RESUMEN
We introduce a quantum virial expansion for the optical response of a doped two-dimensional semiconductor. As we show, this constitutes a perturbatively exact theory in the high-temperature or low-doping regime, where the electrons' thermal wavelength is smaller than their interparticle spacing. We obtain exact analytic expressions for the photoluminescence and we predict new features such as a nontrivial shape of the attractive branch peak related to universal resonant exciton-electron scattering and an associated energy shift from the trion energy. Our theory furthermore allows us to formally unify the two distinct theoretical pictures that have been applied to this system, where we reveal that the predictions of the conventional trion picture correspond to a high-temperature and weak-interaction limit of Fermi-polaron theory. Our results are in excellent agreement with recent experiments on doped monolayer MoSe_{2} and they provide the foundation for modeling a range of emerging optically active materials such as van der Waals heterostructures.
RESUMEN
We theoretically investigate the many-body states of exciton polaritons that can be observed by pump-probe spectroscopy in high-Q inorganic microcavities. Here, a weak-probe "spin-down" polariton is introduced into a coherent state of "spin-up" polaritons created by a strong pump. We show that the ↓ impurities become dressed by excitations of the ↑ medium, and that they form new polaronic quasiparticles that feature two-point and three-point many-body quantum correlations that, in the low density regime, arise from coupling to the vacuum biexciton and triexciton states, respectively. In particular, we find that these correlations generate additional branches and avoided crossings in the ↓ optical transmission spectrum that have a characteristic dependence on the ↑-polariton density. Our results thus demonstrate a way to directly observe correlated many-body states in an exciton-polariton system that go beyond classical mean-field theories.
RESUMEN
Recent years have witnessed novel and exciting advances on the subject of optical coherence and collective phenomena in nanostructures. This volume overviews the forefront progress in this area, collecting nine reviews and ten new contributions by leading experts in the field. The subfields included in this volume span from two-dimensional electron gases, semiconductor excitons, coupled quantum wells, microcavity polaritons, quantum dots and quantum wires. One of the most exciting directions in coupled quantum wells is the possibility to explore novel quantum fluid phases of indirect excitons and the formation of spontaneous coherence. Strong light-matter interaction in semiconductor microcavities has lead to the ability of controlling, manipulating and detecting the matter properties by all optical means. Structures with reduced dimensionality, such as quantum dots and quantum wires, offer the possibility to explore novel physics and new applications for nanoscience technology. Finally, recent advances in probing and controlling spin and charge dynamics in two-dimensional electron gases open new perspectives towards spintronics. The intellectual and applied links between all these problems offer fascinating opportunities for further advances in this field. The editors would like to acknowledge the support of the EU Network `Photon mediated phenomena in semiconductor nanostructures' HPRN-CT-2002-00298 in the preparation of this volume.