Tunable Kondo screening in a quantum dot device

We consider electron transport along a single-mode channel which is in contact, via tunnel junctions in its walls, with two quantum dots. Electron tunneling to and from the dots contributes to the electron backscattering, and thus modifies the channel conductance. If the dots carry spin, the channel conductance becomes temperature dependent due to the Kondo effect. The two-dot device geometry allows for a formation of S=1 localized spin due to the indirect exchange interaction, called Ruderman-Kittel-Kasuya-Yosida interaction. This device offers a possibility to study the crossover between fully screened and under-screened Kondo impurity. We investigate the manifestation of such crossover in the channel conductance

Method and apparatus for measurement of trap density and energy distribution in dielectric films

Trap densities in dielectric films are determined by tunnel injection measurements when the film is incorporated in an insulated-gate field effect transistor. Under applied bias to the transistor gate, carriers (electrons or holes) tunnel into traps in the dielectric film. The resulting space charge tends to change channel conductance. By feeding back a signal from the source contact to the gate electrode, channel conductance is held constant, and by recording the gate voltage as a function of time, trap density can be determined as a function of distance from the dielectric-semiconductor interface. The process is repeated with the gate bias voltage at different levels in order to determine the energy distribution of traps as a function of distance from the interface

U-shaped bilayer graphene channel transistor with very high Ion/Ioff ratio

A novel graphene transistor architecture is reported. The transistor has a U-shaped geometry and was fabricated using a gallium focused ion beam (FIB). The channel conductance was tuned with a back gate. The Ion/Ioff ratio exceeded 10E5

Investigation of the MOST channel conductance in weak inversion

The drain-source conductance of several MOS transistors has been studied as a function of the silicon surface-potential ψs in the weak and intermediate inversion region, under the condition of quasi-thermal equilibrium at room temperature. The silicon surface conductance per square ifG(in□ has been measured to vary exponentially with qψs/kT in weak inversion for excess minority carrier densities extending over the range 105-1011 cm−2. The exponential behaviour of G□ vs. qψs/kT appeared to be insensitive for the presence of interface states, when distributed around peak values as large (As) 6 × 1011/cm2 eV at ≈ 200 meV energy distance from midgap.\ud \ud Garrett and Brattain predicted theoretically that the excess minority carrier surface charge for weak inversion should also be an exponential function of qψs/kT, we conclude that the minority carrier mobility remains constant over the entire weak inversion region.\ud \ud A refined version of the low frequency CV method the so-called ‘split’ CV method has been introduced, which allows a simple determination of the charge trapped in interface states in weak and intermediate inversion as well as a determination of the bulk dope density

Single-channel measurements of an N-acetylneuraminic acid-inducible outer membrane channel in Escherichia coli

NanC is an Escherichia coli outer membrane protein involved in sialic acid (Neu5Ac, i.e., N-acetylneuraminic acid) uptake. Expression of the NanC gene is induced and controlled by Neu5Ac. The transport mechanism of Neu5Ac is not known. The structure of NanC was recently solved (PDB code: 2WJQ) and includes a unique arrangement of positively charged (basic) side chains consistent with a role in acidic sugar transport. However, initial functional measurements of NanC failed to find its role in the transport of sialic acids, perhaps because of the ionic conditions used in the experiments. We show here that the ionic conditions generally preferred for measuring the function of outer-membrane porins are not appropriate for NanC. Single channels of NanC at pH 7.0 have: (1) conductance 100 pS to 800 pS in 100 mM: KCl to 3 M: KCl), (2) anion over cation selectivity (V (reversal) = +16 mV in 250 mM: KCl || 1 M: KCl), and (3) two forms of voltage-dependent gating (channel closures above ±200 mV). Single-channel conductance decreases by 50% when HEPES concentration is increased from 100 ?M: to 100 mM: in 250 mM: KCl at pH 7.4, consistent with the two HEPES binding sites observed in the crystal structure. Studying alternative buffers, we find that phosphate interferes with the channel conductance. Single-channel conductance decreases by 19% when phosphate concentration is increased from 0 mM: to 5 mM: in 250 mM: KCl at pH 8.0. Surprisingly, TRIS in the baths reacts with Ag|AgCl electrodes, producing artifacts even when the electrodes are on the far side of agar-KCl bridges. A suitable baseline solution for NanC is 250 mM: KCl adjusted to pH 7.0 without buffer

Voltage-biased quantum wire with impurities

The bosonization technique to describe correlated electrons in a one-dimensional quantum wire containing impurities is extended to include an applied voltage source. The external reservoirs are shown to lead to a boundary condition for the boson phase fields. We use the formalism to investigate the channel conductance, electroneutrality, and charging effects.Comment: 4 pages REVTeX, incl one figure, to appear in Phys.Rev.Let

A Study of Free Surface and Viscous Effects on Simulated Rough Open Channel Beds

An experiment was designed to eliminate the free surface from simulated naturally roughened open channel beds from which results were compared to data with a free surface from another study. All other pertinent variables were held constant. From this comparison, a relationship was established for the additional energy loss due to the presence of a free surface in the flow over these channel beds.P = 0.23 - 0.28 D/D25where P is the proportion that the channel conductance coefficient (C/g1/2) is reduced due to presence of a free surface, D is the flow depth, K25 is a measurement of roughness height and D/K25is the relative roughness and was varied from 1 to 7. The channel conductance coefficient was found to be non-dependent upon Reynolds number. A parameter describing bed element spacing was identified as the ratio of vertical projected area of all bed elements to the total bed area, and was found to be constant for a particular channel bed. Roughness spacing had only a minor effect on the channel conductance parameter. The channel conductance coefficient was related to the relative roughness by a power function and the following prediction equation was established relating the channel conductance coefficient to the relative roughness and spacing parameter:C/g1/2 = 3.0 (D/K16)0.317 exp(0.007/θ)where D/K16 is the relative roughness and θ is the spacing parameter

Coulomb-Modified Fano Resonance in a One-Lead Quantum Dot

We investigate a tunable Fano interferometer consisting of a quantum dot coupled via tunneling to a one-dimensional channel. In addition to Fano resonance, the channel shows strong Coulomb response to the dot, with a single electron modulating channel conductance by factors of up to 100. Where these effects coexist, lineshapes with up to four extrema are found. A model of Coulomb-modified Fano resonance is developed and gives excellent agreement with experiment.Comment: related papers available at http://marcuslab.harvard.ed