjeet S.
Dhesi
,
Cephise
Cacho
,
Seungnam
Cha
Diamond Proposal Number(s):
[24367, 22901]
Abstract: The recent rise of van der Waals (vdW) crystals has opened new prospects for studying versatile and exotic fundamental physics with future device applications such as twistronics. Even though the recent development on Angle-resolved photoemission spectroscopy (ARPES) with Nano-focusing optics, making clean surfaces and interfaces of chemically transferred crystals have been challenging to obtain high-resolution ARPES spectra. Here, we show that by employing nano-ARPES with submicron sized beam and polystyrene-assisted transfer followed by annealing process in ultra-high vacuum environment, remarkably clear ARPES spectral features such as spin-orbit splitting and band renormalization of CVD-grown, monolayered MoS2 can be measured. Our finding paves a way to exploit chemically transferred crystals for measuring high-resolution ARPES spectra to observe exotic quasi-particles in vdW heterostructures.
|
Jul 2020
|
|
I05-ARPES
|
Diamond Proposal Number(s):
[18705]
Open Access
Abstract: We report a combined experimental and theoretical study of the surface and bulk electronic structure of aluminium diboride, a nonsuperconducting sister compound of the superconductor
MgB
2
. We perform angle-resolved photoemission measurements with variable photon energy, and compare them to density functional theory calculations to disentangle the surface and bulk contributions to the measured spectra. Aluminium diboride is known to be aluminium deficient,
Al
1
−
δ
B
2
, which would be expected to lead to a hole doping as compared to the nominally stoichimoetric compound. Nonetheless, we find that the bulk
σ
states, which mediate superconductivity in
MgB
2
, remain more than
600
meV
below the Fermi level. However, we also observe
σ
states originating from the boron terminated surface, with an order of magnitude smaller binding energy of
70
meV
, and demonstrate how surface hole-doping can bring these across the Fermi level.
|
Jul 2020
|
|
I05-ARPES
|
Alfred J. H.
Jones
,
Ryan
Muzzio
,
Paulina
Majchrzak
,
Sahar
Pakdel
,
Davide
Curcio
,
Klara
Volckaert
,
Deepnarayan
Biswas
,
Jacob
Gobbo
,
Simranjeet
Singh
,
Jeremy T.
Robinson
,
Kenji
Watanabe
,
Takashi
Taniguchi
,
Timur K.
Kim
,
Cephise
Cacho
,
Nicola
Lanata
,
Jill A.
Miwa
,
Philip
Hofmann
,
Jyoti
Katoch
,
Soeren
Ulstrup
Diamond Proposal Number(s):
[24072]
Abstract: The possibility of triggering correlated phenomena by placing a singularity
of the density of states near the Fermi energy remains an intriguing avenue toward engineering the properties of quantum materials. Twisted bilayer gra- phene is a key material in this regard because the superlattice produced by the rotated graphene layers introduces a van Hove singularity and flat bands near the Fermi energy that cause the emergence of numerous correlated phases, including superconductivity. Direct demonstration of electrostatic control of the superlattice bands over a wide energy range has, so far, been critically missing. This work examines the effect of electrical doping on the electronic band structure of twisted bilayer graphene using a back-gated device archi- tecture for angle-resolved photoemission measurements with a nano-focused light spot. A twist angle of 12.2° is selected such that the superlattice Brillouin zone is sufficiently large to enable identification of van Hove singularities and flat band segments in momentum space. The doping dependence of these fea- tures is extracted over an energy range of 0.4 eV, expanding the combinations of twist angle and doping where they can be placed at the Fermi energy and thereby induce new correlated electronic phases in twisted bilayer graphene.
|
Jun 2020
|
|
I05-ARPES
|
Diamond Proposal Number(s):
[23890]
Open Access
Abstract: We measure the electronic structure of FeSe from within individual orthorhombic domains. Enabled by an angle-resolved photoemission spectroscopy beamline with a highly focused beam spot (nano-ARPES), we identify clear stripelike orthorhombic domains in FeSe with a length scale of approximately 1–5 μm. Our photoemission measurements of the Fermi surface and band structure within individual domains reveal a single electron pocket at the Brillouin zone corner. This result provides clear evidence for a one-electron-pocket electronic structure of FeSe, observed without the application of uniaxial strain, and calls for further theoretical insight into this unusual Fermi surface topology. Our results also showcase the potential of nano-ARPES for the study of correlated materials with local domain structures.
|
Jun 2020
|
|
