43,471 research outputs found
Semiconductor quantum dots in high magnetic fields: The composite-fermion view
We review and extend the composite fermion theory for semiconductor quantum
dots in high magnetic fields. The mean-field model of composite fermions is
unsatisfactory for the qualitative physics at high angular momenta. Extensive
numerical calculations demonstrate that the microscopic CF theory, which
incorporates interactions between composite fermions, provides an excellent
qualitative and quantitative account of the quantum dot ground state down to
the largest angular momenta studied, and allows systematic improvements by
inclusion of mixing between composite fermion Landau levels (called
levels).Comment: 13 pages, 8 figure
A Two-Step Etching Method to Fabricate Nanopores in Silicon
A cost effectively method to fabricate nanopores in silicon by only using the
conventional wet-etching technique is developed in this research. The main
concept of the proposed method is a two-step etching process, including a
premier double-sided wet etching and a succeeding track-etching. A special
fixture is designed to hold the pre-etched silicon wafer inside it such that
the track-etching can be effectively carried out. An electrochemical system is
employed to detect and record the ion diffusion current once the pre-etched
cavities are etched into a through nanopore. Experimental results indicate that
the proposed method can cost effectively fabricate nanopores in silicon.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/EDA-Publishing
Microwave-driven ferromagnet--topological-insulator heterostructures: The prospect for giant spin battery effect and quantized charge pump devices
We study heterostructures where a two-dimensional topological insulator (TI)
is attached to two normal metal (NM) electrodes while an island of a
ferromagnetic insulator (FI) with precessing magnetization covers a portion of
its lateral edges to induce time-dependent exchange field underneath via the
magnetic proximity effect. When the FI island covers both lateral edges, such
device pumps pure spin current in the absence of any bias voltage, thereby
acting as an efficient spin battery with giant output current even at very
small microwave power input driving the precession. When only one lateral edge
is covered by the FI island, both charge and spin current are pumped into the
NM electrodes. We delineate conditions for the corresponding conductances
(current-to-microwave-frequency ratio) to be quantized in a wide interval of
precession cone angles, which is robust with respect to weak disorder and can
be further extended by changes in device geometry.Comment: 7 pages, 7 color figures, PDFLaTe
Composite-fermionization of bosons in rapidly rotating atomic traps
The non-perturbative effect of interaction can sometimes make interacting
bosons behave as though they were free fermions. The system of neutral bosons
in a rapidly rotating atomic trap is equivalent to charged bosons coupled to a
magnetic field, which has opened up the possibility of fractional quantum Hall
effect for bosons interacting with a short range interaction. Motivated by the
composite fermion theory of the fractional Hall effect of electrons, we test
the idea that the interacting bosons map into non-interacting spinless fermions
carrying one vortex each, by comparing wave functions incorporating this
physics with exact wave functions available for systems containing up to 12
bosons. We study here the analogy between interacting bosons at filling factors
with non-interacting fermions at for the ground state
as well as the low-energy excited states and find that it provides a good
account of the behavior for small , but interactions between fermions become
increasingly important with . At , which is obtained in the limit
, the fermionization appears to overcompensate for the
repulsive interaction between bosons, producing an {\em attractive}
interactions between fermions, as evidenced by a pairing of fermions here.Comment: 8 pages, 3 figures. Submitted to Phys. Rev.
Directional emission from asymmetric resonant cavities
Asymmetric resonant cavities (ARCs) with highly non-circular but convex
cross-sections are predicted theoretically to have high-Q whispering gallery
modes with very anisotropic emission. We develop a ray dynamics model for the
emission pattern and present numerical and experimental confirmation of the
theory.Comment: 7 pages LaTeX, 3 postscript figure
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