21 research outputs found
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
Isolation and characterization of few-layer black phosphorus
Isolation and characterization of mechanically exfoliated black phosphorus
flakes with a thickness down to two single-layers is presented. A modification
of the mechanical exfoliation method, which provides higher yield of atomically
thin flakes than conventional mechanical exfoliation, has been developed. We
present general guidelines to determine the number of layers using optical
microscopy, Raman spectroscopy and transmission electron microscopy in a fast
and reliable way. Moreover, we demonstrate that the exfoliated flakes are
highly crystalline and that they are stable even in free-standing form through
Raman spectroscopy and transmission electron microscopy measurements. A strong
thickness dependence of the band structure is found by density functional
theory calculations. The exciton binding energy, within an effective mass
approximation, is also calculated for different number of layers. Our
computational results for the optical gap are consistent with preliminary
photoluminescence results on thin flakes. Finally, we study the environmental
stability of black phosphorus flakes finding that the flakes are very
hydrophilic and that long term exposure to air moisture etches black phosphorus
away. Nonetheless, we demonstrate that the aging of the flakes is slow enough
to allow fabrication of field-effect transistors with strong ambipolar
behavior. Density functional theory calculations also give us insight into the
water-induced changes of the structural and electronic properties of black
phosphorus.Comment: 11 main figures, 7 supporting figure
Reducing anionic surfactant adsorption using polyacrylate as sacrificial agent investigated by QCM-D
Surfactant losses by adsorption to rock surfaces make surfactant-based enhanced oil recovery economically less feasible. We investigated polyacrylate (PA) as a sacrificial agent in the reduction of anionic surfactant adsorption with focus on calcite surfaces by using quartz crystal microbalance with dissipation monitoring. It was found that the adsorption of the anionic surfactant alcohol alkoxy sulfate (AAS) followed a Langmuir adsorption isotherm, and the adsorbed amount reached saturation above its critical micellar concentration. Adsorption of PA was a much slower process compared to AAS adsorption. Increasing the calcium ion concentration also increased the amount of AAS adsorbed as well as the mass increase rate of PA adsorption. Experimental results combined with density functional theory calculations indicated that calcium cation bridging was important for anionic surfactant AAS and PA adsorption to calcite surfaces. To effectively reduce the amount of surfactant adsorption, it was needed to preflush with PA, rather than by a simultaneous injection. Preflushing with 30 ppm of PA gave a reduction of AAS adsorption of 30% under high salinity (HS, 31,800 ppm) conditions, compared to 8% reduction under low salinity (LS, 3180 ppm) conditions. In the absence of PA, the amount of adsorbed AAS was reduced by already 50% upon changing from HS to LS conditions. Lower calcium ion concentrations, as under LS conditions, contributed to this observation. On different mineral surfaces, PA reduced the AAS adsorption in the order of alumina > calcite > silica. These results offer important insights into mitigating surfactant adsorption using PA polyelectrolyte as sacrificial agent and contribute to improved flooding strategies with reduced surfactant loss.</p
Entropy-driven formation of large icosahedral colloidal clusters by spherical confinement
Icosahedral symmetry, which is not compatible with truly long-range order, canbefoundinmany systems, such as liquids, glasses, atomic clusters, quasicrystals and virus-capsids(1-12). To obtain arrangements with a high degree of icosahedral order from tens of particles or more, interparticle attractive interactions are considered to be essential(1,3,6-12). Here, we report that entropy and spherical confinement suffice for the formation of icosahedral clusters consisting of up to 100,000 particles. Specifically, by using real-space measurements on nanometre- and micrometre-sized colloids, as well as computer simulations, we show that tens of thousands of hard spheres compressed under spherical confinement spontaneously crystallize into icosahedral clusters that are entropically favoured over the bulk face-centred cubic crystal structure(13,14). Our findings provide insights into the interplay between confinement and crystallization and into how these are connected to the formation of icosahedral structures
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Interfaces
between complex oxides
constitute a unique playground for two-dimensional electron systems
(2DESs), where superconductivity and magnetism can arise from combinations
of bulk insulators. The 2DES at the LaAlO<sub>3</sub>/SrTiO<sub>3</sub> interface is one of the most studied in this regard, and its origin
is determined by the polar field in LaAlO<sub>3</sub> as well as by
the presence of point defects, like oxygen vacancies and intermixed
cations. These defects usually reside in the conduction channel and
are responsible for a decrease of the electronic mobility. In this
work, we use an amorphous WO<sub>3</sub> overlayer to obtain a high-mobility
2DES in WO<sub>3</sub>/LaAlO<sub>3</sub>/SrTiO<sub>3</sub> heterostructures.
The studied system shows a sharp insulator-to-metal transition as
a function of both LaAlO<sub>3</sub> and WO<sub>3</sub> layer thickness.
Low-temperature magnetotransport reveals a strong magnetoresistance
reaching 900% at 10 T and 1.5 K, the presence of multiple conduction
channels with carrier mobility up to 80 000 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, and quantum oscillations of
conductance