PH6: Excitons and Polaritons in Semiconductors: From One-Body to Many-Body Problems

label Diverse autorenew 2025-09-29, 17:01 history_edu Silviu Marinescu
An exciton is a quasiparticle in an interband excited state of semiconductors, a bound state of an electron in a conduction band and a hole in a valence band. This electron-hole (e-h) pair is coupled with a photon to form an exciton polariton (referred to as a polariton), a hybridized substance of an electron, a hole, and a photon. An exciton and a polariton are fundamental elementary particles, which characterize optically excited states of matters, especially insulators and semiconductors. In this course, I shall review theoretical aspects of physics of excitons and polaritons in semiconductors with and without a photon cavity. I will cover from single-body problems to many-body ones to elucidate how they play important roles in optical responses of matters. At the JSS, we will start one-body problems of a Wannier exciton, in particular, its dimensionality, one-photon absorption and two-photon absorption processes. The electron-hole relative motion is influenced by the spatial dimensions in low-dimensional semiconductors, leading to significant changes of the energy structures and optical absorption spectra [1]. To detect low dimensionality of the e-h relative-motion wavefunction, mid-gap two-photon absorption process and its anisotropic polarization dependence are shown to be very powerful [2]. Next, many-body cooperative phenomena related to excitons are surveyed. A DMFT (dynamical mean-field theory) treatment for the "exciton Mott transition," a change from the exciton gas to the electron-hole (e-h) plasma as the e-h density increases, is discussed for bulk semiconductors. In the one-dimensional case, the exciton Mott transition is absent and the insulating "biexciton crystal" state is the most probable ground state at zero temperature, shown by the two-band Tomonaga-Luttinger model [3]. An exciton in metallic wires, i.e., the "Mahan exciton" in one dimension is shown to induce the Fermi-edge singularity in optical spectra [4]. We are also interested in stationary states of semiconductor lasers including carrier-carrier Coulomb scatterings. At low temperature, the BCS-type e-h pairing instability with dephasing induces the "Fano-resonance gain" [5]. There, the single-mode laser operation is modified compared to the conventional laser operation with the Lorentzian-type e-h plasma gain. Lastly, we talk about interacting electron-hole-photon (e-h-p) systems (many polariton systems) with a microcavity. We pay attention both to the stationary nonequilibrium and quasi-thermal equilibrium situations. Macroscopic numbers of the cavity polaritons can be condensed into a single energy level and exhibit polariton BEC in a quasi-thermal equilibrium situation. Here, the stationary state of the system is determined by variational minimization of the Free energy. Internal e-h motion in the polariton condensates is clarified [6]. The polariton BEC is a candidate of a coherent light source, similar to semiconductor lasers. Similarity and difference between the polariton BEC and the cw lasing in stationary nonequilibrium situations should be clarified. We introduce a unified view of these two phenomena in the Coulomb-correlated e-h-p systems [7], based on the Keldysh Green's function formalism, to discuss the crossover from the polariton BEC to "BCS-coupled lasing" as the pumping increases.

Period
06-08-2014 - 08-08-2014 (1 weeks)

Target group
Prerequisites: Quantum Mechanics, Electromagnetism, and Condensed Matter Physics

Course aim
The most important aims of the Summer School are to develop post-graduates scientific readiness and to offer students the possibility to study in a modern, scientific environment and to create connections to the international science community.



Credits
2.0 ECTS creditsObligatory attendance at lectures, and publish a report.Grading: Pass/fail

Course fee
EUR 0[Convert to USD]Participating the Summer School is free of charge, but student have to cover the costs of own travel, accommodation and meals at Jyvskyl.

Course leader
Coordinator: Dr. Pekka Koskinen (University of Jyvskyl, Finland)Lecturer: Prof. Tetsuo Ogawa (Department of Physics, Osaka University, Japan)

Scholarships
The 24th Jyvskyl Summer School is not able to grant any Summer School students financial support. In order to ensure your participation, we recommend that you take steps to secure your own funding, for example, by turning first to your home institution

University of Jyvaskyla Faculty of Mathematics and Science and Faculty of Information Technology
Address: Jyvaskyla Summer School, Faculty of Mathematics and Science P.O.Box 35 (YK312), FIN-40014 University of Jyvaskyla, Finland
Postal code: FIN-40014
City: Jyvaskyla
Country: Finland
Website: http://www.jyu.fi/summerschool
E-mail: jss@jyu.fi
Phone: +358505818351