Real-space observation of emergent magnetic monopoles and associated Dirac strings in artificial kagome spin ice
Real-space observation of emergent magnetic monopoles and associated Dirac strings in artificial kagome spin ice
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DOI：
10.1038/nphys1794
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发表时间：
2011-01-01
期刊：
影响因子：
19.6
通讯作者：
Braun, Hans-Benjamin
中科院分区：
文献类型：
--
作者：
Mengotti, Elena;Heyderman, Laura J.;Braun, Hans-Benjamin
磁单极子被预测为在火绿石自旋冰（一种受挫的磁绝缘体）内出现的分数准粒子。在亚开氏温度下，在焦绿石自旋冰的倒易空间中，用中子散射的方法探测到了伴随狄拉克弦的这种突现单极子的实验特征，但它们的实际空间观测仍然难以捉摸。在这里，我们报告了在室温下使用同步加速器x射线光电发射电子显微镜对二维人工kagome自旋冰中的涌现单极子及其相关狄拉克弦的直接、实时观测。磁化反转通过单极子-反单极子对沿一维狄拉克弦的成核和雪崩型解离进行。这与2D系统中传统的域增长形成鲜明对比，提供了一个由于挫折而导致维度减少的引人注目的例子。用蒙特卡罗模拟定量地解释了观测到的磁滞、单极子密度和一维狄拉克弦雪崩。
Magnetic monopoles have been predicted to occur as emergent fractional quasiparticles inside pyrochlore spin ice, a frustrated magnetic insulator. Experimental signatures of such emergent monopoles accompanied by Dirac strings have been detected by means of neutron scattering in reciprocal space in pyrochlore spin ice at sub-Kelvin temperatures, but their real-space observation has remained elusive. Here we report on direct, real-space observations of emergent monopoles and their associated Dirac strings in two-dimensional (2D) artificial kagome spin ice at room temperature using synchrotron X-ray photoemission electron microscopy. Magnetization reversal proceeds through the nucleation and avalanche-type dissociation of monopole-antimonopole pairs along 1D Dirac strings. This is in sharp contrast to conventional domain growth in 2D systems, providing a striking example of dimensional reduction due to frustration. The observed hysteresis, monopole densities and 1D Dirac-string avalanches are quantitatively explained by Monte Carlo simulations.