Magnetotransport of coupled electron-holes

The carriers in InAs-GaSb double quantum wells are hybrid ``electron-holes''. We study the magnetotransport properties of such particles using a two-component Keldysh technique, which results in a semi-analytic expression for the small-field current. We show that zero temperature current can be large even when the Fermi energy lies within the hybridization gap, a result which cannot be understood within a semiclassical (Boltzmann) approach. Magnetic field dependence of the conductance is also affected significantly by the hybridization of electrons and holes.Comment: 4 pages, 2 figure

Excitonic instability and electric-field-induced phase transition towards a two dimensional exciton condensate

We present an InAs-GaSb-based system in which the electric-field tunability of its 2D energy gap implies a transition towards a thermodynamically stable excitonic condensed phase. Detailed calculations show a 3 meV BCS-like gap appearing in a second-order phase transition with electric field. We find this transition to be very sharp, solely due to exchange interaction, and so, the exciton binding energy is greatly renormalized even at small condensate densities. This density gradually increases with external field, thus enabling the direct probe of the Bose-Einstein to BCS crossover.Comment: LaTex, 11 pages, 3 ps figures, To appear in PR

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 $eV\gg k_{B}T$), 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 $S_{I}(0)$ approaches the Schottky value $2eI$, where $I$ 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

Shrinking limits of silicon MOSFET's: Numerical study of 10-nm-scale devices

We have performed numerical modeling of dual-gate ballistic n-MOSFET's with channel length of the order of 10 nm, including the effects of quantum tunneling along the channel and through the gate oxide. Our analysis includes a self-consistent solution of the full (two-dimensional) electrostatic problem, with account of electric field penetration into the heavily-doped electrodes. The results show that transistors with channel length as small as 8 nm can exhibit either a transconductance up to 4,000 mS/mm or gate modulation of current by more than 8 orders of magnitude, depending on the gate oxide thickness. These characteristics make the devices satisfactory for logic and memory applications, respectively, though their gate threshold voltage is rather sensitive to nanometer-scale variations in the channel length.Comment: 8 pages, 10 figures. Submitted to Special Issue of Superlattices and Microstructures: Third NASA Workshop on Device Modeling, August 199

Current noise in long diffusive SNS junctions in the incoherent MAR regime

Spectral density of current fluctuations at zero frequency is calculated for a long diffusive SNS junction with low-resistive interfaces. At low temperature, T << Delta, the subgap shot noise approaches linear voltage dependence, S=(2/ 3R)(eV + 2Delta), which is the sum of the shot noise of the normal conductor and voltage independent excess noise. This result can also be interpreted as the 1/3-suppressed Poisson noise for the effective charge q = e(1+2Delta/eV) transferred by incoherent multiple Andreev reflections (MAR). At higher temperatures, anomalies of the current noise develop at the gap subharmonics, eV = 2Delta/n. The crossover to the hot electron regime from the MAR regime is analyzed in the limit of small applied voltages.Comment: improved version, to be published in Phys. Rev.

What you know can influence what you are going to know (especially for older adults)

Stimuli related to an individual's knowledge/experience are often more memorable than abstract stimuli, particularly for older adults. This has been found when material that is congruent with knowledge is contrasted with material that is incongruent with knowledge, but there is little research on a possible graded effect of congruency. The present study manipulated the degree of congruency of study material with participants’ knowledge. Young and older participants associated two famous names to nonfamous faces, where the similarity between the nonfamous faces and the real famous individuals varied. These associations were incrementally easier to remember as the name-face combinations became more congruent with prior knowledge, demonstrating a graded congruency effect, as opposed to an effect based simply on the presence or absence of associations to prior knowledge. Older adults tended to show greater susceptibility to the effect than young adults, with a significant age difference for extreme stimuli, in line with previous literature showing that schematic support in memory tasks particularly benefits older adults