Publications by authors named "Jan Aarts"

9 Publications

  • Page 1 of 1

Direct-Write Printing of Josephson Junctions in a Scanning Electron Microscope.

ACS Nano 2021 Jan 24;15(1):322-329. Epub 2020 Nov 24.

Kamerlingh Onnes Laboratory, Leiden University, 2300 RA Leiden, The Netherlands.

Josephson junctions are the building blocks of superconducting electronics, with well-established applications in precision metrology and quantum computing. Fabricating a Josephson junction has been a resource-intensive and multistep procedure, involving lithography and wet-processing, which are not compatible with many applications. Here, we introduce a fully additive direct-write approach, where a scanning electron microscope can print substrate-conformal Josephson devices in a matter of minutes, requiring no additional processing. The junctions are made entirely by electron-beam-induced deposition (EBID) of tungsten carbide. We utilize EBID-tunable material properties to write, in one go, full proximity junctions with superconducting electrodes and metallic weak links and tailor their Josephson coupling. The Josephson behavior of these junctions is established and characterized by their microwave-induced Shapiro response and field-dependent transport. Our efforts provide a versatile and nondestructive alternative to conventional nanofabrication and can be expanded to print three-dimensional superconducting sensor arrays and quantum networks.
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http://dx.doi.org/10.1021/acsnano.0c03656DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7844821PMC
January 2021

Magnetic resonance imaging of spin-wave transport and interference in a magnetic insulator.

Sci Adv 2020 Nov 11;6(46). Epub 2020 Nov 11.

Department of Quantum Nanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, Netherlands.

Spin waves-the elementary excitations of magnetic materials-are prime candidate signal carriers for low-dissipation information processing. Being able to image coherent spin-wave transport is crucial for developing interference-based spin-wave devices. We introduce magnetic resonance imaging of the microwave magnetic stray fields that are generated by spin waves as a new approach for imaging coherent spin-wave transport. We realize this approach using a dense layer of electronic sensor spins in a diamond chip, which combines the ability to detect small magnetic fields with a sensitivity to their polarization. Focusing on a thin-film magnetic insulator, we quantify spin-wave amplitudes, visualize spin-wave dispersion and interference, and demonstrate time-domain measurements of spin-wave packets. We theoretically explain the observed anisotropic spin-wave patterns in terms of chiral spin-wave excitation and stray-field coupling to the sensor spins. Our results pave the way for probing spin waves in atomically thin magnets, even when embedded between opaque materials.
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http://dx.doi.org/10.1126/sciadv.abd3556DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7673737PMC
November 2020

Inhomogeneous superconductivity and quasilinear magnetoresistance at amorphous LaTiO/SrTiOinterfaces.

J Phys Condens Matter 2020 Oct 14. Epub 2020 Oct 14.

Huygens - Kamerlingh Onnes Laboratory, Universiteit Leiden, Leiden, NETHERLANDS.

We have studied the transport properties of LaTiO/SrTiO(LTO/STO) heterostructures. In spite of 2D growth observed in reflection high energy electron diffraction, Transmission Electron Microscopy images revealed that the samples tend to amorphize. Still, we observe that the structures are conducting, and some of them exhibit high conductance and/or superconductivity. We established that conductivity arises mainly on the STO side of the interface, and shows all the signs of the 2-dimensional electron gas usually observed at interfaces between STO and LTO or LaAlO, including the presence of two electron bands and tunability with a gate voltage. Analysis of magnetoresistance (MR) and superconductivity indicates presence of a spatial fluctuations of the electronic properties in our samples. That can explain the observed quasilinear out-of-plane MR, as well as various features of the in-plane MR and the observed superconductivity.
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http://dx.doi.org/10.1088/1361-648X/abc102DOI Listing
October 2020

Electron Trapping Mechanism in LaAlO_{3}/SrTiO_{3} Heterostructures.

Phys Rev Lett 2020 Jan;124(1):017702

Huygens-Kamerlingh Onnes Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands.

In LaAlO_{3}/SrTiO_{3} heterostructures, a still poorly understood phenomenon is that of electron trapping in back-gating experiments. Here, by combining magnetotransport measurements and self-consistent Schrödinger-Poisson calculations, we obtain an empirical relation between the amount of trapped electrons and the gate voltage. The amount of trapped electrons decays exponentially away from the interface. However, contrary to earlier observations, we find that the Fermi level remains well within the quantum well. The enhanced trapping of electrons induced by the gate voltage can therefore not be explained by a thermal escape mechanism. Further gate sweeping experiments strengthen that conclusion. We propose a new mechanism which involves the electromigration and clustering of oxygen vacancies in SrTiO_{3} and argue that such electron trapping is a universal phenomenon in SrTiO_{3}-based two-dimensional electron systems.
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http://dx.doi.org/10.1103/PhysRevLett.124.017702DOI Listing
January 2020

Growing a LaAlO/SrTiO heterostructure on CaNbO nanosheets.

Sci Rep 2019 Nov 26;9(1):17617. Epub 2019 Nov 26.

Huygens - Kamerlingh Onnes Laboratorium, Leiden University, Niels Bohrweg 2, 2300, RA, Leiden, The Netherlands.

The two-dimensional electron liquid which forms between the band insulators LaAlO (LAO) and SrTiO (STO) is a promising component for oxide electronics, but the requirement of using single crystal SrTiO substrates for the growth limits its applications in terms of device fabrication. It is therefore important to find ways to deposit these materials on other substrates, preferably Si, or Si-based, in order to facilitate integration with existing technology. Interesting candidates are micron-sized nanosheets of CaNbO which can be used as seed layers for perovskite materials on any substrate. We have used low-energy electron microscopy (LEEM) with in-situ pulsed laser deposition to study the subsequent growth of STO and LAO on such flakes which were deposited on Si. We can follow the morphology and crystallinity of the layers during growth, as well as fingerprint their electronic properties with angle resolved reflected electron spectroscopy. We find that STO layers, deposited on the nanosheets, can be made crystalline and flat; that LAO can be grown in a layer-by-layer fashion; and that the full heterostructure shows the signature of the formation of a conducting interface.
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http://dx.doi.org/10.1038/s41598-019-53438-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6879749PMC
November 2019

FluoroTome 1: An Apparatus for Tomographic Imaging of Radio-Fluorogenic (RFG) Gels.

Polymers (Basel) 2019 Oct 23;11(11). Epub 2019 Oct 23.

PICO B.V., Jan Tinbergenstraat 4B, 5491 DC Sint-Oedenrode, The Netherlands.

Radio-fluorogenic (RFG) gels become permanently fluorescent when exposed to high-energy radiation with the intensity of the emission proportional to the local dose of radiation absorbed. An apparatus is described, FluoroTome 1, that is capable of taking a series of tomographic images (thin slices) of the fluorescence of such an irradiated RFG gel on-site and within minutes of radiation exposure. These images can then be compiled to construct a 3D movie of the dose distribution within the gel. The historical development via a laboratory-bench prototype to a readily transportable, user-friendly apparatus is described. Instrumental details and performance tests are presented.
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http://dx.doi.org/10.3390/polym11111729DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6918256PMC
October 2019

Quantifying work function differences using low-energy electron microscopy: The case of mixed-terminated strontium titanate.

Ultramicroscopy 2019 05 19;200:43-49. Epub 2019 Feb 19.

Huygens-Kamerlingh Onnes Laboratorium, Leiden University, P.O. Box 9504, Leiden NL-2300 RA, Netherlands.

For many applications, it is important to measure the local work function of a surface with high lateral resolution. Low-energy electron microscopy is regularly employed to this end since it is, in principle, very well suited as it combines high-resolution imaging with high sensitivity to local electrostatic potentials. For surfaces with areas of different work function, however, lateral electrostatic fields inevitably associated with work function discontinuities deflect the low-energy electrons and thereby cause artifacts near these discontinuities. We use ray-tracing simulations to show that these artifacts extend over hundreds of nanometers and cause an overestimation of the true work function difference near the discontinuity by a factor of 1.6 if the standard image analysis methods are used. We demonstrate on a mixed-terminated strontium titanate surface that comparing LEEM data with detailed ray-tracing simulations leads to much a more robust estimate of the work function difference.
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http://dx.doi.org/10.1016/j.ultramic.2019.02.018DOI Listing
May 2019

Controlling supercurrents and their spatial distribution in ferromagnets.

Nat Commun 2017 12 12;8(1):2056. Epub 2017 Dec 12.

Huygens-Kamerlingh Onnes Laboratory, Leiden Institute of Physics, University Leiden, P.O. Box 9504, 2300 RA, Leiden, The Netherlands.

Spin-triplet Cooper pairs induced in ferromagnets form the centrepiece of the emerging field of superconducting spintronics. Usually the focus is on the spin-polarization of the triplets, potentially enabling low-dissipation magnetization switching. However, the magnetic texture which provides the fundamental mechanism for generating triplets also permits control over the spatial distribution of supercurrent. Here we demonstrate the tailoring of distinct supercurrent pathways in the ferromagnetic barrier of a Josephson junction. We combine micromagnetic simulations with three-dimensional supercurrent calculations to design a disk-shaped structure with a ferromagnetic vortex which induces two transport channels across the junction. By using superconducting quantum interferometry, we show the existence of two channels. Moreover, we show how the supercurrent can be controlled by moving the vortex with a magnetic field. This approach paves the way for supercurrent paths to be dynamically reconfigured in order to switch between different functionalities in the same device.
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http://dx.doi.org/10.1038/s41467-017-02236-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5727026PMC
December 2017

Formation mechanism of Ruddlesden-Popper-type antiphase boundaries during the kinetically limited growth of Sr rich SrTiO thin films.

Sci Rep 2016 12 6;6:38296. Epub 2016 Dec 6.

Peter Grünberg Institute (PGI-7), Forschungszentrum Jülich GmbH, 52425, Jülich, Germany.

We elucidated the formation process for Ruddlesden-Popper-type defects during pulsed laser deposition of Sr rich SrTiO thin films by a combined analysis of in-situ atomic force microscopy, low energy electron diffraction and high resolution scanning transmission electron microscopy. At the early growth stage of 1.5 unit cells, the excess Sr results in the formation of SrO on the surface, resulting in a local termination change from TiO to SrO, thereby forming a Sr rich (2 × 2) surface reconstruction. With progressive SrTiO growth, islands with thermodynamically stable SrO rock-salt structure are formed, coexisting with TiO terminated islands. During the overgrowth of these thermodynamically stable islands, both lateral as well as vertical Ruddlesden-Popper-type anti-phase boundaries are formed, accommodating the Sr excess of the SrTiO film. We suggest the formation of thermodynamically stable SrO rock-salt structures as origin for the formation of Ruddlesden-Popper-type antiphase boundaries, which are as a result of kinetic limitations confined to certain regions on the surface.
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http://dx.doi.org/10.1038/srep38296DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5138825PMC
December 2016
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