Center for Materials Theory, Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, Piscataway, New Jersey 08854-8019, USA.
Nature. 2013 Jan 31;493(7434):621-6. doi: 10.1038/nature11820.
The development of collective long-range order by means of phase transitions occurs by the spontaneous breaking of fundamental symmetries. Magnetism is a consequence of broken time-reversal symmetry, whereas superfluidity results from broken gauge invariance. The broken symmetry that develops below 17.5 kelvin in the heavy-fermion compound URu(2)Si(2) has long eluded such identification. Here we show that the recent observation of Ising quasiparticles in URu(2)Si(2) results from a spinor order parameter that breaks double time-reversal symmetry, mixing states of integer and half-integer spin. Such 'hastatic' order hybridizes uranium-atom conduction electrons with Ising 5f(2) states to produce Ising quasiparticles; it accounts for the large entropy of condensation and the magnetic anomaly observed in torque magnetometry. Hastatic order predicts a tiny transverse moment in the conduction-electron 'sea', a colossal Ising anisotropy in the nonlinear susceptibility anomaly and a resonant, energy-dependent nematicity in the tunnelling density of states.
通过相变自发破缺来实现集体长程有序的发展，是由基本对称性的破坏所引起的。磁性是时间反演对称性破缺的结果，而超流性则源于规范不变性的破缺。在重费米子化合物 URu(2)Si(2) 中，在 17.5 开尔文以下发展的破缺对称性长期以来一直难以确定。在这里，我们表明，最近在 URu(2)Si(2) 中观察到的伊辛准粒子，源自于一个破坏双重时间反演对称性的旋量序参量，混合了整数和半整数自旋的状态。这种“停滞”有序混合了铀原子传导电子和伊辛 5f(2)态，产生了伊辛准粒子；它解释了凝聚的大熵和转矩磁强计中观察到的磁异常。停滞有序预测在传导电子“海洋”中存在微小的横向磁矩，在非线性磁化率异常中存在巨大的伊辛各向异性，以及在隧道态密度中存在共振、能量依赖的向列性。
