Abstract:Negative diagonal magneto-conductivity/resistivity is a spectacular- and thought provoking-property of driven, far-from-equilibrium, low dimensional electronic systems. The physical response of this exotic electronic state is not yet fully understood since it is rarely encountered in experiment. The microwave-radiation-induced zero-resistance state in the high mobility GaAs/AlGaAs 2D electron system is believed to be an example where negative magneto-conductivity/resistivity is responsible for the observed phe… Show more
“…With increasing the radiation intensity, the amplitudes of these peak-valley oscillations increase and the magnetoresistivity R xx around the minima of a few lowest-j pairs can drop down to negative in certain ranges, where the formation of current domains, resulting from the electrical instability of a homogeneous negative-resistance state, was considered to be one of possible mechanisms for the observation of zero resistance, [39][40][41] besides several other scenarios in the literature. 42,43 This explanation of ZRS was supported by the further measurements 15,16 of magnetoresistance oscillations and zeroresistance ranges for the same system under separated and combined driving of two radiation fields of frequencies x 1 and x 2 . 10 These bichromatic radiation experiments also disclosed the importance of multiple photon processes with mixing frequencies under intense radiations.…”
We analyze a phase-sensitive contribution to the oscillating magnetoresistance induced by the combined driving of two microwave fields having commensurate frequencies ω1 and ω2 (m1ω1 + m2ω2 = 0 for at least a set of nonzero integers m1 and m2), based on the balance-equation approach to magnetotransport for high-density two-dimensional electron systems. This commensurate oscillating photoresistance not only depends on the frequencies and polarizations of both microwaves, but varies drastically when changing the relative phases of two incident radiation fields. It shows up most significantly in the case of ω2/ω1 = 3 and may lead to a phase-controllable change of more than a factor of two in the total magnetoresistivity in the vicinity of ω1/ωc = 1.5 and 2.5 (ωc is the cyclotron frequency), when both radiation fields are linearly x-direction polarized.
“…With increasing the radiation intensity, the amplitudes of these peak-valley oscillations increase and the magnetoresistivity R xx around the minima of a few lowest-j pairs can drop down to negative in certain ranges, where the formation of current domains, resulting from the electrical instability of a homogeneous negative-resistance state, was considered to be one of possible mechanisms for the observation of zero resistance, [39][40][41] besides several other scenarios in the literature. 42,43 This explanation of ZRS was supported by the further measurements 15,16 of magnetoresistance oscillations and zeroresistance ranges for the same system under separated and combined driving of two radiation fields of frequencies x 1 and x 2 . 10 These bichromatic radiation experiments also disclosed the importance of multiple photon processes with mixing frequencies under intense radiations.…”
We analyze a phase-sensitive contribution to the oscillating magnetoresistance induced by the combined driving of two microwave fields having commensurate frequencies ω1 and ω2 (m1ω1 + m2ω2 = 0 for at least a set of nonzero integers m1 and m2), based on the balance-equation approach to magnetotransport for high-density two-dimensional electron systems. This commensurate oscillating photoresistance not only depends on the frequencies and polarizations of both microwaves, but varies drastically when changing the relative phases of two incident radiation fields. It shows up most significantly in the case of ω2/ω1 = 3 and may lead to a phase-controllable change of more than a factor of two in the total magnetoresistivity in the vicinity of ω1/ωc = 1.5 and 2.5 (ωc is the cyclotron frequency), when both radiation fields are linearly x-direction polarized.
“…Interesting experimental features revealed by prior studies in this field include: (a) the 1/4-cycle phase shift ref. 3 , 4 , (b) the non-linear increase in the amplitude of the radiation-induced oscillations with the microwave power 5 , (c) the sinusoidal dependence of the oscillation amplitude on the linear polarization angle 6 7 , (d) observed correlations between the magneto-resistance oscillations and the microwave reflection from 2DES 8 9 , and other fascinating phenomena 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 .…”
A comparative study of the radiation-induced magnetoresistance oscillations in the
high mobility GaAs/AlGaAs heterostructure two dimensional electron system (2DES)
under linearly- and circularly- polarized microwave excitation indicates a profound
difference in the response observed upon rotating the microwave launcher for the two
cases, although circularly polarized microwave radiation induced magnetoresistance
oscillations observed at low magnetic fields are similar to the oscillations
observed with linearly polarized radiation. For the linearly polarized radiation,
the magnetoresistive response is a strong sinusoidal function of the launcher
rotation (or linear polarization) angle, θ. For circularly
polarized radiation, the oscillatory magnetoresistive response is hardly sensitive
to θ.
A small and narrow negative-magnetoresistance (MR) effect that appears about null magnetic field over the interval −0.025 ≤ B ≤ 0.025 T in magnetotransport studies of the GaAs/AlGaAs 2D system with μ ≈ 107cm2/Vs is experimentally examined as a function of the sample temperature, T. The temperature dependent magnetoresistance data were fit using the Hikami et al. theory, without including the spin-orbit correction, to extract the inelastic length, li, which decreases rapidly with increasing temperature. It turns out that li < le, where le is the elastic length, for all T. Thus, we measured the single particle lifetime, τs, and the single particle mean free path ls = vFτs. A comparison between li and ls indicates that li > ls. The results suggest that the observed small and narrow magnetoresistance effect about null magnetic field could be a manifestation of coherent backscattering due to small angle scattering from remote ionized donors in the high mobility GaAs/AlGaAs 2DES.
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