Polaronic Contributions to Friction in a Manganite Thin Film

Abstract

Despite the huge importance of friction in regulating movement in all natural and technological processes, the mechanisms underlying dissipation at a sliding contact are still a matter of debate. Attempts to explain the dependence of measured frictional losses at nanoscale contacts on the electronic degrees of freedom of the surrounding materials have so far been controversial. Here, it is proposed that friction can be explained by considering the damping of stick-slip pulses in a sliding contact. Based on friction force microscopy studies of La (1−x) Sr x MnO 3 films at the ferromagnetic-metallic to a paramagnetic-polaronic conductor phase transition, it is confirmed that the sliding contact generates thermally-activated slip pulses in the nanoscale contact, and argued that these are damped by direct coupling into the phonon bath. Electron-phonon coupling leads to the formation of Jahn-Teller polarons and to a clear increase in friction in the high-temperature phase. There is neither evidence for direct electronic drag on the atomic force microscope tip nor any indication of contributions from electrostatic forces. This intuitive scenario, that friction is governed by the damping of surface vibrational excitations, provides a basis for reconciling controversies in literature studies as well as suggesting possible tactics for controlling friction.

Noncontact friction: Role of phonon damping and its nonuniversality

“…An AFM tip sliding over a surface is known to perform so-called slip-stick motion [1][2][3][4][5][6][7][8], most naturally understood from the famous Prandtl-Tomlinson model [1,2]. A related question concerns the energy dissipation channels in such a sliding process; contributions have been found from electrostatic interactions [9][10][11], electron excitation on the conduction band [9,12,13], and phonon dynamics [9,[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. More specifically, energy transport by phonons has been conjectured to be responsible for remarkable properties in friction, e.g., in polaronic conductors, where a drastic increase of friction near a phase transition was observed [19,20], or in super conductors [9].…”

“…A related question concerns the energy dissipation channels in such a sliding process; contributions have been found from electrostatic interactions [9][10][11], electron excitation on the conduction band [9,12,13], and phonon dynamics [9,[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. More specifically, energy transport by phonons has been conjectured to be responsible for remarkable properties in friction, e.g., in polaronic conductors, where a drastic increase of friction near a phase transition was observed [19,20], or in super conductors [9]. It has long been an open question, however, precisely what properties of phonons give rise to dissipation in friction; here, recent work suggests the importance of phonon damping [18-20, 24, 27].…”

Nanoscale Friction Measurements on Manganite Thin Films: Which Material Properties are Important?

“…The model predicts that at high velocities thermal vibrations do not contribute and a transition from a logarithmic to no dependency on velocity occurs, which has been observed experimentally. [14,64,67] While the presented model can be used to describe the experimental observation that friction decreases steadily with increasing temperature [1,2,14,70,78] it does not capture the experimentally observed strong increase in friction at cryogenic temperatures. [71,78,79] An approach to incorporate these observations was postulated by Barel et al [80,81] In this multi contact model, the measured friction is not only attributed to the thermally activated crossing of the energy barriers, but also to the dynamic formation and breaking of adhesive contacts in the interface.…”

“…One of the most important extensions is the incorporation of thermal fluctuations, which are used to explain the velocity dependence of friction on the nanometer scale as well as to predict the outcome of temperature dependent friction measurements. [1,2,[64][65][66][67][68][69][70][71] Other models based on the PT-model, such as the Frenken-Kontorova (FK),or the Frenken-Kontorova-Tomlinson (FKT) model extend the contact to numerous point masses, which are in themselves interconnected with springs (see fig. 2.8).…”

“…To further decipher the different contributions, the following section will contain a summary of models used to describe frictional losses due to excitation of phonons and interactions linked to the interactions with the electron system, which are generally assumed to be the dominant dissipation channels. [1,2,[14][15][16][17][18][19][20][21][22][23][24] F F = F ph + F el (2.26)…”