Department of Physics, Texas A&M University, College Station, TX 77843-4242, USA.
Sci Rep. 2013;3:1372. doi: 10.1038/srep01372.
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.
最近，在钇铁石榴石（YIG）薄膜中，描述自旋集体运动的准粒子——磁振子，在室温下被发现经历玻色-爱因斯坦凝聚（BEC）。与其他准粒子 BEC 系统不同，该系统的能谱具有两个简并极小值，这使得系统在动量空间中有可能存在两个凝聚体。最近对厚度为 d = 5 μm 且场强为 H = 1 kOe 的微波泵浦 YIG 薄膜进行的布里渊光散射研究发现，在磁振子能量极小值的特征波矢 Q 处存在低对比度的干涉图案。在本报告中，我们表明，这种调制模式可以定量解释为磁振子进入两个能量极小值的非相等但相干的玻色-爱因斯坦凝聚。我们的理论预测，在改变 d 和 H 时，从高对比度对称状态到低对比度非对称状态的转变，以及一种新型的集体振荡。
