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We investigate the electron transport through a zigzag graphene nanoribbon with a staggered sublattice potential and a certain asymmetric boundary potential. By using the tight binding model to combine with the nonequilibrium Green's function theory and the Landauer-Büttiker formalism, the energy band structure, conductance, and conductance fluctuation are calculated. We find that an energy gap opens up due to the inversion symmetry breaking by the staggered sublattice potential. By further tuning the boundary potential, the gapless valley-dependent edge states are achieved in which the carriers with the different valleys on a given boundary propagate in opposite directions. Furthermore, we study the effect of long range disorder on the transport properties of the valley-dependent edge states. The results show that the conductance plateau 4e2/h contributed by the edge states can be maintained well in a broad range of disorder strength for low-density disorder, indicating the robustness of the valley-dependent transport. In addition, the conductance fluctuation is also studied, and the fluctuation almost vanishes at weak disorder. On the other hand, at intermediate disorder strength with the system in the diffusive regime, the universal conductance fluctuation is exhibited. The conductance fluctuation is independent of various parameters, e.g., the ribbon width, the disorder range, and the disorder density. [ABSTRACT FROM AUTHOR]

The transport property of a superconducting Pb nanobridge, which is carved by focus ion beam technique from an atomically flat single-crystal Pb thin film grown on Si(111) substrate, is investigated. Below the superconducting transition temperature TC, the nanobridge exhibits a series of sharp voltage steps as a function of current. The multiple voltage steps are interpreted as a consequence of spatially localized phase slip centers or hot-spot formation in the bridge. Just below the critical current, the voltages versus current curve shows a power-law behavior in the low temperature region, but Ohmic near the TC. The thermally activated phase slip, quantum phase slip, and imhomogeneity in a one-dimensional superconducting system may contribute to the observed results. [ABSTRACT FROM AUTHOR]

Presents a study that calculated the electronic density of states (DOS) of a two-dimensional electron gas (2DEG) in the presence of an external magnetic field. Problem with the nature of the DOS of a 2DEG; Physical parameters in the DOS theory; Basic limitations of the theory.

Studies the intrinsic exciton transitions in GaN semiconductors. Experimental procedure used; Stability of the semiconductors; Results and discussion of the study.

Diode is a key device in electronics: the charge current can flow through the device under a forward bias, while almost no current flows under a reverse bias. Here, we propose a corresponding device in spintronics: the spin-current diode, in which the forward spin current is large but the reversed one is negligible. We show that the lead/ferromagnetic quantum dot/lead system and the lead/ferromagnetic semiconductor/lead junction can work as spin-current diodes. The spin-current diode, a low dissipation device, may have important applications in spintronics, as the conventional charge-current diode does in electronics. [ABSTRACT FROM AUTHOR]

Using focused ion beam etching technique, the authors fabricated a 28 atomic monolayers thick, 500 nm wide, and 10 μm long Pb nanobridge from an atomically flat Pb thin film grown on Si by molecular beam epitaxy. Electric transport measurements show exotic resistance oscillations in the superconducting state far below its critical field HC and cascading terraces near the superconducting transition region. Furthermore, the bridge shows an unusual semiconducting behavior above the superconducting transition temperature TC. The results are in contrast to those observed in its counterpart of the two-dimensional thin film. [ABSTRACT FROM AUTHOR]

Using atomically flat single-crystal Pb ultrathin films grown on Si(111) substrate by molecular beam epitaxy, we fabricated Pb nanobelts of 28 atomic monolayers thick, 285 nm wide, and 10 μm long by focus ion beam technique. The transport property is measured and the results are compared to the Pb films. We find that below the superconducting transition temperature TC, the resistance of the nanobelts exhibits clear and reproducible oscillations as a function of perpendicular magnetic field, which are not observed in the Pb films. In addition, TC enhancement was also observed in the nanobelts. The results suggest that the single-crystal Pb nanobelts prepared on Si semiconductor substrate offer a great opportunity for integrating superconducting circuits in a single Si chip. [ABSTRACT FROM AUTHOR]

We report intrinsic current-voltage properties of ZnO nanowire measured by a four-tip scanning tunneling microscopy (F-STM). It is found that after bending the nanowire with the F-STM the conductance is reduced by about five orders of magnitude. The cathodoluminescent spectra indicate that the ZnO nanowires contain a sizable amount of defects in the surface region, responsible for their conduction. It is suggested that the observed huge conductance changes are caused by the shifting of the surface defect states in the ZnO nanowires in response to the applied surface strain. [ABSTRACT FROM AUTHOR]