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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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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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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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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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
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P.
Schütz
,
D. V.
Christensen
,
V.
Borisov
,
F.
Pfaff
,
P.
Scheiderer
,
L.
Dudy
,
M.
Zapf
,
J.
Gabel
,
Y. Z.
Chen
,
N.
Pryds
,
Victor
Rogalev
,
V. N.
Strocov
,
C.
Schlueter
,
T.-L.
Lee
,
H. O.
Jeschke
,
R.
Valentí
,
M.
Sing
,
R.
Claessen
Abstract: The spinel/perovskite heterointerface γ−Al2O3/SrTiO3 hosts a two-dimensional electron system (2DES) with electron mobilities exceeding those in its all-perovskite counterpart LaAlO3/SrTiO3 by more than an order of magnitude, despite the abundance of oxygen vacancies which act as electron donors as well as scattering sites. By means of resonant soft x-ray photoemission spectroscopy and ab initio calculations, we reveal the presence of a sharply localized type of oxygen vacancies at the very interface due to the local breaking of the perovskite symmetry. We explain the extraordinarily high mobilities by reduced scattering resulting from the preferential formation of interfacial oxygen vacancies and spatial separation of the resulting 2DES in deeper SrTiO3 layers. Our findings comply with transport studies and pave the way towards defect engineering at interfaces of oxides with different crystal structures.
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Oct 2017
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[9717, 12044, 11394, 14432, 15455]
Abstract: More than a decade after the discovery of the two-dimensional electron system (2DES) at the interface between the band insulators
LaAlO
3
(LAO) and
SrTiO
3
(STO) its microscopic origin is still under debate. Several explanations have been proposed, the main contenders being electron doping by oxygen vacancies and electronic reconstruction, i.e., the redistribution of electrons to the interface to minimize the electrostatic energy in the polar LAO film. However, no experiment thus far could provide unambiguous information on the microscopic origin of the interfacial charge carriers. Here we utilize a novel experimental approach combining photoelectron spectroscopy (PES) with highly brilliant synchrotron radiation and apply it to a set of samples with varying key parameters that are thought to be crucial for the emergence of interfacial conductivity. Based on microscopic insight into the electronic structure, we obtain results tipping the scales in favor of polar discontinuity as a generic, robust driving force for the 2DES formation. Likewise, other functionalities such as magnetism or superconductivity might be switched in all-oxide devices by polarity-driven charge transfer.
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May 2017
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Abstract: Insulating SrTiO3 (STO) can host 2D electron systems (2DESs) on its surfaces, caused by oxygen defects. This study shows that the STO surface exhibits phase separation once the 2DES is formed and relates this inhomogeneity to recently reported magnetic order at STO surfaces and interfaces. The results open pathways to exploit oxygen defects for engineering the electronic and magnetic properties of oxides.
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Sep 2016
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