Abstract
We study nanofriction in an ion Coulomb crystal under the presence of a topological defect. We have previously observed signatures of the pinning to sliding transition i.e. the symmetry breaking at the critical point and the existence of a vibrational soft mode. Here we discuss how they depend on the position of the topological defect and how external potentials, such as anharmonic trapping potentials or differential light pressure, can be used to change the defect position. The resulting forces tend to break the intrinsic crystal symmetry, thereby reducing mode softening near the transition. We show that the topological defect mode is sensitive to differential forces at the 10−24 N level. We find that the local structure and position of the topological defect is essential for the presence of the soft mode and illustrate how the defect changes its properties, when it moves through the crystal.
Highlights
We study nanofriction in an ion Coulomb crystal under the presence of topological defects
Starting with the frequency of the vibrational defect mode for the vertical kink we find, that in contrast to the horizontal topological defect, it does not exhibit a soft mode tending to zero, see Figure 10, or a symmetry breaking at the critical point
We investigated atomic friction in self-organized ion Coulomb crystals with topological defects
Summary
Friction influences many natural phenomena over several orders of magnitude of relevant length scales, from earthquakes to biological molecules [1]. Bylinskii et al were able to trap 5 ions in an optical lattice, demonstrating the onset of reduced friction [14], the velocity dependence of the stick-slip motion [15], as well as single ion multi-slip behavior [16] They observed structural symmetrybreaking at the pinning to sliding transition [17], an Aubry-type (AT) transition. We numerically investigate external forces that break the local crystal symmetry, and influence the mode frequencies of the system. We numerically investigate the motion of extended topological defects through the crystal induced by differential light forces, and discuss the associated periodic change in their physical properties, such as local structure and mode frequency.
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