Giant microwave-induced B -periodic magnetoresistance oscillations in a two-dimensional electron gas with a bridged-gate tunnel point contact

Abstract

We have studied the magnetoresistance of the quantum point contact fabricated on the high mobility two-dimensional electron gas (2DEG) exposed to microwave irradiation. The resistance reveals giant B-periodic oscillations with the relative amplitude ∆R/R of up to 700% resulting from the propagation and interference of the edge magnetoplasmons (EMPs) in the sample. This giant photoconductance is attributed to the considerably large local electron density modulation in the vicinity of the point contact. We have also analyzed the oscillation periods ∆B of the resistance oscillations and, comparing the data with the EMP theory, extracted the EMP interference length L. We have found that the length L substantially exceeds the distance between the contact leads but rather corresponds to the distance between metallic contact pads measured along the edge of the 2DEG. This resolves existing controversy in the literature and should help to properly design highly sensitive microwave and terahertz spectrometers based on the discussed effect. A number of interesting magnetotransport phenomena were discovered in recent years in a two-dimensional electron gas (2DEG) placed in a perpendicular magnetic field B and exposed to microwave (MW) irradiation. In low magnetic fields, corresponding to the condition ω c ω, the so called microwave-induced resistance oscillations (MIRO), with zero-resistance states, were observed 1-4 ; here ω c = eB/m * c and ω = 2πf are the cyclotron and microwave frequencies and m * is the electron effective mass. These oscillations of the diagonal resistance R are periodic in 1/B and are especially pronounced at low temperatures T ≃ 1 K in samples with a high electron mobility.In the opposite regime of higher magnetic fields, ω c ω, another type of magnetoresistance oscillations was discovered 5 . These oscillations are periodic in B and were explained by the excitation and interference of edge magnetoplasmons 6 (EMPs) in the sample. The incident microwave radiation excites oscillating (dipole) electric field at the boundaries between the 2DEG and metallic contacts. These dipole fields generate plasma waves -EMPs -propagating along the sample edge between the contacts on which the magnetoresistance R is measured. Due to the interference of EMPs, generated by different contacts, R oscillates as a function of the parameter qL, where q(ω, B) is the EMP wave-vector and L is the inter-contact distance 5 . In strong magnetic fields q(ω, B) is proportional to ωB/n s , where n s is the electron density 6,7 . This leads to the B-periodic oscillations with the period ∆B ∝ n s /ωL. This theoretically predicted dependence was confirmed by the experiments 5,8 . EMPs have a much smaller damping, as compared to the bulk magnetoplasmons, 6,7 and, in contrast to the MIRO-ZRS effect, the EMP-related oscillations do not require low temperatures and samples with the very high electron mobility: they were observed at least up to T ≃ 80 K 8 . These EMP properties make the considered phenomenon especially promising for the cre...