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The various wireless networks have made the ambient radio frequency signals around the world. Wireless information and power transfer enables the devices to recycle energy from these ambient radio frequency signals and process information simultaneously. In this paper, we develop a wireless information and power transfer protocol in two-way amplify-and-forward relaying channels, where two sources exchange information via an energy harvesting relay node. The relay node collects energy from the received signals and uses it to provide the transmission power to forward the received signals. We analytically derive the exact expressions of the outage probability, the ergodic capacity and the finite-SNR diversity-multiplexing trade-off (DMT). Furthermore, the tight closed-form upper and lower bounds of the outage probability and the ergodic capacity are then developed. Moreover, the impact of the power splitting ratio is also evaluated and analyzed. Finally, we show that compared to the non-cooperative relaying scheme, the proposed protocol is a green solution to offer higher transmission rate and more reliable communication without consuming additional resource., Comment: Submitted to ICC 2014

Using Terahertz Time-Domain Spectroscopy, we study the temperature-dependent complex optical conductivity of the topological insulator, Bi$_{1.5}$Sb$_{0.5}$Te$_{1.8}$Se$_{1.2}$ single-crystal from 5 K to 150 K in the terahertz regime (0.4 -- 3.0 THz). We analyze our experimental results using the Drude-Lorentz model, with the Drude component representing the metallic surface state and the Lorentz term representing the bulk insulating state. We find the conductivity to be dominated by the Drude contribution, suggesting the presence of metallic surface states. The low-frequency real conductivity follows a thermally-activated behavior. Its origin is also discussed., Comment: 5 pages, 5 figures

We present evidence of topological surface states in beta-Ag2Te through first-principles calculations and periodic quantum interference effect in single crystalline nanoribbon. Our first-principles calculations show that beta-Ag2Te is a topological insulator with a gapless Dirac cone with strong anisotropy. To experimentally probe the topological surface state, we synthesized high quality beta-Ag2Te nanoribbons and performed electron transport measurements. The coexistence of pronounced Aharonov-Bohm oscillations and weak Altshuler-Aronov-Spivak oscillations clearly demonstrates coherent electron transport around the perimeter of beta-Ag2Te nanoribbon and therefore the existence of metallic surface states, which is further supported by the temperature dependence of resistivity for beta-Ag2Te nanoribbons with different cross section areas. Highly anisotropic topological surface state of beta-Ag2Te suggests that the material is a promising material for fundamental study and future spintronic devices., Comment: 23 pages, 5 figures

We report experimental evidence of surface dominated transport in single crystalline nanoflake devices of topological insulator Bi1.5Sb0.5Te1.8Se1.2. The resistivity measurements show dramatic difference between the nanoflake devices and bulk single crystal. The resistivity and Hall analysis based on a two-channel model indicates that ~99% surface transport contribution can be realized in 200 nm thick BSTS nanoflake devices. Using standard bottom gate with SiO2 as a dielectric layer, pronounced ambipolar electric field effect was observed in devices fabricated with flakes of 100 - 200 nm thick. Moreover, angle-dependent magneto-resistances of a nanoflake device with thickness of 596 nm are fitted to a universal curve for the perpendicular component of the applied magnetic field. The value of phase coherence length obtained from 2D weak antilocalization fitting further confirmed the surface dominated transport. Our results open a path for realization of novel electric and spintronic devices based on the topological helical surface states., Comment: 20 pages, 4 figures