Bose-Einstein Condensation of Magnons and Potential Device Applications

One goal of this proposal is to independently confirm and then extend the surprising report by a German group that dynamic Bose-Einstein Condensation (BEC) of magnons (the elementary excitations of magnetic systems) can occur under appropriate conditions in thin films of the ferrimagnetic compound Yttrium Iron Garnet (YIG). In parallel we propose to expand our earlier studies on patterned magnetic nanostructures to include objects displaying topologically nontrivial magnetization distributions such as vortices, skyrmions, and Dirac strings. Ordinarily BEC of magnons would be forbidden since their number is not constrained: the inelastic collisions among magnons cause them to appear and disappear and number conservation is a requirement of (equilibrium) BEC. However it has been argued that elastic collisions rapidly bring the magnons into a dynamic thermal equilibrium at much faster time scales; this would allow BEC. What is both surprising and important is that the BEC phenomenon is reported to occur at room temperature. If room temperature BEC is real (confirmed) the potential for applications of what has historically been the largely academic field of BEC (in systems such as liquid helium, cold atoms/molecules, excitons, and even photons), would be greatly expanded since one could then apply modern lithographic tools to make arrays of interacting condensates, possibly allowing the development of room-temperature devices based on quantum superimposed macroscopic condensates with programmable couplings. Since there is no guarantee that the reported observations will be reproducible, the research has a high risk factor; however if the phenomena is real, with the extensions we propose the impact is expected to be transformative. The second component proposed involves microwave characterizations of unusual collective modes of magnetic nanostructures that support topologically non-trivial magnetization distributions. The structures are patterned by e-beam lithograp