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

Abstract

We report on nonlinear transport measurements in a GaAs/AlGaAs quantum well exhibiting a colossal negative magnetoresistance effect. Under applied dc bias, the magnetoresistance becomes nonmonotonic, exhibiting distinct extrema that move to higher magnetic fields with increasing current. 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. While classical memory effects due to a unique disorder landscape appear to be the most likely origin of the observed CNMR, comparison with existing theories [9-11] revealed huge discrepancy in the characteristic B range where the effect is expected to occur. It is thus clear that more studies are needed to shed light on this mysterious phenomenon. In particular, it is very desirable to get insight into the specifics of the underlying disorder potential in the 2DES exhibiting CNMR.The most frequently used and readily available characteristic of the disorder is the electron mobility µ = (en e ρ 0 ) −1 , where n e is the electron density and ρ 0 is the resistivity at B = 0. At low T , the mobility can be expressed as µS , where µ L and µ S account for scattering off long-range (smooth) disorder, e.g. from the remote ionized impurities, and short-range (sharp) disorder, e.g. from the residual background impurities, respectively. Since magnetoresistance sensitively depends on the interplay between smooth and sharp contributions [9,10], it is important to know not only the total µ, but also at least one of its constituents, i.e. µ L or µ S .In principle, µ S can be obtained from non-linear transport measurements, which are known to reveal Hall-field induced resistance oscillations (HIRO) [12][13][14][15][16][17][18][19]. HIRO appear in differential resistivity r and originate from electron transitions between Hall field-tilted Laudau levels due to electron backscattering off impurities. The corresponding scattering rate relies on the commensurability between the cyclotron diameter 2R c and the spatial separation between the levels, and, as a result, is a periodic function of ǫ j ≡ 2eER c /ω c , where E is the Hall field and ω c is the cyclotron frequency. Since backscattering is strongly dominated by sharp disorder, the HIRO amplitude is proportional to µ −1 S . The full result reads [15]:where λ = exp(−π/ω c τ q ) is the Dingl...

Non-Ohmic negative longitudinal magnetoresistance in a two-dimensional electron gas

“…In fact, the R(I) relationship at high currents in Fig. 5(a) is similar to that observed in GaAs quantum wells [36], regardless of the alignment between the electric and magnetic fields.…”

“…Furthermore, non-Ohmic behavior could occur in a 2D system with weak localizations at high dc currents that lead to δ > a, where δ ~ E is the drift distance along the E direction and a is the radius of the scatterers. Such a current-induced 'delocalization' leads to a linear increase of the resistance at high currents as observed in GaAs quantum wells [36]. Our sample at low currents and low magnetic fields (see Fig.…”

“…In a low dimensional system such as our 2DEG samples, quantum interference effects can play an important role in magnetotransport properties. For example, weak localization is one of the quantum interference effects that is considered to be the origin of the negative MRs in graphenes [34] and quantum wells [35,36] under crossed electrical and magnetic fields. When localization occurs in the presence of strong and dilute scatterers [37], the probability for an electron to return to the same impurity is enhanced by the magnetic field, subsequently reducing its probability for an electron to scatter off other impurities and thereby resulting in a negative MR [36].…”

“…For example, weak localization is one of the quantum interference effects that is considered to be the origin of the negative MRs in graphenes [34] and quantum wells [35,36] under crossed electrical and magnetic fields. When localization occurs in the presence of strong and dilute scatterers [37], the probability for an electron to return to the same impurity is enhanced by the magnetic field, subsequently reducing its probability for an electron to scatter off other impurities and thereby resulting in a negative MR [36]. Furthermore, non-Ohmic behavior could occur in a 2D system with weak localizations at high dc currents that lead to δ > a, where δ ~ E is the drift distance along the E direction and a is the radius of the scatterers.…”

“…indicating potential additional contribution from other mechanisms such as memory effects [36,39] that occur only in perpendicular magnetic fields. In other words, NLMRs may be used to identify or distinguish the origin of the negative MRs in out-of-plane fields.…”