2,133 research outputs found
A Simple Method to Measure the Interaction Potential of Dielectric Grains in a Dusty Plasma
A simple minimally perturbative method is introduced which provides the
ability to experimentally measure both the radial confining potential and the
interaction potential between two individual dust particles, levitated in the
sheath of a radio-frequency (RF) argon discharge. In this technique, a single
dust particle is dropped into the plasma sheath to interact with a second
individual dust particle already situated at the system's equilibrium point,
without introducing any external perturbation. The resulting data is analyzed
using a method employing a polynomial fit to the particle displacement(s),
X(t), to reduce uncertainty in calculation. Employing this technique, the
horizontal confinement is shown to be parabolic over a wide range of pressures
and displacements from the equilibrium point. The interaction potential is also
measured and shown to be well-described by a screened Coulomb potential and to
decrease with increasing pressure. Finally, the charge on the particle and the
effective dust screening distance are calculated. It is shown for the first
time experimentally that the charge on a particle in the sheath of an RF plasma
decreases with increasing pressure, in agreement with theoretical predictions.
The screening distance also decreases with increasing pressure as expected.
This technique can be used for rapid determination of particle parameters in
dusty plasma
Two-Dimensional Topological Insulator State and Topological Phase Transition in Bilayer Graphene
We show that gated bilayer graphene hosts a strong topological insulator (TI)
phase in the presence of Rashba spin-orbit (SO) coupling. We find that gated
bilayer graphene under preserved time-reversal symmetry is a quantum valley
Hall insulator for small Rashba SO coupling , and
transitions to a strong TI when ,
where and are respectively the interlayer potential and tunneling
energy. Different from a conventional quantum spin Hall state, the edge modes
of our strong TI phase exhibit both spin and valley filtering, and thus share
the properties of both quantum spin Hall and quantum valley Hall insulators.
The strong TI phase remains robust in the presence of weak graphene intrinsic
SO coupling.Comment: 5 pages and 4 figure
Topological phases in gated bilayer graphene: Effects of Rashba spin-orbit coupling and exchange field
We present a systematic study on the influence of Rashba spin-orbit coupling,
interlayer potential difference and exchange field on the topological
properties of bilayer graphene. In the presence of only Rashba spin-orbit
coupling and interlayer potential difference, the band gap opening due to
broken out-of-plane inversion symmetry offers new possibilities of realizing
tunable topological phase transitions by varying an external gate voltage. We
find a two-dimensional topological insulator phase and a quantum valley
Hall phase in -stacked bilayer graphene and obtain their effective
low-energy Hamiltonians near the Dirac points. For stacking, we do not
find any topological insulator phase in the presence of large Rashba spin-orbit
coupling. When the exchange field is also turned on, the bilayer system
exhibits a rich variety of topological phases including a quantum anomalous
Hall phase, and we obtain the phase diagram as a function of the Rashba
spin-orbit coupling, interlayer potential difference, and exchange field.Comment: 15 pages, 17figures, and 1 tabl
A Combinatorial Approach to Robust PCA
We study the problem of recovering Gaussian data under adversarial
corruptions when the noises are low-rank and the corruptions are on the
coordinate level. Concretely, we assume that the Gaussian noises lie in an
unknown -dimensional subspace , and randomly
chosen coordinates of each data point fall into the control of an adversary.
This setting models the scenario of learning from high-dimensional yet
structured data that are transmitted through a highly-noisy channel, so that
the data points are unlikely to be entirely clean.
Our main result is an efficient algorithm that, when , recovers
every single data point up to a nearly-optimal error of in expectation. At the core of our proof is a new analysis of the
well-known Basis Pursuit (BP) method for recovering a sparse signal, which is
known to succeed under additional assumptions (e.g., incoherence or the
restricted isometry property) on the underlying subspace . In contrast, we
present a novel approach via studying a natural combinatorial problem and show
that, over the randomness in the support of the sparse signal, a
high-probability error bound is possible even if the subspace is arbitrary.Comment: To appear at ITCS 202
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