71 research outputs found
Charge Transport Transitions and Scaling in Disordered Arrays of Metallic Dots
We examine the charge transport through disordered arrays of metallic dots
using numerical simulations. We find power law scaling in the current-voltage
curves for arrays containing no voids, while for void-filled arrays charge
bottlenecks form and a single scaling is absent, in agreement with recent
experiments. In the void-free case we also show that the scaling exponent
depends on the effective dimensionality of the system. For increasing applied
drives we find a transition from 2D disordered filamentary flow near threshold
to a 1D smectic flow which can be identified experimentally using
characteristics in the transport curves and conduction noise.Comment: 4 pages, 4 postscript figure
Two-subband conduction in a gated high density InAlN/AlN/GaN heterostructure
Magnetotransport measurements on an In0.16Al0.84N/AlN/GaN gated Hall bar sample have been performed at 0.28 K. By the application of a gate voltage we were able to vary the total two-dimensional electron gas density from 1.83×1013 to 2.32×1013 cm−2. Two frequency Shubnikov–de Haas oscillations indicate occupation of two subbands by electrons. The density of electrons in the first and second sublevels are found to increase linearly with gate voltage with a slope of 2.01×1012 cm−2/V and 0.47×1012 cm−2/V, respectively. And the quantum lifetimes for the first and second subbands ranged from 0.55 to 0.95×10−13 s and from 1.2 to 2.1×10−13 s
Weak antilocalization and zero-field electron spin splitting in AlGaN/AlN/GaN heterostructures with a polarization induced two-dimensional electron gas
Spin-orbit coupling is studied using the quantum interference corrections to
conductance in AlGaN/AlN/GaN two-dimensional electron systems where the carrier
density is controlled by the persistent photoconductivity effect. All the
samples studied exhibit a weak antilocalization feature with a spin-orbit field
of around 1.8 mT. The zero-field electron spin splitting energies extracted
from the weak antilocalization measurements are found to scale linearly with
the Fermi wavevector with an effective linear spin-orbit coupling parameter
5.5x10^{-13} eV m. The spin-orbit times extracted from our measurements varied
from 0.74 to 8.24 ps within the carrier density range of this experiment.Comment: 16 pages, 4 figure
Temperature and ac Effects on Charge Transport in Metallic Arrays of Dots
We investigate the effects of finite temperature, dc pulse, and ac drives on
the charge transport in metallic arrays using numerical simulations. For finite
temperatures there is a finite conduction threshold which decreases linearly
with temperature. Additionally we find a quadratic scaling of the
current-voltage curves which is independent of temperature for finite
thresholds. These results are in excellent agreement with recent experiments on
2D metallic dot arrays. We have also investigated the effects of an ac drive as
well as a suddenly applied dc drive. With an ac drive the conduction threshold
decreases for fixed frequency and increasing amplitude and saturates for fixed
amplitude and increasing frequency. For sudden applied dc drives below
threshold we observe a long time power law conduction decay.Comment: 6 pages, 7 postscript figure
Quantum oscillations in Kondo Insulator SmB
In Kondo insulator samarium hexaboride SmB, strong correlation and band
hybridization lead to an insulating gap and a diverging resistance at low
temperature. The resistance divergence ends at about 5 Kelvin, a behavior
recently demonstrated to arise from the surface conductance. However, questions
remain whether and where a topological surface state exists. Quantum
oscillations have not been observed to map the Fermi surface. We solve the
problem by resolving the Landau Level quantization and Fermi surface topology
using torque magnetometry. The observed Fermi surface suggests a two
dimensional surface state on the (101) plane. Furthermore, the tracking of the
Landau Levels in the infinite magnetic field limit points to -1/2, which
indicates a 2D Dirac electronic state
Moving Wigner Glasses and Smectics: Dynamics of Disordered Wigner Crystals
We examine the dynamics of driven classical Wigner solids interacting with
quenched disorder from charged impurities. For strong disorder, the initial
motion is plastic -- in the form of crossing winding channels. For increasing
drive, the disordered Wigner glass can reorder to a moving Wigner smectic --
with the electrons moving in non-crossing 1D channels. These different dynamic
phases can be related to the conduction noise and I(V) curves. For strong
disorder, we show criticality in the voltage onset just above depinning. We
also obtain the dynamic phase diagram for driven Wigner solids and prove that
there is a finite threshold for transverse sliding, recently found
experimentally.Comment: 4 pages, 4 postscript figure
Shot noise suppression in multimode ballistic Fermi conductors
We have derived a general formula describing current noise in multimode
ballistic channels connecting source and drain electrodes with Fermi electron
gas. In particular (at ), the expression describes the
nonequilibrium ''shot'' noise, which may be suppressed by both Fermi
correlations and space charge screening. The general formula has been applied
to an approximate model of a 2D nanoscale, ballistic MOSFET. At large negative
gate voltages, when the density of electrons in the channel is small, shot
noise spectral density approaches the Schottky value , where
is the average current. However, at positive gate voltages, when the
maximum potential energy in the channel is below the Fermi level of the
electron source, the noise can be at least an order of magnitude smaller than
the Schottky value, mostly due to Fermi effects.Comment: 4 page
Weak-Localization in Chaotic Versus Non-Chaotic Cavities: A Striking Difference in the Line Shape
We report experimental evidence that chaotic and non-chaotic scattering
through ballistic cavities display distinct signatures in quantum transport. In
the case of non-chaotic cavities, we observe a linear decrease in the average
resistance with magnetic field which contrasts markedly with a Lorentzian
behavior for a chaotic cavity. This difference in line-shape of the
weak-localization peak is related to the differing distribution of areas
enclosed by electron trajectories. In addition, periodic oscillations are
observed which are probably associated with the Aharonov-Bohm effect through a
periodic orbit within the cavities.Comment: 4 pages revtex + 4 figures on request; amc.hub.94.
Degradation in InAlN/GaN-based heterostructure field effect transistors: Role of hot phonons
We report on high electric field stress measurements at room temperature on InAlN/AlN/GaN heterostructure field effect transistor structures. The degradation rate as a function of the average electron density in the GaN channel (as determined by gated Hall bar measurements for the particular gate biases used), has a minimum for electron densities around 1×1013 cm−2, and tends to follow the hot phonon lifetime dependence on electron density. The observations are consistent with the buildup of hot longitudinal optical phonons and their ultrafast decay at about the same electron density in the GaN channel. In part because they have negligible group velocity, the build up of these hot phonons causes local heating, unless they decay rapidly to longitudinal acoustic phonons, and this is likely to cause defect generation which is expected to be aggravated by existing defects. These findings call for modified approaches in modeling device degradation
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