505 research outputs found
Sequential pulsed laser deposition of homoepitaxial SrTiO thin films
Control of thin film stoichiometry is of primary relevance to achieve desired
functionality. Pulsed laser deposition ablating from binary-oxide targets
(sequential deposition) can be applied to precisely control the film
composition, offsetting the importance of growth conditions on the film
stoichiometry. In this work, we demonstrate that the cation stoichiometry of
SrTiO thin films can be finely tuned by sequential deposition from SrO and
TiO targets. Homoepitaxial SrTiO films were deposited at different
substrate temperatures and Ti/Sr pulse ratios, allowing the establishment of a
growth window for stoichiometric SrTiO. The growth kinetics and nucleation
processes were studied by reflection high-energy electron diffraction and
atomic force microscopy, providing information about the growth mode and the
degree of off-stoichiometry. At the optimal (stoichiometric) growth conditions,
films exhibit atomically flat surfaces, whereas off-stoichiometry is
accommodated by crystal defects, 3D islands and/or surface precipitates
depending on the substrate temperature and the excess cation. This technique
opens the way to precisely control stoichiometry and doping of oxide thin
films.Comment: 6 pages, 5 figure
Epitaxial growth and thermodynamic stability of SrIrO3/SrTiO3 heterostructures
Obtaining high-quality thin films of 5d transition metal oxides is essential
to explore the exotic semimetallic and topological phases predicted to arise
from the combination of strong electron correlations and spin-orbit coupling.
Here, we show that the transport properties of SrIrO3 thin films, grown by
pulsed laser deposition, can be optimized by considering the effect of
laser-induced modification of the SrIrO3 target surface. We further demonstrate
that bare SrIrO3 thin films are subject to degradation in air and are highly
sensitive to lithographic processing. A crystalline SrTiO3 cap layer deposited
in-situ is effective in preserving the film quality, allowing us to measure
metallic transport behavior in films with thicknesses down to 4 unit cells. In
addition, the SrTiO3 encapsulation enables the fabrication of devices such as
Hall bars without altering the film properties, allowing precise
(magneto)transport measurements on micro- and nanoscale devices.Comment: 5 pages, 3 figure
Two-dimensional superconductivity at the (111)LaAlO/SrTiO interface
We report on the discovery and transport study of the superconducting ground
state present at the (111)LaAlO/SrTiO interface. The superconducting
transition is consistent with a Berezinskii-Kosterlitz-Thouless transition and
its 2D nature is further corroborated by the anisotropy of the critical
magnetic field, as calculated by Tinkham. The estimated superconducting layer
thickness and coherence length are 10 nm and 60 nm, respectively. The results
of this work provide a new platform to clarify the microscopic details of
superconductivity at LaAlO/SrTiO interfaces, in particular in what
concerns the link with orbital symmetry.Comment: 4 pages, 4 figure
Band inversion driven by electronic correlations at the (111) LaAlO/SrTiO interface
Quantum confinement at complex oxide interfaces establishes an intricate
hierarchy of the strongly correlated -orbitals which is widely recognized as
a source of emergent physics. The most prominent example is the (001)
LaAlO/SrTiO(LAO/STO) interface, which features a dome-shaped phase
diagram of superconducting critical temperature and spin-orbit coupling (SOC)
as a function of electrostatic doping, arising from a selective occupancy of
orbitals of different character. Here we study (111)-oriented LAO/STO
interfaces - where the three orbitals contribute equally to the
sub-band states caused by confinement - and investigate the impact of this
unique feature on electronic transport. We show that transport occurs through
two sets of electron-like sub-bands, and the carrier density of one of the sets
shows a non-monotonic dependence on the sample conductance. Using tight-binding
modeling, we demonstrate that this behavior stems from a band inversion driven
by on-site Coulomb interactions. The balanced contribution of all
orbitals to electronic transport is shown to result in strong SOC with reduced
electrostatic modulation.Comment: 5 pages, 4 figures, (+ supplemental material
Balanced electron-hole transport in spin-orbit semimetal SrIrO3 heterostructures
Relating the band structure of correlated semimetals to their transport
properties is a complex and often open issue. The partial occupation of
numerous electron and hole bands can result in properties that are seemingly in
contrast with one another, complicating the extraction of the transport
coefficients of different bands. The 5d oxide SrIrO3 hosts parabolic bands of
heavy holes and light electrons in gapped Dirac cones due to the interplay
between electron-electron interactions and spin-orbit coupling. We present a
multifold approach relying on different experimental techniques and theoretical
calculations to disentangle its complex electronic properties. By combining
magnetotransport and thermoelectric measurements in a field-effect geometry
with first-principles calculations, we quantitatively determine the transport
coefficients of different conduction channels. Despite their different
dispersion relationships, electrons and holes are found to have strikingly
similar transport coefficients, yielding a holelike response under field-effect
and thermoelectric measurements and a linear, electronlike Hall effect up to 33
T.Comment: 5 pages, 4 figure
Rich Situated Attitudes
We outline a novel theory of natural language meaning, Rich
Situated Semantics [RSS], on which the content of sentential utterances
is semantically rich and informationally situated. In virtue of its situatedness,
an utterance’s rich situated content varies with the informational
situation of the cognitive agent interpreting the utterance. In virtue of its
richness, this content contains information beyond the utterance’s lexically
encoded information. The agent-dependence of rich situated content
solves a number of problems in semantics and the philosophy of language
(cf. [14, 20, 25]). In particular, since RSS varies the granularity of utterance
contents with the interpreting agent’s informational situation, it
solves the problem of finding suitably fine- or coarse-grained objects for
the content of propositional attitudes. In virtue of this variation, a layman
will reason with more propositions than an expert
Coupling charge and topological reconstructions at polar oxide interfaces
In oxide heterostructures, different materials are integrated into a single
artificial crystal, resulting in a breaking of inversion-symmetry across the
heterointerfaces. A notable example is the interface between polar and
non-polar materials, where valence discontinuities lead to otherwise
inaccessible charge and spin states. This approach paved the way to the
discovery of numerous unconventional properties absent in the bulk
constituents. However, control of the geometric structure of the electronic
wavefunctions in correlated oxides remains an open challenge. Here, we create
heterostructures consisting of ultrathin SrRuO, an itinerant ferromagnet
hosting momentum-space sources of Berry curvature, and LaAlO, a polar
wide-bandgap insulator. Transmission electron microscopy reveals an atomically
sharp LaO/RuO/SrO interface configuration, leading to excess charge being
pinned near the LaAlO/SrRuO interface. We demonstrate through
magneto-optical characterization, theoretical calculations and transport
measurements that the real-space charge reconstruction modifies the
momentum-space Berry curvature in SrRuO, driving a reorganization of the
topological charges in the band structure. Our results illustrate how the
topological and magnetic features of oxides can be manipulated by engineering
charge discontinuities at oxide interfaces.Comment: 5 pages main text (4 figures), 29 pages of supplementary informatio
Perspectieven voor hoogveenherstel in Nederland : samenvatting onderzoek en handleiding hoogveenherstel 1998-2010
Het hoogveenareaal in Nederland is door ontginning, turfwinning, boekweitbrandcultuur en verdroging sterk gereduceerd. De water- en nutriëntenhuishouding van de hoogvenen zijn sterk verstoord door deze aantastingen en bovendien door de neerslag van atmosferisch stikstof (N). Verder is door deze aantastingen de variatie in terreincondities die aanwezig is in intacte hoogveenlandschappen, met name gradiënten van de zure, mineraalarme hoogveenkern naar de gebufferde, mineraalrijkere omgeving, afgenomen. Herstelmaatregelen in de hoogveenrestanten hadden wisselend succes: soms herstelden of ontwikkelden zich vegetaties met bultvormende veenmossen, meestal ontstond een drijvende laag Waterveenmos (Sphagnum cuspidatum) of een zure waterplas. Verder bleef Pijpenstrootje (Molinia caerulea) over grote oppervlakten de vegetatie domineren en vestigden zich Berken (Betula spec.). In het kader van het kennisnetwerk ‘Ontwikkeling en Beheer Natuurkwaliteit’ (OBN) is onderzoek gedaan naar de perspectieven voor hoogveenherstel in Nederland. Twee vragen stonden daarbij centraal: 1. Is hoogveenherstel mogelijk bij de huidige hoge atmosferische N-depositie? 2. Onder welke voorwaarden is succesvol herstel van de karakteristieke flora en fauna mogelijk? De belangrijkste conclusies uit dit onderzoek worden in dit rapport beschreven
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