CORDIS - EU research results

Indirect Excitons: Fundamental Physics and Applications

Final Report Summary - INDEX (Indirect Excitons: <br/>Fundamental Physics and Applications)

Indirect excitons are bosonic quasi-particles in semiconductors with unique properties: they have long lifetime and spin-relaxation time, can travel over large distances before recombination, can be cooled down to low temperatures and form a quantum gas, and can be controlled by voltage in-situ. Due to these properties, they form a model system both for the studies of fundamental properties of light and matter and for the development of conceptually new excitonic devices. INDEX explores the potential of indirect excitons (1) for the studies of fundamental physics of cold bosons in solid-state materials, (2) for the development of novel principles for optoelectronic devices, and (3) for the training of a new generation of researchers.
INDEX encompasses all major implementations of indirect excitons in solid state: optically, electrically and magnetically formed indirect excitons in coupled quantum wells, as well as recently developed systems embedded in the active region of the semiconductor microcavity. Our consortium designs and fabricates these high quality semiconductor nanostructures and performs cutting edge optical, magnetic and electrical studies.

INDEX has seven ambitious research objectives:
1. Study exciton condensation in traps
2. Measure dispersion of collective excitations in Quantum Hall Bilayers
3. Develop nonlinear optical properties of indirect excitons in biased microcavities
4. Measure spatial coherence length of indirect excitons in coupled quantum wells
5. Explore transport properties of indirect excitons
6. Measure and optimise exciton spin coherence
7. Design, realise, study and model excitonic devices

In terms of training via research, the main objective of INDEX is to provide a structured network-based training program led by major international scientists in the state-of-the art infrastructure, which covers a portfolio of interdisciplinary techniques.
11 Early Stage Researchers (ESR) have been recruited to work on the project. In addition 3 Experienced Researchers (ER) have been recruited. The network provided 31 years of training via research.

All the researchers recruited to the project received state-of-art-training in relevant laboratory and research skills. Almost all the fellows were seconded in partner and/or associate partner institutions and/or industry to complete their training. This mobility was accompanied by the knowledge transfer, crucial in this rapidly developing field. It was also supported by frequent visits of senior group members across the network, helping to maintain the strong interactions between partners and with industrial sector.
All the fellows benefited from the complementary skills training (e. g. language courses), in their local institutions and at the network level during project events (e. g. “intellectual property”, “from opportunities to commercialization”). Training on essential transferable skills such as scientific presentation and project writing has also been provided on both local level and as a common training combined with the project meetings.

Main scientific achievements of the network include:

1. Evidence for macroscopic coherence and condensation of excitons, including condensation in electrostatic traps.
2. Observation and theoretical description of exciton spin transport and coherence.
3. Evidence of geometrically controlled phase transition and bias-controlled spin transition in exciton-polariton condensates, opening up a new range of devices.
4. Optical detection of excitonic correlations in quantum Hall bilayers.
5. Development of the simulation tool for the fully quantum mechanical study of excitonic devices.
6. Demonstration of Coulomb drag in e-h bilayers with an interlayer barrier thickness of just 5 nm, the narrowest ever realized.
7. Optically controlled excitonic transistor.

These results constitute a major breakthrough in excitonics. Our studies of fundamental physics of cold bosons in solid state allowed for the long sought demonstration of their collective properties. These properties path the way towards new generation of the excitonic devices.

Network results were essentially disseminated through 87 published papers (71 peer reviewed papers and 15 arXiv papers); among them 27 are signed by at least 2 partners from the network and 31 are co-signed by the recruited fellows. More than 137 conference presentations, including invited and plenary talks, where delivered by the members of the INDEX consortium. We also communicate our progress via the project website

INDEX has organized 9 international events in four years, including the kick-off and the mid-term meeting, three international schools, one on Spinoptronics in St-Petersburg (Russia), and two on Indirect Excitons in Erice (Italy) and in Les Houches (France), two International Conferences on Physics of Light-Matter Coupling in Nanostructures, one in Crete (Greece) and one in Montpellier (France), two International Workshops, one on Indirect Excitons in Barcelona (Spain), and one on collective phenomena in two-dimensional systems in Pisa (Italy). Apart from the kick-off meeting, all the events were not only an occasion for brainstorming discussions between the network members, but also the possibility to communicate INDEX scientific results outside the network. All the fellows were provided with the opportunity to present their results during these events, but also during international and national scientific meeting outside the network. All these events provided an opportunity to develop the communication skills of the fellows and create an active, long-term network of young researchers. Their expertise, as well as personal contact developed within the network will help Europe shape the future of excitonics research.

This constitutes a considerable impact of INDEX not only on the European but also international scale. In four years of collaborative research the interactions between network partners have developed significantly, including collaboration with associated partners from US. The creation of strong collaborative tissue and organisation of international scientific events insured the visibility of our research community in both academic and industrial sector. The new excitonic devices developed and patented by INDEX partners may considerably impact the multi-billion euro market of optoelectronics in the near future.

The Network is also active in outreach activities, the researchers and young fellows of INDEX participated in important events across Europe, such as the European Researchers’ Night in Pisa (Italy), “Fete de la Science” in Montpellier and Clermont-Ferrand (France), “Physics at Work” exhibition in Cambridge, “Dia de la Luz” in Barcelona (Spain). The fellows acquired an experience in outreach activities and are aware of importance of such events.

The contacts for the INDEX network are Dr. Maria Vladimirova (Project Coordinator: and Ms. Hélène LEBRUN ANDERSSON (Project Manager:
The INDEX website is at