Microwave response of interacting oxide two-dimensional electron systems

TL;DR

This study investigates microwave-induced phenomena in MgZnO/ZnO two-dimensional electron systems, revealing how electron interactions influence effective mass measurements through cyclotron resonance and resistance oscillations.

Contribution

It provides experimental evidence of interaction-dependent effective mass variations in 2D electron systems using microwave response techniques.

Findings

CR response dominates at low density

MIRO appears at high density

Effective mass from MIRO increases as density decreases

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 high density 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.