BoseEinstein Condensation of Magnons and Spin Superfluidity in the Polar Phase of ^{3}He
Abstract
The polar phase of ^{3}He, which is topological spintriplet superfluid with the Dirac nodal line in the spectrum of Bogoliubov quasiparticles, has been recently stabilized in a nanoconfined geometry. We pump magnetic excitations (magnons) into the sample of polar phase and observe how they form a BoseEinstein condensate, revealed by coherent precession of the magnetization of the sample. Spin superfluidity, which supports this coherence, is associated with the spontaneous breaking of U(1) symmetry by the phase of precession. We observe the corresponding NambuGoldstone boson and measure its mass emerging when applied rf field violates the U(1) symmetry explicitly. We suggest that the magnon BEC in the polar phase is a powerful probe for topological objects such as vortices and solitons and topological nodes in the fermionic spectrum.
 Publication:

Physical Review Letters
 Pub Date:
 July 2018
 DOI:
 10.1103/PhysRevLett.121.025303
 arXiv:
 arXiv:1711.02915
 Bibcode:
 2018PhRvL.121b5303A
 Keywords:

 Condensed Matter  Other Condensed Matter
 EPrint:
 5 pages, 4 figures