Fowler-Nordheim electron tunneling under very intense electric field

In the context of the Fowler-Nordheim tunneling under an electric field of very high strength, electron velocity and drift mobility are calculated as functions of the above strength. In addition, carrier relaxation time is determined.     

A model for engineering the electrical conductance at nanoscale

With the emergence of nanoelectronics faster and denser circuits are being produced, this largely because the aggressive scaling to the nanometer range of the insulating film used as dielectric. Moreover, enhancements of the electrical conductivity of nanofiller based composites can be achieved by the incorporation of conductive nanofillers into polymer matrix. In such systems electron wave-function penetration into the dielectric is important as it leads to undesired or desired leakage currents by tunneling respectively. Therefore, a proper design of the electrical conductance in such structures becomes important in order to control accurately their performance. In this research, a model for engineering the electrical conductance of resistors at nanoscale is presented. The conductance at infinitesimal bias of nanoresistors is modeled within the framework of Landauer's tunneling which results in an exponential integral function for the total electrical conductance. Model takes the effects of azimuthal and inclination angles between nanocontacts into account, as well as the effect of the thickness of the dielectric layer. The model also unveils a U-shaped behavior of the electrical conductance as a function of the azimuthal angle between nanocontacts. As a result, a minimal electrical conductance is predicted when the azimuthal angle reaches 90°.     

Effect of bias voltage and electrodes size on the Pd conductance histograms

Conductance histograms of palladium nanocontacts in ultra high vacuum (UHV) were experimentally studied at room temperature using scanning tunneling microscope (STM). Our results show that the resolution of the pure Pd peaks, at 1.8 and around 3G₀, in the histograms, depends on the bias voltage and the electrodes size. The size of the electrodes should be as small as possible to achieve the higher extraction of hydrogen from them and therefore preventing the diffusion of H from the bulk to the nanocontacts during the conductance measurements, particularly at low bias voltage. This could explain why peaks have not been observed previously in the Pd histograms, using STM techniques in UHV.     

Size-dependent single electron tunneling effect in Au nanoparticles

We investigated single electron tunneling (SET) behavior of dodecanethiol-coated Au nanoparticles of two different sizes (average sizes are 5 nm and 2 nm) using nanogap electrodes, which have a well-defined gap size, at various temperatures. The Coulomb staircases and the Coulomb gap near-zero bias voltage caused by the suppression of the tunneling electrons due to the Coulomb blockade effect were observed in the current-voltage (I-V) curves of both sizes of nanoparticles at a low temperature (10 K). At room temperature, the Coulomb gap was observed only in the I-V curve of the smaller nanoparticles. This result indicates that the charging energy of the smaller nanoparticles is enough to overcome the thermal energy at room temperature. This suggests that it is possible to operate the SET devices at room temperature using the smaller nanoparticles as a Coulomb island.     

Dc conductance of ordered and disordered silicene superlattices

This paper studies the conductance of charge carriers through silicene-based superlattices consisting of monolayer silicene by means of transfer matrix method. At first, we consider the ordered superlattices and drive analytically the transmission probability of Dirac fermions. We show that the number of resonance picks increases with increasing the number of superlattice barriers. In order to the best understand of the appearance of the picks, we exactly studied transmission properties of the silicene superlattice. Also, the effect of disorder on the probability of transmission through the system of various sizes is studied. The short-range correlated disorder is applied on the thickness of electron doped silicene strips as quantum barriers which fluctuates around their mean values. We show that the oscillating conductance as a function of barriers hight suppresses with imposing the disorder in the silicene superlattice. Also, the effect of structural parameters on the conductance of the system is studied.     

量子线/绝缘层/p波超导体结的隧道谱

用Bogoliubov-de Gennes方程来研究量子线/绝缘层/p波超导体结(q/I/p)中的准粒子输运过程，利用推广的Blonder，Tinkham和Klapwijk模型计算绝对零度和有限温度下q/I/p的一级谐波隧道谱.和量子线/绝缘层/d波超导体结的一级谐波隧道谱不同的是q/I/p的一级谐波隧道谱中存在零偏压电导峰.随着q/I/p中绝缘层的势垒散射增强，q/I/p的一级谐波隧道谱中零偏压电导峰变高.     

正常金属/自旋三重态p波超导体结隧道谱的奇异性

利用Blonder，Tinkham和Klapwijk理论计算了正常金属/绝缘层/正常金属/自旋三重态的p波超导体结的隧道谱和平均电流.计算结果表明：在自旋三重态p波超导结的隧道谱中存在零偏压电导峰、零偏压电导凹陷和双凹陷结构，并有微分电导随偏压震荡的现象出现，在I-V曲线上出现电流台阶.这些结果在理论上支持Sr₂RuO₄的超导态是自旋三重态p波超导态. 关键词： 自旋三重态超导体 p波超导体 隧道谱     

石墨烯铁磁-绝缘层-超导结的输运

本文运用平均场模型的Dirac-Bogoliubov-de-Gennes方程和Bolonder-Tinkham-Klapwijk理论研究石墨烯铁磁-绝缘层-超导结的输运性质.研究表明:考虑有限宽度的绝缘层,隧穿电导-电压曲线呈现无衰减的振荡行为;同时隧穿电导随铁磁层中的交换能呈现非单调变化.对上述现象从石墨烯中类Dirac准粒子色散关系密切相关的电子散射过程予以解释.     

A brief semi-quantitative discussion on electrical conductance through resonant states in metallic electrochemical nanowires

Some aspects of electrical conduction through resonant states in metallic electrochemical nanowires are briefly discussed in a semi-quantitative way by means of concepts associated with electron gas, conductance quantization, and Fermi energy level. Aspects related to some experimental data are also discussed.     

Single-molecule conductance measurement of self-assembled organic monolayers using scanning tunneling spectroscopy in combination with statistics analysis

Based on ambient atmosphere scanning tunneling microscope (STM) technique, scanning tunneling spectroscopy (STS) combined with statistics analysis was developed to investigate the single-molecule conductance of various kinds of molecules which were self-assembled on the Au (1 1 1). Conductance histograms obtained from current-voltage curves revealed well-defined peaks at integer multiples of a fundamental conductance and were used to identify the conductance of a single molecule. The conductances of saturated molecules like 1,8-octanedithol and hexanethiocyanate were found to be 0.072 × 10⁻⁴G₀ and 0.06 × 10⁻⁴G₀ respectively and 0.23 × 10⁻⁴G₀ and 0.13 × 10⁻⁴G₀ for unsaturated molecules like 5,5′-dithiol- 2,2′,5′,2″-terthiophene and 4,4′-dithio-tert(phenylene ethylene).     

Zero bias conductance peak in InAs nanowire coupled to superconducting electrodes

We report the occurrence of the zero-bias conductance peak (ZBCP) in an InAs nanowire coupled to PbIn superconductors with varying temperature, bias voltage, and magnetic field. The ZBCP is suppressed with increasing temperature and bias voltage above the Thouless energy of the nanowire. Applying a magnetic field also diminishes the ZBCP when the resultant magnetic flux reaches the magnetic flux quantum h/2e. Our observations are consistent with theoretical expectations of reflectionless tunneling, in which the phase coherence between an electron and its Andreev-reflected hole induces the ZBCP as long as time-reversal symmetry is preserved.     

Single electron tunneling at large conductance: The semiclassical approach

We study the linear conductance of single electron devices showing Coulomb blockade phenomena. Our approach is based on a formally exact path integral representation describing electron tunneling nonperturbatively. The electromagnetic environment of the device is treated in terms of the Caldeira-Leggett model. We obtain the linear conductance from the Kubo formula leading to a formally exact expression which is evaluated in the semiclassical limit. Specifically we consider three models. First, the influence of an electromagnetic environment of arbitrary impedance on a single tunnel junction is studied focusing on the limits of large tunneling conductance and high to moderately low temperatures. The predictions are compared with recent experimental data. Second, the conductance of an array of N tunnel junctions is determined in dependence on the length N of the array and the environmental impedance. Finally, we consider a single electron transistor and compare our results for large tunneling conductance with experimental findings. Received 2 February 2000     

An atomic-molecular orbital formulation to determine electrical conductance of carbon

A brief theoretical study upon electrical conduction in both crystalline and amorphous carbon is carried out by means of atomic and molecular orbitals for determining firstly the local electronic density of states. From this density, the conductance of a carbon nanotube is evaluated as well as the corresponding current intensity.     

On particles tunneling from the Taub-NUT-AdS black hole

This paper discusses tunneling of scalar particles and Dirac particles from the Taub-NUT-AdS black hole by the Hamilton--Jacobi equation, initially used by Angheben et al, and the Dirac equation, recently proposed by Kerner and Mann. This is performed in the dragging coordinate frame so as to avoid the ergosphere dragging effect. A general form is obtained for the temperature of scalar and Dirac particles tunneling from the Taub-NUT-Ads black hole, which is commensurate with other methods as expected.     

Fermions tunneling from the Horowitz-Strominger Dilaton black hole

Based on the work of Kerner and Mann, fermions tunneling from the Horowitz-Strominger Dilaton black hole on the membrane is studied. Owing to the coupling among electromagnetic field, matter field and gravity field, the Dirac equation of charged particles is introduced, and according to that, the expected emission temperature is obtained. After the self-gravitational interaction is considered, it is found that the tunneling rate of fermions also satisfies the underlying Unitary theory as the case of scalar particles. Supported by the Natural Science Foundation of Sichuan Education Office (Grant No. 07ZC039)     

Determination of probe spacings for the precise evaluation of electrical characteristics of a magnetic tunnel junction by in-house current-in-plane tunneling measurements

Magnetic tunnel junctions have not been easily accessible for research because of not only their complicated fabrication processes but also side effects induced during the fabrication. The method utilizing arrays composed of in-line four-point probes with various spacings is promising as an alternative to the fabrication method. We found in the current-in-plane tunneling measurement that the determination of the probe spacing is the most important to evaluate the characteristics of magnetic tunnel junctions. Our simulation indicates that if one would choose at least more than three sets of an array with probe spacings centered at the spacing at which the maximum current-in-plane tunneling magnetoresistance is observed, the statistics should become improved resulting in the accurate evaluation of the properties of tunnel junctions. We also found that the suitable probe spacings with a change in the resistance of electrodes are not as sensitive as those with a change in the RA of the tunnel junction. Our results alert that the failure of selecting suitable probe spacings observes no tunneling signals because tunneling is very sensitive to the resistances of the tunnel junction and electrodes, which makes the current-in-plane tunneling method useless.     

Electrical conductance properties for magnetic tunnel junctions with MgO barriers

We measured inelastic electron tunneling (IET) spectra and conductance for MgO tunneling magnetoresistance (TMR) films to obtain information on the ferromagnetic/barrier layer interface. The IET spectra showed the difference between amorphous and crystalline structures in the barrier. In the magnetic tunnel junction (MTJ) with a crystalline barrier the IET spectra indicated an Mg-O phonon peak at a low bias voltage by measurement with a parallel magnetization configuration. On the other hand, no peak was observed in the MTJ with an amorphous barrier.     

Twofold spin-triplet pairing states and tunneling conductance in ferromagnet/ferromagnet/iron pnictide superconductor heterojunctions

By applying an extended eight-component Bogoliubov–de Gennes equation, we study theoretically the tunneling conductance in clean ferromagnet/ferromagnet/iron pnictide superconductor (FM/FM/iron-based SC) heterojunctions. Under the condition of noncollinear magnetizations, twofold novel Andreev reflections exist due to the existence of two bands in the SC, in which the incident electron and the two Andreev-reflected holes, belonging to the same spin subband, form twofold spin-triplet pairing states near the FM/iron-based SC interface. It is shown that the conversions of the conductance not only between the zero-bias peak and valley at zero energy but also between the peaks and dips at two gap energies are strongly dependent on both the interband coupling strength in the SC and the spin polarization in the FM. The qualitative differences from tunneling into a conventional s$s$-wave SC are also presented, which may help with experimentally probing and identifying the antiphase s$s$-wave pairing symmetry in the iron-based SC.     

The asymmetry of the tunneling time in type II semiconductor heterostructures

The tunneling time asymmetry in type II semiconductor heterostructures is related to the phase difference of the reflection coefficients for the two tunneling directions. Analytical expressions and numerical simulations are given for the difference between the left-to-right and right-to-left tunneling times in asymmetric, single and multiple barrier type II heterostructures.