Photon-assisted shot noise due to the charging effect in a quantum dot device

We have investigated the spectral density of shot noise for an ultra-small quantum dot(QD) system in the Coulomb blockade regime when irradiated with microwave fields (MWFs) by employing a nonequilibrium Green’s function technique. The shot noise is sensitive to Coulomb interaction, and the photon-assisted Coulomb blockade behaviour strongly modifies the mesoscopic transport. We have calculated the first and second derivatives of shot noise in the strong and weak coupling regimes to compare the theoretical results with existing experimental results. In the strong coupling regime, the first and second derivatives of shot noise display Fano type peak-valley structures around the charging channel 2E _c due to Coulomb interaction. When the magnitudes of the MWFs are sufficiently large, the system displays channel blockade due to photon irradiation. The photon-assisted and Coulomb blockade steps in the noise — as well as the resonant behaviour in the differential noise — are smeared by increasing temperature. The Coulomb interaction suppresses the shot noise, but the ac fields can either suppress the shot noise(balanced case) or enhance the shot noise(unbalanced case). The suppression of shot noise caused by ac fields in the balanced case is greater than that caused by Coulomb interaction in our system. Super-Poissonian shot noise may be induced due to the compound effects of strong Coulomb interaction and photon absorption-emission processes.     

准弹道输运纳米MOSFET散粒噪声的抑制研究

目前研究准弹道输运纳米MOSFET散粒噪声的抑制时, 采取了完全不考虑其抑制, 或只强调抑制的存在而并未给出抑制公式的方式进行研究. 本文基于Navid模型推导了准弹道输运纳米MOSFET散粒噪声, 并得到了其在费米作用、库仑作用和二者共同作用三种情形下的抑制因子. 在此基础上, 对各抑制因子随源漏电压、栅极电压、温度及源漏掺杂浓度的变化特性进行了研究. 两者共同作用的抑制因子随源漏电压和栅极电压变化特性与文献中给出的实验结论相符合, 从而对实验上得到两者共同作用下的抑制因子随源漏电压和栅极电压的变化特性给出了理论解释.     

Coulomb blockade without potential barriers

We study transport through a strongly correlated quantum dot and show that Coulomb blockade can appear even in the presence of perfect contacts. This conclusion arises from numerical calculations of the conductance for a microscopic model of spinless fermions in an interacting chain connected to each lead via a completely open channel. The dependence of the conductance on the gate voltage shows well defined Coulomb blockade peaks which are sharpened as the interaction strength is increased. Our numerics is based on the embedding method and the DMRG algorithm. We explain the emergence of Coulomb blockade with perfect contacts by a reduction of the effective coupling matrix elements between many-body states corresponding to successive particle numbers in the interacting region. A perturbative approach, valid in the strong interaction limit, yields an analytic expression for the interaction-induced suppression of the conductance in the Coulomb blockade regime.     

Coulomb interaction and quantum transport through a coherent scatterer

An interplay between charge discreteness, coherent scattering, and Coulomb interaction yields nontrivial effects in quantum transport. We derive a real-time effective action and an equivalent quantum Langevin equation for an arbitrary coherent scatterer and evaluate its current-voltage characteristics in the presence of interactions. Within our model, at large conductances G0 and low T (but outside the instanton-dominated regime), the interaction correction to G0 saturates and causes conductance suppression by a universal factor which depends only on the type of the conductor.     

Different behaviour of local tunneling conductivity for deep and shallow impurities due to Coulomb interaction

Spatial distribution of local tunneling conductivity was investigated for deep and shallow impurities on semiconductor surfaces. Non-equilibrium Coulomb interaction and interference effects were taken into account and analyzed theoretically with the help of Keldysh formalism. Two models were investigated: mean field self-consistent approach for shallow impurity state and Hubbard-I model for deep impurity state. We have found that not only above the impurity but also at the distances comparable to the lattice period both effects interference between direct and resonant tunneling channels and on-site Coulomb repulsion of localized electrons strongly modifies form of tunneling conductivity measured by the scanning tunneling microscopy/spectroscopy (STM/STS).     

Nonlocal composite spin-lattice polarons in high temperature superconductors

The nonlocal nature of the polaron formation in t - t '- t' - J model is studied in large lattices up to 64 sites by developing a new numerical method. We show that the effect of longer-range hoppings t' and t' is a large anisotropy of the electron-phonon interaction (EPI) leading to a completely different influence of EPI on the nodal and antinodal points in agreement with the experiments. Furthermore, nonlocal EPI preserves polaron's quantum motion, which destroys the antiferromagnetic order effectively, even in the strong coupling regime, although the quasiparticle weight in angle-resolved-photoemission spectroscopy is strongly suppressed.     

Full current statistics in the regime of weak coulomb interaction

We evaluate the full statistics of the current via a Coulomb island that is strongly coupled to the leads. This strong coupling weakens Coulomb interaction. We show that in this case the effects of the interaction can be incorporated into the renormalization of transmission eigenvalues of the scatterers that connect the island and the leads. We evaluate the Coulomb blockade gap in the current-voltage characteristics, the value of the gap being exponentially suppressed as compared to the classical charging energy of the island.     

Instabilities in Yukawa Liquids

A strongly coupled Yukawa liquid is a system of charged particles which interact via a screened Coulomb interaction and in which the electrostatic energy between neighboring particles is larger than their thermal energy but not large enough for crystallization. Various plasma systems including ultracold neutral plasmas and complex (dusty) plasmas can exist in this strongly coupled liquid phase.Here we investigate instabilities driven by the relative streaming of plasma components in three‐dimensional Yukawa liquids with a focus on complex plasmas. This includes a dust acoustic instability driven by weakly coupled ions streaming through the dust liquid, and a dust‐dust instability driven by the counter‐streaming of strongly coupled dust grains. Compared to the Vlasov behavior we find there can be a substantial modification of the unstable wavenumber spectrum due to strong coupling effects (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nuclear matter incompressibility effect on the cross-section of fusion reactions with a weakly bound projectile

Fusion reactions with a weakly bound projectile are studied using the double-folding model along with a repulsive interaction modifying term.Using this modified potential,including nuclear matter incompressibility effects,the fusion reaction cross sections and suppression parameters are calculated for9Be+209Bi,208Pb,29Si and27Al reactions.The results show that applying these effects at energies near the Coulomb barrier improves the agreement between the calculated and experimental cross sections,and modifies the mean values of the suppression parameter.     

Coulomb interaction during coherent transport of electrons in quantum wires

A model is found whereby the Coulomb interaction during electron transport in quantum wires of finite length with current-lead contacts can be taken into account exactly (within the framework of the bosonization method). It is established that the charge density distribution along a wire in the case of the real Coulomb interaction is strongly different from the Luttinger liquid model, where the interaction is assumed to be short-ranged. The charge density near the contacts is found to be much higher than in the model with a short-range interaction, but away from the contacts the two densities are closer to each other. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 3, 184–189 (10 February 1998)     

Hund and pair-hopping signatures in transport properties of degenerate nanoscale devices

We investigate the signature of a complete Coulomb interaction in transport properties of double-orbital nanoscale devices. We analyze the specific effects of Hund exchange and pair hopping terms, calculating in particular stability diagrams. It turns out that a crude model, with partial Coulomb interaction, may lead to a misinterpretation of experiments. In addition, it is shown that spectral weight transfers induced by gate and bias voltages strongly influence charge current. The low temperature regime is also investigated, displaying inelastic cotunneling associated with the exchange term, as well as Kondo conductance enhancement.     

Andreev reflection current through a molecule quantum dot in the presence of the electron-phonon interaction and the spin-flip scattering

With the aid of the nonequilibrium Green's function and the Lang-Firsov canonical transformation, we investigate the joint effects of a phononic environment and the spin-flip scattering on the Andreev reflection (AR) in a ferromagnet/single-molecular quantum dot/superconductor (FM/MQD/SC) system. In the presence of the strong electron-phonon interaction (EPI), it is found that the EPI strongly suppresses the AR current (called the Franck-Condon blockade). When the coherent spin-flip (similar to a transverse magnetic field) is taken into account within the MQD, the AR current is significantly enhanced, furthermore, the spin-polarized AR current or even the pure spin-polarized AR current can be generated. By tuning the system parameters, the amplitude and direction of the AR current can be changed, this provides an efficient mechanism for controlling the AR process.     

Antiferromagnetic spin glass in doped Ge near insulator-metal transition

A low-temperature (3–100 K) electron spin resonance (ESR) study of the spin system of neutral As donors in Ge showed that on the insulator side of the insulator-metal transition the single-spin density exponentially disappears as T → 0. Such spins are bound into pairs to give an antiferromagnetic (AF) phase. Upon increasing the temperature the AF phase is destroyed, the single-spin density and, as a result, the ESR absorption signal becomes stronger. The temperature dependences of the densities of the pairs and single spins are typical for a chaotic distribution of neutral donors. In this case, there is no Néel temperature. For a low degree of compensation, the crystal lattice of Ge with the AF phase is actually a nanostructured system characterized by anisotropic internal stresses that are the strongest along one of the [110] directions. These stresses give rise to the anisotropy of the g-factor which is responsible for experimentally observed splitting of the ESR line. The compensating impurities destroy the AF phase and reduce this splitting. Local stresses are present in this case, too, but now they appear because of the Coulomb interaction of oppositely charged impurities and have no preferred orientation.     

Dynamical excitonic effects in metals and semiconductors

The dynamics of an electron-hole pair induced by the time-dependent screened Coulomb interaction is discussed. In contrast to the case where the static electron-hole interaction is considered we demonstrate the occurrence of important dynamical excitonic effects in the solution of the Bethe-Salpeter equation. This is illustrated in the calculated absorption spectra of noble metals (copper and silver) and silicon. Dynamical corrections strongly affect the spectra, partially canceling dynamical self-energy effects and leading to good agreement with experiment.     

Coulomb effects on the formation of proton halo nuclei

This paper makes some qualitative and quantitative analyses about halo formation rules of some mirror nuclei with the relativistic mean-field (RMF) theory and the Woods--Saxon mean-field model. By analysing two opposite effects of Coulomb interaction on the proton halo formation, it finds that the energy level shift has a larger contribution than that of the Coulomb barrier when the mass number A is small, the hindrance of the Coulomb barrier becomes more obvious with the increase of the mass number A, and the overall effect of the Coulomb interaction almost disappears when A≈39 as its two effects counteract with each other.     

Antiferromagnetic order in doped hubbard model under the magnetic field

We investigate the effects of temperature and hole doping on the antiferromagnetic (AF) ground states by considering the system of electrons on a two dimensional square lattice under the external magnetic field. In the mean field calculation of Hubbard Hamiltonian we find out that the magnetic field suppresses the AF order in a unique manner for all parameter values ofT and δ. We obtained the phase diagram of AF order inT-δ plane as a function of Coulomb correlation strength and magnetic field. We find the reentrant behavior of AF order in both the absence and the presence of magnetic field.     

The Linear Optical Polarizability Spectra of Five C78 Isomers

Effects of anisotropy, symmetry, atom arrangement and Coulomb interaction on the linear optical polarizability spectra of five C₇₈ isomers are theoretically studied by using the extended Su-Schrieffer-Heeger model with and without Coulomb interaction. The main results are as follows. 1) The spectra become anisotropic with respect to the direction of the electric field of light. The property is common in the niorlel with and without Coulomb interaction. 2) The symmetry and atom arrangement have grcat effects on the peak positions, strengths, and number. 3) The Coulomb interaction tends to shift peaks to higher energies and enhances the oscillator strengths at higher energies.     

Strongly confined semiconductor quantum dots: Pair excitations and optical properties

This paper reviews a microscopic model of basic electron-hole pair excitation processes in strongly confined semiconductor quantum dots (QD) and their influence on the optical QD properties. The effects of valence band mixing, Coulomb interaction, and surface polarization are taken into account. The exciton and biexciton wave functions and energies are obtained using a numerical diagonalization method. The computed optical spectra, such as absorption, gain, pump-probe, and two-photon absorption, agree well with experiments.     

Monte Carlo simulation of carbon fragmentation at high energies

The dominating decay channels of fragmenting carbon nuclei in high-energy proton-carbon collisions were studied by means of a Monte Carlo simulation. We study the influence of the Coulomb interaction on the energy spectra and two-fragment (energy and angular) correlations between the various fragments in the context of a statistical model. We show that the Coulomb interaction between the fragments strongly affects their energy and angular correlation functions. Qualitative predictions for the exclusive analysis of the various final states are given. Comparison with experiments of this type should soon be possible.