Polariton dynamics, localization and Exceptional Points in terahertz metamaterial coupled systems

• Applicant: Professor Dr. Hartmut G. Roskos
• Subject Area: Experimental Condensed Matter Physics ; Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 442393838

This is an extension of a DFG project on strong and ultrastrong light-matter coupling phenomena involving metamaterials. It has five subtopics, two of which aim to complete prior work of the preceding project phase, while three subtopics have been conceived as new themes from that prior work. Except for one of the subtopics, which deals with the coupling of atomic transitions to resonances of metallic metamaterials, the other four use metamaterials as representing matter which couples to the electromagnetic modes of a Bragg cavity. The coupling is a purely classical one, but the coupled electromagnetic modes can be viewed to quite some extent as the analogs of bosonic plasmon-photon polaritons in quantum electrodynamics, with the oscillators of the metamaterials acting as plasmonic quasi-particles. We will investigate with these coupled systems the following four phenomena: (i) The ultrafast sub-cycle dynamics of the polariton decay when the plasmonic metamaterial resonance is abruptly switched off by a femtosecond laser pulse. (ii) The role of inhomogeneity in the metamaterial system, which has been predicted to have only a small effect on the amount of mode splitting (Rabi splitting), but is to lead to spatial localization of the polariton modes at a threshold amount of inhomogeneity. (iii) The appearance of an Exceptional Point (EP) at a specific coupling strength, where the polaritons abruptly coalesce into a single polariton mode. With the dissipative model system, which we have suggested for the study of the EP, we will investigate the recently invented concept of ‘synthetic complex frequency waves’ for artificial linewidth narrowing of resonances. (iv) We have proposed a model system with two metamaterials in a Bragg cavity, in which the coupling strengths can be tuned continuously. Here, instead of a single EP, one expects the appearance of a continuous EP ‘arc’ in parameter space, which we intend to identify experimentally. As stated above, the fifth subtopic does not involve a Bragg cavity. It uses a metamaterial to couple to electronic transitions of boron dopants in silicon. This happens at cryogenic temperatures when they are not ionized. In the preceding project phase, we employed a metamaterial with split-ring resonators, but did not achieve strong coupling. Here, we will use a metamaterial exhibiting bound states in the continuum which has a much high quality factor. With silicon samples with different thicknesses of the doped layer, we will also investigate the depth down to which one obtains formation of a single polariton line.

• DFG Programme: Research Grants
• International Connection: China
• Cooperation Partner: Professor Lei Cao