Je Huan Koo

Electron plasma wave propagation in external-electrode fluorescent lamps

The optical propagation observed along the positive column of external electrode fluorescent lamps is shown to be an electron plasma wave propagating with the electron thermal speed of (kTe∕m)1∕2. When the luminance of the lamp is 10000–20000cd∕m2, the electron plasma temperature and the plasma density in the positive column are determined to be kTe∼1.26–2.12eV and no∼(1.28–1.69)×1017m−3, respectively.

The spin-gap in high Tc superconductivity

We have investigated the spin-gap in high Tc superconductivity. We obtain the effective exchange integral in the presence of conduction in the ab-plane from the interaction Usd, where the electron–electron interaction is mediated by the localized spin flips. We choose the exchange interaction along the c-axis from the superexchange-type interaction, Usdc. We find the spin-gap from the conducting spin- ladder corresponding to the structure of high Tc superconductors.

Electron drift velocity diagnostics in fine tube external electrode fluorescent lamps

A new non-invasive method for the determination of electron drift velocity has been investigated by measuring the light propagation signals in external electrode fluorescent lamps with two usual operation methods. At the luminance of 12 000 cd m−2 with an operation frequency of 65 kHz, the electron drift velocity in accordance with the propagation speed of light emission is measured to be 2.72 × 105 m s−1. From the electron drift velocity, the electron temperature and the plasma density in the positive column are estimated to be kTe ~ 1.6 eV and ne ~ 4.3 × 1016 m−3, respectively, which agree well with data in the glow discharge plasma of typical fluorescent lamps.

Propagation of a Light-Emitting Wave-Front in a Fine Tube Positive Column Discharge

The propagation velocity of a light-emitting wave-front is observed to be up~2×10+5 m/s before Townsend breakdown and up~5×10+6 m/s after Townsend breakdown along a discharge tube of inner diameter ro~1.2 mm and length of 900 mm relevant to liquid crystal display television backlighting. Before Townsend breakdown, the origin of this wave is the ambipolar diffusion of plasma flux with the propagation speed up∝Da/ro for the plasma bounded by the radius ro with the diffusion coefficient Da along the positive column. After Townsend breakdown, the light-emitting wave-front propagates with the electron plasma wave generated by the pulses of driving voltage. The electron plasma wave propagates such a long distance along the tube without damping due to the effect of localized plasma generation by electron impact ionization collisions. The propagation velocity is described by up~2ue2/ud, which is larger than the electron thermal velocity ue as well as the electron drift velocity ud.

Plasma Diffusion Along a Fine Tube Positive Column

The propagation velocity of light emission is observed to be u_p ~0.92 times10⁺⁵ m/s along a tube of an inner diameter r_o ~1.5 times10^-3 m with an external electrode fluorescent lamp filled with 97% Ne and 3% Ar at a total pressure of 30 torr, a mercury-free lamp without phosphor coating the inside glass wall. The origin of this propagation is shown to be ambipolar diffusion with a plasma diffusion speed of u_p ~ (4.8/r_o)D_a for diffusion coefficient D_a along the positive column. When a high voltage magnitude is applied at the external electrode, a high-density plasma is generated inside the hollow electrode, and the plasma diffuses along the positive column toward the ground electrode.

THE GENERAL KONDO RESISTIVITY BY RENORMALIZED INFINITE SERIES METHOD (RISM)

We investigate the Kondo resistivity using the perturbation methods. We calculate the resistivity above the Kondo temperature using an adjustable infinite series or series from log-function for uncrossed Kondo diagrams. We obtain the energy eigenvalue above the spin glass temperature using this RISM.

Research on Changes in Short Circuit Current of C-Si Solar Cell by Charge Density Waves

We measure solar currents transformed from quantum efficiency as a function of incident angles of solar lights. According to conventional models for solar cells, solar currents can be induced when electrons are separated into electrons and holes in the presence of incident solar lights. On the contrary, solar currents can be possible at the time when pinned charge density waves go beyond the pinning potential barrier under the influence of incident solar beams suggested by some authors. In this experiment, measured solar currents and our theory are in good correspondence to confirm the angle dependence of solar lights.

THE POSSIBILITY OF MAGNETIC FIELD INDUCED SUPERCONDUCTIVITY IN COLOSSAL MAGNETORESISTIVE MANGANITES

We investigate theoretically manganese oxides where the colossal magnetoresistance (CMR) is observed. It is found that CMR is dominated by the internal local field, Hi. In ferromagnetic states, field-induced superconductivity is possible in the case of large magnetic field to reduce Hi near zero.

COEXISTENCE OF SUPERCONDUCTIVITY AND FERROMAGNETISM IN UGe2

We investigate the coexistence of ferromagnetism and superconductivity in UGe2 and Sr2RuO4 in analogy with our previous model3 for high transition temperature superconductivity (HTSC). The Coulomb interaction for triplet electron pairs is reduced by a difference of the exchange interaction. If the electron–electron interaction Usf for UGe2 and Usd for Sr2RuO4 are larger than the reduced Coulomb interaction, superconductivity must happen. Under the same conditions, the coexistence of superconductivity and ferromagnetism is impossible in the case of our scheme, but changing phonons by pressures makes the coexistence possible for UGe2.

Conductivities of zinc oxide by finite block spins

In the current work, we have demonstrated the phase of ZnO by reference to block theory, in which the phase may be considered to show a paramagnetic ordering between block spins, which in turn comprise random spins that have a majority of individual spins in a given direction. By making use of the Curie–Weiss law of block spins for zinc oxide, we obtained the susceptibility for the lower approximation of the Brillouin function and calculated the resistivity. The resistivity of ZnO mainly stems from spin glass-like disorders according to our analysis.