From localization to Landau quantization in a two-dimensional GaAs electron system containing self-assembled InAs quantum dots (original) (raw)
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Physica E: Low-dimensional Systems and Nanostructures, 2002
We investigate the transport properties of two-dimensional electron gases (2DEG) formed in a GaAs=AlGaAs quantum well, where self-assembled InAs quantum dots were grown at the center of the GaAs well. Due to the resulting strain ÿelds repulsive short-range scattering is experienced by the conduction electrons in the 2DEG. In a perpendicular magnetic ÿeld, there are transitions between quantum Hall liquids at ÿlling factors = 1 and 2 and the insulating phase. We show that the boundary of insulator-Quantum Hall transitions can be identiÿed either by analysing the temperature-independent points in xx or from the peaks in xx at low temperatures and both methods give similar results. ?
Journal of Physics: Condensed Matter, 2008
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, magnetoresistivity oscillations due to Landau quantisation 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 localisation. * ctliang@phys.ntu.edu.tw and ochiai@faculty.chiba-u.jp PACS numbers: 72.15.Rn, 71.70.Di, The insulator to quantum Hall (I-QH) transition in a two-dimensional electron system (2DES) at low perpendicular magnetic fields B has attracted much attention [1, 2,. Theoretically, the direct I-QH transition from the insulator to an integer QH state of ν = 1 is forbidden in an infinite, non-interacting 2DES with arbitrary amount of disorder, where ν is the Landau level filling factor [1, 2, 3]. In such a system, the only allowed state at B = 0 is the insulating one, and the 2DES undergoes the I-QH transition to enter the ν = 1 QH state . Realistically, however, only systems of finite sizes are available, and the effects of the electron-electron (e-e) interaction are significant in some 2DESs . As a result, the 2DESs may experience the direct I-QH transition from the low-field insulator to QH states of higher filling factors [2,. Such a transition can be related to the zero-field metal-insulator transition, to which e-e interaction cannot be ignored . Given that most 2DESs show metallic behavior at B=0, the investigation of the direct I-QH transition at low B should be conducted in low-mobility 2DESs [1,.
On the low-field insulator-quantum Hall conductor transitions
Physica E: Low-dimensional Systems and Nanostructures, 2004
We studied the insulator-quantum Hall conductor transition which separates the low-field insulator from the quantum Hall state of the filling factor ν=4 on a gated two-dimensional GaAs electron system containing self-assembled InAs quantum dots.
Journal of Physics: Condensed Matter, 1994
We present low-temperature uanspon measurements on the two-dimensional electron gas in 8-doped GaAs which undergoes an insulatorquantum Hall-insulator vansition as the magnetic field is increased. Both low-and high-field vansitions are marked by pe& in ox, and Lhe temperahlre-independent critical value of oxy of 0.5ez/h per spin. We map out the phase diagram versus disorder and magnetic field and study the t e m p e m dependence of ox* throughout. In the quantum Hall region we observe Molt variable range hopping and, around the high-field transitions, s d i g via a single parameter: z = (S -B')T-"'. The functional dependence on L above this transition is fitted by recent network percolation calculations.
Physical Review Letters, 1999
A metal-insulator transition in two-dimensional electron gases at B = 0 is found in Ga[Al]As heterostructures, where a high density of self-assembled InAs quantum dots is incorporated just 3 nm below the heterointerface. The transition occurs at resistances around h/e 2 and critical carrier densities of 1.2 • 10 11 cm −2. Effects of electron-electron interactions are expected to be rather weak in our samples, while disorder plays a crucial role.
Journal of the Korean Physical Society, 2007
By applying a magnetic field perpendicular to GaAs/AlGaAs two-dimensional electron systems, we study the low-field Landau quantization when the thermal damping is reduced with decreasing the temperature. Magnetooscillations following Shubnikov-de Haas (SdH) formula are observed even when their amplitudes are so large that the deviation to such a formula is expected. Our experimental results show the importance of the positive magneto-resistance to the extension of SdH formula under the damping induced by the disorder.
We present a study of the anisotropic properties of two-dimensional electron gases formed in GaAs/AlGaAs heterostructures in which InAs self-assembled quantum dots have been inserted into the center of a GaAs quantum well. We observe an anisotropic mobility for the orthogonal [110] and [110] directions. The mobility in the [110] direction was found to be up to twice that in the [110] direction. It is suggested that the observed linear ordering of the self-assembled InAs quantum dots in the [110] direction is the cause for the large mobility anisotropy.