Showing papers by "Hiroshi Ishikawa published in 1997"
TL;DR: In this article, temperature dependence of self-formed quantum dot lasers with a multi-stacked dot layer has been investigated in detail, and it was shown that a discontinuous shift of lasing wavelength from the second subband to the ground state is associated with lowering temperature, which is strongly related to emission efficiency of quantum dots and thermal excitation of carriers to higher order subbands.
Abstract: Temperature dependence of self-formed quantum dot lasers with a multi-stacked dot layer has been investigated in detail. Lasers oscillating at different subbands exhibit different behaviors against temperature change both in the spectral characteristics and the threshold current. A discontinuous shift of lasing wavelength from the second subband to the ground state is observed with lowering temperature, which is strongly related to emission efficiency of quantum dots and thermal excitation of carriers to higher-order subbands. High characteristic temperature over 300 K has been achieved in a laser with high-reflection coating on both facets in the temperature range 60–200 K.
88 citations
TL;DR: In this paper, a heavily Pb-doped Bi2Sr2CaCu2Ox (Bi-2212) tape has been prepared using an isothermal partial melting method.
Abstract: A heavily Pb-doped Bi2Sr2CaCu2Ox (Bi-2212) tape has been prepared using an isothermal partial melting method. Width of magnetic hysteresis (ΔM) normalized by ΔM under 0 Oe decreases with increasing magnetic field (H∥c axis) at 20–60 K; this occurs more rapidly in pure Bi-2212 tape (Pb-free tape) than in Pb-doped tape. Irreversibility field under the H∥c axis is elevated by Pb doping at 20–60 K. Moreover, a decrease in transport critical current density (Jc) with increasing H∥c axis is reduced by Pb doping at 20–60 K. In particular, a peak is observed at 2.0 kOe in Jc–H curves at 20 and 30 K. Hole concentration in the Pb-doped tape seems to be close to the optimum, as magnetic superconducting transition starts at 91 K. Therefore, the above results are due to production of new pinning centers induced by applying the magnetic field. It is clear that heavy Pb doping is effective for Bi-2212 polycrystalline tape in producing efficient pinning centers for the H∥c axis as reported in Bi-2212 single crystals.
7 citations