I09-Surface and Interface Structural Analysis
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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.
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Sep 2022
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I09-Surface and Interface Structural Analysis
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Judith
Gabel
,
Matthias
Pickem
,
Philipp
Scheiderer
,
Lenart
Dudy
,
Berengar
Leikert
,
Marius
Fuchs
,
Martin
Stübinger
,
Matthias
Schmitt
,
Julia
Kuespert
,
Giorgio
Sangiovanni
,
Jan M.
Tomczak
,
Karsten
Held
,
Tien-Lin
Lee
,
Ralph
Claessen
,
Michael
Sing
Diamond Proposal Number(s):
[23737, 25151]
Open Access
Abstract: Thin films of transition metal oxides open up a gateway to nanoscale electronic devices beyond silicon characterized by novel electronic functionalities. While such films are commonly prepared in an oxygen atmosphere, they are typically considered to be ideally terminated with the stoichiometric composition. Using the prototypical correlated metal SrVO3 as an example, it is demonstrated that this idealized description overlooks an essential ingredient: oxygen adsorbing at the surface apical sites. The oxygen adatoms, which are present even if the films are kept in an ultrahigh vacuum environment and not explicitly exposed to air, are shown to severely affect the intrinsic electronic structure of a transition metal oxide film. Their presence leads to the formation of an electronically dead surface layer but also alters the band filling and the electron correlations in the thin films. These findings highlight that it is important to take into account surface apical oxygen or—mutatis mutandis—the specific oxygen configuration imposed by a capping layer to predict the behavior of ultrathin films of transition metal oxides near the single unit-cell limit.
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Dec 2021
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I09-Surface and Interface Structural Analysis
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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.
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Sep 2021
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I09-Surface and Interface Structural Analysis
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M.
Stübinger
,
J.
Gabel
,
Philipp
Scheiderer
,
M.
Zapf
,
M.
Schmitt
,
P.
Schütz
,
B.
Leikert
,
J.
Küspert
,
M.
Kamp
,
P. K.
Thakur
,
T.-L.
Lee
,
P.
Potapov
,
A.
Lubk
,
B.
Büchner
,
M.
Sing
,
R.
Claessen
Diamond Proposal Number(s):
[17499, 23737]
Abstract: A heterostructure consisting of the Mott insulator LaVO3 and the band insulator SrTiO3 is considered
a promising candidate for future photovoltaic applications. Not only does the (direct) excitation gap of
LaVO3 match well the solar spectrum, but its correlated nature and predicted built-in potential, owing to the
nonpolar/polar interface when integrated with SrTiO3, also offer remarkable advantages over conventional solar
cells. However, experimental data beyond the observation of a thickness-dependent metal-insulator transition
are scarce and a profound, microscopic understanding of the electronic properties is still lacking. By means of
soft and hard x-ray photoemission spectroscopy as well as resistivity and Hall effect measurements we study the
electrical properties, band bending, and band alignment of LaVO3/SrTiO3 heterostructures. We find a critical
LaVO3 thickness of five unit cells, confinement of the conducting electrons to exclusively Ti 3d states at the
interface, and a potential gradient in the film. From these findings we conclude on electronic reconstruction as
the driving mechanism for the formation of the metallic interface in LaVO3/SrTiO3.
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Jun 2021
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[15856]
Abstract: Depositing disordered Al on top of
Sr
Ti
O
3
is a cheap and easy way to create a two-dimensional electron system in the
Sr
Ti
O
3
surface layers. To facilitate future device applications, we passivate the heterostructure by a disordered
La
Al
O
3
capping layer to study the electronic properties by complementary x-ray photoemission spectroscopy and transport measurements on the very same samples. We also tune the electronic interface properties by adjusting the oxygen pressure during film growth.
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Jun 2021
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I05-ARPES
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V. A.
Rogalev
,
F.
Reis
,
F.
Adler
,
M.
Bauernfeind
,
J.
Erhardt
,
A.
Kowalewski
,
M. R.
Scholz
,
L.
Dudy
,
L. B.
Duffy
,
T.
Hesjedal
,
M.
Hoesch
,
G.
Bihlmayer
,
J.
Schäfer
,
R.
Claessen
Diamond Proposal Number(s):
[10244, 10289, 12892, 15285]
Abstract: We report on the electronic structure of
α
-Sn films in the very low thickness regime grown on InSb(111)A. High-resolution low photon energy angle-resolved photoemission spectroscopy allows for the direct observation of the linearly dispersing two-dimensional (2D) topological surface state (TSS) that exists between the second valence band and the conduction band. The Dirac point of this TSS was found to be 200 meV below the Fermi level in 10-nm-thick films, which enables the observation of the hybridization gap opening at the Dirac point of the TSS for thinner films. The crossover to a quasi-2D electronic structure is accompanied by a full gap opening at the Brillouin-zone center, in agreement with our density functional theory calculations. We further identify the thickness regime of
α
-Sn films where the hybridization gap in the TSS coexists with the topologically nontrivial electronic structure and one can expect the presence of a one-dimensional helical edge state.
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Dec 2019
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I09-Surface and Interface Structural Analysis
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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.
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Jun 2019
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I09-Surface and Interface Structural Analysis
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Philipp
Scheiderer
,
Matthias
Schmitt
,
Judith
Gabel
,
Michael
Zapf
,
Martin
Stuebinger
,
Philipp
Schütz
,
Lenart
Dudy
,
Christoph
Schlueter
,
Tien-Lin
Lee
,
Michael
Sing
,
Ralph
Claessen
Diamond Proposal Number(s):
[14106, 15200, 15856, 18372]
Abstract: The Mott transistor is a paradigm for a new class of electronic devices—often referred to by the term Mottronics—which are based on charge correlations between the electrons. Since correlation‐induced insulating phases of most oxide compounds are usually very robust, new methods have to be developed to push such materials right to the boundary to the metallic phase in order to enable the metal–insulator transition to be switched by electric gating. Here, it is demonstrated that thin films of the prototypical Mott insulator LaTiO3 grown by pulsed laser deposition under oxygen atmosphere are readily tuned by excess oxygen doping across the line of the band‐filling controlled Mott transition in the electronic phase diagram. The detected insulator to metal transition is characterized by a strong change in resistivity of several orders of magnitude. The use of suitable substrates and capping layers to inhibit oxygen diffusion facilitates full control of the oxygen content and renders the films stable against exposure to ambient conditions. These achievements represent a significant advancement in control and tuning of the electronic properties of LaTiO3+x thin films making it a promising channel material in future Mottronic devices.
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May 2018
|
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I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[14432, 11394]
Abstract: Transition metal oxides exhibit a plethora of intrinsic functionalities like superconductivity, magnetism or multiferroicity. To put these to practical use requires the integration of suited oxide materials within thin film structures where the active regions with switchable and tunable physical properties often are the very interfaces. Fundamental knowledge on the chemical and electronic interface structure is key to design target properties for working devices. Here we will show that photoelectron spectroscopy is a powerful tool to obtain such kind of information if high enough photon energies in the soft and hard X-ray regime are employed to enhance the probing depth and hence get access to the electronic structure of buried layers and interfaces.
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Apr 2018
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I05-ARPES
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M. R.
Scholz
,
V. A.
Rogalev
,
L.
Dudy
,
F.
Reis
,
F.
Adler
,
J.
Aulbach
,
L. J.
Collins-Mcintyre
,
L. B.
Duffy
,
H. F.
Yang
,
Y. L.
Chen
,
T.
Hesjedal
,
Z. K.
Liu
,
M.
Hoesch
,
S.
Muff
,
J. H.
Dil
,
J.
Schäfer
,
R.
Claessen
Diamond Proposal Number(s):
[10289, 10244, 12892, 15285]
Abstract: We report on the electronic structure of the elemental topological semimetal α−Sn on InSb(001). High-resolution angle-resolved photoemission data allow us to observe the topological surface state (TSS) that is degenerate with the bulk band structure and show that the former is unaffected by different surface reconstructions. An unintentional p-type doping of the as-grown films was compensated by deposition of potassium or tellurium after the growth, thereby shifting the Dirac point of the surface state below the Fermi level. We show that, while having the potential to break time-reversal symmetry, iron impurities with a coverage of up to 0.25 monolayers do not have any further impact on the surface state beyond that of K or Te. Furthermore, we have measured the spin-momentum locking of electrons from the TSS by means of spin-resolved photoemission. Our results show that the spin vector lies fully in-plane, but it also has a finite radial component. Finally, we analyze the decay of photoholes introduced in the photoemission process, and by this gain insight into the many-body interactions in the system. Surprisingly, we extract quasiparticle lifetimes comparable to other topological materials where the TSS is located within a bulk band gap. We argue that the main decay of photoholes is caused by intraband scattering, while scattering into bulk states is suppressed due to different orbital symmetries of bulk and surface states.
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Feb 2018
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