Observation of Aubry-type transition in finite atom chains via friction

Abstract

The highly nonlinear many-body physics of a chain of mutually interacting atoms in contact with a periodic substrate gives rise to complex static and dynamical phenomena, such as structural phase transitions and friction. In the limit of an infinite chain incommensurate with the substrate, Aubry predicted a transition with increasing substrate potential, from the chain's intrinsic arrangement free to slide on the substrate, to a pinned arrangement favouring the substrate pattern. So far, the Aubry transition has not been observed. Here, using spatially resolved position and friction measurements of cold trapped ions in an optical lattice, we observed a finite version of the Aubry transition and the onset of its hallmark fractal atomic arrangement. Notably, the observed critical lattice depth for few-ion chains agrees well with the infinite-chain prediction. Our results elucidate the connection between competing ordering patterns and superlubricity in nanocontacts-the elementary building blocks of friction.

Current trends in the physics of nanoscale friction

“…Inspired by earlier theoretical suggestions [151][152][153], and as predicted by many-particle models [141,154,155], the experimental setup of a laser-cooled Coulomb crystal of ions moving over a periodic light-field potential highlights the practical feasibility to control friction, from strongly dissipative stick-slip to almost free sliding, by tuning the interface structural mismatch [156] and the optical corrugation [157] at the level of just a few interacting atom system (see Fig. 7).…”

Multislip Friction with a Single Ion

“…This has been demonstrated in AFM simulations [19][20][21][22] and experiments [23][24][25] where single-slip and multislip events have been clearly differentiated. However, in the absence of control over dissipation rates and the microscopic energy landscape, it is difficult to tie the observations to ab initio friction models.Following theoretical proposals [26][27][28][29], we have recently demonstrated a trapped-ion friction emulator with extensive control over all microscopic interface parameters [30][31][32]. In analogy to AFM, the emulator features a small probe (one or several trapped ions) transported over a In this Letter, we study multislip friction in deep substrate potentials.…”

“…We also find that the probabilities agree well with a simple Boltzmann model, despite the dynamical nature of the process. Remarkably, the average frictional energy dissipation U diss and the maximal static friction force F static are mostly unaffected by the transition from the single-slip to the multislip regime, increasing approximately linearly with the depth of the substrate potential.The potential energy landscape experienced by the ion is produced by the combination of an electrostatic harmonic potential provided by a linear Paul trap [41] and a sinusoidal optical lattice [30][31][32]35]. The potential energy of the ion at position x is given by the Prandtl-Tomlinson model [42,43], VðxÞ Ka 2…”

“…The potential energy landscape experienced by the ion is produced by the combination of an electrostatic harmonic potential provided by a linear Paul trap [41] and a sinusoidal optical lattice [30][31][32]35]. The potential energy of the ion at position x is given by the Prandtl-Tomlinson model [42,43], VðxÞ Ka 2…”

“…1(a) and 1(b)] [33][34][35]. To date, we have used the emulator to study the velocity dependence of nanofriction [30], as well as the interplay between superlubricity [31,[36][37][38][39] and the Aubry transition [32]. These studies and a recent study of zigzag ion chains [40] have focused on the single-slip regime.…”