Browsing by Author "Cheng, K. A."

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Enhanced Phase Relaxation in a Hybrid Ferromagnet/Semiconductor System
(2009-07-01)
Chen, Kuang Yao
;
Yang, Chun-Kai
;
Liang, C. -T.
;
Aoki, N.
;
Ochiai, Y.
Hybrid ferromagnet/semiconductor systems have been the focus of considerable attention because of the transport properties of two-dimensional electron systems and their potential applications to magnetic storage and sensing devices. We use the weak localization effect to probe the dephasing mechanism at low temperatures. In our study, the zero-temperature phase-relaxation rate can be enhanced in a hybrid ferromagnet/semiconductor system, which may he due to the inhomogeneous magnetic field emanating from the Ni film. The result may improve understanding of the issue of zero-temperature dephasing in disordered systems.
Probing Insulator-quantum Hall Transitions by Current Heating
(2009-07-01)
Chen, Kuang Yao
;
Liang, C. -T.
;
Aoki, N.
;
Ochiai, Y.
;
Cheng, K. A.
We report a magneto-transport study on the two-dimensional electron system (2DES) in an AlGaAs/GaAs heterostructure. The direct insulator to quantum Hall conductor transition is observed at low temperatures by increasing the magnetic field B perpendicular to the 2DES. We can also observe the transition by varying the current I and find a relation T(e) similar to I(a) between electron effective temperature T(e) and current. Here, a denotes the exponent for the power law. The exponent a, however, can have different values on the two sides of the transition point, which indicates different inelastic scattering mechanisms in the low-field insulator and in the quantum Hall conductor.
Probing Landau quantization with the presence of insulator-quantum Hall transition in a GaAs two-dimensional electron system
(2008-07-23)
Chen, Kuang Yao
;
Chang, Y. H.
;
Liang, C-T
;
Aoki, N.
;
Ochiai, Y.
Magneto-transport measurements are performed on the two-dimensional electron system (2DES) in an AlGaAs/GaAs heterostructure. By increasing the magnetic field perpendicular to the 2DES, magneto-resistivity oscillations due to Landau quantization can be identified just near the direct insulator-quantum Hall (I-QH) transition. However, different mobilities are obtained from the oscillations and transition point. Our study shows that the direct I-QH transition does not always correspond to the onset of strong localization.
Probing mobility gaps at resistivity minima in the integer quantum Hall effect
(2008)
Liang, C. -T.
;
Chen, K. Y.
;
Wu, Jau-Yang
;
Lin, S. D.
;
Lin, Li-Hung
Magneto-transport measurements are performed on the AlGaAs/GaAs quantum Hall (QH) devices fabricated recently by our group. A series of Hall plateaus are observed with increasing the perpendicular magnetic field, and the mobility gaps resulting from localization effects are investigated at the minima in the longitudinal resistivity. Only the gap corresponding to the filling factor i=2 is close to the expected cyclotron energy, and our study supports that the low-field QH conductors may suffer problems due to insufficient localization. The anomalous change on the Hall slope is observed when the i=3 plateau is destroyed by the large current.