I05-ARPES
|
Christopher W.
Nicholson
,
Maxime
Rumo
,
Aki
Pulkkinen
,
Geoffroy
Kremer
,
Björn
Salzmann
,
Marie-laure
Mottas
,
Baptiste
Hildebrand
,
Thomas
Jaouen
,
Timur K.
Kim
,
Saumya
Mukherjee
,
Keyuan
Ma
,
Matthias
Muntwiler
,
Fabian O.
Von Rohr
,
Cephise
Cacho
,
Claude
Monney
Diamond Proposal Number(s):
[24880]
Open Access
Abstract: Strain is ubiquitous in solid-state materials, but despite its fundamental importance and technological relevance, leveraging externally applied strain to gain control over material properties is still in its infancy. In particular, strain control over the diverse phase transitions and topological states in two-dimensional transition metal dichalcogenides remains an open challenge. Here, we exploit uniaxial strain to stabilize the long-debated structural ground state of the 2D topological semimetal IrTe2, which is hidden in unstrained samples. Combined angle-resolved photoemission spectroscopy and scanning tunneling microscopy data reveal the strain-stabilized phase has a 6 × 1 periodicity and undergoes a Lifshitz transition, granting unprecedented spectroscopic access to previously inaccessible type-II topological Dirac states that dominate the modified inter-layer hopping. Supported by density functional theory calculations, we show that strain induces an Ir to Te charge transfer resulting in strongly weakened inter-layer Te bonds and a reshaped energetic landscape favoring the 6×1 phase. Our results highlight the potential to exploit strain-engineered properties in layered materials, particularly in the context of tuning inter-layer behavior.
|
Mar 2021
|
|
I05-ARPES
|
Paulina
Majchrzak
,
Ryan
Muzzio
,
Alfred J. H.
Jones
,
Davide
Curcio
,
Klara
Volckaert
,
Deepnarayan
Biswas
,
Jacob
Gobbo
,
Simranjeet
Singh
,
Jeremy T.
Robinson
,
Kenji
Watanabe
,
Takashi
Taniguchi
,
Timur K.
Kim
,
Cephise
Cacho
,
Jill A.
Miwa
,
Philip
Hofmann
,
Jyoti
Katoch
,
Soeren
Ulstrup
Diamond Proposal Number(s):
[24072]
Open Access
Abstract: To pinpoint the electronic and structural mechanisms that affect intrinsic and extrinsic performance limits of two‐dimensional material devices, it is of critical importance to resolve the electronic properties on the mesoscopic length scale of such devices under operating conditions. The present work utilizes angle‐resolved photoemission spectroscopy with nanoscale spatial resolution (nanoARPES) to map the quasiparticle electronic structure of a twisted bilayer graphene device. The dispersion and linewidth of the Dirac cones associated with top and bottom graphene layers are determined as a function of spatial position on the device under both static and operating conditions. The analysis reveals that microscopic rotational domains in the two graphene layers establish a range of twist angles from 9.8∘ to 12.7∘. Application of current and electrostatic gating lead to strong electric fields with peak strengths of 0.75 V/μm at the rotational domain boundaries in the device. These proof‐of‐principle results demonstrate the potential of nanoARPES to link mesoscale structural variations with electronic states in operating device conditions and to disentangle such extrinsic factors from the intrinsic quasiparticle dispersion.
|
Mar 2021
|
|
I05-ARPES
|
M.
Horio
,
Q.
Wang
,
V.
Granata
,
K. P.
Kramer
,
Y.
Sassa
,
S.
Jöhr
,
D.
Sutter
,
A.
Bold
,
L.
Das
,
Y.
Xu
,
R.
Frison
,
R.
Fittipaldi
,
T. K.
Kim
,
C.
Cacho
,
J. E.
Rault
,
P. Le
Fèvre
,
F.
Bertran
,
N. C.
Plumb
,
M.
Shi
,
A.
Vecchione
,
M. H.
Fischer
,
J.
Chang
Diamond Proposal Number(s):
[20259]
Open Access
Abstract: Electronic band structures in solids stem from a periodic potential reflecting the structure of either the crystal lattice or electronic order. In the stoichiometric ruthenate Ca3Ru2O7, numerous Fermi surface-sensitive probes indicate a low-temperature electronic reconstruction. Yet, the causality and the reconstructed band structure remain unsolved. Here, we show by angle-resolved photoemission spectroscopy, how in Ca3Ru2O7 a C2-symmetric massive Dirac semimetal is realized through a Brillouin-zone preserving electronic reconstruction. This Dirac semimetal emerges in a two-stage transition upon cooling. The Dirac point and band velocities are consistent with constraints set by quantum oscillation, thermodynamic, and transport experiments, suggesting that the complete Fermi surface is resolved. The reconstructed structure—incompatible with translational-symmetry-breaking density waves—serves as an important test for band structure calculations of correlated electron systems.
|
Mar 2021
|
|
I05-ARPES
|
Ryo
Noguchi
,
Masaru
Kobayashi
,
Zhanzhi
Jiang
,
Kenta
Kuroda
,
Takanari
Takahashi
,
Zifan
Xu
,
Daehun
Lee
,
Motoaki
Hirayama
,
Masayuki
Ochi
,
Tetsuroh
Shirasawa
,
Peng
Zhang
,
Chun
Lin
,
Cédric
Bareille
,
Shunsuke
Sakuragi
,
Hiroaki
Tanaka
,
So
Kunisada
,
Kifu
Kurokawa
,
Koichiro
Yaji
,
Ayumi
Harasawa
,
Viktor
Kandyba
,
Alessio
Giampietri
,
Alexei
Barinov
,
Timur K.
Kim
,
Cephise
Cacho
,
Makoto
Hashimoto
,
Donghui
Lu
,
Shik
Shin
,
Ryotaro
Arita
,
Keji
Lai
,
Takao
Sasagawa
,
Takeshi
Kondo
Diamond Proposal Number(s):
[20445]
Abstract: Low-dimensional van der Waals materials have been extensively studied as a platform with which to generate quantum effects. Advancing this research, topological quantum materials with van der Waals structures are currently receiving a great deal of attention. Here, we use the concept of designing topological materials by the van der Waals stacking of quantum spin Hall insulators. Most interestingly, we find that a slight shift of inversion centre in the unit cell caused by a modification of stacking induces a transition from a trivial insulator to a higher-order topological insulator. Based on this, we present angle-resolved photoemission spectroscopy results showing that the real three-dimensional material Bi4Br4 is a higher-order topological insulator. Our demonstration that various topological states can be selected by stacking chains differently, combined with the advantages of van der Waals materials, offers a playground for engineering topologically non-trivial edge states towards future spintronics applications.
|
Jan 2021
|
|
I05-ARPES
|
Niels B. M.
Schroeter
,
Iñigo
Robredo
,
Sebastian
Klemenz
,
Robert J.
Kirby
,
Jonas A.
Krieger
,
Ding
Pei
,
Tianlun
Yu
,
Samuel
Stolz
,
Thorsten
Schmitt
,
Pavel
Dudin
,
Timur K.
Kim
,
Cephise
Cacho
,
Andreas
Schnyder
,
Aitor
Bergara
,
Vladimir N.
Strocov
,
Fernando
De Juan
,
Maia G.
Vergniory
,
Leslie M.
Schoop
Diamond Proposal Number(s):
[26098, 20617]
Open Access
Abstract: Magnetic Weyl semimetals are a newly discovered class of topological materials that may serve as a platform for exotic phenomena, such as axion insulators or the quantum anomalous Hall effect. Here, we use angle-resolved photoelectron spectroscopy and ab initio calculations to discover Weyl cones in CoS2, a ferromagnet with pyrite structure that has been long studied as a candidate for half-metallicity, which makes it an attractive material for spintronic devices. We directly observe the topological Fermi arc surface states that link the Weyl nodes, which will influence the performance of CoS2 as a spin injector by modifying its spin polarization at interfaces. In addition, we directly observe a minority-spin bulk electron pocket in the corner of the Brillouin zone, which proves that CoS2 cannot be a true half-metal.
|
Dec 2020
|
|
I05-ARPES
|
Diamond Proposal Number(s):
[5008, 9689]
Abstract: The role of nematic order for the mechanism of high-temperature superconductivity is highly debated. In most iron-based superconductors (IBSs) the tetragonal symmetry is broken already in the normal state, resulting in orthorhombic lattice distortions, static stripe magnetic order, or both. Superconductivity then emerges, at least at weak doping, already from the state with broken
C
4
rotational symmetry. One of the few stoichiometric IBSs, lithium iron arsenide superconducts below 18 K and does not display either structural or magnetic transition in the normal state. Here we demonstrate, using angle-resolved photoemission spectroscopy, that even the superconducting state in LiFeAs is also a nematic one. We observe spontaneous breaking of the rotational symmetry in the gap amplitude on all Fermi surfaces, as well as unidirectional distortion of the Fermi pockets. Remarkably, these deformations are hardly visible above superconducting
T
c
. Our results demonstrate the realization of the phenomenon of superconductivity-induced nematicity in IBSs, emphasizing the intimate relation between them. We suggest a theoretical explanation based on the emergence of a secondary instability inside the superconducting state, which leads to the nematic order and
s
−
d
mixing in the gap function.
|
Nov 2020
|
|
|
|
Vasily S.
Stolyarov
,
Kirill S.
Pervakov
,
Anna S.
Astrakhantseva
,
Igor A.
Golovchanskiy
,
Denis V.
Vyalikh
,
Timur K.
Kim
,
Sergey V.
Eremeev
,
Vladimir A.
Vlasenko
,
Vladimir M.
Pudalov
,
Alexander A.
Golubov
,
Eugene V.
Chulkov
,
Dimitri
Roditchev
Abstract: In pnictide RbEuFe4As4, superconductivity sets in at 36 K and coexists, below 15–19 K, with the long-range magnetic ordering of Eu 4f spins. Here we report scanning tunneling experiments performed on cold-cleaved single crystals of the compound. The data revealed the coexistence of large Rb-terminated and small Eu-terminated terraces, both manifesting 1 × 2 and 2‾√×2‾√
2
×
2
reconstructions. On 2‾√×2‾√
2
×
2
surfaces, a hidden electronic order with a period ∼5 nm was discovered. A superconducting gap of ∼7 meV was seen to be strongly filled with quasiparticle states. The tunneling spectra compared with density functional theory calculations confirmed that flat electronic bands due to Eu 4f orbitals are situated ∼1.8 eV below the Fermi level and thus do not contribute directly to Cooper pair formation.
|
Oct 2020
|
|
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
|
|
