Nanoscale superconductor/semiconductor hybrid devices are assembled from indium arsenide semiconductor nanowires individually contacted by aluminum-based superconductor electrodes. Below 1 kelvin, the high transparency of the contacts gives rise to proximity-induced superconductivity. The nanowires form superconducting weak links operating as mesoscopic Josephson junctions with electrically tunable coupling. The supercurrent can be switched on/off by a gate voltage acting on the electron density in the nanowire. A variation in gate voltage induces universal fluctuations in the normal-state conductance, which are clearly correlated to critical current fluctuations. The alternating-current Josephson effect gives rise to Shapiro steps in the voltage-current characteristic under microwave irradiation.

We report a novel negative photoconductivity (NPC) mechanism in n-type indium arsenide nanowires (NWs). Photoexcitation significantly suppresses the conductivity with a gain up to 10(5). The origin of NPC is attributed to the depletion of conduction channels by light assisted hot electron trapping, supported by gate voltage threshold shift and wavelength-dependent photoconductance measurements. Scanning photocurrent microscopy excludes the possibility that NPC originates from the NW/metal contacts and reveals a competing positive photoconductivity. The conductivity recovery after illumination substantially slows down at low temperature, indicating a thermally activated detrapping mechanism. At 78 K, the spontaneous recovery of the conductance is completely quenched, resulting in a reversible memory device, which can be switched by light and gate voltage pulses. The novel NPC based optoelectronics may find exciting applications in photodetection and nonvolatile memory with low power consumption.

Superconductor-graphene-superconductor (SGS) junction provides a unique platform to study relativistic electrodynamics of Dirac fermions in graphene combined with proximity-induced superconductivity. We report the observation of the Josephson effect in proximity-coupled superconducting junctions of graphene in contact with Pb 1−x In x (x = 0.07) electrodes for temperatures as high as T = 4.8 K, with a large value of I c R N (∼255 μ V). This demonstrates that Pb 1−x In x SGS junction would facilitate the development of the superconducting quantum information devices and superconductor-enhanced phase-coherent transport of graphene.

Stochastic switching-current distribution in a graphene-based Josephson junction exhibits a crossover from the classical to quantum regime, revealing the macroscopic quantum tunneling of a Josephson phase particle at low temperatures. Microwave spectroscopy measurements indicate a multiphoton absorption process occurring via discrete energy levels in washboard potential well. The crossover temperature for macroscopic quantum tunneling and the quantized level spacing are controlled with the gate voltage, implying its potential application to gate-tunable superconducting quantum bits.

We report electroluminescence (EL) measurements carried out on three-terminal devices incorporating individual n-type CdSe nanowires. Simultaneous optical and electrical measurements reveal that EL occurs near the contact between the nanowire and a positively biased electrode or drain. The surface potential profile, obtained by using Kelvin probe microscopy, shows an abrupt potential drop near the position of the EL spot, while the band profile obtained from scanning photocurrent microscopy indicates the existence of an n-type Schottky barrier at the interface. These observations indicate that light emission occurs through a hole leakage or an inelastic scattering induced by the rapid potential drop at the nanowire-electrode interface.Comment: 12 pages, 4 figure

Semiconductor nanowires provide promising low-dimensional systems for the study of quantum transport phenomena in combination with superconductivity. Here we investigate the competition between the Coulomb blockade effect, Andreev reflection, and quantum interference, in InAs and InP nanowires connected to aluminum-based superconducting electrodes. We compare three limiting cases depending on the tunnel coupling strength and the characteristic Coulomb interaction energy. For weak coupling and large charging energy, negative differential conductance is observed as a direct consequence of the BCS density of states in the leads. For intermediate coupling and charging energy smaller than the superconducting gap, the current-voltage characteristic is dominated by Andreev reflection and Coulomb blockade produces an effect only near zero bias. For almost ideal contact transparencies and negligible charging energy, we observe universal conductance fluctuations whose amplitude is enhanced due to Andreev reflection at the contacts. Doh et al -2 -In recent years semiconductor nanowires (NW's) have attracted a lot of attention owing to their potential for applications in the domain of nanoscale sensors, electronics and photonics.1 Simultaneously, the highly controlled synthesis of homo-and hetero- The NW's employed for this work were synthesized by a vapor-liquid-solid process, in which the semiconducting materials were supplied via laser ablation of ndoped InP or InAs targets. The NW growth was catalyzed by Au nanoparticles predeposited on a Si substrate. After growth, the NW's were dispersed in a chlorobenzene solution and deposited on a p + Si substrate with a 250-nm-thick SiO 2 overlayer. The SC contact electrodes were fabricated by e-beam lithography followed by the e-beam deposition of a Ti(10 nm)/Al(120 nm) bilayer. The NW surface was treated with buffered hydrofluoric acid for 20 s prior to metal evaporation. All low-temperature transport measurements were carried out in a dilution refrigerator equipped with accurately filtered wiring and low-noise electronics. Further details on NW growth, device fabrication, and measurement setup can be found in earlier publications 4,8,17 .The normal state resistance R N , which we define as the dynamic resistance, dV/dI, at a bias voltage, V, of 1 mV and T = 2 K, was found to vary between ~1 to ~10 3 kΩ depending mostly on NW composition and diameter (see Table. S1 and Fig. S1 in the Supplementary Information).We consider first the device with the largest resistance, fabricated from a 36-nm-diam InP NW (see Fig. 1a). The device, labeled as D1, has R N /R Q = 36, where R Q = h/e 2 ~ 25.8 kΩ is the resistance quantum. The NW channel forms a small quantum dot whose low-temperature transport properties are dominated by the Coulomb blockade effect over the whole experimental range, as denoted by the presence of characteristic quasi-periodic peaks 18 in the linear conductance, G (see Fig. 1b). Such Coulomb peakswere measured at T = 20 mK under a perpendicular magnetic field of 0.1 T, ...

In a conventional Josephson junction of graphene, the supercurrent is not turned off even at the charge neutrality point, impeding further development of superconducting quantum information devices based on graphene. Here we fabricate bipolar Josephson junctions of graphene, in which a p-n potential barrier is formed in graphene with two closely spaced superconducting contacts, and realize supercurrent ON/OFF states using electrostatic gating only. The bipolar Josephson junctions of graphene also show fully gate-driven macroscopic quantum tunnelling behaviour of Josephson phase particles in a potential well, where the confinement energy is gate tuneable. We suggest that the supercurrent OFF state is mainly caused by a supercurrent dephasing mechanism due to a random pseudomagnetic field generated by ripples in graphene, in sharp contrast to other nanohybrid Josephson junctions. Our study may pave the way for the development of new gate-tuneable superconducting quantum information devices.

We report on the electrical characteristics of few-layer graphene (FLG) field-effect devices with their various thicknesses. In combination with a ferroelectric polymer layer of poly(vinylidene fluoride/trifluoroethylene) [P(VDF/TrFE)], FLG/ferroelectric devices exhibited nonvolatile resistance changes due to a polarization switching of the P(VDF/TrFE) layer. The bistability and retention properties were highly sensitive to the FLG thickness, which is attributed to a charge screening effect in FLG films.