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Superconductivity through the topological surface states of a Dirac semimetal remains elusive. Here, the authors fabricate a Nb-Cd3As2-Nb Josephson junction and observe supercurrent oscillations from surface Fermi arcs of Cd3As2

Topological semimetals are well known for the linear energy band dispersion in the bulk state and topologically protected surface state with arc-like Fermi surface. The angle resolved photoemission spectroscopy experiments help confirm the existence of linear Dirac (Weyl) cone and Fermi arc. Meantime, the transport experiments are very important for its intimate relationship with possible applications. In this concise review, recent developments of quantum transport in two typical topological semimetals, namely Dirac and Weyl semimetals, are described. The 3D Dirac semimetal phase is revealed by the Shubnikov–de Haas oscillations. The Weyl Fermions-related chiral anomaly effect is evident by negative magnetoresistance, thermal power suppression, and nonlocal measurements. The Fermi arc mechanism is discussed and several corresponding transport evidences have been described. The point contact-induced superconductivity in Dirac and Weyl semimetal is also introduced. Perspectives about the development of topological semimetals and topological superconductors are provided.

Dirac semimetals are a three-dimensional analogue of graphene that can support massless Dirac fermions in their bulk and Fermi-arc surface states. Here, the authors observe Aharonov–Bohm oscillations in transport measurements on Cd3As2nanowires, revealing these exotic surface states.

It has recently been predicted that the surface plasmons are allowed to exist on the interface between a topological insulator and vacuum. Surface plasmons can be employed to enhance the optical emission from various illuminants. Here, we study the photoluminescence properties of the ZnO/Bi2Te3 hybrid structures. Thin flakes of Bi2Te3, a typical three-dimensional topological insulator, were prepared on ZnO crystal surface by mechanical exfoliation method. The ultraviolet emission from ZnO was found to be enhanced by the Bi2Te3 thin flakes, which was attributed to the surface plasmon – photon coupling at the Bi2Te3/ZnO interface.

To enhance performances of graphene/SiO2 based field-effect transistors (FETs), understanding of the transfer of carriers through the graphene/SiO2 interface is crucial. In this paper, we have studied the temperature dependent transfer characters of graphene FETs. Hysteresis loop is shown to be dominated by trapping/detrapping carriers through the graphene/SiO2 interface. [ABSTRACT FROM AUTHOR]

The influence of the barrier between metal electrodes and graphene on the electrical properties was studied on a two-electrode device. A classical barrier model was used to analyze the current-voltage characteristics. Primary parameters including barrier height and effective resistance were achieved. The electron transport properties under magnetic field were further investigated. An abnormal peak-valley-peak shape of voltage-magnetoresistance curve was observed. The underlying mechanisms were discussed under the consideration of the important influence of the contact barrier. Our results indicate electrical properties of graphene based devices are sensitive to the contact interface. [ABSTRACT FROM AUTHOR]

The current-voltage (I-V) characteristics of single ZnO nanowires were measured varying with temperature and illumination. A model of the ZnO nanowire sandwiched by back-to-back diodes was utilized to explain the experimental data. Simulations of the I-V curves exhibited that the surface barrier height was independent of temperature from 180 to 290 K. This work also shows that the larger the incident laser power is, the smaller the contact surface barrier height will be. The photon induced reduction in the surface barrier height is attributed to the photogenerated holes, which result in a shielding effect on the surface trapped electrons. [ABSTRACT FROM AUTHOR]

The failure mechanism analysis on two-terminal Ti[Si.sub.2] nanowire devices is described and electromigration dominant mass migration is verified by energy dispersive spectroscopy. The temperature simulation is used for discussing the contribution of thermomigration.

The growth of silica-sheathed 3C-Fe(sub 7)S(sub 8) products on silicon substrates with FeCl(sub 2) and sulfur precursors at the temperature region of 600-800 degree C is studied. A model that includes the kinetic competition of the adsorption of silica species on Fe2-Fe3-Fe4 units at the 4Fe layer and on the Fe2-Fe3-Fe4-Fe5 units parallel to the c-axis is proposed.

Ursolic acid is a type of pentacyclic triterpene compound with multiple pharmacological activities including cancer resistance, protection from liver injury, antisepsis, anti-inflammation and antiviral activity. The present study aimed to investigate the anticancer effect of ursolic acid. Ursolic acid activates cell apoptosis and its pro-apoptotic mechanism remains to be fully elucidated. Cell Counting kit-8 assays, flow cytometric analysis and analysis of caspase-3 and caspase-9 activity were used to estimate the anticancer effect of ursolic acid on DU145 prostate cancer cells. The protein expression of cytochrome c, rho-associated protein kinase (ROCK), phosphatase and tensin homolog (PTEN) and cofilin-1 were examined using western blot analysis. In the present study, ursolic acid significantly suppressed cell growth and induced apoptosis, as well as increasing caspase-3 and caspase-9 activities of DU145 cells. Furthermore, cytoplasmic and mitochondrial cytochrome c protein expression was significantly activated and suppressed, respectively, by ursolic acid. Ursolic acid significantly suppressed the ROCK/PTEN signaling pathway and inhibited cofilin-1 protein expression in DU145 cells. The results of the present study indicate that the anticancer effect of ursolic acid activates cell apoptosis through ROCK/PTEN mediated mitochondrial translocation of cofilin-1 in prostate cancer. [ABSTRACT FROM AUTHOR]

We report a gate-voltage modulation on the weak anti-localization of individual topological insulator Bi2Se3 nanoribbons. The phase coherence length decreases with decreasing the carrier density of the surface states on the bottom surface of the Bi2Se3 nanoribbon as tuning the gate voltage from 0 to --100 V, indicating that the electron-electron interaction dominates the decoherence at low carrier density. Furthermore, we observe an abnormal conductance decline at positive gate voltage regime, which is ascribed to the capture of surface carriers by the trapping centers in the surface oxidation layer. [ABSTRACT FROM AUTHOR]

The Schottky diodes based on graphene/GaN interface are fabricated and demonstrated for the dual-wavelength photodetection of ultraviolet (UV) and green lights. The physical mechanisms of the photoelectric response of the diodes with different light wavelengths are different. For UV illumination, the photo-generated carriers lower the Schottky barrier and increase the photocurrent. For green light illumination, as the photon energy is smaller than the bandgap of GaN, the hot electrons excited in graphene via internal photoemission are responsible for the photoelectric response. Using graphene as a transparent electrode, the diodes show a ~mS photoresponse, providing an alternative route toward multi-wavelength photodetectors. [ABSTRACT FROM AUTHOR]

We develop a simple method to fabricate the two-stacked graphene monolayers and investigate the electronic transport in such a system. The independence of the two graphene monolayers gives rise to the asymmetric resistance-gate voltage curves and an eight-fold degeneracy of Landau level. The position of the maximum resistance of the transfer curves shifts towards higher gate voltage with increasing magnetic field, which is attributed to the magnetic field induced interlayer decoupling of the stacked graphene monolayers. [ABSTRACT FROM AUTHOR]

We investigate magnetotransport in the vicinity of the charge neutral point (CNP) in bilayer graphene at low temperatures. The CNP is found to vary with applied magnetic fields. Through measuring the transfer curves under different magnetic fields and at different temperatures, the temperature dependence of the peak resistivity at the CNP and under a fixed magnetic field is extracted. At low temperatures, it is found that the peak resistivity at the CNP increases exponentially with decreasing temperature under 14 T, which indicates the gap opening in zero-energy Landau level. The origins of such magnetic field induced insulating behavior are discussed. [ABSTRACT FROM AUTHOR]

Magnetotransport measurements of topological insulators are very important to reveal the exotic topological surface states for spintronic applications. However, the novel properties related to the surface Dirac fermions are usually accompanied by a large linear magnetoresistance under perpendicular magnetic field, which makes the identification of the surface states obscure. Here, we report prominent Shubnikov-de Haas (SdH) oscillations under an in-plane magnetic field, which are identified to originate from the surface states in the sidewalls of topological insulator Bi2Se3 nanoplates. Importantly, the SdH oscillations appear with a dramatically weakened magnetoresistance background, offering an easy path to probe the surface states directly when the coexistence of surface states and bulk conduction is inevitable. Moreover, under a perpendicular magnetic field, the oscillations in Hall conductivity have peak-to-valley amplitudes of 2 e2/h, giving confidence to achieve a quantum Hall effect in this system. A cross-section view of the nanoplate shows that the sidewall is (015) facet dominant and therefore forms a 58° angle with regard to the top/ bottom surface instead of being perpendicular; this gives credit to the surface states' behavior as two-dimensional transport. [ABSTRACT FROM AUTHOR]

We report a new type of memory device based on insulating LaAlO3/SrTiO3 (LAO/STO) hetero-interface. The microstructures of the LAO/STO interface are characterized by Cs-corrected scanning transmission electron microscopy, which reveals the element intermixing at the interface. The inhomogeneous element distribution may result in carrier localization, which is responsible for the insulating state. The insulating state of such interface can be converted to metallic state by light illumination and the metallic state maintains after light off due to giant persistent photoconductivity (PPC) effect. The on/off ratio between the PPC and the initial dark conductance is as large as 105. The metallic state also can be converted back to insulating state by applying gate voltage. Reversible and reproducible resistive switching makes LAO/STO interface promising as a nonvolatile memory. Our results deepen the understanding of PPC phenomenon in LAO/STO, and pave the way for the development of all-oxide electronics integrating information storage devices [ABSTRACT FROM AUTHOR]

We report experimental results on the universal conductance fluctuations (UCFs) in the bilayer graphene system. The UCF properties under different temperatures, magnetic fields and current bias were investigated. An anomalous current-dependent UCF was observed: the rms amplitude of the conductance fluctuations is inversely proportional to the current bias. The detailed physical mechanisms were discussed by involving the confined scattering of chiral fermions in graphene. [ABSTRACT FROM AUTHOR]