Symmetry causes a huge conductance peak in double quantum dots

We predict a huge interference effect contributing to the conductance through large ultra-clean quantum dots of chaotic shape. When a double-dot structure is made such that the dots are the mirror-image of each other, constructive interference can make a tunnel barrier located on the symmetry axis effectively transparent. We show (via theoretical analysis and numerical simulation) that this effect can be orders of magnitude larger than the well-known universal conductance fluctuations and weak-localization (both less than a conductance quantum). A small magnetic field destroys the effect, massively reducing the double-dot conductance; thus a magnetic field detector is obtained, with a similar sensitivity to a SQUID, but requiring no superconductors.Comment: 5pages 3 figures and an appendix ONLY in arXiv versio

Plásticos biodegradáveis: perspectivas de uso.

bitstream/item/89901/1/Proci-07.00259.pd

Plásticos biodegradáveis.

bitstream/item/88178/1/2340001.pd

Geometry-dependent conductance and noise behavior of a graphene ribbon with a series of randomly spaced potential barriers

We perform an envelope-function based numerical analysis of the effect of a sequence of randomly spaced potential barriers on the conductance and shot noise of an armchair graphene ribbon. The behavior is dominated by Klein tunneling and by resonant tunneling and strongly depends on the geometrical details of the device. Klein tunneling effectively filters the modes that can propagate through the device. For a large number of cascaded barriers, this gives rise to different transport regimes for metallic and semiconducting ribbons, with diverging shot noise behaviors. Resonant tunneling is instead energy selective and has quite a different effect depending on whether the barriers are identical or not. We also explore the effect of tilting the barriers with respect to the ribbon edges, observing a transition toward a diffusive transport regime and a one-third shot noise suppression. We investigate this effect, and we find that it takes place also in more traditional semiconducting materials. The results of our analysis could be instrumental for the fabrication of mode-filtering and energy-filtering graphene-based nanodevices. Moreover, our study highlights the importance of the measurement of shot noise as a probe for the nature of the transport regime

Estudo da incorporação de nanosilica em termoplásticos vulcanizados.

PÁGINA 438 EM BRANCO

Termogravimetria de cascas de arroz.

bitstream/CNPDIA-2009-09/11065/1/CT89_2007.pd