Physics Seminar: Spin transport by a supercurrent in a room-temperature magnon Bose-Einstein condensate

Speaker: Dr. Oleksandr Serha
University of Kaiserslautern
Kaiserslautern, Rhineland-Palatinate, Germany

Abstract:
With the fast growth in the volume of information being processed, researchers are charged with the task of finding new ways for fast and energy efficient computing. An extraordinary challenge is the use of macroscopic quantum phenomena such as magnon Bose-Einstein condensates (BEC) for the information transfer and processing.

Here, I present experimental evidence for the excitation of a supercurrent—the transport of angular momentum driven by a phase gradient in the wave function of a magnon BEC. In our experiments, the magnon BEC was formed at room temperature by a para­met­rically populated magnon gas in a single-crystal ferrimagnetic film of yttrium iron garnet (Y3Fe5O12, YIG). The temporal evolutions of the magnon density was studied by wave­vector-, frequen­cy-, time- and space-resolved Brillouin light scattering spectros­copy. It has been found that local heating of the YIG film by focused laser light creates a spatially varying phase shift imprinted into the BEC wavefunction and, thus, propels the outflow of condensed magnons from the heated area. This outflow does not alter the dynamics of a non-coherent gaseous magnon phase but decreases the density of the freely evolving magnon BEC in the heated area. Moreover, it creates a solitary magnon wave, which pro­pa­gates many hundreds of BEC’s wavelengths through the “cold” magnon condensate.