The hysteretic insulator-to-metal transition of VO2 is studied in detail for pulsed laser deposition grown thin films on TiO2 substrates, under variation of temperature and applied bias currents. ...This system is of interest for novel electronics based on memristive concepts, in particular as the resistive transition in these films occurs close to room temperature. Multiple, stable resistance states can be set controllably in the temperature range of the hysteretic phase transition by tailored temperature sweeps or by Joule heating induced by current pulses.
Novel electronic and magnetic phases are being observed at interfaces between insulating, non-magnetic oxide compounds, with the most notable example being the interface between SrTiO3 and LaAlO3. ...The basic properties of these interfaces will be discussed, as well as prospects for applications and possible future developments.
New voices, at last Alisic, Eva; Hilgenkamp, Hans
Science (American Association for the Advancement of Science),
09/2018, Letnik:
361, Številka:
6406
Journal Article
Recenzirano
Odprti dostop
Science academies are well placed to help strengthen national systems of research and innovation, drawing upon the knowledge of experienced scientists across fields. But what about the voices of ...early-career scientists who are impassioned to bolster international, interdisciplinary, and intergenerational dialogue, with the goal of making decision-making evidence-based and inclusive? Since 2000, “young” science academies have emerged across the world. The United States has now joined this movement. In June, the U.S. National Academies launched “New Voices in Sciences, Engineering and Medicine,” comprising 18 early- to midcareer scholars. They will engage in communicating the evidence base for addressing national and global challenges and help diversify the expertise in the National Academies' advisory activities (
www.nationalacademies.org/newvoices
). As New Voices convenes its first meeting next week, what should this organization consider?
Vanadium dioxide (VO2) is widely studied for its prominent insulator–metal transition (IMT) near room temperature, with potential applications in novel memory devices and brain-inspired neuromorphic ...computing. We report on the fabrication of in-plane VO2 metal–insulator–metal structures and reproducible switching measurements in these two-terminal devices. Resistive switching can be achieved by applying voltage or current bias, which creates Joule heating in the device and triggers the IMT. We analyze the current/voltage-induced resistive switching characteristics, including a pronounced intermediate state in the reset from the low to the high resistance state. Controllable switching behavior is demonstrated between multiple resistance levels over several orders of magnitude, allowing for multibit operation. This multi-level operation of the VO2-bridge devices results from exploiting sub-hysteresis loops by Joule heating.
A large variety of transport properties have been observed at the interface between the insulating oxides SrTiO3 and LaAlO3 such as insulation, 2D interface metallicity, 3D bulk metallicity, magnetic ...scattering, and superconductivity. The relation between the structure and the properties of the SrTiO3/LaAlO3 interface can be explained in a meaningful way by taking into account the relative contribution of three structural aspects: oxygen vacancies, structural deformations (including cation disorder), and electronic interface reconstruction. The emerging phase diagram is much richer than for related bulk oxides due to the occurrence of interface electronic reconstruction. The observation of this interface phenomenon is a display of recent advances in thin film deposition and characterization techniques, and provides an extension to the range of exceptional electronic properties of complex oxides.
The interface between the insulating oxides SrTiO3 and LaAlO3 shows a variety of transport properties. The properties of the interface can be explained by three structural aspects: oxygen vacancies, structural deformations (including cation disorder), and electronic interface reconstruction. Irrespective of the origin of mobile charge at these heterointerfaces, once harnessed and controlled all could lead to heterostructures, where the properties are determined by strong correlation effects, and therefore full of surprises.
An array of superconducting islands placed on a normal metal film offers a tunable realization of nanopatterned superconductivity. This system enables investigation of the nature of competing vortex ...states and phase transitions between them. A square array creates the eggcrate potential in which magnetic field–induced vortices are frozen into a vortex insulator. We observed a vortex insulator–vortex metal transition driven by the applied electric current and determined critical exponents that coincided with those for thermodynamic liquid-gas transition. Our findings offer a comprehensive description of dynamic critical behavior and establish a deep connection between equilibrium and nonequilibrium phase transitions.
Josephson Memories Hilgenkamp, Hans
Journal of superconductivity and novel magnetism,
06/2021, Letnik:
34, Številka:
6
Journal Article
Recenzirano
Odprti dostop
A brief overview will be provided on superconducting memory elements incorporating Josephson junctions, from the tunneling cryotrons in the 1960's to contemporary RSFQ devices, with an outlook to ...future developments such as Josephson junction-based neuromorphic circuitry.
The synthesis of materials with well‐controlled composition and structure improves our understanding of their intrinsic electrical transport properties. Recent developments in atomically controlled ...growth have been shown to be crucial in enabling the study of new physical phenomena in epitaxial oxide heterostructures. Nevertheless, these phenomena can be influenced by the presence of defects that act as extrinsic sources of both doping and impurity scattering. Control over the nature and density of such defects is therefore necessary to fully understand the intrinsic materials properties and exploit them in future device technologies. Here, it is shown that incorporation of a strontium copper oxide nano‐layer strongly reduces the impurity scattering at conducting interfaces in oxide LaAlO3–SrTiO3(001) heterostructures, opening the door to high carrier mobility materials. It is proposed that this remote cuprate layer facilitates enhanced suppression of oxygen defects by reducing the kinetic barrier for oxygen exchange in the hetero‐interfacial film system. This design concept of controlled defect engineering can be of significant importance in applications in which enhanced oxygen surface exchange plays a crucial role.
Defect engineering of conducting interfaces in oxide LaAlO3–SrTiO3(001) heterostructures by incorporation of a strontium copper oxide nanolayer strongly reduces the impurity scattering, opening the door to high carrier mobility materials. This remote cuprate layer facilitates enhanced suppression of oxygen defects by reducing the kinetic barrier for oxygen surface exchange in the hetero‐interfacial film system.
Abstract
The glass-like vortex distribution in pulsed laser deposited YBa
2
Cu
3
O
7 −
x
thin films is observed by scanning superconducting quantum interference device microscopy and analysed for ...ordering after cooling in magnetic fields significantly smaller than the Earth's field. Autocorrelation calculations on this distribution show a weak short-range positional order, while Delaunay triangulation shows a near-complete lack of orientational order. The distribution of these vortices is finally characterised as an isotropic vortex glass. Abnormally closely spaced groups of vortices, which are statistically unlikely to occur, are observed above a threshold magnetic field. The origin of these groups is discussed, but will require further investigation.
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