马约拉纳零能模的输运探测

理论预言拓扑超导体能够承载服从非阿贝尔统计的伊辛任意子—马约拉纳零能模,因而可用于实现容错的拓扑量子计算,是凝聚态领域最受关注的前沿课题之一.本文重点回顾了电学输运手段在研究马约拉纳零能模中的应用.在简要介绍拓扑超导、马约拉纳零能模和非阿贝尔统计等基本概念的基础上,对当前实现拓扑超导的多种方案进行了总结.重点介绍了利用低温输运手段探测马约拉纳零能模的实验方法,涵盖了超导/纳米线中广泛使用的电子隧穿谱、库仑阻塞谱和非局域电导探测,以及约瑟夫森器件中使用的(逆)交流约瑟夫森效应探测和电流(能量)相位关系的探测.同时,对利用上述测量手段得到的实验结果可能存在的平庸解释进行了必要的补充和说明.最后对马约拉纳零能模的输运探测进行了总结与展望.

基于最佳浆骨比的混凝土配合比设计方法研究

传统混凝土配合比设计方法是计算—试配法,其依据是普通混凝土的一般经验规律。尽管经过试配调整,但最终配合比往往并不是最优的,难以适应骨料变异大、耐久性指标的实际要求。通过对已知骨料试配获得骨料的最紧密堆积及最佳浆骨比,然后借助影响混凝土主要性能的已知规律,推导建立了基于最佳浆骨比的混凝土配合比计算方法,其实质是试配—计算—试配法。实例表明该方法能适应不同原材料条件下高性能混凝土配合比设计要求。

基于多传感器的方舱猪舍猪只采食行为分析系统

针对当前市面上的方舱猪舍猪只缺乏综合管理和对个体的精准饲养,设计基于多传感器的方舱猪舍猪只采食行为分析系统。首先通过RFID技术建立猪只档案,识别猪只的身份信息;然后采用基于改进的自适应的高斯混合模型的猪只运动判别算法,判断猪只是否进入采食区域;最后通过称重传感器获取猪只的采食数据。通过上述方法系统能够准确锁定采食猪只的身份以及采食时间、采食频率、采食量。为验证系统的可行性,设计四因素三水平试验,探究读写器功率、标签靠近速度、射频频率、标签靠近方向对RFID识别效果的影响。试验结果表明:读写器功率为27 dBm、标签靠近速度慢、射频频率为920.75 MHz、标签靠近方向为横向会使得电子标签在距离天线0.5 m的范围内识别效果最好。同时进行猪只个体的饲喂测定试验,发现系统的误差为0.08%~0.1%,能够满足猪场的使用要求。

Gate-Tunable Negative Differential Conductance in Hybrid Semiconductor–Superconductor Devices

Negative differential conductance(NDC)serves as a crucial characteristic that reveals various underlying physics and transport process in hybrid superconducting devices.We report the observation of gate-tunable NDC outside the superconducting energy gap on two types of hybrid semiconductor–superconductor devices,i.e.,normal metal–superconducting nanowire–normal metal and normal metal–superconducting nanowire–superconductor devices.Specifically,we study the dependence of the NDCs on back-gate voltage and magnetic field.When the back-gate voltage decreases,these NDCs weaken and evolve into positive differential conductance dips;and meanwhile they move away from the superconducting gap towards high bias voltage,and disappear eventually.In addition,with the increase of magnetic field,the NDCs/dips follow the evolution of the superconducting gap,and disappear when the gap closes.We interpret these observations and reach a good agreement by combining the Blonder–Tinkham–Klapwijk(BTK)model and the critical supercurrent effect in the nanowire,which we call the BTK-supercurrent model.Our results provide an in-depth understanding of the tunneling transport in hybrid semiconductor–superconductor devices.

RFID技术在生猪养殖业中的应用现状与展望

射频识别(Radio Frequency Identification)技术是一种通过无线射频方式来进行非接触式数据通信的自动识别技术。通过对电子标签进行读写,达到数据交换的目的。笔者主要介绍了RFID技术的基本概念及特点,分析了RFID技术在我国生猪养殖业中的应用现状及存在的问题,明确了RFID技术对生猪养殖业自动化发展的重要性,提出了RFID技术在生猪养殖业中的发展趋势,以期为今后RFID技术在生猪养殖业中的应用发展提供研究基础。

混杂SIFCON材料力学性能试验研究

SIFCON 工艺是美国 LANKARD 材料试验室发明的一种制作高含量钢纤维混凝土制品的方法。在基体中加入 PP 改性聚丙稀纤维,对混杂 SIFCON 工艺成型的高含量钢纤维混凝土进行了系列的材料力学性能试验研究。

Superconductivity in Mg-Doped Layered Intermetallic Compound NbB2

We have performed low temperature resistivity p（T） and specific heat C（T） measurements on a superconducting polycrystalline Nb0.75Mg0.25B2 sample. The results indicate that the superconducting transition temperature is -4.6 K. The zero temperature upper critical field determined from the resistivity and specific heat is 3123 Oe. The electronic coefficient of specific heat γn=4.51 mJmol^-1K^2 and the Debye temperature θD=419 K are obtained by fitting the zero-field specific heat data in the normal state. At low temperatures, the electronic specific heat in the superconducting state follows Ces/γnTc = 2.84 exp（-1.21Tc/T）. This indicates that the superconducting pairing in Nb0.75Mg0.25B2 has s-wave symmetry.

异位发酵床垫料水分蒸发规律试验研究

为了研究环境温湿度及发酵温度对垫料水分蒸发的影响规律。本研究通过BBD试验设计法设计了四因素三水平正交试验,以谷壳和发酵床垫料为试验物料,选取发酵时温度、垫料的初含水率、外界环境温度和湿度四个试验因素来研究对垫料水分蒸发量的影响。结果表明:发酵时温度、外界环境温度和湿度对发酵床运行过程中水分蒸发量影响显著,当所选物料为谷壳时,垫料的初含水率不显著,当所选物料为发酵床垫料时,垫料的初含水率对发酵床运行过程中水分蒸发量影响显著。且在发酵时温度为70℃,垫料的初含水率为60%,外界环境温度为35℃,外界环境湿度为70%的试验条件下发酵床运行过程中水分蒸发量最大。通过多元线性回归方法,得到了两种物料的水分蒸发量与发酵时温度、垫料的初含水率、外界环境温度和湿度等四个因素的回归模型。本研究为确定合理加入粪污量,调节水分提供理论基础,及为以后含水率检测传感器的设计提供研究基础。

Observation of an Even-Odd Asymmetric Transport in High Landau Levels

Magnetotransport experiments including tilt fields are performed on ultrahigh mobility L-shaped Hall-bar samples of GaAs/AlGaAs quantum wells. The low-temperature longitudinal resistivity （ρxx） data demonstrate that a striking even-odd asymmetric transport exists along the [110] direction at half filling in N ≥ 2 high Landau levels. Although the origin for the peculiar even-odd asymmetry remains unclear, we propose that the coupling strength between electrons within the same Landau level and between the neighboring two Landau levels should be considered in future studies. The tilt field data show that the in-plane field can suppress the formation of both bubble and stripe phases.

基于介电特性的水果成熟度无损检测研究进展

介绍了近年来应用在水果的成熟度判定和品质筛选上的一种无损检测技术——介电特性检测技术,详细介绍了介电特性测定水果成熟度的基本原理、介电特性测量技术及各测量技术的优缺点,综述了平行极板技术与同轴探头技术在水果成熟度检测上的应用。同时,指出了目前我国在该领域研究中存在的问题和今后的研究重点。

Quasi-Two-Dimensional Nature of High-Tc Superconductivity in Iron-Based(Li,Fe)OHFeSe

The intercalated iron selenide(Li,Fe)OHFeSe has a strongly layered structure analogous to the quasi-twodimensional(2D)bismuth cuprate superconductors,and exhibits both high-temperature(Tc)and topological superconductivity.However,the issue of its superconductivity dimensionality has not yet been fully investigated so far.Here we report that the quasi-2D superconductivity features,including the high anisotropyγ=151 and the associated quasi-2D vortices,are also revealed for(Li,Fe)OHFeSe,based on systematic experiments of the electrical transport and magnetization and model fittings.Thus,we establish a new vortex phase diagram for(Li,Fe)OHFeSe,which delineates an emergent quasi-2D vortex-liquid state,and a subsequent vortex-solid dimensional crossover from a pancake-like to a three-dimensional state with decreasing temperature and magnetic field.Furthermore,we find that all the quasi-2D characteristics revealed here for the high-Tciron selenide superconductor are very similar to those reported for high-Tcbismuth cuprate superconductors.

Pressure-Induced Metallization and Structural Phase Transition in the Quasi-One-Dimensional TlFeSe2

We report a comprehensive high-pressure study on the monoclinic TIFeSe2 single crystal,which is an antiferromagnetic jnsulator with quasi-one-dimensional crystal structure at ambient pressure.It is found that TIFeSe2 undergoes a pressure-induced structural transformation from the monoclinic phase to an orthorhombic structure above Pc≈13 GPa,accompanied with a large volume collapse of ΔV/V0=8.3%.In the low-pressure monoclinic phase,the insulating state is easily metallized at pressures above 2 GPa;while possible superconductivity with Tconset^2 K is found to emerge above 30 GPa in the high-pressure phase.Such a great tunability of TIFeSe2 under pressure indicates that the ternary AFeSe2 system(A=Tl,K,Cs,Rb) should be taken as an important platform for explorations of interesting phenomena such as insulator-metal transition,dimensionality crossover,and superconductivity.

Giant magnetic moment at open ends of multiwalled carbon nanotubes

The attractions of cantilevers made of multiwalled carbon nanotubes（MWNTs） and secured on one end are studied in the non-uniform magnetic field of a permanent magnet. Under an optical microscope, the positions and the corresponding deflections of the original cantilevers（with iron catalytic nanoparticles at the free end） and corresponding cut-off cantilevers（the free ends consisting of open ends of MWNTs） are studied. Both kinds of CNT cantilevers are found to be attracted by the magnet, and the point of application of force is proven to be at the tip of the cantilever. By measuring and comparing deflections between these two kinds of cantilevers, the magnetic moment at the open ends of the CNTs can be quantified.Due to the unexpectedly high value of the magnetic moment at the open ends of carbon nanotubes, it is called giant magnetic moment, and its possible mechanisms are proposed and discussed.

Single Crystal Growth and Magnetoresistivity of Topological Semimetal CoSi

We report single crystal growth of CoSi, which has recently been recognized as a new type of topological semimetal hosting fourfold and sixfold degenerate nodes. The Shubnikov–de Haas quantum oscillation(QO) is observed on our crystals. There are two frequencies originating from almost isotropic bulk electron Fermi surfaces, in accordance with band structure calculations. The effective mass, scattering rate, and QO phase difference of the two frequencies are extracted and discussed.

Anisotropic Applied Field Dependency of Two Successive Magnetic Transitions in LiCu2O2

The anisotropy of two successive transitions of the spin-ladder compound LiCu2O2 is studied by the specific heat （ C） under magnetic fields with H / / c and H / / ab （written as H^c and H^ab in the following） up to 14 T. The peak of specific heat at 24.5 K in zero field shifts to lower temperature when the field is increased and the magnitude of the peak is suppressed by the field. On the contrary, the peak of 22.5 K shifts to higher temperature, especially at 14 T. Its magnitude increases in the field of H^c, whereas it decreases in the field of H^ab. We calculate the entropy change between 21 K and 63 K. The different influence of the spin ordering by fields of different direction is obtained. Our experimental results suggest a mixed state between the long range incommensurate helimagnetic ground state and the higher-T short-range dimer liquid state. The temperature range of mixed state is shrunk with the increasing field. Possible mechanism is discussed.

Ac Josephson effect in Corbino-geometry Josephson junctions constructed on Bi_(2)Te_(3) surface

Recently, a Corbino-geometry type of Josephson junction constructed on the surface of topological insulators has been proposed for hosting and braiding Majorana zero modes. As a first step to test this proposal, we successfully fabricated Corbino-geometry Josephson junctions(JJs) on the surface of Bi_(2)Te_(3) flakes. Ac Josephson effect with fractional Shapiro steps was observed in the Corbino-geometry JJs while the flux in the junction area was quantized. By analyzing the experimental data using the resistively shunted Josephson junction model, we found that the Corbino-geometry JJs exhibit a skewed current-phase relation due to its high transparency. The results suggest that Corbino-geometry JJs constructed on the surface of topological insulators may provide a promising platform for studying Majorana-related physics.

Anomalous Josephson Effect in Topological Insulator-Based Josephson Trijunction

We studied anomalous Josephson effect(AJE) in Josephson trijunctions fabricated on Bi_(2)Se_(3), and found that the AJE in T-shaped trijunctions significantly alters the Majorana phase diagram of the trijunctions, when an in-plane magnetic field is applied parallel to two of the three single junctions. Such a phenomenon in topological insulator-based Josephson trijunction provides unambiguous evidence for the existence of AJE in the system, and may provide an additional knob for controlling the Majorana bound states in the Fu–Kane scheme of topological quantum computation.

Spatially resolved gap closing in single Josephson junctions constructed on Bi2Te3 surface

Full gap closing is a prerequisite for hosting Majorana zero modes in Josephson junctions on the surface of topological insulators.Previously,we have observed direct experimental evidence of gap closing in Josephson junctions constructed on Bi2Te3 surface.In this paper we report further investigations on the position dependence of gap closing as a function of magnetic flux in single Josephson junctions constructed on Bi2Te3 surface.

Coulomb-Dominated Oscillations in Fabry-Perot Quantum Hall Interferometers

Periodic resistance oscillations in Fabry-Perot quantum Hall interferometers are observed at integer filling factors of the constrictions, fc=1, 2, 3, 4, 5 and 6. Rather than the Aharonov-Bohm interference, these oscillations are attributed to the Coulomb interactions between interfering edge states and localized states in the central island of an interferometer, as confirmed by the observation of a positive slope for the lines of constant oscillation phase in the image plot of resistance in the 13 Vs plane. Similar resistance oscillations are also observed when the area A of the center regime and the backseattering probability of interfering edge states are varied, by changing the side-gate voltages and the configuration of the quantum point contacts, respectively. The oscillation amplitudes decay exponentially with temperature in the ramge of 40mK〈 T ≤ 130 mK, with a characteristic temperature T0 -25 mK, consistent with recent theoretical and experimental works.

Transport Studies on GaAs/AlGaAs Two-Dimensional Electron Systems Modulated by Triangular Array of Antidots

Triangular antidot lattices of various periods and aspect ratios are fabricated on high mobility GaAs/AlGaAs two-dimensional electron systems（2DESs）,and are characterized by magneto-transport measurements at low temperatures down to 300 mK. Commensurability peaks are generally observed in the magneto-resistivity ρ（xx）,and remarkable similarity between dρ（xy）/dB and ρ（xx） is found. In samples of relatively large aspect ratio d/a, the Aharonov-Bohm-type oscillations are clearly observed in both ρ（xx） and ρ（xy）, as well as the quenching of the Hall resistivity ρ（xy） in the vicinity of B = 0. These observations evince the good quality of our samples, and attest to the adequate preparation for fabricating antidot lattices of a reduced period to realize artificial graphene from GaAs/AlGaAs 2DESs.