The origin of the pseudogap region below a temperature T* is at the heart of the mysteries of cuprate high-temperature superconductors. Unusual properties of the pseudogap phase, such as broken time-reversal and inversion symmetry are observed in several symmetry-sensitive experiments: polarized neutron diffraction, optical birefringence, dichroic angle-resolved photoemission spectroscopy, second harmonic generation, and polar Kerr effect. These properties suggest that the pseudogap region is a genuine thermodynamic phase and are predicted by theories invoking ordered loop currents or other forms of intra-unit-cell (IUC) magnetic order. However, muon spin rotation (μSR) and nuclear magnetic resonance (NMR) experiments do not see the static local fields expected for magnetic order, leaving room for skepticism. The magnetic resonance probes have much longer time scales, however, over which local fields could be averaged by fluctuations. The observable effect of the fluctuations in magnetic resonance is then dynamic relaxation. We have measured dynamic muon spin relaxation rates in single crystals of YBa2Cu3O y (6.72 < y < 6.95) and have discovered "slow" fluctuating magnetic fields with magnitudes and fluctuation rates of the expected orders of magnitude that set in consistently at temperatures Tmag ≈ T*. The absence of any static field (to which μSR would be linearly sensitive) is consistent with the finite correlation length from neutron diffraction. Equally important, these fluctuations exhibit the critical slowing down at Tmag expected near a time-reversal symmetry breaking transition. Our results explain the absence of static magnetism and provide support for the existence of IUC magnetic order in the pseudogap phase.

中文翻译：

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在YBa2Cu3O y的拟能隙相中发现了缓慢的磁起伏和临界变慢。

低于温度T *的伪间隙区域的起源是铜酸盐高温超导体之谜的核心。在几个对对称敏感的实验中观察到伪间隙相的异常性质，例如破碎的时间反转和反转对称性：极化中子衍射，光学双折射，二向色角分辨光发射光谱，二次谐波产生和极性克尔效应。这些性质表明伪间隙区域是真正的热力学阶段，并且是通过调用有序环路电流或其他形式的单元内（IUC）磁阶的理论预测的。但是，μ自旋旋转（μSR）和核磁共振（NMR）实验没有看到预期的磁阶静态局部场，这给怀疑论留下了空间。磁共振探头具有更长的时间标度，但是在该时间标度上可以通过波动来平均局部磁场。磁共振波动的可观察到的效果就是动态弛豫。我们已经测量了YBa2Cu3O y（6.72 <y <6.95）单晶中的动态μ子自旋弛豫率，并且发现了“慢”起伏的磁场，其幅度和预期的数量级波动率在温度Tmag≈T时始终保持不变。 *。没有任何静态场（μSR对线性场是敏感的）与中子衍射产生的有限相关长度是一致的。同样重要的是，这些波动显示出在Tmag处出现的严重减速，这是在时间反转对称中断过渡附近预期的。