Current-distance-voltage characteristics of electron tunneling through an electrochemical STM junction

We have studied the electron tunneling process through an electrochemical scanning tunneling microscopic (STM) junction formed by a gold tip and a gold electrode immersed in an inert NaClO₄ solution. Current-distance-voltage characteristics of the tunneling process are examined by simultaneous measurement of tunneling current, voltage, and distance. The results indicate that the tunneling voltage across the junction changes with tunneling distance; however, tunneling conductance is an inverse exponential function of distance over the entire investigated range of tunneling current, voltage, and distance. The results provide clear evidence for the validity of a one-dimensional tunneling model for the aqueous tunneling process. Implications of the observation are mentioned with regard to the distance-dependent STM imaging and the origin of a low tunneling barrier height.     

High-fidelity resonant tunneling passage in three-waveguide system

An N-stage three-waveguide system is proposed to improve the robustness and the fidelity of the resonant tunneling passage.The analytic solutions to the tunneling dynamics at the output are derived.When the number of subsystems increases,tunneling efficiency approaches to 100%in a large range and resonant tunneling is robust against variations in the phase mismatch and peak tunneling rate.     

Spatial effects of Fano resonance in local tunneling conductivity in vicinity of impurity on semiconductor surface

We present the results of local tunneling conductivity spatial distribution detailed theoretical investigations in vicinity of impurity atom for a wide range of applied bias voltage. We observed Fano resonance in tunneling conductivity resulting from interference between resonant tunneling channel through impurity energy level and direct tunneling channel between the tunneling contact leads. We have found that interference between tunneling channels strongly modifies form of tunneling conductivity measured by the scanning tunneling microscopy/spectroscopy (STM/STS) depending on the distance value from the impurity.     

Effect of frequency dependent electron-electron interaction on resonant tunneling

In electron resonant tunneling through a double barrier structure, we show that dynamical electron-electron interactions in the resonant well can give rise to additional tunneling satellites due to collective electronic excitations. We present a first principle treatment for frequency-dependent electron-electron interactions in the resonant tunneling problem. The result confirms the previously proposed plasmon assisted resonant tunneling mechanism. We also find that the particle-hole excitation has very little effect on resonant tunneling. Our result can be applied to study the effects of various electronic excitations on the resonant tunneling of electrons.     

Convergent expansions for tunneling

A new method to compute effects of tunneling in one-dimensional multiple well is developed. A tunneling parameter built with physical quantities is introduced to measure the splitting between eigenvalues due to tunneling. These splittings are given by convergent series in term of this tunneling parameter for a wide class of double well.     

Theory of single molecule vibrational spectroscopy and microscopy

We have carried out a density functional study of vibrationally inelastic tunneling in the scanning tunneling microscope of acetylene on copper. Our approach is based on a many-body generalization of the Tersoff-Hamann theory. We explain why only the carbon-hydrogen stretch modes are observed in terms of inelastic and elastic contributions to the tunneling conductance. The inelastic tunneling is found to be efficient and highly localized in space without any resonant interaction and to be governed by a vibration-induced change in tunneling amplitude.     

Transient tunneling spectroscopy (TTS) study of electron tunneling from phosphorus atoms in silicon

Recently developed method of transient tunneling spectroscopy (TTS) is applied to investigate the tunneling dynamics of electrons from phosphorus atoms to the silicon conduction band. In contrast to the conventional constant-current spectroscopic tunneling techniques, in TTS one monitors the evolution of the tunneling process in time. Various difficulties, which may be encountered in the measurements of the tunneling time by TTS, are discussed and illustrated. The temperature dependence of the tunneling time for an isolated phosphorus atom is presented, and possible mechanisms responsible for the decrease of the tunneling time with the lattice temperature T, at T15 K, are discussed.     

Double tunneling: An overlooked quantum effect in anionic molecular clusters

Simultaneous tunneling of an electron and nuclei in hydrogen-bonded molecular clusters which support a dipole bound electron is reported. A whole class of systems including hydrogen halide and water dimer anions is predicted to exhibit this effect. A measurable signature of double tunneling is a strong reduction of the tunneling splitting compared to the neutral cluster. Quantum mechanical calculations give for the hydrogen fluoride dimer anion a ground-state tunneling splitting of 114 MHz, while for the first excited vibrational state the tunneling splitting reaches 4.20 GHz.     

Resonant tunneling through double-barrier structures on graphene

Quantum resonant tunneling behaviors of double-barrier structures on graphene are investigated under the tightbinding approximation. The Klein tunneling and resonant tunneling are demonstrated for the quasiparticles with energy close to the Dirac points. The Klein tunneling vanishes by increasing the height of the potential barriers to more than 300 meV. The Dirac transport properties continuously change to the Schro¨dinger ones. It is found that the peaks of resonant tunneling approximate to the eigen-levels of graphene nanoribbons under appropriate boundary conditions. A comparison between the zigzag- and armchair-edge barriers is given.     

Few-boson dynamics in double wells: from single-atom to correlated pair tunneling

We investigate few-boson tunneling in a one-dimensional double well, covering the full crossover from weak interactions to the fermionization limit of strong correlations. Based on exact quantum-dynamical calculations, it is found that the tunneling dynamics of two atoms evolves from Rabi oscillations to correlated pair tunneling as we increase the interaction strength. Near the fermionization limit, fragmented-pair tunneling is observed and analyzed in terms of the population imbalance and two-body correlations. For more atoms, the tunneling dynamics near fermionization is shown to be sensitive to both atom number and initial configuration.     

Level width of a quasibound state in a double-barrier parabolic-well resonant tunneling structure

Taking exact Airy functions and Hermitian functions as envelope functions, we investigate in detail the level width of a quasibound state for electrons coherent resonant tunneling through symmetric and asymmetric double-barrier parabolic-well resonant tunneling structures (DBRT) with the transfer-matrix formalism. It is found that for the symmetric structure and the asymmetric structure with left barrier thicker than the right one, both the level width and the peak value vary monotonously with increasing applied bias, but for the asymmetric DBRT structure with left barrier thinner than the right one, they change nonmonotonously. The nonmonotonous variations of the level width and the peak value reflect the transition of tunneling type (i.e. first from incompletely resonant tunneling to completely resonant tunneling, and then from completely resonant tunneling back to incompletely resonant tunneling). The effects of well width, barrier thickness and barrier height on the level width and the peak value are also inspected.     

Effects of static and random magnetic fields on atoms in a gray optical lattice

We study magnetic field-induced modifications of the well-to-well tunneling behavior of atoms in a one-dimensional grey optical lattice. Measurements of the tunneling frequency as a function of the applied magnetic field reveal several tunneling resonances. We further show that the tunneling signal can be suppressed by randomly varying the symmetry of the potential wells. The tunneling is suppressed most effectively if the autocorrelation time of the lattice-well variation is on the order of the tunneling time. Experimental and theoretical results are in good agreement.     

Tunneling Dynamics of Two-Species Bose-Einstein Condensates with Feshbach Resonances

We investigate tunneling dynamics of atomic group consisting of three atoms in Bose-Einstein condensateswith Feshbach resonance. It is shown that the tunneling of the atom group depends not only on the inter-atomicnonlinear interactions and the initial number of atoms in these condensates, but also on the tunneling coupling betweenthe atomic condensate and the three-atomic molecular condensate. It is found that besides oscillating tunneling currentbetween the atomic condensate and the molecular condensate, the nonlinear atomic group tunneling dynamics sustains aself-maintained population imbalance: a macroscopic quantum self-trapping effect. The influence of de-coherence causedby non-condensate atoms on the tunneling dynamics is studied. It is indicated that de-coherence suppresses the atomicgroup tunneling.     

Features of the tunneling of a system with an internal degree of freedom through a potential barrier

The tunneling of a quantum system with an internal degree of freedom through a potential barrier is considered. Based on the exact numerical solution to the nonstationary Schrödinger equation, the tunneling of a model two-particle system through a potential barrier is studied and the dependences of the tunneling transparency of the barrier on the parameters of the wave packet that describes the system at the initial moment are obtained. A sharp increase in the tunneling probability related to the formation of a long-lived quasibound state of the system in the barrier region is demonstrated. A simple analytical model of the tunneling of a system with an internal degree of freedom that allows for a qualitative interpretation of the main features of the tunneling is constructed.     

Andreev and single-particle tunneling spectra of underdoped cuprate superconductors

We study tunneling spectroscopy between a normal metal and an underdoped cuprate superconductor modeled by a phenomenological theory in which the pseudogap is a precursor to the undoped Mott insulator. In the low barrier tunneling limit, the spectra are enhanced by Andreev reflection only within a voltage region of the small superconducting energy gap. In the high barrier tunneling limit, the spectra show a large energy pseudogap associated with single particle tunneling. Our theory semiquantitatively describes the two gap behavior observed in tunneling experiments.     

Quasi-distribution of tunneling time

Using real time Feynman histories, a quasi-distribution of tunneling time Q(τ) is introduced. For the tunneling time of resident time type, an explicit expression for Q is shown for square barriers. Q becomes oscillatory as the barrier becomes opaque. Some well-known tunneling times fall within the range of τ where Q takes non-negligible values. The formal “average” and the “variance” of the tunneling time are found to be related to known tunneling times. It is thus demonstrated that the quasi-distribution extracts the temporal information about tunneling from real time Feynman histories.     

含单负介质层受阻全内反射结构的光子隧穿现象研究

利用稳定相位理论得到了光子穿越含单负介质层受阻全内反射结构的隧穿时间以及光子穿透光学势垒后产生的横向位移.分析结果表明，当势垒为单负介质时，光子隧穿可能表现出负的隧穿时间和负的横向位移.隧穿时间和横向位移存在Hartman效应，使得光子隧穿过程具有超光速性质.此外，基于TM波和TE波通过负介电常数介质和负磁导率介质势垒产生的横向位移的方向正好相反，得到了一种有效的区分两类单负介质的方法. 关键词： 光子隧穿 负折射 单负介质 超光速     

Tunneling Dynamics of Two-Species Bose-Einstein Condensates with Feshbach Resonances

We investigate tunneling dynamics of atomic group consisting of three atoms in Bose-Einstein condensates with Feshbach resonance. It is shown that the tunneling of the atom group depends not only on the inter-atomic nonlinear interactions and the initial number of atoms in these condensates, but also on the tunneling coupling between the atomic condensate and the three-atomic molecular condensate. It is found that besides oscillating tunneling current between the atomic condensate and the molecular condensate, the nonlinear atomic group tunneling dynamics sustains a self-maintained population imbalance: a macroscopic quantum self-trapping effect. The influence of de-coherence caused by non-condensate atoms on the tunneling dynamics is studied. It is indicated that de-coherence suppresses the atomic group tunneling.     

Effects of barrier fluctuation on the tunneling dynamics in the presence of classical chaos in a mixed quantum-classical system

We present a numerical investigation of the tunneling dynamics of a particle moving in a bistable potential with fluctuating barrier which is coupled to a non-integrable classical system and study the interplay between classical chaos and barrier fluctuation in the tunneling dynamics. We found that the coupling of the quantum system with the classical subsystem decreases the tunneling rate irrespective of whether the classical subsystem is regular or chaotic and also irrespective of the fact that whether the barrier fluctuates or not. Presence of classical chaos always enhances the tunneling rate constant. The effect of barrier fluctuation on the tunneling rate in a mixed quantum-classical system is to suppress the tunneling rate. In contrast to the case of regular subsystem, the suppression arising due to barrier fluctuation is more visible when the subsystem is chaotic.      

半导体量子器件物理讲座第四讲 共振隧穿器件及其电路应用

当一个电子的能量低于势垒高度时,它仍可以隧穿通过势垒,在一定条件下,双势垒结构中电子的隧穿几率甚至可以接近1,利用这种共振隧穿现象可以做成共振隧穿二极管,它的电流－电压特性曲线中会出现负微分电阻,利用这种负阻效应可以做成高频振荡器和倍频器等电子器件,双势垒结构与通常的双极晶体管结合可以做成共振隧穿双极晶体管,它们可以用来做成多态记忆器和模数转换器等器件。