Renormalized Landau quasiparticle dispersion revealed by photoluminescence spectra from a two-dimensional Fermi liquid at the MgZnO/ZnO heterointerface

We analyze the low-temperature photoluminescence spectra from two-dimensional electron systems (2DESs) confined at ${\mathrm{Mg}}_{x}{\mathrm{Zn}}_{1\ensuremath{-}x}\mathrm{O}$/ZnO heterojunctions as the electron density is decreased from $2.3\ifmmode\times\else\texttimes\fi{}{10}^{12}$ to $3.5\ifmmode\times\else\texttimes\fi{}{10}^{11}$ ${\mathrm{cm}}^{\ensuremath{-}2}$. The value of the quasiparticle optical density-of-states mass is directly extracted from the width of the 2DES photoluminescence band and is shown to renormalize and double from the value close to that of bulk ZnO material, $0.3{m}_{0}$ (${m}_{0}$ is the bare electron mass), to $0.6{m}_{0}$ due to electron-electron interactions as the interaction parameter ${r}_{s}$ increases from 2.4 to 6.5. The experimentally probed quasiparticle energies far exceed the limits of Landau's Fermi-liquid theory.