Experimental observation of Josephson oscillations in a room-temperature Bose-Einstein magnon condensate

Alexander J. E. Kreil; Halyna Yu. Musiienko-Shmarova; Pascal Frey; Anna Pomyalov; Victor S. L'vov; Gennadii A. Melkov; Alexander A. Serga; Burkard Hillebrands

doi:10.1103/PhysRevB.104.144414

Experimental observation of Josephson oscillations in a room-temperature Bose-Einstein magnon condensate

Alexander J. E. Kreil, Halyna Yu. Musiienko-Shmarova, Pascal Frey, Anna Pomyalov, Victor S. L'vov, Gennadii A. Melkov, Alexander A. Serga, Burkard Hillebrands

DOI 10.1103/PhysRevB.104.144414 · Physical Review B

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Abstract

The alternating current (ac) Josephson effect in a time-independent spatially inhomogeneous setting is manifested by the occurrence of Josephson oscillations—periodic macroscopic phase-induced collective motions of the quantum condensate. So far, this phenomenon was observed at cryogenic temperatures in superconductors, in superfluid helium, and in Bose-Einstein condensates (BECs) of trapped atoms. Here, we report on the discovery of the ac Josephson effect in a magnon BEC carried by a room-temperature ferrimagnetic film. The BEC is formed in a parametrically populated magnon gas in the spatial vicinity of a magnetic trench created by a dc electric current. 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 BEC in the nearby regions. Our findings advance the physics of room-temperature macroscopic quantum phenomena and will allow for their application for data processing in magnon spintronics devices.