I05-ARPES
|
I.
Cucchi
,
A.
Marrazzo
,
E.
Cappelli
,
S.
Ricco
,
F. Y.
Bruno
,
S.
Lisi
,
M.
Hoesch
,
T. K.
Kim
,
C.
Cacho
,
C.
Besnard
,
E.
Giannini
,
N.
Marzari
,
M.
Gibertini
,
F.
Baumberger
,
A.
Tamai
Diamond Proposal Number(s):
[18952]
Abstract: We report high-resolution angle-resolved photoemission measurements on single crystals of
Pt
2
HgSe
3
grown by high-pressure synthesis. Our data reveal a gapped Dirac nodal line whose (001) projection separates the surface Brillouin zone in topological and trivial areas. In the nontrivial
k
-space range, we find surface states with multiple saddle points in the dispersion, resulting in two van Hove singularities in the surface density of states. Based on density-functional theory calculations, we identify these surface states as signatures of a topological crystalline state, which coexists with a weak topological phase.
|
Feb 2020
|
|
I05-ARPES
|
Veronika
Sunko
,
Edgar
Abarca Morales
,
Igor
Markovic
,
Mark E.
Barber
,
Dijana
Milosavljević
,
Federico
Mazzola
,
Dmitry A.
Sokolov
,
Naoki
Kikugawa
,
Cephise
Cacho
,
Pavel
Dudin
,
Helge
Rosner
,
Clifford
Hicks
,
Philip D. C.
King
,
Andrew P.
Mackenzie
Diamond Proposal Number(s):
[20427]
Open Access
Abstract: Pressure represents a clean tuning parameter for traversing the complex phase diagrams of interacting electron systems, and as such has proved of key importance in the study of quantum materials. Application of controlled uniaxial pressure has recently been shown to more than double the transition temperature of the unconventional superconductor Sr2RuO4, leading to a pronounced peak in Tc versus strain whose origin is still under active debate. Here we develop a simple and compact method to passively apply large uniaxial pressures in restricted sample environments, and utilise this to study the evolution of the electronic structure of Sr2RuO4 using angle-resolved photoemission. We directly visualise how uniaxial stress drives a Lifshitz transition of the γ-band Fermi surface, pointing to the key role of strain-tuning its associated van Hove singularity to the Fermi level in mediating the peak in Tc. Our measurements provide stringent constraints for theoretical models of the strain-tuned electronic structure evolution of Sr2RuO4. More generally, our experimental approach opens the door to future studies of strain-tuned phase transitions not only using photoemission but also other experimental techniques where large pressure cells or piezoelectric-based devices may be difficult to implement.
|
Dec 2019
|
|
I05-ARPES
|
Raphael C.
Vidal
,
Alexander
Zeugner
,
Jorge I.
Facio
,
Rajyavardhan
Ray
,
M. Hossein
Haghighi
,
Anja U. B.
Wolter
,
Laura T.
Corredor Bohorquez
,
Federico
Caglieris
,
Simon
Moser
,
Tim
Figgemeier
,
Thiago R. F.
Peixoto
,
Hari Babu
Vasili
,
Manuel
Valvidares
,
Sungwon
Jung
,
Cephise
Cacho
,
Alexey
Alfonsov
,
Kavita
Mehlawat
,
Vladislav
Kataev
,
Christian
Hess
,
Manuel
Richter
,
Bernd
Büchner
,
Jeroen
Van Den Brink
,
Michael
Ruck
,
Friedrich
Reinert
,
Hendrik
Bentmann
,
Anna
Isaeva
Diamond Proposal Number(s):
[22468]
Open Access
Abstract: Combinations of nontrivial band topology and long-range magnetic order hold promise for realizations of novel spintronic phenomena, such as the quantum anomalous Hall effect and the topological magnetoelectric effect. Following theoretical advances, material candidates are emerging. Yet, so far a compound that combines a band-inverted electronic structure with an intrinsic net magnetization remains unrealized.
MnBi
2
Te
4
has been established as the first antiferromagnetic topological insulator and constitutes the progenitor of a modular
(
Bi
2
Te
3
)
n
(
MnBi
2
Te
4
)
series. Here, for
n
=
1
, we confirm a nonstoichiometric composition proximate to
MnBi
4
Te
7
. We establish an antiferromagnetic state below 13 K followed by a state with a net magnetization and ferromagnetic-like hysteresis below 5 K. Angle-resolved photoemission experiments and density-functional calculations reveal a topologically nontrivial surface state on the
MnBi
4
Te
7
(
0001
)
surface, analogous to the nonmagnetic parent compound
Bi
2
Te
3
. Our results establish
MnBi
4
Te
7
as the first band-inverted compound with intrinsic net magnetization providing a versatile platform for the realization of magnetic topological states of matter.
|
Dec 2019
|
|
I05-ARPES
|
Y. J.
Chen
,
L. X.
Xu
,
J. H.
Li
,
Y. W.
Li
,
H. Y.
Wang
,
C. F.
Zhang
,
H.
Li
,
Y.
Wu
,
A. J.
Liang
,
C.
Chen
,
S. W.
Jung
,
C.
Cacho
,
Y. H.
Mao
,
S.
Liu
,
M. X.
Wang
,
Y. F.
Guo
,
Y.
Xu
,
Z. K.
Liu
,
L. X.
Yang
,
Y. L.
Chen
Diamond Proposal Number(s):
[23648, 24827]
Open Access
Abstract: The intrinsic magnetic topological insulator
MnBi
2
Te
4
exhibits rich topological effects such as quantum anomalous Hall effect and axion electrodynamics. Here, by combining the use of synchrotron and laser light sources, we carry out comprehensive and high-resolution angle-resolved photoemission spectroscopy studies on
MnBi
2
Te
4
and clearly identify its topological electronic structure. In contrast to theoretical predictions and previous studies, we observe topological surface states with diminished gap forming a characteristic Dirac cone. We argue that the topological surface states are mediated by multidomains of different magnetization orientations. In addition, the temperature evolution of the energy bands clearly reveals their interplay with the magnetic phase transition by showing interesting differences between the bulk and surface states, respectively. The investigation of the detailed electronic structure of
MnBi
2
Te
4
and its temperature evolution provides important insight into not only the exotic properties of
MnBi
2
Te
4
, but also the generic understanding of the interplay between magnetism and topological electronic structure in magnetic topological quantum materials.
|
Nov 2019
|
|
I05-ARPES
|
R. C.
Vidal
,
H.
Bentmann
,
T. R. F.
Peixoto
,
A.
Zeugner
,
S.
Moser
,
C.-h.
Min
,
S.
Schatz
,
K.
Kissner
,
M.
Unzelmann
,
C. I.
Fornari
,
H. B.
Vasili
,
M.
Valvidares
,
K.
Sakamoto
,
D.
Mondal
,
J.
Fujii
,
I.
Vobornik
,
S.
Jung
,
C.
Cacho
,
T. K.
Kim
,
R. J.
Koch
,
C.
Jozwiak
,
A.
Bostwick
,
J. D.
Denlinger
,
E.
Rotenberg
,
J.
Buck
,
M.
Hoesch
,
F.
Diekmann
,
S.
Rohlf
,
M.
Kalläne
,
K.
Rossnagel
,
M. M.
Otrokov
,
E. V.
Chulkov
,
M.
Ruck
,
A.
Isaeva
,
F.
Reinert
Diamond Proposal Number(s):
[19278, 22468]
Abstract: The layered van der Waals antiferromagnet
MnBi
2
Te
4
has been predicted to combine the band ordering of archetypical topological insulators such as
Bi
2
Te
3
with the magnetism of Mn, making this material a viable candidate for the realization of various magnetic topological states. We have systematically investigated the surface electronic structure of
MnBi
2
Te
4
(0001) single crystals by use of spin- and angle-resolved photoelectron spectroscopy experiments. In line with theoretical predictions, the results reveal a surface state in the bulk band gap and they provide evidence for the influence of exchange interaction and spin-orbit coupling on the surface electronic structure.
|
Sep 2019
|
|
I05-ARPES
|
D. F.
Liu
,
A. J.
Liang
,
E. K.
Liu
,
Q. N.
Xu
,
Y. W.
Li
,
C.
Chen
,
D.
Pei
,
W. J.
Shi
,
S. K.
Mo
,
P.
Dudin
,
T.
Kim
,
C.
Cacho
,
G.
Li
,
Y.
Sun
,
L. X.
Yang
,
Z. K.
Liu
,
S. S. P.
Parkin
,
C.
Felser
,
Y. L.
Chen
Diamond Proposal Number(s):
[22367, 20683]
Abstract: Weyl semimetals are crystalline solids that host emergent relativistic Weyl fermions and have characteristic surface Fermi-arcs in their electronic structure. Weyl semimetals with broken time reversal symmetry are difficult to identify unambiguously. In this work, using angle-resolved photoemission spectroscopy, we visualized the electronic structure of the ferromagnetic crystal Co3Sn2S2 and discovered its characteristic surface Fermi-arcs and linear bulk band dispersions across the Weyl points. These results establish Co3Sn2S2 as a magnetic Weyl semimetal that may serve as a platform for realizing phenomena such as chiral magnetic effects, unusually large anomalous Hall effect and quantum anomalous Hall effect.
|
Sep 2019
|
|
I05-ARPES
|
Soeren
Ulstrup
,
Cristina E.
Giusca
,
Jill A.
Miwa
,
Charlotte
Sanders
,
Alex
Browning
,
Pavel
Dudin
,
Cephise
Cacho
,
Olga
Kazakova
,
D. Kurt
Gaskill
,
Rachael L.
Myers-ward
,
Tianyi
Zhang
,
Mauricio
Terrones
,
Philip
Hofmann
Diamond Proposal Number(s):
[19260]
Open Access
Abstract: Control of atomic-scale interfaces between materials with distinct electronic structures is crucial for the design and fabrication of most electronic devices. In the case of two-dimensional materials, disparate electronic structures can be realized even within a single uniform sheet, merely by locally applying different vertical gate voltages. Here, we utilize the inherently nano-structured single layer and bilayer graphene on silicon carbide to investigate lateral electronic structure variations in an adjacent single layer of tungsten disulfide (WS2). The electronic band alignments are mapped in energy and momentum space using angle-resolved photoemission with a spatial resolution on the order of 500 nm (nanoARPES). We find that the WS2 band offsets track the work function of the underlying single layer and bilayer graphene, and we relate such changes to observed lateral patterns of exciton and trion luminescence from WS2.
|
Jul 2019
|
|
I05-ARPES
|
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.
|
May 2019
|
|
I05-ARPES
|
Diamond Proposal Number(s):
[21083]
Abstract: Identifying the electron dynamics in CuO chains has been elusive in Y-Ba-Cu-O (YBCO) cuprate systems when using standard angle-resolved photoemission spectroscopy (ARPES); a cleaved sample exhibits areas terminated by both CuO chains or BaO layers, and the size of a typical beam results in ARPES signals that are superposed from both terminations. Here, we employ spatially resolved ARPES with a submicrometric beam (nano-ARPES) to reveal the surface-termination-dependent electronic structures of the double CuO chains in
YBa
2
Cu
4
O
8
. We present an observation of sharp metallic dispersions and Fermi surfaces of the double CuO chains buried underneath the
CuO
2
-plane block on a BaO-terminated surface. While the observed Fermi surfaces of the CuO chains are highly one dimensional, the electrons in the CuO chains do not undergo significant electron correlations and no signature of a Tomonaga-Luttinger liquid or a marginal Fermi liquid is found. Our work represents an important experimental step toward understanding the charge dynamics and provides a starting basis for modeling the high-
T
c
superconductivity in YBCO cuprate systems.
|
Apr 2019
|
|
