Collective quantum transport and light-assisted superconductivity

• Applicant: Professor Dr. Sven Höfling
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449424711

Contemporary condensed matter physics is a foundation of the present-day electronics and technology. When merged with optics, it represents a powerful platform for modern ultrafast devices. At the same time, multiple phenomena lying at the border of these two realms, where solid-state systems are strongly coupled to light, are still to be explored, and potentially contain fundamental effects yet to be discovered. In particular, the regime of the strong light-matter coupling appears in nanostructures with pronounced excitonic resonance placed inside an optical resonator, where hybrid light-matter quasiparticles, known as cavity polaritons, emerge. Polaritonics is a rapidly developing field, however, one aspect in polariton physics, namely, corresponding quantum statistical properties of quasiparticles and resulting quantum correlations, was mainly overlooked up to now. While the matter part of a polariton is represented by an exciton, made from an electron and a hole that obey Fermi statistics, the light part is formed by a cavity photon obeying Bose statistics. Furthermore, adding extra layers to the device, one can bring purely fermionic species – electrons – into play.In the context of the physics of Bose-Fermi mixtures, novel two-dimensional materials – with prominent examples of atomically-thin layers of transition metal dichalcogenides and graphene – combine many desirable properties, from strong optical response to relative simplicity and low cost of preparation, and allow to create the structures consisting of one or several isolated layers hosting particles with different statistics. The interplay between the two conceptually different statistics brings a new twist into the domain of polaritonics, and presents an opportunity for observation of novel quantum collective phases unattainable in other kind of systems. In this project, we will explore how large optical nonlinearities and strong quantum correlations, stemming from the effects of the hybrid quantum statistics, appear in the regime of the strong light-matter coupling. Proposed studies include superfluidity, correlations, drag effects and superconductivity in such multi-layer systems of electrons and polaritons in a microcavity, with the development of specific designs of geometries favorable for the observation of record-high optical nonlinearities, collective quantum transport, and light-assisted superconducting behavior.To achieve the ambitious goals of this project that closely entwines theory and experiment, we bring together a strong German-Russian academic consortium in the field of polaritonics and two-dimensional materials. The international team unites world-leading theoreticians who will build the microscopic theory of solid-state Bose-Fermi mixtures in layered geometries, and unmatched experimental facilities necessary to develop the novel structures and observe the proposed phenomena.

• DFG Programme: Research Grants
• International Connection: Russia
• Partner Organisation: Russian Foundation for Basic Research, until 3/2022
• Cooperation Partner: Professor Dr. Yuri E. Lozovik, until 3/2022