With the fast growth in the volume of information being processed, researchers are charged with the primary task of finding new ways for fast and efficient processing and transfer of data. Dynamic eigen-excitations of a magnetically ordered body — spin waves and their quanta magnons — open up a very promising branch of high-speed and low-power information processing. Magnons are bosons, and thus they are able to form spontaneously a spatially extended, coherent macroscopic quantum state described by a single coherent wavefunction — a magnon Bose-Einstein condensate (BEC). A magnon BEC can be established independently of the magnon excitation mechanism and this can be achieved at room temperature. The information transfer can be realized by means of magnon supercurrents, which constitute the transport of angular momentum, driven by a phase gradient in the magnon-condensate wave function.
The SuperMagnonics project aimed at the realization and investigation of macroscopic quantum transport phenomena at room temperature as a novel approach for information processing technology. To reach these ambitious goals, the SuperMagnonics project specifically addressed several significant and strongly interlinked scientific objectives. In addition, in the course of the project, new and initially not forseen discoveries have been made. The scientific objectives and the main new discoveries are:
* Establishing the foundation of magnon supercurrent physics, which expanded the existing knowledge relating to magnon condensates.
* Investigation of magnon supercurrents induced by a phase gradient. It focused on the realization of magnon supercurrents in different physical environments, which allowed for the ascending control of supercurrent formation, manipulation, and detection.
* Investigation of Josephson-like magnon supercurrents and the realization of magnonic Josephson junctions. It covered studies of connected magnonic macroscopic quantum states with a supercurrent driven by the phase difference, addressing the magnon Josephson effect.
* Realization of magnon supercurrents controlled by an electric potential. For this, the magnon version of the Aharonov-Casher effect was exploited, where the phase of a magnon condensate is controlled by an electric field. This approach allows for fundamentally new means of magnon control.
* Discovery of second sound in magnon BECs, named magnonic Boboliubov waves. This surprising discovery was not foreseen when the project was drafted. Boboliubov waves are excitations of a magnon condensate, which travel with a velocity comparable to sound velocity.
* Discovery of magnon BEC formation by a rapid cooling process. This is a new mechanism that can be used in a very versatile way in small magnetic structures. This discovery was not foreseen when the project was drafted. It was made via a close cooperation with work in the ERC Starting Grant 678309 “MagnonCircuits” by Andrii Chumak, who worked at that time in the group of the PI.
* Investigation of magnon thermalization processes and the discovery of the phenomenon of double accumulation of magnetoelastic bosons—hybrid quasiparticles formed by the coupling of magnons and phonons in an overpopulated magnon gas.
