2,738 research outputs found
Strongly enhanced effective mass in dilute two-dimensional electron systems: System-independent origin
We measure the effective mass in a dilute two-dimensional electron system in
(111)-silicon by analyzing temperature dependence of the Shubnikov-de Haas
oscillations in the low-temperature limit. A strong enhancement of the
effective mass with decreasing electron density is observed. The mass
renormalization as a function of the interaction parameter r_s is in good
agreement with that reported for (100)-silicon, which shows that the relative
mass enhancement is system- and disorder-independent being determined by
electron-electron interactions only.Comment: As publishe
Characteristics of ferroelectric-ferroelastic domains in N{\'e}el-type skyrmion host GaVS
GaVS is a multiferroic semiconductor hosting N{\'e}el-type magnetic
skyrmions dressed with electric polarization. At T = 42K, the compound
undergoes a structural phase transition of weakly first-order, from a
non-centrosymmetric cubic phase at high temperatures to a polar rhombohedral
structure at low temperatures. Below T, ferroelectric domains are formed
with the electric polarization pointing along any of the four axes. Although in this material the size and the shape of the
ferroelectric-ferroelastic domains may act as important limiting factors in the
formation of the N{\'e}el-type skyrmion lattice emerging below T=13\:K, the
characteristics of polar domains in GaVS have not been studied yet.
Here, we report on the inspection of the local-scale ferroelectric domain
distribution in rhombohedral GaVS using low-temperature piezoresponse
force microscopy. We observed mechanically and electrically compatible lamellar
domain patterns, where the lamellae are aligned parallel to the (100)-type
planes with a typical spacing between 100 nm-1.2 m. We expect that the
control of ferroelectric domain size in polar skyrmion hosts can be exploited
for the spatial confinement and manupulation of N{\'e}el-type skyrmions
Out of equilibrium electronic transport properties of a misfit cobaltite thin film
We report on transport measurements in a thin film of the 2D misfit Cobaltite
. Dc magnetoresistance measurements obey the modified
variable range hopping law expected for a soft Coulomb gap. When the sample is
cooled down, we observe large telegraphic-like fluctuations. At low
temperature, these slow fluctuations have non Gaussian statistics, and are
stable under a large magnetic field. These results suggest that the low
temperature state is a glassy electronic state. Resistance relaxation and
memory effects of pure magnetic origin are also observed, but without aging
phenomena. This indicates that these magnetic effects are not glassy-like and
are not directly coupled to the electronic part.Comment: accepted in Phys Rev B, Brief report
A Self-learning Nonlinear Variable Gain Proportional Derivative (PD) Controller in Robot Manipulators
This paper proposes a nonlinear variable gain Proportional-Derivative (PD) controller
that exhibits self-constructing and self-learning capabilities. In this method, the
conventional linear PD controller is augmented with a nonlinear variable PD gain control
signal using a dynamic structural network. The dynamic structural network known as
Growing Multi-Experts etwork grows in time by placing hidden nodes in regions of the
state space visited by the system during operation. This results in a network that is
"economic" in terms of network sileo The proposed approach enhances the adaptability
of conventional PD controller while preserving its' linear structure. Based on the
simulation study on variable load and friction compensation, the fast adaptation is shown
to be able to compensate the non-linearity and the uncertainty in the robotic system
Study of Magnetic Properties of A_2B^'NbO_6 (A=Ba,Sr, (BaSr): and B^'=Fe and Mn) double perovskites
We have studied the magnetic properties of Ba_2FeNbO_6 and Ba_2MnNbO_6. it is
seen that Ba_2FeNbO_6 is an antiferromagnet with a weak ferromagnetic behaviour
at 5K while Ba_2MnNbO_6 shows two magnetic transitions one at 45 K and the
other at 12K. Electron spin resonance (ESR) measurements at room temperature
show that the Mn compound does not show any Jahn-Teller distortion. It is also
seen that the Neel temperature of the A_2FeNbO_6 (A=Ba,Sr, BaSr) compounds do
not vary significantly. However variations in the average A-site ionic radius
influence the formation of short range correlations that persist above T_N.Comment: 10 oages, 5 figures, MMM, to appear in J.Appl.Phy
On the Electron-Electron Interactions in Two Dimensions
In this paper, we analyze several experiments that address the effects of
electron-electron interactions in 2D electron (hole) systems in the regime of
low carrier density. The interaction effects result in renormalization of the
effective spin susceptibility, effective mass, and g*-factor. We found a good
agreement among the data obtained for different 2D electron systems by several
experimental teams using different measuring techniques. We conclude that the
renormalization is not strongly affected by the material or sample-dependent
parameters such as the potential well width, disorder (the carrier mobility),
and the bare (band) mass. We demonstrate that the apparent disagreement between
the reported results on various 2D electron systems originates mainly from
different interpretations of similar "raw" data. Several important issues
should be taken into account in the data processing, among them the dependences
of the effective mass and spin susceptibility on the in-plane field, and the
temperature dependence of the Dingle temperature. The remaining disagreement
between the data for various 2D electron systems, on one hand, and the 2D hole
system in GaAs, on the other hand, may indicate more complex character of
electron-electron interactions in the latter system.Comment: Added refs; corrected typos. 19 pages, 7 figures. To be published in:
Chapter 19, Proceedings of the EURESCO conference "Fundamental Problems of
Mesoscopic Physics ", Granada, 200
Dynamic Behavior in Piezoresponse Force Microscopy
Frequency dependent dynamic behavior in Piezoresponse Force Microscopy (PFM)
implemented on a beam-deflection atomic force microscope (AFM) is analyzed
using a combination of modeling and experimental measurements. The PFM signal
comprises contributions from local electrostatic forces acting on the tip,
distributed forces acting on the cantilever, and three components of the
electromechanical response vector. These interactions result in the bending and
torsion of the cantilever, detected as vertical and lateral PFM signals. The
relative magnitudes of these contributions depend on geometric parameters of
the system, the stiffness and frictional forces of tip-surface junction, and
operation frequencies. The dynamic signal formation mechanism in PFM is
analyzed and conditions for optimal PFM imaging are formulated. The
experimental approach for probing cantilever dynamics using frequency-bias
spectroscopy and deconvolution of electromechanical and electrostatic contrast
is implemented.Comment: 65 pages, 15 figures, high quality version available upon reques
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