1,499 research outputs found
Microwave shielding of transparent and conducting single-walled carbon nanotube films
The authors measured the transport properties of single-walled carbon
nanotube (SWCNT) films in the microwave frequency range from 10 MHz to 30 GHz
by using the Corbino reflection technique from temperatures of 20-400 K. Based
on the real and imaginary parts of the microwave conductivity, they calculated
the shielding effectiveness for various film thicknesses. Shielding
effectiveness of 43 dB at 10 MHz and 28 dB at 10 GHz are found for films with
90% optical transmittance, which suggests that SWCNT films are promising as a
type of transparent microwave shielding material. By combining their data with
those from the literature, the conductivity of SWCNT films was established in a
broad frequency range from dc to visible.Comment: 4 pages, 4 figure
Proposal for a Topological Plasmon Spin Rectifier
We propose a device in which the spin-polarized AC plasmon mode in the
surface state of a topological insulator nanostructure induces a static spin
accumulation in a resonant, normal metal structure coupled to it. Using a
finite-difference time-domain model, we simulate this spin-pump mechanism with
drift, diffusion, relaxation, and precession in a magnetic field. This
optically-driven system can serve as a DC "spin battery" for spintronic
devices.Comment: Eq. 1 corrected; Figs 3 and 4 update
Transport properties of quantum dots with hard walls
Quantum dots are fabricated in a Ga[Al]As-heterostructure by local oxidation
with an atomic force microscope. This technique, in combination with top gate
voltages, allows us to generate steep walls at the confining edges and small
lateral depletion lengths. The confinement is characterized by low-temperature
magnetotransport measurements, from which the dots' energy spectrum is
reconstructed. We find that in small dots, the addition spectrum can
qualitatively be described within a Fock-Darwin model. For a quantitative
analysis, however, a hard-wall confinement has to be considered. In large dots,
the energy level spectrum deviates even qualitatively from a Fock-Darwin model.
The maximum wall steepness achieved is of the order of 0.4 meV/nm.Comment: 9 pages, 5 figure
Transport properties of quantum dots with hard walls
Quantum dots are fabricated in a Ga[Al]As-heterostructure by local oxidation
with an atomic force microscope. This technique, in combination with top gate
voltages, allows us to generate steep walls at the confining edges and small
lateral depletion lengths. The confinement is characterized by low-temperature
magnetotransport measurements, from which the dots' energy spectrum is
reconstructed. We find that in small dots, the addition spectrum can
qualitatively be described within a Fock-Darwin model. For a quantitative
analysis, however, a hard-wall confinement has to be considered. In large dots,
the energy level spectrum deviates even qualitatively from a Fock-Darwin model.
The maximum wall steepness achieved is of the order of 0.4 meV/nm.Comment: 9 pages, 5 figure
Universal conductance fluctuations in Dirac materials in the presence of long-range disorder
We study quantum transport in Dirac materials with a single fermionic Dirac
cone (strong topological insulators and graphene in the absence of intervalley
coupling) in the presence of non-Gaussian long-range disorder. We show, by
directly calculating numerically the conductance fluctuations, that in the
limit of very large system size and disorder strength, quantum transport
becomes universal. However, a systematic deviation away from universality is
obtained for realistic system parameters. By comparing our results to existing
experimental data on 1/f noise, we suggest that many of the graphene samples
studied to date are in a non-universal crossover regime of conductance
fluctuations.Comment: 5 pages, 3 figures. Published versio
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