Macroscopic quantum states in antiferromagnets:
Bose-Einstein condensation of anti-ferro-magnons
Dmytro Bozhko, University of Colorado Colorado Springs (Principal Investigator)
Zbigniew Celinski, University of Colorado Colorado Springs (Co-Investigator)
Valentine Novosad, Argonne National Laboratory (Co-Investigator)
Bosons are particles of integer spin that support the formation of the fundamental macroscopic quantum state – Bose-Einstein condensate (BEC). Since its experimental discovery in 1995, BEC became a hot topic in physics. Nowadays, BECs were experimentally observed in a variety of different systems, including real particles such as ultra-cold gases as well as quasiparticles like exciton-polaritons and photons. Quanta of collective spin excitations (magnons) in ferrimagnets, quantum magnets, and liquid helium 3He were also found to form BEC under special conditions. The BEC phenomenon has already found its first applications for quantum computing noise reduction. Recently, antiferromagnetic (AFM) materials have attracted remarkable interest from the scientific community due to their unique properties – high operating frequencies combined with significantly suppressed stray fields.
This proposal aims to realize for the first time the BEC of magnons in AFMs (anti-ferro-magnons) and study its properties in a wide frequency range from GHz to THz in a broad range of temperatures from ambient to the quantum limit. The range of materials for investigations includes fluorides, oxides, and synthetic AFMs. The main scientific objectives of this 3-year proposal are: (1) Realization of AFM BEC through rapid cooling using a broad range of micro-structured AFMs; (2) Realization of microwave-pumped anti-ferro-magnetic BEC employing AFMs that exhibit resonances in tens of GHz; (3) Realization of magnon BEC in synthetic AFMs such as Fe/Cu/Fe and Fe/Cr/Fe through both parametric microwave pumping and rapid cooling techniques; (4) Observation and study of macroscopic quantum phenomena in AFMs: anti-ferro-magnonic BEC supercurrents, Bogoliubov waves, magnon Josephson effect, and second sound. Besides the four listed above scientific aims, the important objective of this proposal is to build significant research and educational capacity at the University of Colorado Colorado Springs to explore the quantum properties of magnetic systems that will allow to enhance quantum workforce development in DOE.
The proposed aims are going to be realized using a combination of various state-of-the-art fabrication and measurement techniques. The samples will be grown using molecular beam epitaxy and nanostructured using electron beam lithography and reactive ion etching. The AFM BEC will be detected using time-, space-, and wavevector-resolved Brillouin light scattering and microscopy, and microwave spectroscopy. To perform these measurements in a wide range of temperatures, the team will build a cryostat capable of reaching temperatures of 3 K together with optical and microwave access. Measurements of AFM dynamics in the single-quanta limit will be performed at Argonne National Laboratory in the dilution 3He-4He fridge.
The expected outcomes of the proposal will help us to understand the fundamental aspects of AFM physics as well as make progress in applied material science. We plan the experimental demonstration of anti-ferro-magnonic BEC achieved in a fundamentally different way from earlier experiments as well as to provide important insights into the properties of AFMs at low and ultra-low temperatures. Moreover, all the efforts will serve the higher purpose to build foundations to study properties of matter at macro- and nanoscale to provide research-backed education for training the new generation of highly-skilled STEM workforce.
