Quantum Interference of Surface States in Bismuth Nanowires in Transverse Magnetic Fields

We report the results of studies of the magnetoresistance (MR) and electric field effect (EFE) of single-crystal Bi nanowires with diameter d<80 nm at low temperatures. Single-crystal nanowire samples were prepared by the Taylor-Ulitovsky technique; they were cylindrical single crystals with the $(10\bar{1}1)$ orientation along the wire axis where the C ₃ axis was inclined at an angle of 70^° to the wire axis. According to theory of S. Murakami, bismuth bilayers can exhibit the quantum spin Hall effect. A Bi crystal can be viewed as a stacking of bilayers with a honeycomblike lattice structure along the [111] direction. An interpretation of transverse MR oscillations with using this theory is presented.     

Magnetic Torque Measurements on Bi2201 Single Crystal in High Magnetic Fields

The magnetic field direction dependence of the magnetic torque in the superconducting state of Bi ₂ Sr _1.65 La _0.35 CuO ₆₊ (Bi2201) single crystal has been measured in several static magnetic fields up to 200 kOe. The applied field dependence of the anisotropy parameter, , defined by the square root of the effective mass ratio has been obtained by fitting the magnetic torque curves at 17 K by means of the effective mass model. For Bi ₂ Sr ₂ CaCu ₂ O ₈₊ (Bi2212), the values up to 210 kOe were reported previously. At each field, for Bi2201 is larger than that for Bi2212. Since the value decreases as the field increases both for Bi2201 and Bi2212, the reduction of by the application of the high magnetic field is considered to be common for Bi-based layered superconductors.     

Laser-Controlled Magnetization in a Single Magnetic Semiconductor Quantum Dot

The photoluminescene signal of individual semimagnetic CdSe–Zn_0.75Mn_0.25Se quantum dots is used to study the magnetization of the Mn²⁺ spin system in the exchange field of a single exciton. We demonstrate that by increasing the laser excitation power a significant blue shift of the photoluminescence signal occurs. This is attributed to a laser-induced demagnetization, i.e. the laser-generated carriers heat the Mn²⁺ spin system via spin–flip exchange scattering.     

铋纳米线和纳米片的制备

通过调控水和乙二胺溶液的组份控制产物的形貌和结构,制备了铋纳米线和铋纳米片,研究了组份变化对产物形貌结构的影响,并依此提出了乙二胺模板效应以及由乙二胺引起的从动力学向热力学转换控制晶体生长的生长机制.铋纳米线的体膨胀系数随着温度的升高减小,并在一转变温度(455℃左右,低于块体的转变温度)变为负值.     

Anisotropy of Iodine Intercalated Bi2212 Single Crystals by Magnetic Torque

The magnetic torque of iodine intercalated Bi₂Sr₂CaCu₂O₈₊ (I-Bi2212) single crystals has been measured under magnetic fields up to 8 kOe in the temperatures from 4.2 to 100 K. The anisotropy parameter for the 1-Bi2212 determined by London model is smaller than that for the pure Bi₂Sr₂CaCu₂O₈₊ (Bi2212). A sharp peak C1 due to the intrinsic pinning and an extra peak C2 due to the dimensional crossover of the pancake vortex are observed in the magnetic field direction dependence of the torque. The reduced temperature at which the peak C1 appears with decreasing temperature is T/T _c=0.82, which is lower than T/T _c=0.97 for the pure Bi2212. The dimensional crossover field for the I-Bi2212 obtained from the peak C2 is larger than that for the pure Bi2212. According to these results, it is concluded that the iodine intercalation causes the enhancement of interlayer coupling.     

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.     

超薄铋薄膜的量子尺寸效应

采用基于密度泛函理论的第一性原理方法,研究了2～16层Bi(111)薄膜的表面能和功函数,它们展现出量子尺寸效应引起的奇偶振荡.解释这种振荡需要考虑表面投影能带结构,振荡周期与量子阱态在二维布里渊区中高对称点费米能级处的穿越有关,量子阱态穿越费米能级亦引起态密度在费米能级处振荡,预示传导性质的振荡转变.     

Magnetic Quantum Rotors

A new quantum system, magnetic quantum rotors, is presented. A magnetic rotor—a rotor possessing nonzero spin—is exemplified by the oxygen molecule. Of the exchange, spin-orbital, and spin-figure interactions contributed by the spin degree of freedoms only the latter was taken into consideration in this study. Phase diagrams of magnetic quantum linear rotors in a crystal field are studied for a system where all angular momentum states are allowed (all-J system) and for one where angular momentum is restricted to have odd values (odd-J system). It is found that depending on the crystal field and the value of the spin-figure coupling constant the orientational phase transition line can display a set of critical points (one, two, three or none in the case of the all-J systems and one, two or no critical points in the case of the odd-J systems) which are responsible for the topology of the phase diagram.     

Quantum Interference in Bismuth Nanowires: Evidence for Surface Charges

We report the results of studies of the transverse magnetoresistance (MR) of single-crystal Bi nanowires with diameter d<80 nm. The single-crystal nanowire samples were prepared by the Taylor-Ulitovsky technique. Due to the semimetal-to-semiconductor transformation and high density of surface states with strong spin-orbit interactions, the charge carriers are confined to the conducting tube made of surface states. The non monotonic changes of transverse MR that are equidistant in a direct magnetic field were observed at low temperatures in a wide range of magnetic fields up to 14 T. The period of oscillations depends on the wire diameter d as for the case of longitudinal MR. An interpretation of transverse MR oscillations is presented.     

Droplet Oscillations in High Gradient Static Magnetic Field

In high intensity and high gradient magnetic fields the volumetric force on diamagnetic material, such as water, leads to conditions very similar to microgravity in a terrestrial laboratory. In principle, this opens the possibility to determine material properties of liquid samples without wall contact, even for electrically non-conducting materials. In contrast, AC field levitation is used for conductors, but then terrestrial conditions lead to turbulent flow driven by Lorentz forces. DC field damping of the flow is feasible and indeed practiced to allow property measurements. However, the AC/DC field combination acts preferentially on certain oscillation modes and leads to a shift in the droplet oscillation spectrum.What is the cause? A nonlinear spectral numerical model is presented, to address these problems.     

Magnetic Anisotropy and de Haas–van Alphen Oscillations in a Bi Microwire Array Studied via Cantilever Magnetometry at Low Temperatures

We report measurements of the low temperature (T=0.5 K) oscillatory magnetization in a high-density array of 50μm diameter wires of polycrystalline Bi utilizing a high sensitivity silicon cantilever magnetometer. We find that the magnetic response is strongly anisotropic, being much larger for magnetic field perpendicular than for fields parallel to the wire-axis. We argue that this is a geometric effect caused by the large aspect ratio of the individual microwires in the array. The magnetic response of the microwires is dominated by the light electrons due to the larger cyclotron orbits in comparison with the heavier holes. We find that de Haas–van Alphen oscillations are easily resolved, and discuss the application of this technique to the study of Bi nanowire arrays.     

The Quantum Phase Slip Phenomenon in Superconducting Nanowires with High-Impedance Environment

Quantum phase slip (QPS) is the particular manifestation of quantum fluctuations of the order parameter of a current-biased quasi-1D superconductor. The QPS event(s) can be considered a dynamic equivalent of tunneling through conventional Josephson junction containing static in space and time weak link(s). At low temperatures T<<T _c, the QPS effect leads to finite resistivity of narrow superconducting channels and suppresses persistent currents in tiny nanorings. Here, we demonstrate that the quantum tunneling of phase may result in Coulomb blockade: superconducting nanowire, imbedded in high-Ohmic environment, below a certain bias voltage behaves as an insulator.     

Generation of Terahertz Radiation in Magnetic Junctions Based on Nanowires

Technical Physics Letters - A system of spin-injection emitters employing magnetic junctions based on an array of parallel nanodimensional wires has been studied. Manufacturing technology and...     

磁性金属Fe纳米线的制备及其性能

本文尝试采用纳米Au颗粒作为催化剂,利用化学气相沉积法合成铁纳米线。并着重研究了不同沉积温度对纳米线生长过程的影响。研究结果表明,过低沉积温度无法分解二茂铁,而过高沉积温度则会导致二茂铁高温分解副反应发生,生成大量碳颗粒,从而阻碍铁纳米线的生长。作者在600℃沉积温度下,以二茂铁为反应前驱体和蓝宝石作为基板,通过纳米Au颗粒的催化作用首次成功获得了大批量的铁单晶纳米线,并进一步揭示了纳米线的气-固生长机制。此外,本文还对合成的单晶Fe纳米线的磁各向异性进行了探讨。     

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.     

Site-Specific Magnetic Assembly of Nanowires for Sensor Arrays Fabrication

The effect of variation in local magnetic field on magnetic assembly of 30 and 200 nm diameter Ni nanowires synthesized by template directed electrodeposition was investigated with different materials (Ni–Ni and Ni–Au) and shapes of electrodes. Ni–Au paired electrodes improved confinement of the assembled Ni nanowires across the electrode gap because of the narrower distribution of magnetic field around the gap between the two electrodes. Simulation results indicated a local magnetic field strength at the electrode tip increased by a factor of 2.5 with the use of a needle-shape electrode as compared to rectangular-shape electrode. The resistance of nanowire interconnects increased as the applied voltage was raised, and under the same applied voltage, the increase in resistance is further enhanced at lower temperatures because of higher current density.      

Heusler合金磁性纳米线的制备方法及磁性的研究进展

磁性纳米线发展至今,已在高密度垂直磁性存储器、传感器、生物医学、催化剂等领域得到广泛应用.其中,Heusler合金磁性纳米线(Heu-sler alloy magnetic nanowires,HAMNWs)因其优异的性能备受关注.然而,目前HAMNWs制备工艺尚未成熟,存在组分偏差、结构无序、形貌不均等问题,阻碍了其基本物理性质的研究和功能器件的应用设计.当前已有的HAMNWs制备方法包括扩散驱动退火法、模板辅助法、化学合成退火法、分子束外延法、静电纺丝法、电沉积法等,这些方法各有其优势和缺陷.其中,SBA-15模板辅助的化学合成退火法制备的HAMNWs组分精确、结构高度有序,但该模板与AAO模板相比,孔道均一性相对较差,导致纳米线形貌均一性和有序性较弱;分子束外延法可以实现纳米线以原子级精度生长,然而,其制备设备昂贵、操作复杂,难以推广普及;扩散驱动退火法主要针对二元核壳型HAMNWs,而对于三元HAMNWs,其适用难度较大;静电纺丝法对组分和结构的控制较好,但对纳米线的形貌均一性控制较弱,整体呈纤维状;电沉积法制备的纳米线形貌均一可控,但对于含有难共沉积元素的合金纳米线,其组分和结构控制都较差.本文综述了HAMNWs的制备方法,详细对比了各种方法的优缺点;重点针对直流、脉冲、交流电沉积法制备过程中不同的生长机理进行了讨论,并在此基础上分析了纳米线生长过程中各种因素的影响与调控.同时还对纳米线的基本物理性质和磁性参数进行了归纳总结,最后对未来HAMN-Ws的制备及应用发展进行了展望.     

Conductivity of Bismuth Nanowires at Low Temperatures in Transverse Magnetic Field

We investigate theoretically and experimentally the conductivity of bismuth nanowires at low temperatures in a uniform magnetic field directed perpendicularly to the wire axis. Using the Kubo formula, we calculate the conductivity for the cases of systems with degenerate and nondegenerate carrier gas with elastic acoustic-phonon scattering of carriers. Size, temperature, and field dependence of the conductivity of a Bi quantum wire are discussed in detail. For a nanowire with nondegenerate carrier gas, the conductivity depends exponentially on a combination of field, temperature, and wire diameter. For a semimetallic Bi quantum wire can be observed the negative magnetoresistance.