Quantum-confined semiconductor structures provide an ideal laboratory in which to study exotic quantum phenomena in a highly controllable manner. In particular, a high magnetic field can control the densities of states and dephasing times of electrons through Landau quantization and Zeeman splitting while adding quantum mechanical phases to the electronic wavefunctions. Here, we study many-body processes of excitons in quantum wells in high magnetic fields. Excitons consist of correlated electron-hole (e-h) pairs, which form "hydrogenic" internal states in addition to continua due to their center-of-mass motion and induce a rich variety of effects in optical spectra. We have shown that 2-D magneto-excitons are stable against a Mott transition at ultrahigh densities.

We have recently obtained evidence of superfluorescence -- a type of superradiance, i.e., cooporative recombination of high-density e-h pairs resulting in busts of coherent radiation. The concept of superradiance has recently been discussed in a diverse range of contexts in which coherent coupling of constituent particles governs their cooperative dynamics: cavity quantum electrodynamics, quantum phase transitions and plasmonics. Here we observe intense, delayed bursts of coherent radiation from a photo-excited semiconductor and interpret it as superfluorescence, where macroscopic coherence spontaneously appears from initially incoherent e-h pairs. The coherence then decays superradiantly, with a concomitant abrupt decrease in population from full inversion to zero. This is the first observation of superfluorescence in a dense semiconductor plasma, where decoherence is much faster than radiative decay, a situation never encountered in atomic cases. Nonetheless, a many-body cooperative state of phased electron–hole 'dipoles' does emerge at high magnetic fields and low temperatures, producing giant superfluorescent pulses. The solid-state realization of superfluorescence resulted in unprecedented controllability, promising tunable sources of coherent pulses.

See a preprint of our paper just accepted by Nature Physics: G. T. Noe et al., “Giant Superfluorescent Bursts from a Semiconductor Magnetoplasma,"published online on January 29, 2012. (abstract; see also Rice News).

Selected Publications:

J. Lee et al., "Robust, Stable Single-Exciton Emission from an Ultrahigh-Density Magneto-plasma," arXiv:1009.3067v1.

Y. D. Jho et al., "Cooperative Recombination of Electron-Hole Pairs in Semiconductor Quantum Wells under Quantizing Magnetic Fields," Phys. Rev. B 81, 155314 (2010). (abstract, full text)

Y. D. Jho et al., "Superfluorescence from Dense Electron-Hole Plasmas under High Magnetic Fields," J. Mod. Opt. 53, 2325 (2006). (full text)

Y. D. Jho et al., "Cooperative Recombination of a Quantized High-Density Electron-Hole Plasma in Semiconductor Quantum Wells," Phys. Rev. Lett. 96, 237401 (2006). (abstract, full text)

Y. D. Jho et al., "Role of Coulomb Interactions in Dark-Bright Magneto-Exciton Mixing in Strained Quantum Wells," Phys. Rev. B 72, 045340 (2005). (abstract, full text)

F. V. Kyrychenko et al., "Interband Magnetoabsorption Study of the Shift of the Fermi Energy of a 2DEG with an In-plane Magnetic Field," Physica E 22, 624 (2004). (full text)