Browsing by Author "Liang, C. -T."

Now showing 1 - 11 of 11

Controllable Disorder in a Hybrid Nanoelectronic System: Realization of a Superconducting Diode
(2013-07-24)
Lo, Shun-Tsung
;
Chen, Kuang Yao
;
Lin, Sheng-Di
;
Wu, J-Y.
;
Lin, T. L.
We have studied a hybrid nanoelectronic system which consists of an AlGaAs/GaAs two-dimensional electron gas (2DEG) in close proximity (similar to 70 nm) to an Al superconducting nanofilm. By tuning the current through the Al film, we can change the conductance of the 2DEG and furthermore vary the effective disorder in the Al superconducting film in a controllable way. When a high current is injected into the film, screening which couples the Al film and the 2DEG results in a collapse of anti-symmetric behavior in the current-voltage characteristics, V(I) similar to - V(-I), which holds true in a conventional superconductor. Our results may open a new avenue of experimentally realizing a superconducting diode.
Crossover from negative to positive magnetoresistance in a Si delta-doped GaAs single quantum well
(2010-07-01)
Lo, Shun-Tsung
;
Chen, Kuang Yao
;
Su, Yi-Chun
;
Liang, C. -T.
;
Chang, Y. H.
We have performed magnetoresistance measurements on a Si delta-doped GaAs single quantum well With increasing temperature T, a crossover from negative magnetoresistance (NMR) to positive magnetoresistance (PMR) can be observed Our experimental results suggest that such a crossover corresponds to a transition from variable range hopping regime to activated electron transport. This is also consistent with the measured non-monotonic carrier density dependence on T. (C) 2010 Elsevier Ltd All rights reserved.
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.
Huge positive magnetoresistance in a gated AlGaAs/GaAs high electron mobility transistor structure at high temperatures
(2008-03-31)
Liang, C. -T.
;
Tseng, Yen Shung
;
Wu, Jau-Yang
;
Lin, Sheng-Di
;
Yang, Chun-Kai
Magnetoresistivity measurements on a gated AlGaAs/GaAs high electron mobility transistor (HEMT) structure were performed at high temperatures T. By changing the applied gate voltage V(g), we can investigate the observed huge positive magnetoresistance (PMR) at different effective disorder and density inhomogeneity within the same HEMT structure. The observed PMR value increases with increasing disorder in the depletion mode (V(g)<= 0). Moreover, the PMR value is not limited by the quality of the HEMT structure at T=80 K. Such results pave the way for low-cost, high-throughput GaAs-based HEMT fabrication for future magnetic sensing and recording devices fully compatible with the mature HEMT technology. (C) 2008 American Institute of Physics.
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 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.
Probing the coexistence of semiclassical transport and localization in a two-dimensional electron gas using microwave radiation
(2013-03-01)
Hsu, Chang-Shun
;
Kannan, E. S.
;
Portal, J-C.
;
Liang, C. -T.
;
Huang, C. F.
We have performed magnetoresistance measurements on a GaAs/AlGaAs two-dimensional electron gas under microwave heating. Both the magneto-oscillations and magnetoresistance minima are used as electron thermometers to determine the electron effective temperature T-e. When there is no clear cyclotron gap, it is found that T-e determined from these two methods can be substantially different such that we can still distinguish localized electrons from the semiclassical conducting ones. The almost constant T-e obtained from the magnetoresistance minima reveals the survived equivalence between different Landau-band tails under insufficient localization. (C) 2012 Elsevier Ltd. All rights reserved.
Probing the onset of strong localization and electron-electron interactions with the presence of a direct insulator-quantum Hall transition
(2010-10-01)
Lo, Shun-Tsung
;
Chen, Kuang Yao
;
Lin, T. L.
;
Lin, Li-Hung
;
Luo, Dong-Sheng
We have performed low-temperature transport measurements on a disordered two-dimensional electron system (2DES). Features of the strong localization leading to the quantum Hall effect are observed after the 2DES undergoes a direct insulator-quantum Hall transition on increasing the perpendicular magnetic field. However, such a transition does not correspond to the onset of strong localization. The temperature dependences of the Hall resistivity and Hall conductivity reveal the importance of the electron-electron interaction effects for the observed transition in our study. (C) 2010 Elsevier Ltd. All rights reserved.
Probing the onset of strong localization and electron-electron interactions with the presence of a direct insulator-quantum Hall transition
(2010-10-01)
Lo, Shun-Tsung
;
Chen, Kuang Yao
;
Lin, T. L.
;
Lin, Li-Hung
;
Luo, Dong-Sheng
We have performed low-temperature transport measurements on a disordered two-dimensional electron system (2DES). Features of the strong localization leading to the quantum Hall effect are observed after the 2DES undergoes a direct insulator-quantum Hall transition on increasing the perpendicular magnetic field. However, such a transition does not correspond to the onset of strong localization. The temperature dependences of the Hall resistivity and Hall conductivity reveal the importance of the electron-electron interaction effects for the observed transition in our study. (C) 2010 Elsevier Ltd. All rights reserved.
Spin-orbit-coupled superconductivity
(2014-06-25)
Lo, Shun-Tsung
;
Lin, Shih-Wei
;
Wang, Yi-Ting
;
Lin, Sheng-Di
;
Liang, C. -T.
Superconductivity and spin-orbit (SO) interaction have been two separate emerging fields until very recently that the correlation between them seemed to be observed. However, previous experiments concerning SO coupling are performed far beyond the superconducting state and thus a direct demonstration of how SO coupling affects superconductivity remains elusive. Here we investigate the SO coupling in the critical region of superconducting transition on Al nanofilms, in which the strength of disorder and spin relaxation by SO coupling are changed by varying the film thickness. At temperatures T sufficiently above the superconducting critical temperature T-c, clear signature of SO coupling reveals itself in showing a magneto-resistivity peak. When T < T-c, the resistivity peak can still be observed; however, its line-shape is now affected by the onset of the quasi two-dimensional superconductivity. By studying such magneto-resistivity peaks under different strength of spin relaxation, we highlight the important effects of SO interaction on superconductivity.
Superconductivity in an Aluminum Film Grown by Molecular Beam Epitaxy
(2012-08-01)
Liang, C. -T.
;
Yeh, M. -R.
;
Lin, S. D.
;
Lin, S. W.
;
Wu, J. Y.
We report on superconductivity in an aluminum film grown on a GaAs substrate by molecular beam epitaxy (MBE). We show that the quality of the MBE-grown sample is better than that of its counterpart prepared by electron gun evaporation. This is evidenced by the observed much lower resistivity, higher critical current, longer coherence length, and downward critical field-temperature characteristic H-c(T). Our results suggest that a MBE-grown Al thin film can be used to study superconductivity in a relatively clean metal.