Magnetoresistance anisotropy of a one-dimensional superconducting niobium strip

We investigated confinement effects on the resistive anisotropy of a superconducting niobium strip with a rectangular cross section. When its transverse dimensions are comparable to the superconducting coherence length, the angle dependent magnetoresistances at a fixed temperature can be scaled as R(theta,H) = R(H/Hctheta) where Hctheta =Hc0(cos2theta + gamma(-2)sin2theta)(-1/2) is the angular dependent critical field, gamma is the width to thickness ratio, and Hc0 is the critical field in the thickness direction at theta=0 degrees . The results can be understood in terms of the anisotropic diamagnetic energy for a given field in a one-dimensional superconductor.     

Ultrafast room temperature NH3 sensing with positively gated reduced graphene oxide field-effect transistors

Reduced graphene oxide (R-GO) under a positive gate potential (n-type conductance) exhibits an instantaneous response and fast recovery for NH(3) sensing, far superior to the performance in p-mode at zero/negative gate potential. Our findings have important implications for fast, repeatable, room temperature gas detection using graphene/R-GO.     

Bis-trifluoromethyl Effect: Doubled Transitions in the Rotational Spectra of Hexafluoroisobutene, (CF(3))(2)C═CH(2)

Rotational spectra for hexafluoroisobutene, and its (13)C isotopologues, have been recorded between 8 and 16 GHz using a chirped pulse, Fourier transform microwave spectrometer. Notably, all spectra observed are doubled with separations between the doublets being between 1 and 60 MHz. We propose that the bis-trifluoromethyl groups of the target molecule are staggered in the equilibrium configuration, and that a novel, out-of-phase rotation through a F-CCC-F planar configuration with low barrier (<100 cm(-1)), leads to the observed doubled rotational spectra.     

Thin film ferroelectric photonic crystals and their application to thermo-optic switches

Two-dimensional photonic crystals (PhC) using epitaxial ferroelectric, barium titanate (BTO) thin films as the dielectric medium were fabricated and their thermo-optical response measured and compared to theory. The nanopatterned PhC consists of a square array of air holes 300 nm deep, a period of 780 nm and area 200 × 200 μm². The large refractive index of BTO leads to a high contrast structure that shows strong optical diffraction. Optical diffraction is analyzed along the 〈1 0〉 and 〈1 1〉 directions from phase grating measurements. The thermal tunability of BTO PhC is characterized from the attenuation of the first order diffraction. There is a 3 dB extinction ratio when the temperature increases by 120 °C, which corresponds to an increase of 0.05 in the BTO refractive index. Finite difference time domain (FDTD) technique is used to calculate the PhC band structure and the temperature dependence of the diffraction efficiency. The large change in the diffraction efficiency indicates that thermally tunable BTO PhCs may be useful as active ultra-compact photonic switches.