Cooperative Recombination of a Quantized High-Density Electron-Hole Plasma in Semiconductor Quantum Wells

We investigate photoluminescence from a high-density electron-hole plasma in semiconductor quantum wells created via intense femtosecond excitation in a strong perpendicular magnetic field, a fully quantized and tunable system. At a critical magnetic field strength and excitation fluence, we observe a clear transition in the band-edge photoluminescence from omnidirectional output to a randomly directed but highly collimated beam. In addition, changes in the linewidth, carrier density, and magnetic field scaling of the photoluminescence spectral features correlate precisely with the onset of random directionality, indicative of cooperative recombination from a high-density population of free carriers in a semiconductor environment.

Figure 1

Emission spectra as a function of (a) magnetic field for fixed fluence ($0.62\mathrm{mJ}/{\mathrm{cm}}^2$) and (b) fluence for a fixed field (20 T). To compare the edge (red line) to center (blue line) collection in the inset of Fig. 1a, the opposite face is multiplied by 5000. The inset in (b) shows how the threshold magnetic field depends on temperature.

Figure 2

Emission strength and linewidth of the narrow peak from the 0-0 LL versus (a) $B$ and (b),(c),(d) $F_{\mathrm{laser}}$ for different pump spot sizes. Both $B$ and $F_{\mathrm{laser}}$ are on a logarithmic scale. The inset of (a) shows the convolution method using a Lorentzian for the sharp peak and a Gaussian for the broader lower-energy peak. The blue (green) lines in (a)–(d) indicate the superlinear (linear) regime.

Figure 3

(a) Experimental schematic showing single-shot excitation and collection. (b) Four representative emission spectra from edge 1 (black) and edge 2 (red) fibers, excited from single laser pulse and measured simultaneously. Normalized emission strength from the 0th LL versus shot number in the (c) SF regime and (d) ASE regime.