4,208 research outputs found

    Magnetic Penetration Depth Measurements of Pr2x_{2-x}Cex_xCuO4δ_{4-\delta} Films on Buffered Substrates: Evidence for a Nodeless Gap

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    We report measurements of the inverse squared magnetic penetration depth, λ2(T)\lambda^{-2}(T), in Pr2x_{2-x}Cex_{x}CuO4δ_{4-\delta} (0.115x0.1520.115 \leq x \leq 0.152) superconducting films grown on SrTiO3_3 (001) substrates coated with a buffer layer of insulating Pr2_{2}CuO4_{4}. λ2(0)\lambda^{-2}(0), TcT_c and normal-state resistivities of these films indicate that they are clean and homogeneous. Over a wide range of Ce doping, 0.124x0.1440.124\leq x \leq 0.144, λ2(T)\lambda^{-2}(T) at low TT is flat: it changes by less than 0.15% over a factor of 3 change in TT, indicating a gap in the superconducting density of states. Fits to the first 5% decrease in λ2(T)\lambda^{-2}(T) produce values of the minimum superconducting gap in the range of 0.29Δmin/kBTc1.010.29\leq\Delta_{\rm min}/k_BT_c\leq1.01.Comment: 4 pages 5 figure

    Far-infrared and submillimeter-wave conductivity in electron-doped cuprate La_{2-x}Ce_xCuO_4

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    We performed far-infrared and submillimeter-wave conductivity experiments in the electron-doped cuprate La_{2-x}Ce_xCuO_4 with x = 0.081 (underdoped regime, T_c = 25 K). The onset of the absorption in the superconducting state is gradual in frequency and is inconsistent with the isotropic s-wave gap. Instead, a narrow quasiparticle peak is observed at zero frequency and a second peak at finite frequencies, clear fingerprints of the conductivity in a d-wave superconductor. A far-infrared conductivity peak can be attributed to 4Delta_0, or to 2Delta_0 + Delta_spin, where Delta_spin is the resonance frequency of the spin-fluctuations. The infrared conductivity as well as the suppression of the quasiparticle scattering rate below T_c are qualitatively similar to the results in the hole-doped cuprates.Comment: 5 pages, 4 figures include

    On the peak in the far-infrared conductivity of strongly anisotropic cuprates

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    We investigate the far-infrared and submillimeter-wave conductivity of electron-doped La_(2-x)Ce_xCuO_4 tilted 1 degree off from the ab-plane. The effective conductivity measured for this tilt angle reveals an intensive peak at finite frequency (\nu ~ 50 cm{-1}) due to a mixing of the in-plane and out-of-plane responses. The peak disappears for the pure in-plane response and transforms to the Drude-like contribution. Comparative analysis of the mixed and the in-plane contributions allows to extract the c-axis conductivity which shows a Josephson plasma resonance at 11.7 cm{-1} in the superconducting state.Comment: 4 pages, 4 figures include

    Observation of Andreev bound states in bicrystal grain-boundary Josephson junctions of the electron doped superconductor LaCeCuO

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    We observe a zero-bias conductance peak (ZBCP) in the ab-plane quasiparticle tunneling spectra of thin film grain-boundary Josephson junctions made of the electron doped cuprate superconductor LaCeCuO. An applied magnetic field reduces the spectral weight around zero energy and shifts it non-linearly to higher energies consistent with a Doppler shift of the Andreev bound states (ABS) energy. For all magnetic fields the ZBCP appears simultaneously with the onset of superconductivity. These observations strongly suggest that the ZBCP results from the formation of ABS at the junction interfaces, and, consequently, that there is a sign change in the symmetry of the superconducting order parameter of this compound consistent with a d-wave symmetry.Comment: 9 pages, 7 figures; December 2004, accepted for publication in Phys. Rev.

    Synthesis of infinite-layer LaNiO2 films by metal-organic deposition

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    We report the synthesis of infinite-layer LaNiO2 thin films by metal organic decomposition. Our work is aimed to synthesize perovskite-like oxides with 3d9 electronic configuration, which is common to high-Tc copper oxides. The 3d9 configuration is very rare in oxides other than cuprates. Ni1+ oxides, even though Ni1+ is an unusual oxidation state, may be one of very few candidates. One example of the Ni1+ phases is infinite-layer LaNiO2. The bulk synthesis of LaNiO2 is difficult, but we demonstrate in this article that the thin-film synthesis of LaNiO2 by metal organic decomposition is rather easy. This is due to the advantage of thin films with a large-surface-to-volume ratio, which makes oxygen diffusion prompt. Resistivity measurements indicate that LaNiO2 is essentially a metal but unfortunately with no trace of superconductivity yet.Comment: 13 pages, 4 figure

    Metal-insulator transition and the Pr3+^{3+}/Pr4+^{4+} valence shift in (Pr1y_{1-y}Yy_{y})0.7_{0.7}Ca0.3_{0.3}CoO3_3

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    The magnetic, electric and thermal properties of the (Ln1yLn_{1-y}Yy_{y})0.7_{0.7}Ca0.3_{0.3}CoO3_3 perovskites (LnLn~=~Pr, Nd) were investigated down to very low temperatures. The main attention was given to a peculiar metal-insulator transition, which is observed in the praseodymium based samples with y=0.075y=0.075 and 0.15 at TMI=64T_{M-I}=64 and 132~K, respectively. The study suggests that the transition, reported originally in Pr0.5_{0.5}Ca0.5_{0.5}CoO3_3, is not due to a mere change of cobalt ions from the intermediate- to the low-spin states, but is associated also with a significant electron transfer between Pr3+^{3+} and Co3+^{3+}/Co4+^{4+} sites, so that the praseodymium ions occur below TMIT_{M-I} in a mixed Pr3+^{3+}/Pr4+^{4+} valence. The presence of Pr4+^{4+} ions in the insulating phase of the yttrium doped samples (Pr1y_{1-y}Yy_{y})0.7_{0.7}Ca0.3_{0.3}CoO3_3 is evidenced by Schottky peak originating in Zeeman splitting of the ground state Kramers doublet. The peak is absent in pure Pr0.7_{0.7}Ca0.3_{0.3}CoO3_3 in which metallic phase, based solely on non-Kramers Pr3+^{3+} ions, is retained down to the lowest temperature.Comment: 10 figure

    Development of a low-mass and high-efficiency charged particle detector

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    We developed a low-mass and high-efficiency charged particle detector for an experimental study of the rare decay KLπ0ννˉK_L \rightarrow \pi^0 \nu \bar{\nu}. The detector is important to suppress the background with charged particles to the level below the signal branching ratio predicted by the Standard Model (O(1011^{-11})). The detector consists of two layers of 3-mm-thick plastic scintillators with wavelength shifting fibers embedded and Multi Pixel Photon Counters for readout. We manufactured the counter and evaluated the performance such as light yield, timing resolution, and efficiency. With this design, we achieved the inefficiency per layer against penetrating charged particles to be less than 1.5×1051.5 \times 10^{-5}, which satisfies the requirement of the KOTO experiment determined from simulation studies.Comment: 20 pages, 18 figure
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