Two-dimensional double-quantum spectroscopy: peak shapes as a sensitive probe of carrier interactions in quantum wells

TL;DR

This study uses 2D double-quantum spectroscopy to detect carrier interactions in quantum wells at lower densities than previously observed, revealing how peak shapes indicate underlying interactions and decoherence effects.

Contribution

It demonstrates that 2D double-quantum spectral peak shapes can sensitively probe carrier interactions at low excitation densities in quantum wells, revealing effects previously hidden.

Findings

Carrier interactions occur at densities below $10^{8}$ carriers/cm$^{2}$.

Tilted peak shapes indicate inhomogeneous broadening dominance.

Pure-decoherence can obscure peak tilt, affecting interpretation.

Abstract

We identify carrier scattering at densities below which it has previously been observed in semiconductor quantum wells. These effects are evident in the peakshapes of 2D double-quantum spectra, which change as a function of excitation density. At high excitation densities ($\geq 10^{9}$ carriers/,cm$^{-2}$) we observe untilted peaks similar to those reported in previous experiments. At low excitation densities (<$10^{8}$ carriers cm$^{-2}$) we observe narrower, tilted peaks. Using a simple simulation, we show that tilted peak-shapes are expected in double-quantum spectra when inhomogeneous broadening is much larger than homogeneous broadening, and that fast pure-decoherence of the double-quantum coherence can obscure this peak tilt. These results show that carrier interactions are important at lower densities than previously expected, and that the `natural' double-quantum peakshapes are hidden by carrier interactions at the excitation densities typically used. Furthermore, these results demonstrate that analysis of 2D peak-shapes in double-quantum spectroscopy provides an incisive tool for identifying interactions at low excitation density.