Browsing by Author "Hsue, YC"

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Andreev scattering in semiconductor-superconductor junctions containing a finite width semiconductor region applied by magnetic fields
(2004-05-01)
Hsue, YC
;
Yang, TJ
;
Gu, BY
;
Wang, J
;
電子物理學系
We present numerical studies of conductance of quasi-particles (QPs) in junctions consisting of semiconductor (Sm) two-dimensional electronic gas (2DEG) and superconductor (S) containing a finite width 2DEG region (referred to magnetic barrier) applied by a magnetic field perpendicular to the 2DEG plane. Total conductance as a function of beta = mu(N)/homega(c), (where mu(N) is the chemical potential of semiconductor and omega(c) = eB/cm(N)(*) is the cyclotron frequency) strongly depends on the normal or superconducting state of the superconductor. It demonstrates that the Andreev reflection (AR) plays a dominant role. The total conductance of G((NBN)) or G((NBS)) as a function of beta for the NBN or NBS junction displays monotonically increasing behavior with different rising slopes. We observe the existence of a critical magnetic field for switching off the conductance. This critical field of G((NBS)) is a half of that of G((NBN)) in the matching case of the Fermi level and effective mass of QPs in materials forming the junctions. G((NBS)) is usually larger than G((NBN)) for a given magnetic field. The 3D plot of the conductance G((NBN)) and G((NBS)) as functions of beta and the incident angle theta of the QPs displays a flat plateau over a finite domain region of [beta,theta]. However, in the mismatching case of the Fermi energy and effective mass of QPs, G((NBS)) is lower than G((NBN)) because the AR of the holelike QPs now becomes incomplete and normal reflection (NR) of the electronlike QPs is considerably enhanced. The corresponding 3D plot of conductance against beta and theta exhibits heavy spike oscillations around its occupied boundary. We present explicit analytic expressions of the conductance of QPs for this model junction on the basis of classical cyclotron orbit of the QPs in magnetic fields and the quantum mechanical calculation. The characteristics of conductance can be well interpreted by this phenomenological physical picture.
Applying a modified plane-wave expansion method to the calculations of transmittivity and reflectivity of a semi-infinite photonic crystal
(2004-07-01)
Hsue, YC
;
Yang, TJ
;
電子物理學系
;
Department of Electrophysics
We propose a modified plane-wave expansion method to calculate transmittivity and reflectivity of a semi-infinite photonic crystal (PC) with interface. This method is based on an expanded completeness basis, including both the propagation and evanescence modes. We use this approach to deal with two kinds of problems: one is to determine the normal direction of the largest attenuation strength for a semi-infinite PC in the gap frequencies; the other is to calculate the transmittivity and reflectivity of a PC slab. To demonstrate the extensive utilization of our approach, we revisit the same system as studied by K. Sakoda [Phys. Rev. B 52, 8992 (1995)] and find that our results are in good agreement with ones obtained by Sakoda's paper.
Contour of the attenuated length of an evanescent wave at constant frequency within a band gap of photonic crystal
(2004-02-01)
Hsue, YC
;
Yang, TJ
;
電子物理學系
;
Department of Electrophysics
The plane wave method is normally applied to determine the eigenfrequency of a two-dimensional (2D) photonic crystal. A slight change to this eigenvalue equation makes the wave number its eigenvalue providing a direct means to determine the attenuated length of the evanescent modes at the frequency within the photonic band gap. The contour of the length of attenuation of the evanescent modes in a square lattice can be determined using the proposed wave number eigenvalue equation. The wave number eigenvalue equation for the two-dimensional (3D) photonic crystal can also be obtained using a derivation similar to that for the 2D photonic crystal. Possible applications of the proposed calculation-method are presented. (C) 2003 Elsevier Ltd. All rights reserved.
Magnetoconductance oscillations in semiconductor-superconductor junctions with a laterally isolating barrier layer inside semiconductor region
(2003-07-01)
Hsue, YC
;
Yang, TJ
;
Gu, BY
;
Wang, J
;
電子物理學系
The oscillatory characteristics of magnetoconductance for a junction composed of a superconductor and a semiconductor, in which two parallel quantum wave guides are coupled with each other through a potential barrier layer, are studied systematically. To model the imperfectness of the interface, we introduce a delta-function scattering potential barrier lying close to the interface of the junction. The magnetoconductance oscillations (MCO) in this system stem from two sources: one is the interference of wave functions of quasi-particles due to multiple Andreev reflections at the interface; the other is attributed to the variation of the number of the propagation modes when introducing the isolating barrier layer. The introduction of the isolating layer in the quantum wave-guides strongly modifies MCO. We also present a physical picture for the MCO based on a phenomenological argument. The theoretically fitted results are in good agreement with numerical ones.
Oscillations of magnetoconductance in semiconductor-superconductor junctions with a laterally potential barrier isolator inside semiconductor region
(2003-05-01)
Yang, TJ
;
Hsue, YC
;
Gu, BY
;
電子物理學系
;
Department of Electrophysics
Magnetoconductance (MC) injunctions of a superconductor and a semiconductor (Sm) consisting of two parallel quantum waveguides (QW) coupled through a potential barrier under a perpendicular applied magnetic field in the semiconductor region is studied theoretically. The results of MC showing a series of oscillations with stepwise platform and spikes may be understood well within the phenomenological argument similar to Y. Asano (Phys. Rev. B 61 (2000) 1732) proposed. The oscillatory peaks of the MC in the dual QW are found essentially due to the variation of the number of the propagation modes. (C) 2003 Elsevier Science B.V. All rights reserved.