Chiral Symmetry Breaking in Superfluid 3He-A
Chiral Symmetry Breaking in Superfluid 3He-A
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DOI：
10.1126/science.1236509
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发表时间：
2013-07
期刊：
影响因子：
56.9
通讯作者：
H. Ikegami;Y. Tsutsumi;K. Kono
中科院分区：
文献类型：
--
作者：
H. Ikegami;Y. Tsutsumi;K. Kono
当一个旋转的物体被置于循环流体中时，它两侧的压力不平衡会引起一种叫做马格纳斯力的偏转力。这种效应的量子模拟已经被预测出现在3He的低温A相中，在那里形成超流体的库珀对具有特定的手性。杂质穿过这样的超流体时，会受到偏转力的作用，偏转力的方向由这些对的手性决定。Ikegami等人（第59页）将杂质捕获在3He的自由表面下，使其运动，并通过测量横向电流差证明了这种偏转力的存在。在不同的冷却运行中，偏转的符号有所不同，表明系统在进入超流体阶段时选择了一种或另一种手性——这是自发对称性破缺的特征。氦-3表面下杂质的不对称偏转揭示了超流体A相的手性。自发对称破缺是物理学许多分支中的一个重要概念。在氦-3 （3He）中，对称性的破坏导致了超流体相3He- a的轨道手性。手性是3He-A的基本性质，但其直接检测一直具有挑战性。我们报告了通过在3He-A的自由表面下捕获电子的输运测量直接检测手性。特别是，我们观察到运动电子所经历的所谓的内在马格纳斯力；力的方向直接反映了手性。我们进一步表明，在超流体过渡时，系统选择了右手性或左手性。这种选择的观察直接证明了手性对称性的破缺。
Quantum Handedness When a rotating object is placed in circulating fluid, an imbalance of pressures on either side of it causes a deflecting force called the Magnus force. The quantum analog of this effect has been predicted to appear in the low-temperature A phase of 3He, where the Cooper pairs forming the superfluid have a specific handedness. An impurity traveling through such a superfluid would experience a deflecting force in the direction determined by the chirality of the pairs. Ikegami et al. (p. 59) trapped impurities beneath the free surface of 3He, set them in motion, and demonstrated the existence of this deflecting force by measuring the differential transverse current. The sign of the deflection varied over different cooling runs, indicating that the system was choosing one or the other chirality upon entering the superfluid phase—a signature of spontaneous symmetry breaking. The asymmetric deflection of impurities beneath the surface of helium-3 reveals the handedness of the superfluid A phase. Spontaneous symmetry breaking is an important concept in many branches of physics. In helium-3 (3He), the breaking of symmetry leads to the orbital chirality in the superfluid phase known as 3He-A. Chirality is a fundamental property of 3He-A, but its direct detection has been challenging. We report direct detection of chirality by transport measurements of electrons trapped below a free surface of 3He-A. In particular, we observed the so-called intrinsic Magnus force experienced by a moving electron; the direction of the force directly reflected the chirality. We further showed that, at the superfluid transition, the system selected either right- or left-handed chirality. The observation of such selection directly demonstrates chiral symmetry breaking.