Theory of Spin-Split Cyclotron Resonance in the Extreme Quantum Limit

TL;DR

This paper interprets recent cyclotron resonance experiments in 2D electron gases, revealing how spin-splitting, thermal effects, and Coulomb interactions influence the resonance spectrum, and introduces a sum rule for spin polarization measurement.

Contribution

It provides a theoretical framework explaining experimental observations and derives an $f$-sum rule to determine spin polarization directly from spectra.

Findings

Resonance spectrum depends on Landau level occupancy and temperature.

Spin-splitting and Coulomb interactions significantly affect resonance behavior.

Derived an $f$-sum rule for measuring spin polarization from spectra.

Abstract

We present an interpretation of recent cyclotron resonance experiments on the two-dimensional electron gas in GaAs/AlGaAs heterostructures. We show that the observed dependence of the resonance spectrum on Landau level occupancy and temperature arises from the interplay of three factors: spin-splitting of the cyclotron frequency; thermal population of the two spin states; and coupling of the resonances for each spin orientation by Coulomb interactions. In addition, we derive an $f$-sum rule which allows spin polarisation to be determined directly from resonance spectra.