Indirect excitons in nitrides, PhD

Laboratoire Charles Coulomb (L2C) was created on January 1st, 2011. Multi-thematic Physics Research Laboratory, the L2C is a Joint Research Unit (UMR 5221) between CNRS and Université Montpellier. For the realization of this research project, the scholarship holder will join the OECS team, which is part of the PEPS research axis at L2C. This team has acquired a solid expertise in the field of quantum states of matter, optics and magnetism. The team relies on unique experimental setups, including optical microscopy, pump-probe spectroscopy and spin noise spectroscopy.

This research proposal aims at exploring (i) novel semiconductor nanostructures hosting Coulomb bound electron-hole pairs which have a large built-in static dipole moment - indirect excitons (IXs), and (ii) emerging collective states that these IXs form. Relying on the strong dipolar interactions between IXs, strong correlations, collective phenomena and even the transition to new emergent many-body quantum phases are predicted. This research topic belongs then to a very active field of material physics spreading over solid-state and atomic physics. It covers collective quantum phenomena, including Bose-Einstein condensation (first demonstrated in cold atomic gases), topological states, dipolar liquids and supersolids. The resulting states of matter provide extraordinary optical, electrical, and thermal functionalities (e. g. macroscopic coherence) and apart from their fundamental interest (unique variety of the tunable many-body states) are promising for applications in quantum electronics, photonics and sensing. Compared to atomic systems, collective states of excitons offer higher critical temperature (kelvins vs. microkelvins for atoms), and also much greater versatility via heterostructure engineering. In this context IXs are unique quasi-particles, which provide new degrees of freedom as compared to atomic gases, such as a four-component internal spin, and a giant electric dipole that can be engineered and manipulated. It is predicted to favor the formation of various ordered states in the quantum regime, which are intensively studied and debated.
In collaboration with CRHEA, the host team has developed design, growth, fabrication techniques, as well as optical and electrical characterization approaches to address GaN-based IXs and their quantum properties. We have also pioneered the control of thermalized cold and dense IX gases in electrostatic traps in GaN QWs. The most recent data on magnetic field dependence of IX emission suggest the onset of a collective strongly correlated state at high exciton densities. We stress the uniqueness of these measurements for GaN-based heterostructures, that were made possible by engineering the systems with a suitable tradeoff between dipole moment and the binding energy. L2C and its partners within ANR-funded consortium IXTASE (CRHEA, LPCNO, INSP) have proven their expertise in this rapidly developing research domain and embody both theoretical and experimental expertise to uncover various collective phases of IXs ensembles.