Physik Department, Technische Universität München, Garching, Germany.
Phys Rev Lett. 2011 Nov 11;107(20):207207. doi: 10.1103/PhysRevLett.107.207207.
Theory predicts the low temperature magnetic excitations in spin ices consist of deconfined magnetic charges, or monopoles. A recent transverse-field (TF) muon spin rotation (μSR) experiment [S. T. Bramwell et al., Nature (London) 461, 956 (2009)] reports results claiming to be consistent with the temperature and magnetic field dependence anticipated for monopole nucleation-the so-called second Wien effect. We demonstrate via a new series of μSR experiments in Dy(2)Ti(2)O(7) that such an effect is not observable in a TF μSR experiment. Rather, as found in many highly frustrated magnetic materials, we observe spin fluctuations which become temperature independent at low temperatures, behavior which dominates over any possible signature of thermally nucleated monopole excitations.
理论预测，在自旋冰中的低温磁激发由去禁闭的磁荷或磁单极子组成。最近的一项横向磁场（TF）μ 子自旋旋转（μSR）实验 [S. T. Bramwell 等人，《自然》（伦敦）461,956（2009）] 报告了结果，声称与预期的磁单极子成核的温度和磁场依赖性一致，即所谓的第二维恩效应。我们通过 Dy(2)Ti(2)O(7)中的一系列新 μSR 实验证明，在 TF μSR 实验中，这种效应是不可观察的。相反，正如在许多高度受挫的磁性材料中发现的那样，我们观察到自旋涨落，在低温下变得与温度无关，这种行为主导了任何可能的热核单极子激发的特征。
