Magnetoresistance in a high-mobility two-dimensional electron gas

Abstract

In a high-mobility two-dimensional electron gas (2DEG) in a GaAs/Al 0.3 Ga 0.7 As quantum well we observe a strong magnetoresistance. In lowering the electron density, the magnetoresistance gets more pronounced and reaches values of more than 300%. We observe that the huge magnetoresistance vanishes when increasing the temperature. An additional density-dependent factor is introduced to be able to fit the parabolic magnetoresistance to the electron-electron interaction correction. Since the first observation of the fractional quantum Hall effect (FQHE) 1,2 the quality and the mobility of the two-dimensional electron gas (2DEG) increased by more than two orders of magnitude. The increased mobility has allowed not only the observation of the FQHE at many different filling factors and smaller magnetic fields but also many new effects. So, microwave-induced oscillations were observed, which were up to now not fully understood. [3][4][5] In weak magnetic fields the increased mobility enabled also the observation of phonon-induced resistance oscillations, which are caused by inelastic scattering between electrons and three-dimensional acoustic phonons. 6,7 The period of phonon-induced oscillations is tunable by an additional dc electric field. 8,9 Also a new type of QHE was enabled in high mobility 2DEGs, the re-entrant integer quantum Hall effect (RIQHE). 10,11 In the regime of the RIQHE the longitudinal resistance between integer filling factors decreases to zero suggesting fractional filling factors, but the corresponding Hall plateaus are quantized at integer values.Here we will present the observation of a huge magnetoresistance in a high mobility 2DEG which depends strongly on electron density and temperature.Our samples were cleaved from a wafer of a high-mobility GaAs/Al 0.3 Ga 0.7 As quantum well grown by molecular-beam epitaxy. The quantum well has a width of 30 nm and is Si-doped from both sides. The 2DEG is located 150 nm beneath the surface and has an electron density of n e ≈ 3.1 × 10 11 cm −2 and a mobility of μ ≈ 11.9 × 10 6 cm 2 /Vs in the dark. The specimens are Hall bars with a total length of 1.2 μm, a width of w = 200 μm and a potential probe spacing of l = 275 μm [see Fig. 1(a)]. The Hall bars were defined by photolithography and wet etching. Different ungated and gated samples were used for the magnetotransport measurements. In the case of the gated sample there is an additional layer of 600 nm PMMA between the Hall bar and the metallic top-gate to avoid leakage current. We apply top-gate voltages up to −6 V to manipulate the electron density. Our measurements were performed in a dilution refrigerator with a base temperature of 20 mK. The measurements were carried out by using low-frequency (13 Hz) lock-in technique.Figure 1(a) shows the longitudinal resistance R xx and the Hall resistance R xy vs. magnetic field B to demonstrate the quality of our samples. A series of different fractional quantum Hall states appears for filling factor ν < 2. We observe also the filling factor ν = 5/2. Over the ...

Nonlinear transport in two-dimensional electron gas exhibiting colossal negative magnetoresistance

“…In the range of magnetic fields corresponding to the resistivity minimum at zero bias, the resistivity increases linearly with current and the rate of this increase scales with the inverse magnetic field. The latter observation is consistent with the theory, proposed more than 35 years ago, considering classical memory effects in the presence of strong, dilute scatterersThe interest to low-field magnetotransport in twodimensional electron systems (2DES) has been recently revived owing to several experiments reporting unexpectedly strong negative magnetoresistance in GaAs/AlGaAs heterostructures [1][2][3][4][5][6][7][8]. One prominent example is the observation of a colossal negative magnetoresistance (CNMR), which is marked by a sharp drop of the resistivity ρ(B) followed by a saturation at the magnetic field…”

“…The interest to low-field magnetotransport in twodimensional electron systems (2DES) has been recently revived owing to several experiments reporting unexpectedly strong negative magnetoresistance in GaAs/AlGaAs heterostructures [1][2][3][4][5][6][7][8]. One prominent example is the observation of a colossal negative magnetoresistance (CNMR), which is marked by a sharp drop of the resistivity ρ(B) followed by a saturation at the magnetic field B ≈ B ⋆ ≈ 1 kG, close to ρ ⋆ ≡ ρ(B ⋆ ) 0.1ρ 0 , at temperature T 1 K [7].…”

Nonlinear response in overlapping and separated Landau levels of GaAs quantum wells

“…(3). Finally, we mention a recently reported negative magnetoresistivity effect 55,56 which occurs in the same range of magnetic fields and is strongly temperature dependent. Unfortunately, separating all these contributions does not appear feasible at this point.…”

Theoretical model for negative giant magnetoresistance in ultrahigh-mobility 2D electron systems

“…Therefore, we must conclude that, in some way, the two physical phenomena have to be connected or share the same physical origin. The first experiment to obtaine NGMR, (without irradiation) was carried out by Paalanen et al [20] and later on by Bockhorn et al [21], where they study the dependence of NGMR on temperature and electron density. Next, Y. Dai et al [22], reported on the dependence of NGMR on an in-plane B.…”

“…For the experimental parameters that we are dealing with [21][22][23], we have estimated that ξ DC ∼ 1 − 2 V/m. On the other hand for low B ∼ 0.04 − 0.05 T, we have obtained that, in average, in the advanced distance corresponding to a scattering jump, the LL are tilted an energy ∆ ≃ 3.10 −5 eV.…”