Showing papers by "Tae Won Noh published in 1987"
TL;DR: The infrared and far-infrared properties of sintered La/sub 2/NiO/sub 4/ and La/ sub 1.85/Sr/sub 0.15/CuO/ sub 4-//sub y/ grains are modeled accurately within the effective-medium approximation.
Abstract: The infrared and far-infrared properties of sintered La/sub 2/NiO/sub 4/ and La/sub 1.85/Sr/sub 0.15/CuO/sub 4-//sub y/ are modeled accurately within the effective-medium approximation. The electrodynamic properties of La/sub 1.85/Sr/sub 0.15/CuO/sub 4-//sub y/ grains are highly anisotropic with the strong 0.5-eV electronic transition polarized along the low-conductivity crystal direction. The apparent superconducting gap frequency for the sintered material depends crucially on the grain geometry. Our experimental data are fit with needlelike crystallites and 2..delta../k/sub B/T/sub 0/ = 2.6.
39 citations
TL;DR: The product of the Drude model parameters indicates that the plasma oscillations are overdamped and the free-carrier electrodynamics are well described by a frequency-dependent scattering rate which rises linearly in frequency from the dc value and saturates at a value consistent with scattering at the unitarity limit.
Abstract: The conductivity of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}y}$ in the normal state has been obtained from a measurement of the reflectivity over a wide frequency range. The product of the Drude model parameters ${\ensuremath{\omega}}_{p}\ensuremath{\tau}l1$ indicates that the plasma oscillations are overdamped. The free-carrier electrodynamics are well described by a frequency-dependent scattering rate which rises linearly in frequency from the dc value and saturates at a value consistent with scattering at the unitarity limit with a concomitant frequency-dependent mass enhancement.
25 citations
TL;DR: It is found that the lowest ir-active phonon polarized in the high-conductivity plane produces structure in the superconducting gap, the lowest-frequency phonon perpendicular to the plane is overdamped, and the electronic susceptibility is more isotropic for YBa/sub 2/Cu/sub 3/O/sub 7-//sub y/ than for La/sub 1.85/Sr/sub 0.15/CuO/ sub 4-// sub y/.
Abstract: The reflectivity in the superconducting and normal states of YBa/sub 2/Cu/sub 3/O/sub 7-//sub y/ has been reproduced with the effective-medium theory plus an anisotropic dielectric function and the Mattis-Bardeen conductivity with a gap value 2..delta../k/sub B/T/sub c/ = 2.5 to 2.7. We find that the lowest ir-active phonon polarized in the high-conductivity plane produces structure in the superconducting gap, the lowest-frequency phonon perpendicular to the plane is overdamped, and that the electronic susceptibility is more isotropic for YBa/sub 2/Cu/sub 3/O/sub 7-//sub y/ than for La/sub 1.85/Sr/sub 0.15/CuO/sub 4-//sub y/.
15 citations
TL;DR: In this paper, the Mattis-Bardeen theory was used to obtain gap values for the reflectivity of bulk samples, films and single crystals of high-Tc materials.
Abstract: We report measurements of the reflectivity of bulk samples, films and single crystals of high Tc materials. The data are fitted with the Mattis-Bardeen theory to obtain gap values. For sintered samples we find 2Δ/kTc = 2.6, while for YBa2Cu3O7-y films and single crystals 2Δ/kTc = 6.4 and 7.7 respectively.
2 citations
TL;DR: In this article, the magnetic properties in the superconducting state of a composite sample with approximately 35% Y1Ba2Cu3O7-δ and a Tc of 87K were compared with results on a corresponding single phase sample.
2 citations
01 Oct 1987
TL;DR: In this paper, the infrared and far-infrared properties of sintered La/sub 2/Ni0/sub 4/ and La /sub 1.85/Sr/sub 0.15/CuO /sub 4-y/ grains are modeled accurately within the effective medium approximation.
Abstract: The infrared and far-infrared properties of sintered La/sub 2/Ni0/sub 4/ and La/sub 1.85/Sr/sub 0.15/CuO/sub 4-y/ are modeled accurately within the effective-medium approximation. The electrodynamic properties of La/sub 1.85/Sr/sub 0.15/CuO/sub 4-y/ grains are highly anisotropic with the strong 0.5-eV electronic transition polarized along the low-conductivity crystal direction. The apparent superconducting gap frequency for the sintered material depends crucially on the grain geometry. Our experimental data are fit with needle-like crystallines and grain geometry.
1 citations