Browsing by Author "Tang, Chi-Shung"

Now showing 1 - 5 of 5

Double-finger-gate controlled spin-resolved resonant quantum transport in the presence of a Rashba-Zeeman gap
(2015-03-04)
Tang, Chi-Shung
;
Tseng, Shu-Ting
;
Gudmundsson, Vidar
;
Cheng, Shun-Jen
;
電子物理學系
We investigate double finger gate (DFG) controlled spin-resolved resonant transport properties in an n-type quantum channel with a Rashba-Zeeman (RZ) subband energy gap. By appropriately tuning the DFG in the strong Rashba coupling regime, resonant state structures in conductance can be found that are sensitive to the length of the DFG system. Furthermore, a hole-like bound state feature below the RZ gap and an electron-like quasi-bound state feature at the threshold of the upper spin branch can be found that is insensitive to the length of the DFG system.
Engineered spin-state transitions of two interacting electrons in semiconductor nanowire quantum dots
(2010-06-11)
Chen, Yan-Ting
;
Cheng, Shun-Jen
;
Tang, Chi-Shung
;
電子物理學系
;
Department of Electrophysics
Spin properties of two interacting electrons in a quantum dot (QD) embedded in a nanowire with controlled aspect ratio and longitudinal magnetic fields are investigated by using a configuration-interaction (CI) method. The developed CI theory based on a three-dimensional parabolic model provides explicit formulations of the Coulomb matrix elements and allows for straightforward and efficient numerical implementation. Our studies reveal fruitful features of spin-singlet-triplet transitions of two electrons confined in a nanowire QD, as a consequence of the competing effects of geometry-controlled kinetic-energy quantization, Coulomb interaction, and spin-Zeeman energy. The developed theory is further employed to study various spin states of two quantum-confined electrons in the regime of "crossover" dimensionality, from quasi-two-dimensional (disklike) QDs to finite one-dimensional (rodlike) QDs.
Finger-gate manipulated quantum transport in a semiconductor narrow constriction with spin-orbit interactions and Zeeman effect
(2012-09-24)
Tang, Chi-Shung
;
Chang, Shu-Yu
;
Cheng, Shun-Jen
;
電子物理學系
;
Department of Electrophysics
The authors investigate quantum transport in a narrow constriction fabricated by narrow-band-gap semiconductor materials with spin-orbit couplings. We consider the Rashba-Dresselhaus (RD) spin-orbit interactions (SOIs) and the Zeeman effect induced by an in-plane magnetic field along the transport direction. The interplay of the RD SOI and the Zeeman effect may induce a SOI-Zeeman gap and influence the transport properties. We demonstrate that an attractive scattering potential may induce an electronlike quasi-bound-state feature and manifest the RD-SOI-Zeeman induced Fano line shape in conductance. Furthermore, a repulsive scattering potential may induce a holelike quasi-bound-state feature on the subband top of the lower spin branch.
Finger-gate manipulated quantum transport in Dirac materials
(2015-05-27)
Kleftogiannis, Ioannis
;
Tang, Chi-Shung
;
Cheng, Shun-Jen
;
電子物理學系
;
Department of Electrophysics
We investigate the quantum transport properties of multichannel nanoribbons made of materials described by the Dirac equation, under an in-plane magnetic field. In the low energy regime, positive and negative finger-gate potentials allow the electrons to make intra-subband transitions via hole-like or electron-like quasibound states (QBS), respectively, resulting in dips in the conductance. In the high energy regime, double dip structures in the conductance are found, attributed to spin-flip or spin-nonflip inter-subband transitions through the QBSs. Inverting the finger-gate polarity offers the possibility to manipulate the spin polarized electronic transport to achieve a controlled spin-switch.
Spectral properties and magneto-optical excitations in semiconductor double rings under Rashba spin-orbit interaction
(2007-04-01)
Kuan, Wen-Hsuan
;
Tang, Chi-Shung
;
Chang, Cheng-Hung
;
物理研究所
;
Institute of Physics
We have numerically solved the Hamiltonian of an electron in a semiconductor double ring subjected to the magnetic flux and Rashba spin-orbit interaction. It is found that the Aharonov-Bohm energy spectrum reveals multizigzag periodic structures. The investigations of spin-dependent electron dynamics via Rabi oscillations in two-level and three-level systems demonstrate the possibility of manipulating quantum states. Our results show that the optimal control of photon-assisted inter-ring transitions can be achieved by employing cascade-type and Lambda-type transition mechanisms. Under chirped pulse impulsions, a robust and complete transfer of an electron to the final state is shown to coincide with the estimation of the Landau-Zener formula.