Hsu Chun-Chih, Takahashi Hiroto, Jerzembeck Fabian, Dasini Jahnatta, Carroll Chaia, Dusad Ritika, Ward Jonathan, Dawson Catherine, Sharma Sudarshan, Luke Graeme M, Blundell Stephen J, Castelnovo Claudio, Hallén Jonathan N, Moessner Roderich, Davis J C Séamus
Clarendon Laboratory, Oxford University, Oxford OX1 3PU, United Kingdom.
Max-Planck Institute for Chemical Physics of Solids, Dresden D-01187, Germany.
Proc Natl Acad Sci U S A. 2024 May 21;121(21):e2320384121. doi: 10.1073/pnas.2320384121. Epub 2024 May 14.
A recent advance in the study of emergent magnetic monopoles was the discovery that monopole motion is restricted to dynamical fractal trajectories [J. N. Hallén , , 1218 (2022)], thus explaining the characteristics of magnetic monopole noise spectra [R. Dusad , 234 (2019); A. M. Samarakoon , , e2117453119 (2022)]. Here, we apply this novel theory to explore the dynamics of field-driven monopole currents, finding them composed of two quite distinct transport processes: initially swift fractal rearrangements of local monopole configurations followed by conventional monopole diffusion. This theory also predicts a characteristic frequency dependence of the dissipative loss angle for AC field-driven currents. To explore these novel perspectives on monopole transport, we introduce simultaneous monopole current control and measurement techniques using SQUID-based monopole current sensors. For the canonical material DyTiO, we measure [Formula: see text], the time dependence of magnetic flux threading the sample when a net monopole current [Formula: see text] is generated by applying an external magnetic field [Formula: see text] These experiments find a sharp dichotomy of monopole currents, separated by their distinct relaxation time constants before and after ~[Formula: see text] from monopole current initiation. Application of sinusoidal magnetic fields [Formula: see text] generates oscillating monopole currents whose loss angle [Formula: see text] exhibits a characteristic transition at frequency [Formula: see text] over the same temperature range. Finally, the magnetic noise power is also dichotomic, diminishing sharply after ~[Formula: see text]. This complex phenomenology represents an unprecedented form of dynamical heterogeneity generated by the interplay of fractionalization and local spin configurational symmetry.
最近在新兴磁单极子研究方面的一项进展是发现单极子运动局限于动态分形轨迹[J. N. 哈伦， ，1218 (2022)]，从而解释了磁单极子噪声谱的特征[R. 杜萨德 ，234 (2019); A. M. 萨马拉孔 ， ，e2117453119 (2022)]。在此，我们应用这一新颖理论来探索场驱动单极子电流的动力学，发现它们由两个截然不同的输运过程组成：局部单极子构型最初迅速的分形重排，随后是传统的单极子扩散。该理论还预测了交流场驱动电流的耗散损耗角的特征频率依赖性。为了探索这些关于单极子输运的新颖观点，我们引入了基于超导量子干涉器件（SQUID）的单极子电流传感器来同时进行单极子电流控制和测量技术。对于典型材料DyTiO，我们测量了[公式：见正文]，即当通过施加外部磁场[公式：见正文]产生净单极子电流[公式：见正文]时穿过样品的磁通量的时间依赖性。这些实验发现单极子电流存在明显的二分法，在单极子电流启动后约[公式：见正文]之前和之后，它们具有不同的弛豫时间常数。施加正弦磁场[公式：见正文]会产生振荡单极子电流，其损耗角[公式：见正文]在相同温度范围内的频率[公式：见正文]处呈现特征转变。最后，磁噪声功率也是二分的，在约[公式：见正文]之后急剧减小。这种复杂的现象学代表了由分数化和局部自旋构型对称性相互作用产生的一种前所未有的动态非均匀形式。
