I09-Surface and Interface Structural Analysis
|
Gian Marco
Pierantozzi
,
Alessandro
De Vita
,
Chiara
Bigi
,
Xin
Gui
,
Hung-Ju
Tien
,
Debashis
Mondal
,
Federico
Mazzola
,
Jun
Fujii
,
Ivana
Vobornik
,
Giovanni
Vinai
,
Alessandro
Sala
,
Cristina
Africh
,
Tien-Lin
Lee
,
Giorgio
Rossi
,
Tay-Rong
Chang
,
Weiwei
Xie
,
Robert J.
Cava
,
Giancarlo
Panaccione
Diamond Proposal Number(s):
[24968]
Open Access
Abstract: We unravel the interplay of topological properties and the layered (anti)ferromagnetic ordering in EuSn2P2, using spin and chemical selective electron and X-ray spectroscopies supported by first-principle calculations. We reveal the presence of in-plane long-range ferromagnetic order triggering topological invariants and resulting in the multiple protection of topological Dirac states. We provide clear evidence that layer-dependent spin-momentum locking coexists with ferromagnetism in this material, a cohabitation that promotes EuSn2P2 as a prime candidate axion insulator for topological antiferromagnetic spintronics applications.
|
Jan 2022
|
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I05-ARPES
|
D. F.
Liu
,
L. Y.
Wei
,
C. C.
Le
,
H. Y.
Wang
,
X.
Zhang
,
N.
Kumar
,
C.
Shekhar
,
N. B. M.
Schröter
,
Y. W.
Li
,
D.
Pei
,
L. X.
Xu
,
P.
Dudin
,
T. K.
Kim
,
C.
Cacho
,
J.
Fujii
,
I.
Vobornik
,
M. X.
Wang
,
L. X.
Yang
,
Z. K.
Liu
,
Y. F.
Guo
,
J. P.
Hu
,
C.
Felser
,
S. S. P.
Parkin
,
Y. L.
Chen
Diamond Proposal Number(s):
[18005]
Open Access
Abstract: Dirac semimetals are classified into different phases based on the types of Dirac fermions. Tuning the transition among different types of Dirac fermions in one system remains a challenge. Recently, KMgBi was predicted to be located at a critical state in which various types of Dirac fermions can be induced owing to the existence of a flatband. Here, we carried out systematic studies on the electronic structure of KMgBi single crystals by combining angle-resolve photoemission spectroscopy and scanning tunneling microscopy/spectroscopy. The flatband was clearly observed near the Fermi level. We also revealed a small bandgap of ∼20 meV between the flatband and the conduction band. These results demonstrate the critical states of KMgBi that transition among various types of Dirac fermions can be tuned in one system.
|
Jun 2021
|
|
I05-ARPES
I10-Beamline for Advanced Dichroism
|
Matthew D.
Watson
,
Igor
Markovic
,
Federico
Mazzola
,
Akhil
Rajan
,
Edgar A.
Morales
,
David
Burn
,
Thorsten
Hesjedal
,
Gerrit
Van Der Laan
,
Saumya
Mukherjee
,
Timur K.
Kim
,
Chiara
Bigi
,
Ivana
Vobornik
,
Monica
Ciomaga Hatnean
,
Geetha
Balakrishnan
,
Philip D. C.
King
Diamond Proposal Number(s):
[21986, 22794, 23785]
Abstract: We investigate the temperature-dependent electronic structure of the van der Waals ferromagnet, CrGeTe3. Using angle-resolved photoemission spectroscopy, we identify atomic- and orbital-specific band shifts upon cooling through TC. From these, together with x-ray absorption spectroscopy and x-ray magnetic circular dichroism measurements, we identify the states created by a covalent bond between the Te 5p and the Cr eg orbitals as the primary driver of the ferromagnetic ordering in this system, while it is the Cr t2g states that carry the majority of the spin moment. The t2g states furthermore exhibit a marked bandwidth increase and a remarkable lifetime enhancement upon entering the ordered phase, pointing to a delicate interplay between localized and itinerant states in this family of layered ferromagnets.
|
May 2020
|
|
I09-Surface and Interface Structural Analysis
|
Chiara
Bigi
,
Zhenkun
Tang
,
Gian Marco
Pierantozzi
,
Pasquale
Orgiani
,
Pranab Kumar
Das
,
Jun
Fujii
,
Ivana
Vobornik
,
Tommaso
Pincelli
,
Alessandro
Troglia
,
Tien-Lin
Lee
,
Regina
Ciancio
,
Goran
Drazic
,
Alberto
Verdini
,
Anna
Regoutz
,
Phil D. C.
King
,
Deepnarayan
Biswas
,
Giorgio
Rossi
,
Giancarlo
Panaccione
,
Annabella
Selloni
Diamond Proposal Number(s):
[16041]
Abstract: Two-dimensional (2D) metallic states induced by oxygen vacancies (
V
O
s
) at oxide surfaces and interfaces provide opportunities for the development of advanced applications, but the ability to control the behavior of these states is still limited. We used angle resolved photoelectron spectroscopy combined with density-functional theory (DFT) to study the reactivity of
V
O
-induced states at the (001) surface of anatase
TiO
2
, where both 2D metallic and deeper lying in-gap states (IGs) are observed. The 2D and IG states exhibit remarkably different evolutions when the surface is exposed to molecular
O
2
: while IGs are almost completely quenched, the metallic states are only weakly affected. DFT calculations indeed show that the IGs originate from surface
V
O
s
and remain localized at the surface, where they can promptly react with
O
2
. In contrast, the metallic states originate from subsurface vacancies whose migration to the surface for recombination with
O
2
is kinetically hindered on anatase
TiO
2
(001), thus making them much less sensitive to oxygen dosing.
|
Feb 2020
|
|
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
|
O. J.
Clark
,
F.
Mazzola
,
I.
Markovic
,
J. M.
Riley
,
J.
Feng
,
B.-J.
Yang
,
K.
Sumida
,
T.
Okuda
,
J.
Fujii
,
I.
Vobornik
,
T. K.
Kim
,
K.
Okawa
,
T.
Sasagawa
,
M. S.
Bahramy
,
P. D. C.
King
Diamond Proposal Number(s):
[14927, 16262]
Abstract: The band inversions that generate the topologically non-trivial band gaps of topological insulators and the isolated Dirac touching points of three-dimensional Dirac semimetals generally arise from the crossings of electronic states derived from different orbital manifolds. Recently, the concept of single orbital-manifold band inversions occurring along high-symmetry lines has been demonstrated, stabilising multiple bulk and surface Dirac fermions. Here, we discuss the underlying ingredients necessary to achieve such phases, and discuss their existence within the family of transition metal dichalcogenides. We show how their three-dimensional band structures naturally produce only small k z projected band gaps, and demonstrate how these play a significant role in shaping the surface electronic structure of these materials. We demonstrate, through spin- and angle-resolved photoemission and density functional theory calculations, how the surface electronic structures of the group-X TMDs PtSe2 and PdTe2 are host to up to five distinct surface states, each with complex band dispersions and spin textures. Finally, we discuss how the origin of several recently-realised instances of topological phenomena in systems outside of the TMDs, including the iron-based superconductors, can be understood as a consequence of the same underlying mechanism driving k z -mediated band inversions in the TMDs.
|
Mar 2019
|
|
|
|
Pranab Kumar
Das
,
Jagoda
Sławińska
,
Ivana
Vobornik
,
Jun
Fujii
,
Anna
Regoutz
,
Juhan M.
Kahk
,
David O.
Scanlon
,
Benjamin J.
Morgan
,
Cormac
Mcguinness
,
Evgeny
Plekhanov
,
Domenico
Di Sante
,
Ying-Sheng
Huang
,
Ruei-San
Chen
,
Giorgio
Rossi
,
Silvia
Picozzi
,
William R.
Branford
,
Giancarlo
Panaccione
,
David J.
Payne
Abstract: The delicate interplay of electronic charge, spin, and orbital degrees of freedom is in the heart of many novel phenomena across the transition metal oxide family. Here, by combining high-resolution angle-resolved photoemission spectroscopy and first principles calculations (with and without spin-orbit coupling), the electronic structure of the rutile binary iridate, IrO2, is investigated. The detailed study of electronic bands measured on a high-quality single crystalline sample and use of a wide range of photon energy provide a huge improvement over the previous studies. The excellent agreement between theory and experimental results shows that the single-particle DFT description of IrO2 band structure is adequate, without the need of invoking any treatment of correlation effects. Although many observed features point to a 3D nature of the electronic structure, clear surface effects are revealed. The discussion of the orbital character of the relevant bands crossing the Fermi level sheds light on spin-orbit-coupling-driven phenomena in this material, unveiling a spin-orbit-induced avoided crossing, a property likely to play a key role in its large spin Hall effect.
|
Jun 2018
|
|
I05-ARPES
|
O. J.
Clark
,
M. J.
Neat
,
K.
Okawa
,
L.
Bawden
,
I.
Markovic
,
Federico
Mazzola
,
J.
Feng
,
V.
Sunko
,
J. M.
Riley
,
W.
Meevasana
,
J.
Fujii
,
I.
Vobornik
,
T. K.
Kim
,
M.
Hoesch
,
T.
Sasagawa
,
P.
Wahl
,
M. S.
Bahramy
,
P. D. C.
King
Diamond Proposal Number(s):
[9500, 12469, 13438, 16262]
Abstract: We study the low-energy surface electronic structure of the transition-metal dichalcogenide superconductor PdTe2 by spin- and angle-resolved photoemission, scanning tunneling microscopy, and density-functional theory-based supercell calculations. Comparing PdTe2 with its sister compound PtSe2, we demonstrate how enhanced interlayer hopping in the Te-based material drives a band inversion within the antibonding p-orbital manifold well above the Fermi level. We show how this mediates spin-polarized topological surface states which form rich multivalley Fermi surfaces with complex spin textures. Scanning tunneling spectroscopy reveals type-II superconductivity at the surface, and moreover shows no evidence for an unconventional component of its superconducting order parameter, despite the presence of topological surface states.
|
Apr 2018
|
|
I05-ARPES
|
M. S.
Bahramy
,
O. J.
Clark
,
B.-J.
Yang
,
J.
Feng
,
L.
Bawden
,
J. M.
Riley
,
I.
Markovic
,
F.
Mazzola
,
V.
Sunko
,
D.
Biswas
,
S. P.
Cooil
,
M.
Jorge
,
J. W.
Wells
,
M.
Leandersson
,
T.
Balasubramanian
,
J.
Fujii
,
I.
Vobornik
,
J. E.
Rault
,
T. K.
Kim
,
M.
Hoesch
,
K.
Okawa
,
M.
Asakawa
,
T.
Sasagawa
,
T.
Eknapakul
,
W.
Meevasana
,
P. D. C.
King
Diamond Proposal Number(s):
[2469, 9500, 13438, 14927]
Abstract: Transition-metal dichalcogenides (TMDs) are renowned for their rich and varied bulk properties, while their single-layer variants have become one of the most prominent examples of two-dimensional materials beyond graphene. Their disparate ground states largely depend on transition metal d-electron-derived electronic states, on which the vast majority of attention has been concentrated to date. Here, we focus on the chalcogen-derived states. From density-functional theory calculations together with spin- and angle-resolved photoemission, we find that these generically host a co-existence of type-I and type-II three-dimensional bulk Dirac fermions as well as ladders of topological surface states and surface resonances. We demonstrate how these naturally arise within a single p-orbital manifold as a general consequence of a trigonal crystal field, and as such can be expected across a large number of compounds. Already, we demonstrate their existence in six separate TMDs, opening routes to tune, and ultimately exploit, their topological physics.
|
Nov 2017
|
|
I05-ARPES
|
V.
Sunko
,
H.
Rosner
,
P.
Kushwaha
,
S.
Khim
,
F.
Mazzola
,
L.
Bawden
,
O. J.
Clark
,
J. M.
Riley
,
D.
Kasinathan
,
M. W.
Haverkort
,
T. K.
Kim
,
M.
Hoesch
,
J.
Fujii
,
I.
Vobornik
,
A. P.
Mackenzie
,
P.
King
Diamond Proposal Number(s):
[12469, 14927, 18267]
Abstract: Engineering and enhancing the breaking of inversion symmetry in solids—that is, allowing electrons to differentiate between ‘up’ and ‘down’—is a key goal in condensed-matter physics and materials science because it can be used to stabilize states that are of fundamental interest and also have potential practical applications. Examples include improved ferroelectrics for memory devices and materials that host Majorana zero modes for quantum computing1, 2. Although inversion symmetry is naturally broken in several crystalline environments, such as at surfaces and interfaces, maximizing the influence of this effect on the electronic states of interest remains a challenge. Here we present a mechanism for realizing a much larger coupling of inversion-symmetry breaking to itinerant surface electrons than is typically achieved. The key element is a pronounced asymmetry of surface hopping energies—that is, a kinetic-energy-coupled inversion-symmetry breaking, the energy scale of which is a substantial fraction of the bandwidth. Using spin- and angle-resolved photoemission spectroscopy, we demonstrate that such a strong inversion-symmetry breaking, when combined with spin–orbit interactions, can mediate Rashba-like3, 4 spin splittings that are much larger than would typically be expected. The energy scale of the inversion-symmetry breaking that we achieve is so large that the spin splitting in the CoO2- and RhO2-derived surface states of delafossite oxides becomes controlled by the full atomic spin–orbit coupling of the 3d and 4d transition metals, resulting in some of the largest known Rashba-like3, 4 spin splittings. The core structural building blocks that facilitate the bandwidth-scaled inversion-symmetry breaking are common to numerous materials. Our findings therefore provide opportunities for creating spin-textured states and suggest routes to interfacial control of inversion-symmetry breaking in designer heterostructures of oxides and other material classes.
|
Sep 2017
|
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