Dipolar exciton hydrodynamics, controlled interactions and multi-functional integration: towards an exciton-based opto-electronic multiplexer
Final Report Abstract
A dipolar {or indirect) exciton (IX) in semiconductor nanostructures is an exciton consisting of an electron and a hole confined in two closely spaced quantum wells (QWs) by means of an electric field applied across the structure. The charge separation enhances the IX radiative lifetime (up to the ms-range) while still maintaining the electron-hole Coulomb interaction. The long lifetimes allow for the storage of a large density of cold excitons, as well as for their transport and manipulation in the ns time scale, thus making these particles attractive from the opto-electronic devices point of view. In addition, their dipolar nature induces a strong exciton-exciton interactions. Finally, IXs are composite bosons and, therefore, susceptible to collective bosonic effects like superfluidity and Bose-Einstein condensation. Within this project, we have investigated the dynamics of cold IX fluids in confined dynamical potentials and their exploitation for device applications. Here we demonstrate that IX Gaussian packets can be efficiently transported for hundreds of μm with a minor distortion of their shape. We show that the long-range acoustic transport of IXs can be combined with electrostatic gates to realize an acoustic exciton multiplexer (EXAM), a scalable device capable of storing and interconnecting IX systems separated by millimeter distances. This represents an important achievement since scalability is presently a major barrier for the integration of different functionalities in opto-electronic quantum devices. The SAW-driven long-range IX flow can be efficiently controlled by an acoustic exciton transistor (EXAT) placed on the transport. The mechanisms for the acoustic transport as well as for the IX transfer between beams is supported by numerical simulations based on a theoretical model for hydrodynamics of interacting dipolar excitons. This device is a proof-of-concept for "all exciton" electrooptic devices. These studies represent a significant step toward the integration of a wide set of optoelectronic functionalities on a single chip. The spatial separation of the particles is also expected to increase the spin lifetime. We show that IXs spins can travel up to distances approaching 20 μm while precessing in the spin orbit effective magnetic field. We also demonstrate that the precessing IX spins can be manipulated both with electric and magnetic fields. The control and manipulation of IX spins represents a significant step towards spintronlc devices. Finally, we introduced new methods to calibrate the exciton density, and the interaction energy of the particles was used as a sensitive tool for measuring the particle correlations within the excitonic fluid. Through careful measurements we showed, for the first time, evidence for classical and quantum particle correlation regimes and the transition between them.
Publications
- "Remote Dipolar Interactions for Objective Density Calibration and Flow Control of Excitonic Fluids" Phys. Rev. Lett 106, 126402 (2011)
K. Cohen, R. Rapaport and P. V. Santos
- "Particle correlations and evidence for dark state condensation in a cold dipolar exciton fluid ", Nature Communications 4, 2335 (2013)
Y. Shilo, K. Cohen, B. Lail - "Coherent spin transport in indirect exciton structures". Phys Rev B (2014)
A. Violante, R. Hey and P. V. Santos
- "Indirect exciton dynamics in moving potentials". New J. Phys. 89, 085313 (2014)
A. Violante, K. Cohen, S. Lazic, R. Hey, R. Rapaport, and P. V. Santos
- "Scalable interconnections for remote indirect exciton systems based on acoustic transport", Phys. Rev.B 89 085313(2014)
S. Lazic, A. Violante, K. Cohen, R. Hey, R. Rapaport, and P. V. Santos
(See online at https://doi.org/10.1103/PhysRevB.89.085313)
