Conductance Noise Research Articles

One-channel conductor coupled to a quantum of resistance: Exact ac conductance and finite-frequency noise

We consider a one-channel coherent conductor with a good transmission embedded into an Ohmic environment, the impedance of which is equal to the quantum of resistance ${R}_{q}=h/{e}^{2}$ below the $RC$ frequency. This choice is motivated by the mapping of this problem to a Tomonaga-Luttinger liquid with one impurity, the interaction parameter of which corresponds to the specific value $K=1/2$, allowing for a refermionization procedure. The ``new'' fermions have an energy-dependent transmission amplitude, which incorporates the strong correlation effects and yields the exact dc current and zero-frequency noise through expressions similar to those of the scattering approach. We recall and discuss these results for our present purpose. Then, we compute the finite-frequency differential conductance and the finite-frequency nonsymmetrized noise. Contrary to intuitive expectation, both can not be expressed within the scattering approach for the new fermions, even though they are still determined by the transmission amplitude. Even more, the finite-frequency conductance obeys an exact relation in terms of the dc current, which is similar to that derived perturbatively with respect to weak tunneling within the Tien-Gordon theory, and extended recently to arbitrary strongly interacting systems coupled eventually to an environment and/or with a fractional charge. We also show that the emission excess noise vanishes exactly above $eV$, even though the underlying Tomonaga-Luttinger liquid model corresponds to a many-body correlated system. Our results apply for all ranges of temperature, voltages, and frequencies below the $RC$ frequency, and they allow us to explore fully the quantum regime.

Analytical Integrate-and-Fire Neuron Models with Conductance-Based Dynamics and Realistic Postsynaptic Potential Time Course for Event-Driven Simulation Strategies

In a previous paper (Rudolph & Destexhe, 2006), we proposed various models, the gIF neuron models, of analytical integrate-and-fire (IF) neurons with conductance-based (COBA) dynamics for use in event-driven simulations. These models are based on an analytical approximation of the differential equation describing the IF neuron with exponential synaptic conductances and were successfully tested with respect to their response to random and oscillating inputs. Because they are analytical and mathematically simple, the gIF models are best suited for fast event-driven simulation strategies. However, the drawback of such models is they rely on a nonrealistic postsynaptic potential (PSP) time course, consisting of a discontinuous jump followed by a decay governed by the membrane time constant. Here, we address this limitation by conceiving an analytical approximation of the COBA IF neuron model with the full PSP time course. The subthreshold and suprathreshold response of this gIF4 model reproduces remarkably well the postsynaptic responses of the numerically solved passive membrane equation subject to conductance noise, while gaining at least two orders of magnitude in computational performance. Although the analytical structure of the gIF4 model is more complex than that of its predecessors due to the necessity of calculating future spike times, a simple and fast algorithmic implementation for use in large-scale neural network simulations is proposed.

Information Transmission in Cercal Giant Interneurons Is Unaffected by Axonal Conduction Noise

What are the fundamental constraints on the precision and accuracy with which nervous systems can process information? One constraint must reflect the intrinsic “noisiness” of the mechanisms that transmit information between nerve cells. Most neurons transmit information through the probabilistic generation and propagation of spikes along axons, and recent modeling studies suggest that noise from spike propagation might pose a significant constraint on the rate at which information could be transmitted between neurons. However, the magnitude and functional significance of this noise source in actual cells remains poorly understood. We measured variability in conduction time along the axons of identified neurons in the cercal sensory system of the cricket Acheta domesticus, and used information theory to calculate the effects of this variability on sensory coding. We found that the variability in spike propagation speed is not large enough to constrain the accuracy of neural encoding in this system.

Proposal and Verification of a Technique for Reducing Leakage Current Using Zero-Sequence Voltage

This paper proposes a technique for reducing the leakage current that flows into a power source as conductive noise. Output voltages of an inverter system consist of a d-axis voltage that generates a flux current, a q-axis voltage that generates a torque current, and a zero-sequence voltage. The zero-sequence voltage does not affect the driving characteristics of the load. The proposed method applies a zero-sequence voltage to the output voltage references in a circuit containing grounding capacitors. As a result, the fundamental frequency component of the zero-sequence voltage produced by the inverter decreases and the leakage current reduces. This allows a decrease in the size of the common-mode chokes. The leakage current can be reduced further by increasing the additional zero-sequence voltage reference. The experimental results show that the proposed method can reduce the leakage current when the zero-sequence voltage is applied.

Study on Soft Switching Technology to Reduce Electromagnetic Interference of PWM Inverter

To reduce the electromagnetic interference(EMI) of traditional PWM inverter, the paper puts forward a novel soft switching PWM inverter, expounds the inverter's configuration and working principle, analyses it's realization method, and validates it through simulation and experiment. The EMI conductive noise of AC inverter system was measured, analyzed and compared under hard switching and soft switching respectively. It testifies the validity of soft switching inverter on reducing EMI.

骨導雑音法におけるオープン型耳せんの使用と基準レベルの検討

骨導聴力検査で一側ごとの閾値の測定が困難な場合に骨導雑音法による測定が可能であるが, 較正の煩雑さ等から臨床検査として普及していない。本法の改良と普及促進を目的に, 本法で気導閾値測定に用いるイヤホンの装着にオープン型耳せんを用いることにより外耳道閉鎖効果の抑制を試み, 骨導雑音の基準レベルの推定値をもとに骨導雑音の客観較正を行い, 通常の骨導検査法と骨導雑音法により正常耳の骨導閾値を求め比較した。その結果, オープン型耳せん付きイヤホンの装着による有意な外耳道閉鎖効果はみられないことが確認された。骨導雑音の基準レベルは (基準等価閾値の力のレベル+4dB) に等しいと推定した。これに基く較正を行い骨導雑音法で測定した骨導閾値は, 通常の方法で得られた骨導閾値と平均値が5dB以内で一致した。以上より, 今回推定した基準レベルで較正した骨導雑音法による骨導閾値は, 通常の骨導閾値と等価であることが示唆された。

Electronic band gap and transport in Fibonacci quasi-periodic graphene superlattice

We investigate electronic band gap and transport in Fibonacci quasi-periodic graphene superlattice. It is found that such structure can possess a zero-k¯ gap which exists in all Fibonacci sequences. Different from Bragg gap, zero-k¯ gap associated with Dirac point is less sensitive to the incidence angle and lattice constants. The defect mode appeared inside the zero-k¯ gap has a great effect on transmission, conductance, and shot noise, which can be applicable to control the electron transport.

Electronic transport through side-contacted graphene nanoribbons: effects of overlap,aspect ratio and orientation

We numerically calculate the conductance and shot noise Fano factor of graphenenanoribbons (GNRs) side-contacted to metallic leads. A tight-binding model andLandauer’s formalism are used in combination with a modified recursion method forGreen’s functions. The interfaces are modeled as a contact region between aninfinite metallic electrode and a segment of the GNR put on top of it. The keyquestion to answer in this study is how the size and orientation of the GNR and theGNR/electrode interface area influence the transport properties. It turns out that ingeneral the transport characteristics depend strongly on overlap, meant as theratio between the electrode-supported GNR length and the unsupported one.Moreover, a speed of convergence (with the overlap length) depends on both thetransport direction and the aspect ratio of the GNR. It is shown that a shortoverlap interface is often, but not always, advantageous in nanoelectronics. Thesefindings reconcile some seemingly conflicting opinions reported in the literature.

Numerical analysis on thickness effect of magnetic thin films on conduction noise absorption in microstrip line

Noise absorbing properties of two kinds of magnetic thin films (one is electrically conductive Co-Zr-O granular thin film and the other is Ni-Zn ferrite thin film with high electrical resistivity) are analyzed by the finite element method (FEM) with various film thicknesses. For the Ni-Zn ferrite film with high electrical resistivity (∼2 × 10 2 Ωm), a low reflection parameter (S11) value is predicted, and the value does not significantly change with increased film thickness up to 10 μm. However, the transmission parameter (S21) is reduced with increased film thickness due to increased power absorption by magnetic loss. For the Co-Zr-O thin films with low electrical resistivity (∼1.6 × 10−5 Ωm), however, reflection signal is increased with increased film thickness due to diminished sheet resistance of the thin film. Transmission loss is not very sensitive to the thickness of the conductive film. Large power absorption is, therefore, predicted for conductive film of smaller thickness. It is concluded that film thickness is an important control parameter for the achievement of a highly absorptive thin film with increased electrical conductivity.

Anomalous Charge Tunneling in Fractional Quantum Hall Edge States at a Filling Factorν=5/2

We explain effective charge anomalies recently observed for fractional quantum Hall edge states at ν=5/2 [M. Dolev, Y. Gross, Y. C. Chung, M. Heiblum, V. Umansky, and D. Mahalu, Phys. Rev. B 81, 161303(R) (2010)]. The experimental data of differential conductance and excess noise are fitted, using the anti-Pfaffian model, by properly taking into account renormalizations of the Luttinger parameters induced by the coupling of the system with an intrinsic 1/f noise. We demonstrate that a peculiar agglomerate excitation with charge e/2, double the expected e/4 charge, dominates the transport properties at low energies.

Continuous production of glass-coated microwires and the applications for broadband noise suppression composite sheets

A system and a method were developed for continuous production of glass-coated microwires with controllable glass thickness and metallic core diameter. Fe–Si–Al flakes were fabricated by planetary ball milling using ethanol as a dispersant. A composite noise suppression sheet was prepared with glass-coated microwires combined with Fe–Si–Al flakes. The characteristics of the conduction noise suppression of the composite sheet were evaluated on a microstrip line in gigahertz frequencies. The conduction electromagnetic noise was effectively suppressed by the composite sheet in broad-band frequency region; the power loss is greater than 70% in the frequency range from 0.7 to 8.5GHz.

Two-level DC current power-exchange system based on structures with switched capacitors for autonomous power systems

A new method of constructing single- and multicycle power-exchange systems of autonomous DC current sources based on bilateral resonant-type DC voltage capacitor converters with high efficiency and low conductive pulse noise is considered. The specific features of the operation of exchange systems are studied and expressions for calculating their energy factors and the parameters of elements of the power circuit are obtained.

Conductance and shot noise in graphene superlattice

The conductance and the shot noise were investigated in graphene superlattice. A new Dirac point appears in the graphene superlattice and the position of the new Dirac point depends on the ratio of the width of the barriers to that of the wells. At the new Dirac point the conductance is minimum and the Fano factor reaches its max value 1/3. This Dirac point is robust against the magnetic field. In the energy window below the Dirac point, the magnetic field weakens the conductance but enhances the Fano factor.

Dark states in transport through triple quantum dots: The role of cotunneling

We analyze transport properties of coherent triple-quantum-dot systems in triangular geometry, weakly coupled to external leads. The real-time diagrammatic technique up to the second order is used to determine conductance and shot noise in the sequential tunneling and cotunneling regimes. In particular, we focus on the transport regime where the triple dot is trapped in a dark state and the system is in the interchannel Coulomb blockade, which leads to negative differential conductance. We show that although sequential transport is then exponentially suppressed, the blockade can be lifted by cotunneling processes. It is also shown that the shot noise in this transport regime is generally super-Poissonian, but the corresponding Fano factor is reduced when the cotunneling processes are included.

Effects of aspect ratio on permeability and power loss of the magnetic nanoparticle composites

The complex permeabilities of the permalloy nanorods and their composite in nonmagnetic matrix were calculated by the semi-empirical method. The mixture of nanorods with different aspect ratios exhibited the broadband frequency behaviors of the permeability. For the near-field conduction noise suppression applications, the electromagnetic wave absorption of the magnetic composite was evaluated by coplanar waveguide method. The permeability and the power loss effects of composite with the aspect ratios of nanorods were evaluated with the change of composite thickness.

Conduction Noise Absorption by Sn-O Thin Films on Microstrip Lines

Conduction Noise Absorption by Sn-O Thin Films on Microstrip Lines

Kondo effects and shot noise enhancement in a laterally coupled double quantum dot

The spin and orbital Kondo effects and the related shot noise for a laterally coupled double quantum dot are studied taking account of coherent indirect coupling via a reservoir. We calculate the linear conductance and shot noise for various charge states to distinguish between the spin and orbital Kondo effects. We find that a novel antiferromagnetic exchange coupling can be generated by the coherent indirect coupling, and it works to suppress the spin Kondo effect when each quantum dot holds just one electron. We also show that we can capture the feature of the pseudospin Kondo effect from the shot noise measurement.

Evidence of gate-tunable topological excitations in two-dimensional electron systems

We report experimental observations of a new mechanism of charge transport in two-dimensional electron systems (2DESs) in the presence of strong Coulomb interaction and disorder. We show that at low enough temperature the conductivity tends to zero at a nonzero carrier density, which represents the point of essential singularity in a Berezinskii-Kosterlitz-Thouless-like transition. Our experiments with many 2DESs in GaAs/AlGaAs heterostructures suggest that the charge transport at low carrier densities is due to the melting of an underlying ordered ground state through proliferation of topological defects. Independent measurement of low-frequency conductivity noise supports this scenario.

Quantized Conductance at the Majorana Phase Transition in a Disordered Superconducting Wire

Superconducting wires without time-reversal and spin-rotation symmetries can be driven into a topological phase that supports Majorana bound states. Direct detection of these zero-energy states is complicated by the proliferation of low-lying excitations in a disordered multimode wire. We show that the phase transition itself is signaled by a quantized thermal conductance and electrical shot noise power, irrespective of the degree of disorder. In a ring geometry, the phase transition is signaled by a period doubling of the magnetoconductance oscillations. These signatures directly follow from the identification of the sign of the determinant of the reflection matrix as a topological quantum number.

Conduction noise absorption by fiber-reinforced epoxy composites with carbon nanotubes

Nearly all electronic equipment is susceptible to malfunction as a result of electromagnetic interference. In this study, glass fiber, and carbon fiber as a type reinforcement and epoxy as a matrix material were used to fabricate composite materials. In an attempt to increase the conduction noise absorption, carbon nanotubes were grown on the surface of glass fibers and carbon fibers. A microstrip line with characteristic impedance of 50 Ω in connection with network analyzer was used to measure the conduction noise absorption. In comparing a glass fiber/epoxy composite with a GF-CNT/Ep composite, it was demonstrated that the CNTs significantly influence the noise absorption property mainly due to increase in electric conductivity. In the carbon fiber composites, however, the effectiveness of CNTs on the degree of electric conductivity is negligible, resulting in a small change in reflection and transmission of an electromagnetic wave.