Microwave response of interacting oxide two-dimensional electron systems

Abstract

We present an experimental study on microwave illuminated high mobility MgZnO/ZnO based two-dimensional electron systems with different electron densities and, hence, varying Coulomb interaction strength. The photoresponse of the low-temperature dc resistance in perpendicular magnetic field is examined in low and high density samples over a broad range of illumination frequencies. In low density samples a response due to cyclotron resonance (CR) absorption dominates, while highdensity samples exhibit pronounced microwave-induced resistance oscillations (MIRO). Microwave transmission experiments serve as a complementary means of detecting the CR over the entire range of electron densities and as a reference for the band mass unrenormalized by interactions. Both CR and MIRO-associated features in the resistance permit extraction of the effective mass of electrons but yield two distinct values. The conventional cyclotron mass representing center-of-mass dynamics exhibits no change with density and coincides with the band electron mass of bulk ZnO, while MIRO mass reveals a systematic increase with lowering electron density consistent with renormalization expected in interacting Fermi liquids.

Observation of High Harmonics of the Cyclotron Resonance in Microwave Transmission of a High-Mobility Two-Dimensional Electron System

“…In contrast, the quasiparticle effective mass, m = 0.068 m 0 , determined from the period of ω/ω c -magnetooscillations in both the microwave transmission and dc resistance, represents the LL spacing in the vicinity of the Fermi level where the microwave-assisted scattering processes take place. This mass should therefore be sensitive to the Fermi-liquid renormalizations and can significantly differ from m CR as confirmed by previous MIRO observations in several materials [33,[77][78][79]. Our data involve a large number of oscillation periods in both δR and |t + | 2 and thus enable a precise determination of m. The results presented in Fig.…”

“…( 3)) in the dynamic conductivity coincide. Taking into account that, unlike MIRO, quantum oscillations in transmission become more pronounced for lower transport mobility, this opens up an opportunity to explore the renormalization effects [33,[77][78][79] in a broader class of 2DES.…”