Effects of Magnetic Quantum Dots on Magnetoconductance in Quantum Wires

We present a theoretical study of electronic transport in quantum wires (narrow two-dimensional electron gas) with array of magnetic quantum dots. Each magnetic quantum dot is defined by a small circular region where the strength of perpendicular magnetic field is modulated. By making use of a newly developed calculation method based on the gauge transformations, we calculated the conductance as a function of the external perpendicular magnetic field. Our numerical calculations show that the magnetoconductance is very sensitive to the number of magnetic quantum dots in the field region where the direction of the net magnetic field in dot regions is antiparallel to the external magnetic field.     

Magnetic Ordering of Focused-Ion-Beam Structured Cobalt-Platinum Dots for Field-Coupled Computing

This paper presents an experimental and computational study of dipolar ordering phenomena in ion-beam patterned Co/Pt multilayers. The fabrication and the patterning of the layers were chosen to achieve single-domain dots, which show strong magnetic coupling and are uniform in their magnetic properties. We find that antiferromagnetic-like ordering can extend to as many as several hundred adjacent dots. Micromagnetic simulations reproduce the experimentally observed ordering and suggest that such multilayers are promising candidates for field-coupled computing devices.     

Vortex States of a Three-Dimensional Mesoscopic Superconducting Torus in an External Magnetic Field

The time-dependent Ginzburg–Landau equations have been solved numerically by the finite-element method for a three-dimensional mesoscopic superconducting torus. We obtain the different vortex patterns as a function of the applied field perpendicular to its surface. And we find that multivortex states are ground state in a three-dimensional mesoscopic torus. These results show that our approach is effective and useful to interpret experimental data on vortex states in mesoscopic superconductors.     

Valence Band Structure of Coupled Diluted Magnetic Quantum Dots

The valence band structure of double InAs/GaAs diluted magnetic vertical quantum dots has been studied in the frame of multiband k⋅p calculation. We find that due to anisotropic effective mass, the ground state can be tuned from the characteristic of heavy- to light-hole state through just changing the parameter of quantum coupling between two QDs. We also show how this crossover manifests itself in the p–d exchange interaction between hole and Mn spins.     

Quantum Computation and Quantum Coherence in Mesoscopic Josephson Junctions

Macroscopic quantum dynamics of Josephson junctions hasattracted recently renewed interest in the context of quantumcomputation. Quantum coherence of the charge states in asingle-Cooper-pair box or the flux states in an rf SQUID canbe used to create charge and flux qubits for quantumcomputation. The aim of this paper is to give a briefintroduction to the basic concepts of quantum computation withJosephson junctions and to discuss the theory of quantumcoherence in the rf-stimulated macroscopic resonanttunneling of flux in SQUID's. The results for resonant fluxtunneling show that the quantum coherent flux oscillationsshould lead to splitting of resonant tunneling peaks,indicating that the resonant tunneling can be a convenienttool for studying macroscopic quantum coherence of flux.     

Nucleation of Vortices and Anti-Vortices in Mesoscopic Superconducting Discs

We investigate the nucleation of vortices and anti-vortices in a small superconducting disc. We formulate the Gibbs free energy of the disc with an arbitrary number of vortices and anti-vortices as a function of temperature and applied magnetic field and minimize the energy to obtain the optimal position of vortices for different applied fields and temperatures. We also analyse the stability of anti-vortices inside the disc.     

Spin Injection Processes in ZnSe-Based Double Quantum Dots of Diluted Magnetic Semiconductors

Spin injection processes in the double quantum dots of ZnSe-based diluted magnetic semiconductors are discussed. Double quantum dots are fabricated from ZnSe-based double quantum wells by electron beam lithography and wet etching. In these samples, the photo-excited carriers in the magnetic dots are injected into the non-magnetic dots. The circular polarization degrees of photoluminescence from the non-magnetic dots are measured by micro-photoluminescence measurement system under the magnetic field up to 5 T. The maximum spin polarization degrees of injected carriers determined from our experiment are 10% for double quantum wells and 15% for double quantum dots. The spin injection efficiency was estimated both from the observed circular polarization degree and the diffusion length of carriers. We concluded that the spin injection efficiency is increased in the double quantum dots.     

Quantum Crystal Oscillations in a Superfluid Liquid

We study the hydrodynamics of quantum ⁴He crystal oscillations in a superfluid liquid with involving the dynamics of atomically rough surfaces. It is shown that, due to enhancement of the kinetic growth coefficient as the temperature lowers, the reaction force of the liquid applied to the ⁴He crystal changes its character from the inertial to the viscous one vanishing as T→0. The model is confirmed by the experiments on the oscillations of the ⁴He crystal within the temperature range 0.54–1.43 K at frequencies 484 and 211 Hz. New type of a hydrodynamic instability is found. The instability occurs provided that the oscillation amplitude of the velocity becomes higher than ～3 cm/s.     

Glowing Graphene Quantum Dots and Carbon Dots: Properties,Syntheses, and Biological Applications

The emerging graphene quantum dots (GQDs) and carbon dots (C‐dots) have gained tremendous attention for their enormous potentials for biomedical applications, owing to their unique and tunable photoluminescence properties, exceptional physicochemical properties, high photostability, biocompatibility, and small size. This article aims to update the latest results in this rapidly evolving field and to provide critical insights to inspire more exciting developments. We comparatively review the properties and synthesis methods of these carbon nanodots and place emphasis on their biological (both fundamental and theranostic) applications.     

Ⅱ-Ⅵ型量子点的制备、修饰及其生物应用

根据近10年的研究情况对Ⅱ-Ⅵ型量子点的制备、修饰进行了介绍,分析了量子点制备过程中的优、缺点. 探讨了Ⅱ-Ⅵ量子点在生物应用的最新研究成果,并对其研究前景进行了预测.     

Superconducting and Charge Ordering Phases of Two-Dimensional Organic Conductors

In order to investigate relationships between superconducting phase and charge ordered one, the uniaxial strain method is applied to the superconducting salt α-(BEDT-TTF)₂NH₄Hg(SCN)₄ and the organic conductor α-(BEDT-TTF)₂CsCd(SCN)₄. Both salts preserve metallic states under a-axial strain and show insulating behaviours under c-axial strain. These results suggest that i) c-axial strain controls the electronic properties of the α-type salts, and ii) the insulating state in the vicinity of the superconducting phase of α-(BEDT-TTF)₂NH₄Hg(SCN)₄ is a charge ordered phase, as expected from the comparison in the lattice parameters with the charge ordered salt θ-(BEDT-TTF)₂RbZn(SCN)₄.     

稀磁掺杂MnxGe1-x量子点的制备及应用

作为一种新兴的稀磁掺杂半导体材料,Mn_xGe_(1-x)量子点的自旋电子学性能在最近几年内取得了较为重大的突破。本文针对现有Mn_xGe_(1-x)量子点的稀磁掺杂制备方法及与制备方法相关联的磁电子学性能展开论述,并详细介绍了Mn_xGe_(1-x)量子点在生长过程中Mn原子与生长表面之间的相互作用、形貌转变以及迄今为止对基于这种纳米材料进行的自旋电子学应用的尝试。最后,展望了Mn_xGe_(1-x)量子点未来研究的重点和亟待解决的问题。     

Magneto-Optical Study of Multiple Layers of Self-Assembled Quantum Dots Involving Diluted Magnetic Semiconductors

Magneto-optical experiments were carried out on structures comprised of multiple layers of self-assembled quantum dots (QDs) involving diluted magnetic semiconductors (DMSs). Photoluminescence (PL) from interband ground state transitions was clearly observed in these DMS-based QD systems. The PL energy from QD multilayers appears at a lower energy than that emitted by a single QD layer, suggesting that there exists electronic coupling between the QD layers. When an external magnetic field is applied, the PL peaks from QDs both in single-layer and in multilayer form exhibit large Zeeman shifts and a significant enhancement of intensity, a behavior that is typical for many low dimensional systems involving DMSs. In contrast to this behavior, however, we have observed a decrease of the PL intensity as a function of magnetic field in multilayer structures where alternating QW layers contain DMS and non-DMS QDs. We will show evidence that this effect arises from carrier transfer between pairs of QDs from adjacent layers (double QDs) due to the large Zeeman shifts of the conduction and valence bands characteristic of DMS QDs.     

Efficient Capture and Simple Quantification of Circulating Tumor Cells Using Quantum Dots and Magnetic Beads

Circulating tumor cells (CTCs) are valuable biomarkers for monitoring the status of cancer patients and drug efficacy. However, the number of CTCs in the blood is extremely low, and the isolation and detection of CTCs with high efficiency and sensitivity remain a challenge. Here, we present an approach to the efficient capturing and simple quantification of CTCs using quantum dots and magnetic beads. Anti‐EpCAM antibody‐conjugated quantum dots are used for the targeting and quantification of CTCs, and quantum‐dot‐attached CTCs are isolated using anti‐IgG‐modified magnetic beads. Our approach is shown to result in a capture efficiency of about 70%–80%, enabling the simple quantification of captured CTCs based on the fluorescence intensity of the quantum dots. The present method can be used effectively in the capturing and simple quantification of CTCs with high efficiency for cancer diagnosis and monitoring.     

量子点的应用及研究进展

基于量子点具有激发光谱宽、发射光谱窄、荧光量子产率高和寿命长等特殊的性质,被认为是一种比荧光染料分子更理想的生物探针。详细介绍了国内外的几种量子点制备方法及其表面修饰,另外综述了量子点在生物学的应用。     

Spin Effects in Lateral Quantum Dots

We present the review of our work on spin effects in single lateral quantum dots with the emphasis on the results of Coulomb blockade spectroscopy studies. Realization of a spin-based quantum bit proposal in a lateral quantum dot is discussed. Described are the ways of isolating a single electron spin in a dot containing only one as well as many electrons. Demonstrated is a current readout of spin transitions in a dot by means of spin blockade spectroscopy due to spin polarized injection/detection mechanism in a lateral dot. Discussed are transitions induced both by changing a magnetic field and a number of electrons in a dot with the emphasis on the effects observed close to filling factor in a dot = 2.     

Materials Physics and Quantum Coherence in Superconducting Qubits

Nonidealities of real superconductors in the form of residual rf losses and conductance below the superconducting energy gap in tunneling Josephson junctions are discussed as possible sources of decoherence in Josehphson junction flux qubits. The purpose of the paper is pedagogical and aimed at taking a first step in a unified view of the quantum behavior of superconducting qubits and the realities of the materials out of which they are constructed. The need for a dialog between the quantum physicist and the materials physicist is stressed. Residual rf losses and localized states in junction barriers are identified as important subjects for this dialog.