Measuring the spin polarization and Zeeman energy of a spin-polarized electron gas: Comparison between Raman scattering and photoluminescence

TL;DR

This study compares Raman scattering and photoluminescence techniques to measure spin polarization and Zeeman energy in a 2D electron gas, revealing differences at high densities due to many-body effects.

Contribution

It provides a comparative analysis of two spectroscopic methods for characterizing spin-polarized electron gases, highlighting the impact of electron-electron interactions on measurements.

Findings

Raman scattering measures Fermi energy consistent with photoluminescence at moderate densities.

Discrepancies in spin polarization measurements increase at high electron densities.

Many-body interactions cause effective mass renormalization affecting measurement accuracy.

Abstract

We compare resonant electronic Raman scattering and photoluminescence measurements for the characterization of a spin-polarized two-dimensional electron gas embedded in $\text{Cd}_{1-x}\text{Mn}_x\text{Te}$ single quantum wells. From Raman scattering by single-particle excitations in a zero magnetic field, we measure the Fermi velocity and then obtain the Fermi energy (as well as the electron density), which is comparable to that extracted from photoluminescence for moderate electron densities, assuming a bare band-edge mass. At large electron densities, the Fermi energies derived from Raman scattering and photoluminescence differ. For an applied in-plane magnetic field and zero wave vector transferred to the electron gas, Raman scattering spectra show peaks at both the Zeeman energy $Z$, resulting from collective excitations of the spin-polarized electron gas, and the one electron spin-flip energy $Z^*$. Magneto-photoluminescence spectra show conduction band splitting that are equivalent to $Z$, suggesting that collective effects are present in the photoluminescence spectra. Assuming (as before) an uncorrected mass, the degree of spin polarization $\zeta$ determined from the magneto-photoluminescence lineshape is found to differ from that derived from the magnetic field dependent Raman scattering measurements for large electron densities. We attribute the discrepancy in measuring $\zeta$ and the Fermi energy to the renormalized mass resulting from many-body electron-electron interactions.