Polarytony magnonowo-plazmonowe: nowe kwazicząstki w ciele stałym

The leading goal of the Spin-2-Plasm project is to demonstrate and explore the functionalities of a new type of lowenergy excitations: hybrid magnon-plasmon modes. Such quasiparticles will allow electrical control and readout of magnetic states with terahertz (THz) frequencies, which is necessary for ultrafast communications, memories, and other technologies. Current research in two-dimensional antiferromagnetic (2DAFM) materials offers an unprecedented possibility to show such a coupling, using magnons in 2DAFMs and plasmons in two-dimensional electron gas (2DEG). This is possible because both excitations have resonant frequencies in the same range of terahertz (THz) frequencies. This effect could be observed in heterostructures of high electron mobility 2DEG interfaced with 2DAFMs, as predicted theoretically. We also set out to achieve magnon-plasmon coupling by using a mediating electromagnetic cavity mode. For that second method, as an intermediate step to reach our goal, we also plan to achieve strong magnon-photon coupling at THz frequencies with small volumes of 2DAFM. This can be achieved by placing a 2DAFM in a split ring resonator (SRR). Special care will be taken on designing such a resonator that would fit specifically this purpose, as typically such resonators are designed to couple to dielectric, not magnetic, properties of matter. It was already shown that plasmon-polaritons are formed with SRR atop 2DEG using THz methods. Here, we want to observe magnonpolaritons using THz optical methods and Raman scattering. Observation of magnon-photon coupling using THz techniques would allow the detection of resonance in few-layered 2DAFMs or magnetic thin films. Furthermore, observation of strong magnon-photon coupling using Raman scattering would open a new avenue of research for this technique, as it is not used for magnon-photon coupling research. In general, the optical observation of THz magnonpolaritons is scientifically attractive because the research on strong light-matter coupling in the THz range is much less developed than in other parts of the electromagnetic spectrum. Moreover, magnetic excitations have the advantage of narrow line widths that are crucial for light-matter coupling research and applications. Successful results of this part of the proposal might serve, similarly to other polariton systems, as a platform for future studies of quantum effects in 2DAFMs. In Spin-2-Plasm, we would like to study the interaction of two different THz excitations - magnons and plasmons - that are very rarely investigated together. The interaction of these two types of waves is expected to result in new hybrid modes, allowing tuning spin waves with electric fields. Several theoretical papers predict magnon-plasmon hybridization in one hypothetical material hosting these two excitations. However, we think that the idea of interfacing two different materials has more chance of succeeding. There are predictions of such a coupling in 2DAFM/2DEG heterostructures. Both plasmons in 2DEG and magnons in 2DAFM have frequencies in the THz range, which makes them ideal candidates for achieving magnon-plasmon coupling. Therefore, current developments in the field of 2DAFMs offer an unprecedented opportunity to achieve magnon-plasmon coupling. Results on magnon-photon coupling, described in the previous paragraph, may allow magnon-plasmon coupling via an electromagnetic cavity mode resonating at a similar frequency. The structures created during this proposal will be also used for the electrical detection of their resonances. Electrical detection of polariton states might offer better responsivities to THz radiation because employed cavity modes concentrate electromagnetic energy. Electrical contacts also offer the possibility of electrical manipulation of properties of 2DAFMs, which, regarding applications, is the most valuable outcome of the proposed research. The feasibility of the project is supported by the applicant’s preliminary spectroscopy results showing strong magnonphoton coupling at about 0.4 THz using a bulk sample of 2DAFM MnPSe3 in a Fabry-Pérot type cavity. The experience of the applicant and the Institute of High Pressure Physics in THz techniques, processing of two-dimensional materials, and technological processing supported by experience in theoretical modeling of magnetism at Adam Mickiewicz University secures a successful realization of the proposal.