Four-terminal resistance in a clean interacting quantum wire with invasive contacts

We investigate the behavior of the four-terminal resistance R_4pt$R_{4\mathit{pt}}$ in an interacting quantum wire described by a Luttinger liquid with an applied bias voltage V and coupled to two voltage probes. We extend previous results, obtained for very weakly coupled contacts, to the case in which the effects of the probes become non-trivially correlated.     

铝单丝Z箍缩形成无核冕结构的物理分析

针对铝单丝Z箍缩负载,计算其可形成金属蒸气而不形成核冕等离子体的电路和负载参数范围。提出了铝丝电爆炸形成金属蒸气的能量沉积判据和击穿电压判据;建立了热动力学模型,选取电路参数使得金属丝气化时放电回路电流恰好迅速下降,从而避免发生电压击穿。计算了典型电路下的负载电流、电压、电阻及沉积能量的变化曲线,并分析了回路总电感、充电电压以及负载丝长度、直径对其的影响规律。计算结果表明:当储能电容为150pF、充电电压为65kV、回路电感为300nH时,可驱动直径20μm、长2cm的铝丝电爆炸形成铝丝蒸气。快电流前沿、小丝直径和较短的丝长度有助于提高负载中的单位质量沉积能量,容易电爆炸形成金属蒸气负载。     

铝单丝Z箍缩形成无核冕结构的物理分析

针对铝单丝Z箍缩负载,计算其可形成金属蒸气而不形成核冕等离子体的电路和负载参数范围。提出了铝丝电爆炸形成金属蒸气的能量沉积判据和击穿电压判据;建立了热动力学模型,选取电路参数使得金属丝气化时放电回路电流恰好迅速下降,从而避免发生电压击穿。计算了典型电路下的负载电流、电压、电阻及沉积能量的变化曲线,并分析了回路总电感、充电电压以及负载丝长度、直径对其的影响规律。计算结果表明：当储能电容为150 pF、充电电压为65 kV、回路电感为300 nH时,可驱动直径20 m、长2 cm的铝丝电爆炸形成铝丝蒸气。快电流前沿、小丝直径和较短的丝长度有助于提高负载中的单位质量沉积能量,容易电爆炸形成金属蒸气负载。     

电爆炸法制备Fe3O4纳米颗粒及其物相研究

搭建了电爆炸金属丝实验平台,在空气中电爆炸铁丝来制备纳米金属颗粒。利用电阻分压器与Rogowski线圈来测量电爆炸过程中铁丝上的负载电压与电流。将负载电压与电流之积进行时间积分来估算沉积在铁丝上的能量。使用光电探测器对电爆炸过程中产生的等离子体发光信号进行探测。对铁丝电爆炸后形成的产物使用高倍显微镜、扫描电镜（SEM）、透射电镜（TEM）、能谱分析仪（EDS）以及X射线衍射仪（XRD）进行观测,来研究其物相特性。实验结果表明：电爆炸过程中,当铁丝由液相变为气相时,其电阻急剧增加,因此电流几乎不能流过铁丝,同时铁丝上的负载电压会趋近于电容器的初始充电电压。随着能量的持续积累,等离子体在爆炸腔中形成。由于原本被阻断的电流能够从低电阻等离子体中流过,因此电压电流波形变为欠阻尼波形。电爆炸铁丝所得的产物为Fe3O4纳米颗粒,其中大部分呈规则的球形。Fe3O4纳米颗粒的粒径主要分布在30~60 nm之间,并且符合对数正态分布。     

电爆炸法制备Fe3O4纳米颗粒及其物相研究

搭建了电爆炸金属丝实验平台,在空气中电爆炸铁丝来制备纳米金属颗粒。利用电阻分压器与Rogowski线圈来测量电爆炸过程中铁丝上的负载电压与电流。将负载电压与电流之积进行时间积分来估算沉积在铁丝上的能量。使用光电探测器对电爆炸过程中产生的等离子体发光信号进行探测。对铁丝电爆炸后形成的产物使用高倍显微镜、扫描电镜（SEM）、透射电镜（TEM）、能谱分析仪（EDS）以及X射线衍射仪（XRD）进行观测,来研究其物相特性。实验结果表明:电爆炸过程中,当铁丝由液相变为气相时,其电阻急剧增加,因此电流几乎不能流过铁丝,同时铁丝上的负载电压会趋近于电容器的初始充电电压。随着能量的持续积累,等离子体在爆炸腔中形成。由于原本被阻断的电流能够从低电阻等离子体中流过,因此电压电流波形变为欠阻尼波形。电爆炸铁丝所得的产物为Fe3O4纳米颗粒,其中大部分呈规则的球形。Fe3O4纳米颗粒的粒径主要分布在30~60 nm之间,并且符合对数正态分布。     

Temperature dependence of coulomb drag between finite-length quantum wires

We evaluate the Coulomb drag current in two finite-length Tomonaga-Luttinger-liquid wires coupled by an electrostatic backscattering interaction. The drag current in one wire shows oscillations as a function of the bias voltage applied to the other wire, reflecting interferences of the plasmon standing waves in the interacting wires. In agreement with this picture, the amplitude of the current oscillations is reduced with increasing temperature. This is a clear signature of non-Fermi-liquid physics because for coupled Fermi liquids the drag resistance is always expected to increase as the temperature is raised.     

Noise in the wire: The real impact of wire resistance for the Johnson(-like) noise based secure communicator

We re-evaluate the impact of wire resistance on the noise voltage and current in the Johnson(-like) noise based secure communicator, correcting the result presented in [J. Scheuer, A. Yariv, Phys. Lett. A 359 (2006) 737]. The analysis shown here is based on the fluctuation-dissipation and the linear response theorems. The results indicate that the impact of wire resistance in practical communicators is significantly lower than the previous estimation.     

Large enhancement of domain wall-induced anomalous magnetoresistance in ferrimagnetic Tb/Co wires: The effect of injecting spin Hall current

We demonstrated domain wall (DW)-induced anomalous magnetoresistance (MR) generated in asymmetric and symmetric ferrimagnetic Tb/Co multilayered, and Tb–Co alloyed wires. The extraordinary Hall effect (EHE)-induced circulating currents in the vicinity of DWs between longitudinal voltage probes are assigned to the anomalous MR. A large anomalous MR ~1.5% was obtained in the asymmetric Tb/Co multilayered wire. The large MR can be attributed to an addition of spin Hall current with a long coherence length from an adjacent Pt layer. These results open new possibilities for the use of ferrimagnetic multilayered wires beyond multi-function devices.     

Onset of energy dissipation in ballistic atomic wires

Electronic transport at finite voltages in free-standing gold atomic chains of up to seven atoms in length is studied at low temperatures using a scanning tunneling microscope. The conductance vs voltage curves show that transport in these single-mode ballistic atomic wires is nondissipative up to a finite voltage threshold of the order of several mV. The onset of dissipation and resistance within the wire corresponds to the excitation of the atomic vibrations by the electrons traversing the wire and is very sensitive to strain.     

10MeV LIA加速电压、电子束流测试

描述了中物院流体物理研究所10MeV电子直线感应加速器（10MeV LIA）加速电压、电子束流波形测试方法,主要介绍了为探测加速腔电压波形而设计的电容性高压脉冲探头（CVP探头）及其测试方法,并介绍了用电阻环四象限点监测束流质心位置及束流强度的方法,以及加速腔电压的叠加测试方法。     

Negative four-terminal resistance as a probe of crossed Andreev reflection

We report on the experimental investigation of electronic transport in superconductor-ferromagnet spin-valve structures. Our samples consist of two ferromagnetic iron leads forming planar tunnel contacts to a superconducting aluminum wire. Current is injected into one of the contacts while the voltage is monitored at the other, thus defining a four-probe resistance. At energies below the superconducting gap, we observe a negative four-probe resistance that can be explained by crossed Andreev reflection. PACS 74.45.+c; 85.75.-d; 03.67.Mn     

10MeVLIA加速电压、电子束流测试

描述了中物院流体物理研究所１０ＭｅＶ电子直线感应加速器（１０ＭｅＶＬＩＡ）加速电压、电子束流波形测试方法，主要介绍了为探测加速腔电压波形而设计的电容性高压脉冲探头（ＣＶＰ探头）及其测试方法，并介绍了用电阻环四象限点监测束流质心位置及束流强度的方法。     

Out-of-equilibrium Kondo effect in a mesoscopic device

We study the nonequilibrium regime of the Kondo effect in a quantum dot laterally coupled to a narrow wire. We observe a split Kondo resonance when a finite bias voltage is imposed across the wire. The splitting is attributed to the creation of a double-step Fermi distribution function in the wire. Kondo correlations are strongly suppressed when the voltage across the wire exceeds the Kondo temperature. A perpendicular magnetic field enables us to selectively control the coupling between the dot and the two Fermi seas in the wire. Already at fields of order 0.1 T only the Kondo resonance associated with the strongly coupled reservoir survives.     

Exploding wires in air and vacuum

An apparatus for studies of wire explosions in air at atmospheric as well as reduced pressures is described. A theoretical treatment of the discharge circuit is presented. In this treatment the external resistance and inductance as well as the wire inductance (all as functions of time) have been taken into consideration. It is then possible to calculate the wire variables — current, resistance, resistive voltage drop, effect, and energy input — as functions of time from thedI/dt waveform experimentally obtained. Wire variables of Ni- and W-wires exploded both in air and vacuum are presented as well as a discussion of these.     

Effects of circuit parameters on the electrical explosion of wires

The numerous papers [1–4] on exploding wires give mainly qualitative explanations of some of the processes and inadequate quantitive evidence, in spite of the practical importance of the technique. The present paper reports the effects of source parameters (voltage, capacity, inductance, stored energy) and of load parameters (specific resistance, diameter, resistance) on the energy deposited in the wire before rupture, and on the time and rate of deposition.We are indebted to Professor A. A. Vorob'ev for his interest in this work.     

Compressibility measurements of quasi-one-dimensional quantum wires

We report measurements of the compressibility of a one-dimensional quantum wire, defined in the upper well of a GaAs/AlGaAs double quantum well heterostructure. A wire defined simultaneously in the lower well probes the ability of the upper wire to screen the electric field from a biased surface gate. The technique is sensitive enough to resolve spin splitting of the subbands in the presence of an in-plane magnetic field. We measure a compressibility signal due to the 0.7 structure and study its evolution with increasing temperature and magnetic field. We see no evidence of the formation of the quasibound state predicted by the Kondo model, instead our data are consistent with theories which predict that the 0.7 structure arises as a result of spontaneous spin polarization.     

DC voltage profile of a 1D pumped wire with two dynamical and one static impurities

In this work we study the behavior of the voltage profile of a 1D quantum wire with an impurity when transport is induced by two ac voltages that oscillating with a phase lag define a quantum pump. The voltage profile sensed along the wire by the voltage probe, that we assume weakly coupled to the system, exhibits a Friedel's oscillations structure inside the region delimited by the position of the two ac voltages that induce transport. On the other hand, outside this region the oscillations are suppressed. Using perturbation theory in the coupling constant of the voltage probe we derived analytical expressions for the DC current valid for the adiabatic regime. We also compare our analytical results with the exact numerical calculations using Keldysh non-equilibrium Green's functions formalism.     

Multiprobe quantum spin Hall bars

We analyze electron transport in multiprobe quantum spin Hall (QSH) bars using the Büttiker formalism and draw parallels with their quantum Hall (QH) counterparts. We find that in a QSH bar the measured resistance changes upon introducing side voltage probes, in contrast to the QH case. We also study four- and six-terminal geometries and derive the expressions for the resistances. For these our analysis is generalized from the single-channel to the multi-channel case and to the inclusion of backscattering originating from a constriction placed within the bar.     

Inhomogeneity of currents in a wire array during its explodingphase

The current in a wire array during its exploding phase has been studied. The wire array consisting of many thin wires is used as a plasma source in a z-pinch X-ray radiation system. The current distribution in the exploding wire array plays an important role in producing an initial symmetrical plasma. In the present experiment, four tungsten wires of 0.1 mm in diameter were exploded in a vacuum. The experiment was carried out with an inductive voltage adder pulsed power generator providing a current of 160 kA at quarter period of 1.8 μs The currents through and the voltage across the wires were measured simultaneously. It was found that the currents in the wires were inhomogeneous, especially after the wires became plasma. Once the currents became inhomogeneous, the inhomogeneity remained throughout the discharge. It was also studied how the dimensions of the wires affected the homogeneity of the currents. Wires of different lengths or different cross sectional areas resulted in strong inhomogeneities of the currents. The wires with shorter length or smaller cross-sectional area became plasmas earlier than other wires. Thus, the resistances of the wires were not equal. These differences in the resistance caused the inhomogeneity of the currents     

Tunable quantum dot resonator embedded in a quantum wire

Combined quantum wire and quantum dot system is theoretically predicted to show unique conductance properties associated with Coulomb interactions. We use a split gate technique to fabricate a quantum wire containing a quantum dot with two tunable potential barriers in a two-dimensional electron gas. We observe the effects of the quantum dot cavity on the electron transport through the quantum wire, such as Coulomb oscillations near the pinch-off voltage and periodic conductance oscillations on the first conductance plateau.