Periodic Reporting for period 4 - SuperMagnonics (Supercurrents of Magnon Condensates for Advanced Magnonics)
Reporting period: 2021-04-01 to 2022-03-31
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.
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.
ERC AdG SuperMagnonics, a highly significant project for the field of magnonics, has been successful in realizing a new macroscopic quantum phenomenon, magnon supercurrents, and demonstrating its potential applicability to information processing technologies. We have succeeded in developing working methods for generating, detecting, and manipulating supercurrents in magnon BECs. This shaped the field of macroscopic quantum-state magnonics that will pave the way for information technology based on magnon supercurrents in the long term.
The SuperMagnonics project resulted in a number of scientific achievements. All of them were advertised at a large variety of conferences and published in a number of articles. The obtained results are published or accepted for publication in 21 high-rank journals, as well as some of the latest achievements submitted for publication. In addition, 5 PhD works were successfully completed, and corresponding theses were published. The SuperMagnonics Team has presented results more than 60 times at many international conferences, including 40 invited talks.
The major research and technological achievements of the SuperMagnonics project are:
* Successful creation of magnon condensates and supercurrents in a wide range of parameters, such as the external magnetic field, the temperature, and the spatial confinement;
* The fundamentally new phenomenon of microwave-free formation of the magnon BEC by rapid cooling;
* Long-distance spin transport using magnon supercurrents and Bogoliubov waves;
* Discovery of a novel mechanism of the transport of angular momentum in obliquely magnetized films;
* Creation of a space-time crystal with tunable periodicity in time and space in the magnon BEC;
* Observation of Josephson oscillations in a room-temperature magnon condensate;
* Experimental discovery of the magnon Aharonov-Casher effect, which consists of the geometrical accumulation of the phase of magnons as they pass through an electric field region;
* Double accumulation and anisotropic transport of magnetoelastic bosons;
* A new type of wavevector-resolved Brillouin Light Scattering (BLS) spectroscopy;
* Achievements beyond planned objectives: Proposal of a classic version of several qubit functionalities using a two-component magnon BEC in a room-temperature YIG film, and the realization of the magnonic STImulated Raman Adiabatic Passage process (m-STIRAP).
The SuperMagnonics project resulted in a number of scientific achievements. All of them were advertised at a large variety of conferences and published in a number of articles. The obtained results are published or accepted for publication in 21 high-rank journals, as well as some of the latest achievements submitted for publication. In addition, 5 PhD works were successfully completed, and corresponding theses were published. The SuperMagnonics Team has presented results more than 60 times at many international conferences, including 40 invited talks.
The major research and technological achievements of the SuperMagnonics project are:
* Successful creation of magnon condensates and supercurrents in a wide range of parameters, such as the external magnetic field, the temperature, and the spatial confinement;
* The fundamentally new phenomenon of microwave-free formation of the magnon BEC by rapid cooling;
* Long-distance spin transport using magnon supercurrents and Bogoliubov waves;
* Discovery of a novel mechanism of the transport of angular momentum in obliquely magnetized films;
* Creation of a space-time crystal with tunable periodicity in time and space in the magnon BEC;
* Observation of Josephson oscillations in a room-temperature magnon condensate;
* Experimental discovery of the magnon Aharonov-Casher effect, which consists of the geometrical accumulation of the phase of magnons as they pass through an electric field region;
* Double accumulation and anisotropic transport of magnetoelastic bosons;
* A new type of wavevector-resolved Brillouin Light Scattering (BLS) spectroscopy;
* Achievements beyond planned objectives: Proposal of a classic version of several qubit functionalities using a two-component magnon BEC in a room-temperature YIG film, and the realization of the magnonic STImulated Raman Adiabatic Passage process (m-STIRAP).
The successful implementation of the SuperMagnonics project led to many fruitful discoveries beyond the state of the art. For instance, the discovery of the long-distance supercurrent transport in the form of Bogoliubov second-sound waves further advanced the frontier of the physics of quasiparticles. Also, the discovery of a novel way to create a magnon BEC by rapid cooling paved the way for on-chip solid-state quantum computing. The injection mechanism is originally incoherent and can be applied to other bosonic systems such as exciton-polaritons and photons in cavities. The proposed tunable magnon space-time crystal in the magnon BEC represents an example of a nonlinear Floquet system and therefore serves as a bridge between magnonics and classical nonlinear wave physics on the one hand and the Floquet time-crystal description of periodically driven systems on the other. Also, we report on the discovery of the ac Josephson effect in a magnon BEC carried by a room-temperature ferrimagnetic film. The appearance of the Josephson effect is manifested by oscillations of the magnon BEC density in the trench, caused by a coherent phase shift between this BEC and the BECs in the nearby regions. Along with this, the magnon Aharonov-Casher effect (ACE) was experimentally demonstrated, which will allow for efficient phase manipulation of magnon currents and is very promising for novel magnonic applications. Finally, a classical analog of several qubit functionalities using a two-component magnon BEC formed at opposite wavevectors is proposed.
All these groundbreaking discoveries will help in the further realization of the overarching aim of the SuperMagnonics project – to pave the way for a magnon supercurrent-based information processing technology.
All these groundbreaking discoveries will help in the further realization of the overarching aim of the SuperMagnonics project – to pave the way for a magnon supercurrent-based information processing technology.