4,518 research outputs found

    Direct sampling of the Susskind-Glogower phase distributions

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    Coarse-grained phase distributions are introduced that approximate to the Susskind--Glogower cosine and sine phase distributions. The integral relations between the phase distributions and the phase-parametrized field-strength distributions observable in balanced homodyning are derived and the integral kernels are analyzed. It is shown that the phase distributions can be directly sampled from the field-strength distributions which offers the possibility of measuring the Susskind--Glogower cosine and sine phase distributions with sufficiently well accuracy. Numerical simulations are performed to demonstrate the applicability of the method.Comment: 10 figures using a4.st

    Optical Study of the Free Carrier Response of LaTiO3/SrTiO3 Superlattices

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    We used infrared spectroscopic ellipsometry to investigate the electronic properties of LaTiO3/SrTiO3 superlattices (SLs). Our results indicated that, independent of the SL periodicity and individual layer-thickness, the SLs exhibited a Drude metallic response with sheet carrier density per interface ~3x10^14 cm^-2. This is probably due to the leakage of d-electrons at interfaces from the Mott insulator LaTiO3 to the band insulator SrTiO3. We observed a carrier relaxation time ~ 35 fs and mobility ~ 35 cm^2V^-1s^-1 at 10 K, and an unusual temperature dependence of carrier density that was attributed to the dielectric screening of quantum paraelectric SrTiO3.Comment: 4 pages, 4 figure

    Frictional Drag between Two Dilute Two-Dimensional Hole Layers

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    We report drag measurements on dilute double layer two-dimensional hole systems in the regime of r_s=19~39. We observed a strong enhancement of the drag over the simple Boltzmann calculations of Coulomb interaction, and deviations from the T^2 dependence which cannot be explained by phonon-mediated, plasmon-enhanced, or disorder-related processes. We suggest that this deviation results from interaction effects in the dilute regime.Comment: 4 pages, 3 figures, accepted in Phys. Rev. Lett. Added single layer transport dat

    Magnetic Field Induced Insulating Phases at Large rsr_s

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    Exploring a backgated low density two-dimensional hole sample in the large rsr_s regime we found a surprisingly rich phase diagram. At the highest densities, beside the ν=1/3\nu=1/3, 2/3, and 2/5 fractional quantum Hall states, we observe both of the previously reported high field insulating and reentrant insulating phases. As the density is lowered, the reentrant insulating phase initially strengthens, then it unexpectedly starts weakening until it completely dissapears. At the lowest densities the terminal quantum Hall state moves from ν=1/3\nu=1/3 to ν=1\nu=1. The intricate behavior of the insulating phases can be explained by a non-monotonic melting line in the ν\nu-rsr_s phase space

    Topological insulators in the quaternary chalcogenide compounds and ternary famatinite compounds

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    We present first-principles calculations to predict several three dimensional (3D) topological insulators in quaternary chalcogenide compounds which are made of I2_2-II-IV-VI4_4 compositions and in ternary compositions of I3_3-V-VI4_4 famatinite compounds. Among the large members of these two families, we give examples of naturally occurring compounds which are mainly Cu-based chalcogenides. We show that these materials are candidates of 3D topological insulators or can be tuned to obtain topological phase transition by manipulating the atomic number of the other cation and anion elements. A band inversion can occur at a single point Γ\Gamma with considerably large inversion strength, in addition to the opening of a bulk band gap throughout the Brillouin zone. We also demonstrate that both of these families are related to each other by cross-substitutions of cations in the underlying tetragonal structure and that one can suitably tune their topological properties in a desired manner.Comment: 7 pages, 4 figure

    F-TOUCH Sensor: Concurrent Geometry Per-ception and Multi-axis Force Measurement

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    Dielectric constants of Ir, Ru, Pt, and IrO2: Contributions from bound charges

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    We investigated the dielectric functions ϵ\epsilon(ω\omega) of Ir, Ru, Pt, and IrO2_2, which are commonly used as electrodes in ferroelectric thin film applications. In particular, we investigated the contributions from bound charges ϵb\epsilon^{b}(ω\omega), since these are important scientifically as well as technologically: the ϵ1b\epsilon_1^{b}(0) of a metal electrode is one of the major factors determining the depolarization field inside a ferroelectric capacitor. To obtain ϵ1b\epsilon_1^{b}(0), we measured reflectivity spectra of sputtered Pt, Ir, Ru, and IrO2 films in a wide photon energy range between 3.7 meV and 20 eV. We used a Kramers-Kronig transformation to obtain real and imaginary dielectric functions, and then used Drude-Lorentz oscillator fittings to extract ϵ1b\epsilon_1^{b}(0) values. Ir, Ru, Pt, and IrO2_2 produced experimental ϵ1b\epsilon_1^{b}(0) values of 48±\pm10, 82±\pm10, 58±\pm10, and 29±\pm5, respectively, which are in good agreement with values obtained using first-principles calculations. These values are much higher than those for noble metals such as Cu, Ag, and Au because transition metals and IrO2_2 have such strong d-d transitions below 2.0 eV. High ϵ1b\epsilon_1^{b}(0) values will reduce the depolarization field in ferroelectric capacitors, making these materials good candidates for use as electrodes in ferroelectric applications.Comment: 26 pages, 6 figures, 2 table
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