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Linear colossal magnetoresistance driven by magnetic textures in LaTiO3 thin films on SrTiO3
Authors:
Teresa Tschirner,
Berengar Leikert,
Felix Kern,
Daniel Wolf,
Axel Lubk,
Martin Kamp,
Kirill Miller,
Fabian Hartmann,
Sven Höfling,
Bernd Büchner,
Joseph Dufouleur,
Marc Gabay,
Michael Sing,
Ralph Claessen,
Louis Veyrat
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. One of its principal origins is local mobility or density inhomogeneities, often structural, which in the Parish-Littlewood theory leads to an unsaturating LMR proportional to mobility. Structural disorder, however, a…
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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. One of its principal origins is local mobility or density inhomogeneities, often structural, which in the Parish-Littlewood theory leads to an unsaturating LMR proportional to mobility. Structural disorder, however, also tends to limit the mobility and hence the overall LMR amplitude. An alternative route to achieve large LMR is via non-structural inhomogeneities which do not affect the zero field mobility, like magnetic domains. Here, linear positive magnetoresistance caused by magnetic texture is reported in \ch{LaTiO3}/\ch{SrTiO3} heterostructures. The LMR amplitude reaches up to 6500\% at 9T. This colossal value is understood by the unusual combination of a very high thin film mobility, up to 40 000 cm$^2$/V.s, and a very large coverage of low-mobility regions. These regions correlate with a striped magnetic structure, compatible with a spiral magnetic texture in the \ch{LaTiO3} film, revealed by low temperature Lorentz transmission electron microscopy. These results provide a novel route for the engineering of large-LMR devices.
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Submitted 14 October, 2022;
originally announced October 2022.
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Electron Holographic Mapping of Structural and Electronic Reconstruction at Mono- and Bilayer Steps of h-BN
Authors:
Subakti Subakti,
Mohammadreza Daqiqshirazi,
Daniel Wolf,
Martin Linck,
Felix L. Kern,
Mitisha Jain,
Silvan Kretschmer,
Arkady V. Krasheninnikov,
Thomas Brumme,
Axel Lubk
Abstract:
Here, by making use of medium and high resolution autocorrected off-axis electron holography, we directly probe the electrostatic potential as well as in-plane and out-of-plane charge delocalization at edges and steps in multilayer hexagonal boron nitride. In combination with ab-initio calculations, the data allows to directly reveal the formation of out-of-plane covalent bonds at folded zig-zag e…
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Here, by making use of medium and high resolution autocorrected off-axis electron holography, we directly probe the electrostatic potential as well as in-plane and out-of-plane charge delocalization at edges and steps in multilayer hexagonal boron nitride. In combination with ab-initio calculations, the data allows to directly reveal the formation of out-of-plane covalent bonds at folded zig-zag edges and steps comprising two monolayers and the absence of which at monolayer steps. The technique paves the way for studying other charge (de)localization phenomena in 2D materials, e.g., at polar edges, topological edge states and defects.
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Submitted 8 October, 2022;
originally announced October 2022.
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Autocorrected Off-axis Holography of 2D Materials
Authors:
Felix Kern,
Martin Linck,
Daniel Wolf,
Nasim Alem,
Himani Arora,
Sibylle Gemming,
Artur Erbe,
Alex Zettl,
Bernd Büchner,
Axel Lubk
Abstract:
The reduced dimensionality in two-dimensional materials leads a wealth of unusual properties, which are currently explored for both fundamental and applied sciences. In order to study the crystal structure, edge states, the formation of defects and grain boundaries, or the impact of adsorbates, high resolution microscopy techniques are indispensible. Here we report on the development of an electro…
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The reduced dimensionality in two-dimensional materials leads a wealth of unusual properties, which are currently explored for both fundamental and applied sciences. In order to study the crystal structure, edge states, the formation of defects and grain boundaries, or the impact of adsorbates, high resolution microscopy techniques are indispensible. Here we report on the development of an electron holography (EH) transmission electron microscopy (TEM) technique, which facilitates high spatial resolution by an automatic correction of geometric aberrations. Distinguished features of EH beyond conventional TEM imaging are the gap-free spatial information signal transfer and higher dose efficiency for certain spatial frequency bands as well as direct access to the projected electrostatic potential of the 2D material. We demonstrate these features at the example of h-BN, at which we measure the electrostatic potential as a function of layer number down to the monolayer limit and obtain evidence for a systematic increase of the potential at the zig-zag edges.
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Submitted 25 June, 2020; v1 submitted 24 June, 2020;
originally announced June 2020.
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The Dresden in-situ (S)TEM special with a continuous-flow liquid-helium cryostat
Authors:
Felix Börrnert,
Felix Kern,
Franziska Seifert,
Thomas Riedel,
Heiko Müller,
Bernd Büchner,
Axel Lubk
Abstract:
Fundamental solid state physics phenomena typically occur at very low temperatures, requiring liquid helium cooling in experimental studies. Transmission electron microscopy is a well-established characterization method, which allows probing crucial materials properties down to nanometer and even atomic resolution. Due to the limited space in the object plane, however, suitable liquid-helium cooli…
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Fundamental solid state physics phenomena typically occur at very low temperatures, requiring liquid helium cooling in experimental studies. Transmission electron microscopy is a well-established characterization method, which allows probing crucial materials properties down to nanometer and even atomic resolution. Due to the limited space in the object plane, however, suitable liquid-helium cooling is very challenging. To overcome this limitation, resolving power was sacrificed in our Dresden in-situ (S)TEM special, resulting in more than 60 mm usable experimental space in all directions with the specimen in the center. With the installation of a continuous-flow liquid-helium cryostat, any temperature between 6.5 K and 400 K can be set precisely and kept for days. The information limit of the Dresden in-situ (S)TEM special is about 5 nm. It is shown that the resolution of the Dresden in-situ (S)TEM special is currently not limited by aberrations, but by external instabilities, that are currently addressed.
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Submitted 1 October, 2019;
originally announced October 2019.