Polaronic Contributions to Friction in a Manganite Thin Film

TL;DR

This study investigates how polaronic effects, specifically electron-phonon interactions and Jahn-Teller polarons, influence nanoscale friction in manganite thin films, revealing damping of slip pulses as a key mechanism.

Contribution

It demonstrates that friction in manganite films is governed by damping of thermally-activated slip pulses due to electron-phonon coupling, especially near phase transitions.

Findings

Friction increases with temperature in the high-temperature phase.

No evidence of electronic drag or electrostatic contributions to friction.

Friction is linked to damping of surface vibrational excitations.

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 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 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 phonon bath. Electron-phonon coupling leads to the formation of Jahn-Teller polarons and a clear increase in friction in the high temperature phase. There is no 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.