912 research outputs found
Mesoscopic magnetoelectric effect in chaotic quantum dots
The magnitude of the inverse Faraday effect (IFE), a static magnetization due
to an ac electric field, can be strongly increased in a mesoscopic sample,
sensitive to time-reversal symmetry (TRS) breaking. Random rectification of ac
voltages leads to a magnetization flux, which can be detected by an asymmetry
of Hall resistances in a multi-terminal setup. In the absence of applied
magnetic field through a chaotic quantum dot the IFE scale, quadratic in
voltage, is found as an analytic function of the ac frequency, screening, and
coupling to the contacts and floating probes, and numerically it does not show
any effect of spin-orbit interaction. Our results qualitatively agree with a
recent experiment on TRS-breaking in a six-terminal Hall cross.Comment: 4+ pages, 2 figures; v2-published version, small change
Relation among concentrations of incorporated Mn atoms, ionized Mn acceptors, and holes in p-(Ga,Mn)As epilayers
The amount of ionized Mn acceptors in various p-type Mn-doped GaAs epilayers
has been evaluated by electrochemical capacitance-voltage measurements, and has
been compared systematically with concentrations of incorporated Mn atoms and
holes for wide range of Mn concentration (10^17 ~ 10^21 cm^-3). Quantitative
assessment of anomalous Hall effect at room temperature is also carried out for
the first time.Comment: 8 pages, 4 figures, tabl
Optimized fabrication of high quality La0.67Sr0.33MnO3 thin films considering all essential characteristics
In this article, an overview of the fabrication and properties of high
quality La0.67Sr0.33MnO3 (LSMO) thin films is given. A high quality LSMO film
combines a smooth surface morphology with a large magnetization and a small
residual resistivity, while avoiding precipitates and surface segregation. In
literature, typically only a few of these issues are adressed. We therefore
present a thorough characterization of our films, which were grown by pulsed
laser deposition. The films were characterized with reflection high energy
electron diffraction, atomic force microscopy, x-ray diffraction, magnetization
and transport measurements, x-ray photoelectron spectroscopy and scanning
transmission electron microscopy. The films have a saturation magnetization of
4.0 {\mu}B/Mn, a Curie temperature of 350 K and a residual resistivity of 60
{\mu}{\Omega}cm. These results indicate that high quality films, combining both
large magnetization and small residual resistivity, were realized. A comparison
between different samples presented in literature shows that focussing on a
single property is insufficient for the optimization of the deposition process.
For high quality films, all properties have to be adressed. For LSMO devices,
the thin film quality is crucial for the device performance. Therefore, this
research is important for the application of LSMO in devices.Comment: Accepted for publication in Journal of Physics D - Applied Physic
Extraordinary Magnetoresistance in Hybrid Semiconductor-Metal Systems
We show that extraordinary magnetoresistance (EMR) arises in systems
consisting of two components; a semiconducting ring with a metallic inclusion
embedded. The im- portant aspect of this discovery is that the system must have
a quasi-two-dimensional character. Using the same materials and geometries for
the samples as in experiments by Solin et al.[1;2], we show that such systems
indeed exhibit a huge magnetoresistance. The magnetoresistance arises due to
the switching of electrical current paths passing through the metallic
inclusion. Diagrams illustrating the flow of the current density within the
samples are utilised in discussion of the mechanism responsible for the
magnetoresistance effect. Extensions are then suggested which may be applicable
to the silver chalcogenides. Our theory offers an excellent description and
explanation of experiments where a huge magnetoresistance has been
discovered[2;3].Comment: 12 Pages, 5 Figure
Generalized four-point characterization method for resistive and capacitive contacts
In this paper, a four-point characterization method is developed for
resistive samples connected to either resistive or capacitive contacts.
Provided the circuit equivalent of the complete measurement system is known
including coaxial cable and connector capacitances as well as source output and
amplifier input impedances, a frequency range and capacitive scaling factor can
be determined, whereby four-point characterization can be performed. The
technique is demonstrated with a discrete element test sample over a wide
frequency range using lock-in measurement techniques from 1 Hz - 100 kHz. The
data fit well with a circuit simulation of the entire measurement system. A
high impedance preamplifier input stage gives best results, since lock-in input
impedances may differ from manufacturer specifications. The analysis presented
here establishes the utility of capacitive contacts for four-point
characterizations at low frequency.Comment: 21 pages, 10 figure
Insulator-to-metal transition in sulfur-doped silicon
We observe an insulator-to-metal (I-M) transition in crystalline silicon
doped with sulfur to non- equilibrium concentrations using ion implantation
followed by pulsed laser melting and rapid resolidification. This I-M
transition is due to a dopant known to produce only deep levels at equilibrium
concentrations. Temperature-dependent conductivity and Hall effect measurements
for temperatures T > 1.7 K both indicate that a transition from insulating to
metallic conduction occurs at a sulfur concentration between 1.8 and 4.3 x
10^20 cm-3. Conduction in insulating samples is consistent with variable range
hopping with a Coulomb gap. The capacity for deep states to effect metallic
conduction by delocalization is the only known route to bulk intermediate band
photovoltaics in silicon.Comment: Submission formatting; 4 journal pages equivalen
Versatile and scalable fabrication method for laser-generated focused ultrasound transducers
A versatile and scalable fabrication method for laser-generated focused ultrasound transducers is proposed. The method is based on stamping a coated negative mold onto polydimethylsiloxane, and it can be adapted to include different optical absorbers that are directly transferred or synthesized in situ. Transducers with a range of sizes down to 3 mm in diameter are presented, incorporating two carbonaceous (multiwalled carbon nanoparticles and candle soot nanoparticles) and one plasmonic (gold nanoparticles) optically absorbing component. The fabricated transducers operate at central frequencies in the vicinity of 10 MHz with bandwidths in the range of 15–20 MHz. A transducer with a diameter of 5 mm was found to generate a positive peak pressure greater than 35 MPa in the focal zone with a tight focal spot of 150 μm in lateral width. Ultrasound cavitation on the tip of an optical fiber was demonstrated in water for a transducer with a diameter as small as 3 mm
Long-range nonlocal flow of vortices in narrow superconducting channels
We report a new nonlocal effect in vortex matter, where an electric current
confined to a small region of a long and sufficiently narrow superconducting
wire causes vortex flow at distances hundreds of inter-vortex separations away.
The observed remote traffic of vortices is attributed to a very efficient
transfer of a local strain through the one-dimensional vortex lattice, even in
the presence of disorder. We also observe mesoscopic fluctuations in the
nonlocal vortex flow, which arise due to "traffic jams" when vortex
arrangements do not match a local geometry of a superconducting channel.Comment: a slightly longer version of a tentatively accepted PR
Supramolecular copolymerization driven by integrative self-sorting of hydrogen-bonded rosettes.
Molecular recognition to preorganize noncovalently polymerizable supramolecular complexes is a characteristic process of natural supramolecular polymers, and such recognition processes allow for dynamic self-alteration, yielding complex polymer systems with extraordinarily high efficiency in their targeted function. We herein show an example of such molecular recognition-controlled kinetic assembly/disassembly processes within artificial supramolecular polymer systems using six-membered hydrogen-bonded supramolecular complexes (rosettes). Electron-rich and poor monomers are prepared that kinetically coassemble through a temperature-controlled protocol into amorphous coaggregates comprising a diverse mixture of rosettes. Over days, the electrostatic interaction between two monomers induces an integrative self-sorting of rosettes. While the electron-rich monomer inherently forms toroidal homopolymers, the additional electrostatic interaction that can also guide rosette association allows helicoidal growth of supramolecular copolymers that are comprised of an alternating array of two monomers. Upon heating, the helicoidal copolymers undergo a catastrophic transition into amorphous coaggregates via entropy-driven randomization of the monomers in the rosette
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