In ordinary life we are always surrounded by energy in the form of heat. Heat in solid matter are vibrations of the atoms from their equilibrium positions. At absolute zero temperature there are no such vibrations, while at higher temperatures they start to move in a way that are described as phonons. In a similar manner heat in magnets also consists of changes in the direction of the individual magnetic moments in a magnet which are described as magnons.
In this project we will try to understand how we can control the coupling and flow of energy between the vibrations in atomic positions (phonons) and changes in the magnetic direction (magnons) through varying the external magnetic fields on a specifically designed magnet.
The ultimate goal is to control the energy flow in manner so that we can direct enough energy supplied in the form of heat energy into a single magnonic state in the form a uniform magnetic precession. If the energy flow becomes large enough this becomes a state with specific quantum properties (a Bose-Einstein Condensate) which could open a new route to operate quantum computing based on local magnetic waves that we can control through the magnetization direction of the magnet.
To measure these vibrations and to create model systems we will use layer-by-layer grown oxides where we can tune properties through composition. In addition, we will control both phonons and magnons through making small nano-meter sized magnets. To measure and verify what we do we will use both own-developed scanning tunneling microscopes, collaborations in Sweden, Spain and Japan to be able to use the latest experimental techniques within advanced light-based characterization in the far infrared (THz) as well as electron microscopes that collect electrons emitted from the materials by light
The project will enable the design, realisation and understanding of a highly coupled oxide based phonon-magnon system. This is motivated by that all these excitations are in the thermal region. Accordingly being able to understand and control these excitations will allow for controlling thermal excitations that may be used for all-thermal signal processing. The project will push the knowledge of phonon-magnon interactions in the chosen model systems (LFO and LSMO) so that we can tailor films to optimise the coupling between the two modes. The aim is to understand the coupling, be able to switch the system with magnetisation direction and to be able to pump magnon Bose-Einstein condensates through phonons.
• We will be the first to understand and comprehensively map out phonon-magnon interactions in a oxide system through dynamic X-PEEM, THz and ultrafast optical spectroscopy and point contact based excitation. We will do this through tuning material properties through layer by layer growth of ferromagnetic LSMO films and antiferromagnetic LFO films and nano structuring of those. The systematic approach will open up new understanding on the tunability and underlying physics of these systems.
• We will turn the coupling through growing dedicated films and structuring at the micro-nano scale to match the phonon-magnon coupling and to achieve coupling dependent on the static magnetic orientation of the active elements.
• We will utilise up-conversion on the substrate, and high efficient point contacts pump a magnon Bose-Einstein condensate through phonons. This ability will signify a paradigm shift in the usability of such condensates, in particular for developing magnonic applications and components.
• We will develop STM-based point contact spectroscopy and improve optical probing in the THz region. This are novel new generic method for probing in THz-regime and will impact the development and our understanding of the complexity of low energy bosonic systems.