I09-Surface and Interface Structural Analysis
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Open Access
Abstract: The three-dimensional recording scheme of time-of-flight momentum microscopes (ToF-MMs) is advantageous for fast mapping of the photoelectron distribution in (E,k) parameter space over the entire Brillouin zone. However, the 2 ns pulse period of most synchrotrons is too short for pure ToF photoelectron spectroscopy. The use of a hemispherical analyzer (HSA) as a pre-filter allows ToF-MM at such high pulse rates. The first HSA & ToF hybrid MM is operated at the soft X-ray branch of beamline I09 at the Diamond Light Source, UK. The photon energy ranges from 105 eV to 2 keV, with circular polarization available for hν ≥ 145 eV. The HSA reduces the transmitted energy band to typically 0.5 eV, which is then further analyzed by ToF recording. In initial experiments, the overall efficiency gain when switching from the standard 2D (kx,ky) mode to the 3D (kx,ky,Ekin) hybrid mode was about 24. This value is determined by the number of resolved kinetic energies (here 12) and the transmission gain of the electron optics due to the high pass energy of the HSA in hybrid mode (Epass up to 500 eV). The transmission gain depends on the size of the photon footprint on the sample. Under k-imaging conditions, the energy and momentum resolution are 10.2 meV (FWHM) (4.2 meV with 200 μm slits and Epass = 8 eV) and 0.010 Å-1. The energy filtered X-PEEM mode showed a spatial resolution of 250 nm. As examples, we show 2D band mapping of bilayer graphene, 3D mapping of the Fermi surface of Cu, circular dichroic ARPES for intercalated indenene layers, and the sp valence band of Au. Full-field photoelectron diffraction patterns of Ge show rich structure in k-field diameters of up to 6 Å-1.
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May 2025
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I09-Surface and Interface Structural Analysis
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H. J.
Elmers
,
O.
Tkach
,
Y.
Lytvynenko
,
P.
Yogi
,
M.
Schmitt
,
D.
Biswas
,
J.
Liu
,
S. V.
Chernov
,
Quynh
Nguyen
,
M.
Hoesch
,
D.
Kutnyakhov
,
N.
Wind
,
L.
Wenthaus
,
M.
Scholz
,
K.
Rossnagel
,
A.
Gloskovskii
,
C.
Schlueter
,
A.
Winkelmann
,
A. A.
Haghighirad
,
T.-L.
Lee
,
M.
Sing
,
R.
Claessen
,
M.
Le Tacon
,
J.
Demsar
,
G.
Schönhense
,
O.
Fedchenko
Diamond Proposal Number(s):
[33765]
Abstract: Using x-ray photoelectron diffraction (XPD) and angle-resolved photoemission spectroscopy, we study photoemission intensity changes related to changes in the geometric and electronic structure in the kagome metal CsV3Sb5 upon transition to an unconventional charge density wave (CDW) state. The XPD patterns reveal the presence of a chiral atomic structure in the CDW phase. Furthermore, using circularly polarized x-rays, we have found a pronounced nontrivial circular dichroism in the angular distribution of the valence band photoemission in the CDW phase, indicating a chirality of the electronic structure. This observation is consistent with the proposed orbital loop current order. In view of a negligible spontaneous Kerr signal in recent magneto-optical studies, the results suggest an antiferromagnetic coupling of the orbital magnetic moments along the 𝑐 axis. While the inherent structural chirality may also induce circular dichroism, the observed asymmetry values seem to be too large in the case of the weak structural distortions caused by the CDW.
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Mar 2025
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I05-ARPES
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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.
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May 2024
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I05-ARPES
I09-Surface and Interface Structural Analysis
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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.
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Feb 2024
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I09-Surface and Interface Structural Analysis
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Teresa
Tschirner
,
Berengar
Leikert
,
Felix
Kern
,
Daniel
Wolf
,
Axel
Lubk
,
Martin
Kamp
,
Kirill
Miller
,
Fabian
Hartmann
,
Sven
Höfling
,
Judith
Gabel
,
Matthias
Schmitt
,
Martin
Stuebinger
,
Julia
Küspert
,
Tien-Lin
Lee
,
Bernd
Büchner
,
Joseph
Dufouleur
,
Marc
Gabay
,
Michael
Sing
,
Ralph
Claessen
,
Louis
Veyrat
Diamond Proposal Number(s):
[21676]
Abstract: Linear magnetoresistance (LMR) is of particular interest for memory, electronics, and sensing applications, especially when it does not saturate over a wide range of magnetic fields. Structural disorder, however, also tends to limit the mobility and hence the overall LMR amplitude. An alternative route to achieve large LMR is via nonstructural inhomogeneities which do not affect the zero field mobility, like magnetic domains. Here, we report a colossal positive linear magnetoresistance in
La
TiO
3
/
Sr
TiO
3
heterostructures, with amplitude up to 6500% at 9T at low temperature. The colossal amplitude of the LMR, one of the largest in oxide heterostructure, stems from the unusual combination of a very high heterostructure mobility, up to 40 000
cm
2
V
−
1
s
−
1
, and a very large coverage of low-mobility regions. Low-temperature Lorentz transmission electron microscopy measurements further reveals a striped magnetic structure at the sub-
µ
m
scale in the
La
TiO
3
layer, compatible with in-plane spiral magnetism, with very high surface coverage. We propose that the low-mobility regions and striped magnetic regions are correlated, we model the increase in scattering induced by the magnetic texture, and we show that the non saturating LMR fits the Parish-Littlewood scenario. Our results provide a novel route for the engineering of large-LMR systems, using magnetic texture.
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Dec 2023
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Abstract: We conducted a thorough investigation into the temperature dependence of the metallic-like bands of Si(553)-Au using angular-resolved photoemission spectroscopy (ARPES). Our study addresses the challenges posed by the short-term stability of the surface and photo-voltage effects, which we overcame to extract changes in the band-filling and Fermi-velocity. Our findings shed light on the low-temperature phase of the step edge in Si(553)-Au, which has been a topic of ongoing debate regarding its structural or electronic nature. Through comparison with theoretical predictions of a structural-related low-temperature to high-temperature phase transition, we discovered that the band-filling and Fermi-velocity do not change accordingly, thereby ruling out this scenario. Our study contributes to a better understanding of this material system and provides an important reference for future research.
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Jul 2023
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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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