Semiconductor nanocylindrical heterolayer in a radial electrostatic field: The electronic spectrum and optical properties

In the effective-mass approximation the single-electron states in a semiconductor cylindrical nanolayer under the presence of lateral-radial electrical field in the regime of strong quantization are considered. The explicit form of the energy spectrum and envelope wave functions of single-electron states is obtained in the cases of “large” and “moderate” radii of the system. The corresponding absorption characteristics of interband optical transitions in the layer under the presence of radial field are calculated.     

Superconducting phase transitions in quantum dots

In NdN and SdS nanostructures, anomalous ground states with a non-integer average number of electrons in the quantum dots d occur. These states correspond to pair or single-electron superconductivity and are separated from states with a definite (integer) number of electrons by, as a rule, second-order phase transitions. The characteristic features of the pair and single-electron superconducting Josephson current in SdS are discussed. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 9, 618–623 (10 November 1996)     

基于库仑阻塞原理的多值存储器

设计了一种基于库仑阻塞原理的新型单电子多值存储器.器件包括两个多隧穿结结构和一个单电子晶体管，其中单电子晶体管起到一个静电计的作用来实现数据的读取.两个隧穿结库仑阻塞区域的大小不同使得器件具有三个稳定的存储状态.利用这个原理可以制备出多值的动态随机存储器和非挥发性的随机存储器.这种低功耗的单电子多值存储器可以实现信息的超高密度存储. 关键词： 库仑阻塞 单电子晶体管     

Wave-function mapping of InAs quantum dots by scanning tunneling spectroscopy

Scanning tunneling spectroscopy is used to investigate the single-electron states and the corresponding squared wave functions of single and freestanding strain-induced InAs quantum dots grown on GaAs(001). Several peaks are found in dI/dV curves, which belong to different single-electron states. Spatially resolved dI/dV images reveal (000), (100), (010), (200), and (300) states, where the numbers describe the number of nodes in [11;0], [110], and [001] directions, respectively. The total number and energetic sequence of states is different for different dots. Interestingly, the (010) state is often missing, even when (200) and (300) states are present. We interpret this anisotropy in electronic structure as a consequence of the shape asymmetry of the dots.     

多岛单电子晶体管的实现及其源漏特性分析

在淀积有纳米间隙栅电极、源电极和漏电极的衬底上生长量子点，制作出多岛结构的单电子晶体管.在77K温度下对源漏特性进行了测试，得到了库仑阻塞特性.并且成功抑制了单岛单电子晶体管中易出现的共隧穿效应，观察到较大的库仑阈值电压.对试验数据进行了分析，阐明了岛的不同结构组态产生的不同输运效果. 关键词： 单电子晶体管 量子点 库仑阻塞     

Molecular states observed in a single pair of strongly coupled self-assembled InAs quantum dots

Molecular states in a single pair of strongly coupled self-assembled InAs quantum dots are investigated using a sub-micron sized single-electron transistor containing just a few pairs of coupled InAs dots embedded in a GaAs matrix. We observe a series of well-formed Coulomb diamonds with charging energy of less than 5 meV, which are much smaller than those reported previously. This is because electrons are occupied in molecular states, which are spread over both dots and occupy a large volume. In the measurement of ground and excited state single-electron transport spectra with a magnetic field, we find that the electrons are sequentially trapped in symmetric and anti-symmetric states. This result is well explained by numerical calculation using an exact diagonalization method.     

The geometric mean density of states and its application to one-dimensional nonuniform systems

By using the measure of the ratio R of the geometric mean of the local density of states (LDOS) and the arithmetic mean of LDOS, the localization properties can be efficiently characterized in one-dimensional nonuniform single-electron and two-interacting-particle (TIP) systems. For single-electron systems, the extended and localized states can be distinguished by the ratio R. There are sharp transitions in the ratio R at mobility edges. For TIP systems, the localization properties of particle states can also be reflected by the ratio R. These results are in accordance with what obtained by other methods. Therefore, the ratio R is a suitable quantity to characterize the localization properties of particle states for these 1D nonuniform systems.     

Stability of ferromagnetism in the Hubbard model on the kagome lattice

The Hubbard model on the kagome lattice has highly degenerate ground states (the flat lowest band) in the corresponding single-electron problem and exhibits the so-called flat-band ferromagnetism in the many-electron ground states as was found by Mielke [J. Phys. A 24, L73 (1991)]]. Here we study the model obtained by adding extra hopping terms to the above model. The lowest single-electron band becomes dispersive, and there is no band gap between the lowest band and the other band. We prove that, at half filling of the lowest band, the ground states of this perturbed model remain saturated ferromagnetic if the lowest band is nearly flat.     

Single-electron coherence: Finite temperature versus pure dephasing

We analyze a coherent injection of single electrons on top of the Fermi sea in two situations, at finite-temperature and in the presence of pure dephasing. Both finite-temperature and pure dephasing change the property of the injected quantum states from pure to mixed. However, we show that the temperature-induced mixedness does not alter the coherence properties of these single-electron states. In particular two such mixed states exhibit perfect antibunching while colliding at an electronic wave splitter. This is in striking difference with the dephasing-induced mixedness which suppresses antibunching. On the contrary, a single-particle shot noise is suppressed at finite temperatures but is not affected by pure dephasing. This work therefore extends the investigation of the coherence properties of single-electron states to the case of mixed states and clarifies the difference between different types of mixedness.     

Reprint of : Single-electron coherence: Finite temperature versus pure dephasing

We analyze a coherent injection of single electrons on top of the Fermi sea in two situations, at finite-temperature and in the presence of pure dephasing. Both finite-temperature and pure dephasing change the property of the injected quantum states from pure to mixed. However, we show that the temperature-induced mixedness does not alter the coherence properties of these single-electron states. In particular two such mixed states exhibit perfect antibunching while colliding at an electronic wave splitter. This is in striking difference with the dephasing-induced mixedness which suppresses antibunching. On the contrary, a single-particle shot noise is suppressed at finite temperatures but is not affected by pure dephasing. This work therefore extends the investigation of the coherence properties of single-electron states to the case of mixed states and clarifies the difference between different types of mixedness.     

Singlet two-electron states in superconducting materials based on iron pnictides

Two-electron states with a zero pulse for the symmetry group of superconducting materials based on iron pnictides are considered. Cases are established for the introduction of one or two additional quantum numbers, notably, the internal quantum number, which characterizes single-electron states, or an additional quantum number, i.e. the irreducible representation index of the intermediate group. The octet structure of zeros observed in photoelectron spectra and the phase difference between the two-electron states on various Fermi surfaces are interpreted.     

Ni—Cr非中心对称准晶的电子性质

在单电子、紧束缚和最近邻相互作用条件下，本文利用迁移模型分析和计算了单种原子、单健长的二维十二次准晶的电子性质，包括电子能谱、积分态密度和判断电子波函数局域性的一阶矩、二阶矩、反参加比等参数。我们发现电子能谱没有正常简并，只有偶然简并，以及电子只有中间态，没有扩展态和局域态。     

Ni-Cr非中心对称准晶的电子性质

在单电子、紧束缚和最近邻相互作用条件下，本文利用迁移模型分析和计算了单种原子、单键长的二维十二次准晶的电子性质，包括电子能谱、积分态密度和判断电子波函数局域性的一阶矩、二阶矩、反参加比等参数。我们发现电子能谱没有正常简并，只有偶然简并，以及电子只有中间态，没有扩展态和局域态。     

Alternative generalized master equation approach to the dc phonon-assisted hopping

As the momentum operator has no diagonal elements between localized states, the hopping conduction theory should be formulated in terms of the linear response of the site-off-diagonal elements of the single-electron density matrix to an external field. A theory of this kind, starting from generalized master equations and yielding the dc phonon-assisted hopping conductivity and thermopower is formulated. This is an alternative to the usual approach treating the current conduction via a time-derivative of the electric dipole momentum.Stimulating discussions with Dr. B. Velický turning the present author's attention to his own old ideas about the hopping conduction via off-diagonal elements of the single-electron density matrix are appreciated.     

Coulomb oscillations of conductance in an open ring interferometer in a strong magnetic field

Under the conditions corresponding to tunnel-coupled edge current states in an open ring interferometer, oscillations of conductance as a function of gate voltage with two noticeably different periods are observed. The large-period oscillations are attributed to the electron tunneling between the source and drain regions via a closed edge state of the ring, when an integral number of magnetic flux quanta passes through its contour at the Fermi level. The small-period oscillations are explained by the effect of single-electron variations of the ring potential on the transparency of the barriers between the localized and delocalized edge states of the interfer-ometer.     

Multiple Andreev reflections in a carbon nanotube quantum dot

We report resonant multiple Andreev reflections in a multiwall carbon nanotube quantum dot coupled to superconducting leads. The position and magnitude of the subharmonic gap structure is found to depend strongly on the level positions of the single-electron states which are adjusted with a gate electrode. We discuss a theoretical model of the device and compare the calculated differential conductance with the experimental data.     

The symmetry of three-electron states in a quantized magnetic field

The states of itinerant electrons on the finite square lattice in a quantized magnetic field are discussed. The single-electron states are classified by irreducible representations (IRs) of the magnetic translation group.The representation correspond to the Landau level, whereas its basis functions are analogs of the cyclotronic orbits. The filling factor of the Landau level is considered in the frame of multi-electron functions. Corresponding states are classified by the IR of MTG as well as by the irreducible representation of a symmetric group (permuting the electrons) and a unitary group (permuting electron states). The discussion is restricted to the case when the magnetic flux per unit cell of the two-dimensional square lattice is a rational number in terms of magnetic flux quanta. The additional parameter of the model is the Hubbard interaction between electrons.     

Metallic ferromagnetism in the Hubbard model: a rigorous example

We present the first rigorous example of the Hubbard model in any dimension which exhibits metallic ferromagnetism. The model is a genuine Hubbard model with short-range hopping and on-site Coulomb repulsion, and has many single-electron bands. In the limit where the band gap and the Coulomb repulsion become infinite, we prove that the ground states are completely ferromagnetic and at the same time conducting.     

Few-electron molecular states and their transitions in a single InAs quantum dot molecule

We study electronic configurations in a single pair of vertically coupled self-assembled InAs quantum dots, holding just a few electrons. By comparing the experimental data of nonlinear single-electron transport spectra in a magnetic field with many-body calculations, we identify the spin and orbital configurations to confirm the formation of molecular states by filling both the quantum mechanically coupled symmetric and antisymmetric states. Filling of the antisymmetric states is less favored with increasing magnetic field, and this leads to various magnetic field induced transitions in the molecular states.     

Ab initio modelling of band states in doped diamond

Presented in this study is an analysis of the electronic properties of doped diamond calculated using the Vienna ab initio simulation package, employing density functional theory within the generalized-gradient approximation. The dopants studied here have been inserted substitutionally into a 64-atom diamond supercell and include the single-electron acceptors boron and aluminium, the single-electron donors nitrogen and phosphorus and the double-electron donors oxygen and sulphur. Co-doping of diamond with sulphur and boron has also been briefly examined. The doped supercells have been relaxed, followed by calculation of electronic properties from the electronic density of states such as the indirect bandgap E _g, the valence bandwidth and an examination of the acceptor and donor states in the bandgap. It is anticipated that this study will provide a useful comparison of the third- and fourth-row donors and acceptors in diamond.