The sliding motion of objects is typically governed by their friction with the underlying surface. Compared to translational friction, however, rotational friction has received much less attention. Here, we experimentally and theoretically study the rotational depinning and orientational dynamics of two-dimensional colloidal crystalline clusters on periodically corrugated surfaces in the presence of magnetically exerted torques. We demonstrate that the traversing of locally commensurate areas of the moiré pattern through the edges of clusters, which is hindered by potential barriers during cluster rotation, controls its rotational depinning. The experimentally measured depinning thresholds as a function of cluster size strikingly collapse onto a universal theoretical curve which predicts the possibility of a superlow-static-torque state for large clusters. We further reveal a cluster-size-independent rotation-translation depinning transition when lattice-matched clusters are driven jointly by a torque and a force. Our work provides guidelines to the design of nanomechanical devices that involve rotational motions on atomic surfaces.

中文翻译：

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莫尔图案演化耦合晶体界面处的旋转摩擦和平移摩擦

物体的滑动运动通常由它们与下面的表面的摩擦来控制。然而，与平移摩擦相比，旋转摩擦受到的关注要少得多。在这里，我们在实验和理论上研究了在存在磁力施加扭矩的情况下，周期性波纹表面上二维胶体晶体簇的旋转脱钉和取向动力学。我们证明，通过集群边缘的莫尔图案局部相称区域的遍历，在集群旋转过程中受到潜在障碍的阻碍，控制了其旋转脱钉。实验测量的作为集群大小函数的脱钉阈值惊人地崩溃到一条通用理论曲线上，该曲线预测了大型集群的超低静态扭矩状态的可能性。当晶格匹配的簇由扭矩和力共同驱动时，我们进一步揭示了与簇大小无关的旋转平移脱钉转换。我们的工作为涉及原子表面旋转运动的纳米机械装置的设计提供了指导。