Browsing by Author "Chen, K"

Now showing 1 - 3 of 3

Investigation of hysteresis and transport critical current under field cycle for Bi-based multifilamentary tapes
(1996-04-01)
Horng, L
;
Chen, K
;
Lee, WD
;
Yang, TJ
;
電子物理學系
The transport properties of Hi-based multifilamentary tapes on magnetic field have been studied. The tapes were fabricated by powder-in-silver tubing technique followed by appropriate sintering. The hysteretic behavior of transport critical current of the tapes with bending strain has been investigated. The experimental data are obtained at 77 K under field cycling from 0 to 1000 G to 0. The critical current density under a field does not vary when bending strain is smaller than a critical bending strain, and then decreases gradually with increasing bending strain. The normalized values are unaffected by bending strain up to 1.31%. The remnant magnetic filed H-m associated with the flux pinning force is obtained by an empirical expression, which is similar to generalized critical state model. The H-m is almost a constant for all bending strain. This observation indicates that the intrinsic pinning properties are not varied with bending strain.
Transmission properties of electrons in a T-type opened quantum waveguide with inhomogeneous magnetic fields
(1999-03-30)
Chen, K
;
Gu, BY
;
Lin, YK
;
Chuu, DS
;
電子物理學系
We calculate the quantum-mechanical transmission of electrons in a T-shaped opened quantum waveguide (TOQW) subjected to an inhomogeneous magnetic field perpendicular to the TOQW plane with the use of the mode-matching technique. An electron incident through one branch of the waveguide can travel into the other two channels in the quantum ballistic regime. We find that transmission coefficients in two channels exhibit quite difference from each other and depend sensitively on geometric parameters and magnetic configurations. Sharp peaks with unity amplitude and deep dips are observed in transmission spectrum as a function of the Fermi energy of the incident electrons at some high fields. We also study the variation of transmission with magnetic field and find that the transmission exhibits various patterns such as step drop, deep dips, wide valley, large oscillations, or without any structure, sensitively depending on the incident electron energy and magnetic confinement configurations. It is expected that by applying inhomogeneous magnetic fields to the TOQW with appropriate magnetic configuration one may provide an available way to control transmission property of the TOQW to match practical requirements in devices.
Triplet exciton formation and decay in polyfluorene light-emitting diodes
(2005-09-01)
Liao, HH
;
Meng, HF
;
Horng, SF
;
Shy, JT
;
Chen, K
We study the triplet excitons in poly (9,9-dioctylfluorene-2,7-diyl) light-emitting diode using infrared induced absorption. The infrared absorption is exclusively due to the triplet excitons and there is no spectral overlap with any other species. A strong suppression of the triplet exciton density relative to the singlet by voltage is observed. Through an unique independent measurement on the triplet exciton lifetime it is shown that the suppression solely comes from triplet exciton quenching by current injection. The triplet-to-singlet exciton formation ratio is independent of voltage as well as temperature, implying a spin-independent exciton formation.