Phase Diagram for Magnon Condensate in Yttrium Iron Garnet Film
Abstract
Recently, magnons, which are quasiparticles describing the collective motion of spins, were found to undergo Bose-Einstein condensation (BEC) at room temperature in films of Yttrium Iron Garnet (YIG). Unlike other quasiparticle BEC systems, this system has a spectrum with two degenerate minima, which makes it possible for the system to have two condensates in momentum space. Recent Brillouin Light Scattering studies for a microwave-pumped YIG film of thickness d = 5 μm and field H = 1 kOe find a low-contrast interference pattern at the characteristic wavevector Q of the magnon energy minimum. In this report, we show that this modulation pattern can be quantitatively explained as due to unequal but coherent Bose-Einstein condensation of magnons into the two energy minima. Our theory predicts a transition from a high-contrast symmetric state to a low-contrast non-symmetric state on varying the d and H, and a new type of collective oscillation.
- Publication:
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Scientific Reports
- Pub Date:
- March 2013
- DOI:
- 10.1038/srep01372
- arXiv:
- arXiv:1302.6128
- Bibcode:
- 2013NatSR...3E1372L
- Keywords:
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- Condensed Matter - Quantum Gases;
- Condensed Matter - Statistical Mechanics
- E-Print:
- 6 figures. Accepted by Nature Scientific Reports