I05-ARPES
|
Jonas
Erhardt
,
Cedric
Schmitt
,
Philipp
Eck
,
Matthias
Schmitt
,
Philipp
Kessler
,
Kyungchan
Lee
,
Timur
Kim
,
Cephise
Cacho
,
Iulia
Cojocariu
,
Daniel
Baranowski
,
Vitaliy
Feyer
,
Louis
Veyrat
,
Giorgio
Sangiovanni
,
Ralph
Claessen
,
Simon
Moser
Diamond Proposal Number(s):
[30583]
Abstract: The demonstration of a topological band inversion constitutes the most elementary proof of a quantum spin Hall insulator (QSHI). On a fundamental level, such an inverted band gap is intrinsically related to the bulk Berry curvature, a gauge-invariant fingerprint of the wave function’s quantum geometric properties in Hilbert space. Intimately tied to orbital angular momentum (OAM), the Berry curvature can be, in principle, extracted from circular dichroism in angle-resolved photoemission spectroscopy (CD-ARPES), were it not for interfering final state photoelectron emission channels that obscure the initial state OAM signature. Here, we outline a full-experimental strategy to avoid such interference artifacts and isolate the clean OAM from the CD-ARPES response. Bench-marking this strategy for the recently discovered atomic monolayer system indenene, we demonstrate its distinct QSHI character and establish CD-ARPES as a scalable bulk probe to experimentally classify the topology of two-dimensional quantum materials with time reversal symmetry.
|
May 2024
|
|
I05-ARPES
I09-Surface and Interface Structural Analysis
|
Cedric
Schmitt
,
Jonas
Erhardt
,
Philipp
Eck
,
Matthias
Schmitt
,
Kyungchan
Lee
,
Philipp
Keßler
,
Tim
Wagner
,
Merit
Spring
,
Bing
Liu
,
Stefan
Enzner
,
Martin
Kamp
,
Vedran
Jovic
,
Chris
Jozwiak
,
Aaron
Bostwick
,
Eli
Rotenberg
,
Timur
Kim
,
Cephise
Cacho
,
Tien-Lin
Lee
,
Giorgio
Sangiovanni
,
Simon
Moser
,
Ralph
Claessen
Diamond Proposal Number(s):
[31808, 25151, 30583]
Open Access
Abstract: Atomic monolayers on semiconductor surfaces represent an emerging class of functional quantum materials in the two-dimensional limit — ranging from superconductors and Mott insulators to ferroelectrics and quantum spin Hall insulators. Indenene, a triangular monolayer of indium with a gap of ~ 120 meV is a quantum spin Hall insulator whose micron-scale epitaxial growth on SiC(0001) makes it technologically relevant. However, its suitability for room-temperature spintronics is challenged by the instability of its topological character in air. It is imperative to develop a strategy to protect the topological nature of indenene during ex situ processing and device fabrication. Here we show that intercalation of indenene into epitaxial graphene provides effective protection from the oxidising environment, while preserving an intact topological character. Our approach opens a rich realm of ex situ experimental opportunities, priming monolayer quantum spin Hall insulators for realistic device fabrication and access to topologically protected edge channels.
|
Feb 2024
|
|
I05-ARPES
|
Masafumi
Horio
,
Filomena
Forte
,
Denys
Sutter
,
Minjae
Kim
,
Claudia G.
Fatuzzo
,
Christian E.
Matt
,
Simon
Moser
,
Tetsuya
Wada
,
Veronica
Granata
,
Rosalba
Fittipaldi
,
Yasmine
Sassa
,
Gianmarco
Gatti
,
Henrik M.
Ronnow
,
Moritz
Hoesch
,
Timur K.
Kim
,
Chris
Jozwiak
,
Aaron
Bostwick
,
Eli
Rotenberg
,
Iwao
Matsuda
,
Antoine
Georges
,
Giorgio
Sangiovanni
,
Antonio
Vecchione
,
Mario
Cuoco
,
Johan
Chang
Diamond Proposal Number(s):
[10550]
Open Access
Abstract: Doped Mott insulators are the starting point for interesting physics such as high temperature superconductivity and quantum spin liquids. For multi-band Mott insulators, orbital selective ground states have been envisioned. However, orbital selective metals and Mott insulators have been difficult to realize experimentally. Here we demonstrate by photoemission spectroscopy how Ca2RuO4, upon alkali-metal surface doping, develops a single-band metal skin. Our dynamical mean field theory calculations reveal that homogeneous electron doping of Ca2RuO4 results in a multi-band metal. All together, our results provide evidence for an orbital-selective Mott insulator breakdown, which is unachievable via simple electron doping. Supported by a cluster model and cluster perturbation theory calculations, we demonstrate a type of skin metal-insulator transition induced by surface dopants that orbital-selectively hybridize with the bulk Mott state and in turn produce coherent in-gap states.
|
Nov 2023
|
|
I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[25151]
Abstract: Indenene─the triangular single layer phase of indium─is a novel large gap (∼120 meV) quantum spin Hall (QSH) insulator that stabilizes on SiC(0001) substrates. Thanks to excellent lattice matching, indenene nucleates in monodomains that are promising for devices if synthesized in the micrometer range. Here, we establish a simple, but robust and scalable indenene fabrication protocol based on an initial Stranski–Krastanov growth stage followed by a short anneal whose temperature selects between a three, two, or one monolayer In coverage. Their specific structural and electronic properties produce distinct fingerprints in experimental surface characterization by electron microscopy, diffraction, and spectroscopy, thus providing an efficient metric for the synthesis of large scale high-quality indenene on SiC.
|
Sep 2022
|
|
I09-Surface and Interface Structural Analysis
|
Maximilian
Bauernfeind
,
Jonas
Erhardt
,
Philipp
Eck
,
Pardeep K.
Thakur
,
Judith
Gabel
,
Tien-Lin
Lee
,
Jörg
Schäfer
,
Simon
Moser
,
Domenico
Di Sante
,
Ralph
Claessen
,
Giorgio
Sangiovanni
Diamond Proposal Number(s):
[26419, 25151]
Open Access
Abstract: Large-gap quantum spin Hall insulators are promising materials for room-temperature applications based on Dirac fermions. Key to engineer the topologically non-trivial band ordering and sizable band gaps is strong spin-orbit interaction. Following Kane and Mele’s original suggestion, one approach is to synthesize monolayers of heavy atoms with honeycomb coordination accommodated on templates with hexagonal symmetry. Yet, in the majority of cases, this recipe leads to triangular lattices, typically hosting metals or trivial insulators. Here, we conceive and realize “indenene”, a triangular monolayer of indium on SiC exhibiting non-trivial valley physics driven by local spin-orbit coupling, which prevails over inversion-symmetry breaking terms. By means of tunneling microscopy of the 2D bulk we identify the quantum spin Hall phase of this triangular lattice and unveil how a hidden honeycomb connectivity emerges from interference patterns in Bloch px ± ipy-derived wave functions.
|
Sep 2021
|
|
I05-ARPES
|
M. M.
Otrokov
,
I. I.
Klimovskikh
,
H.
Bentmann
,
D.
Estyunin
,
A.
Zeugner
,
Z. S.
Aliev
,
S.
Gaß
,
A. U. B.
Wolter
,
A. V.
Koroleva
,
A. M.
Shikin
,
M.
Blanco-Rey
,
M.
Hoffmann
,
I. P.
Rusinov
,
A. Yu.
Vyazovskaya
,
S. V.
Eremeev
,
Yu. M.
Koroteev
,
V. M.
Kuznetsov
,
F.
Freyse
,
J.
Sánchez-Barriga
,
I. R.
Amiraslanov
,
M. B.
Babanly
,
N. T.
Mamedov
,
N. A.
Abdullayev
,
V. N.
Zverev
,
A.
Alfonsov
,
V.
Kataev
,
B.
Büchner
,
E. F.
Schwier
,
S.
Kumar
,
A.
Kimura
,
L.
Petaccia
,
G.
Di Santo
,
R. C.
Vidal
,
S.
Schatz
,
K.
Kißner
,
M.
Unzelmann
,
C. H.
Min
,
Simon
Moser
,
T. R. F.
Peixoto
,
F.
Reinert
,
A.
Ernst
,
P. M.
Echenique
,
A.
Isaeva
,
E. V.
Chulkov
Abstract: Magnetic topological insulators are narrow-gap semiconductor materials that combine non-trivial band topology and magnetic order. Unlike their nonmagnetic counterparts, magnetic topological insulators may have some of the surfaces gapped, which enables a number of exotic phenomena that have potential applications in spintronics, such as the quantum anomalous Hall effect and chiral Majorana fermions. So far, magnetic topological insulators have only been created by means of doping nonmagnetic topological insulators with 3d transition-metal elements; however, such an approach leads to strongly inhomogeneous magnetic and electronic properties of these materials, restricting the observation of important effects to very low temperatures. An intrinsic magnetic topological insulator—a stoichiometric well ordered magnetic compound—could be an ideal solution to these problems, but no such material has been observed so far. Here we predict by ab initio calculations and further confirm using various experimental techniques the realization of an antiferromagnetic topological insulator in the layered van der Waals compound MnBi2Te4. The antiferromagnetic ordering that MnBi2Te4 shows makes it invariant with respect to the combination of the time-reversal and primitive-lattice translation symmetries, giving rise to a ℤ2 topological classification; ℤ2 = 1 for MnBi2Te4, confirming its topologically nontrivial nature. Our experiments indicate that the symmetry-breaking (0001) surface of MnBi2Te4 exhibits a large bandgap in the topological surface state. We expect this property to eventually enable the observation of a number of fundamental phenomena, among them quantized magnetoelectric coupling and axion electrodynamics. Other exotic phenomena could become accessible at much higher temperatures than those reached so far, such as the quantum anomalous Hall effect and chiral Majorana fermions.
|
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
|
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
|
|
I09-Surface and Interface Structural Analysis
|
Tomáš
Rauch
,
Victor A.
Rogalev
,
Maximilian
Bauernfeind
,
Julian
Maklar
,
Felix
Reis
,
Florian
Adler
,
Simon
Moser
,
Johannes
Weis
,
Tien-Lin
Lee
,
Pardeep K.
Thakur
,
Jörg
Schäfer
,
Ralph
Claessen
,
Jürgen
Henk
,
Ingrid
Mertig
Diamond Proposal Number(s):
[19512]
Abstract: The diamond and zinc-blende semiconductors are well-known and have been widely studied for decades. Yet, their electronic structure still surprises with unexpected topological properties of the valence bands. In this joint theoretical and experimental investigation, we demonstrate for the benchmark compounds InSb and GaAs that the electronic structure features topological surface states below the Fermi energy. Our parity analysis shows that the spin-orbit split-off band near the valence band maximum exhibits a strong topologically nontrivial behavior characterized by the
Z
2
invariants
(
1
;
000
)
. The nontrivial character is a consequence of the nonzero spin-orbit coupling and is imposed by the chosen constituents, in contrast to the conventional topological phase transition mechanism which relies on tuning parameters in the system Hamiltonian. Ab initio-based tight-binding calculations resolve topological surface states in the occupied electronic structure of InSb and GaAs, further confirmed experimentally by soft x-ray angle-resolved photoemission from both materials. Our findings are valid for all other materials whose valence bands are adiabatically linked to those of InSb, i.e., many diamond and zinc-blende semiconductors, as well as other related materials, such as half-Heusler compounds.
|
Jun 2019
|
|
