Switching friction at a manganite surface using electric fields

Abstract

We report active control of the friction force at the contact between a nanoscale asperity and a La0.55Ca0.45MnO3 (LCMO) thin film using electric fields. We use friction force microscopy under ultrahigh vacuum conditions to measure the friction force as we change the film resistive state by electric field-induced resistive switching. Friction forces are high in the insulating state and clearly change to lower values when the probed local region is switched to the conducting state. Upon switching back to an insulating state, the friction forces increase again. Thus, we demonstrate active control of friction without having to change the contact temperature or pressure. By comparing with measurements of friction at the metal-to-insulator transition and with the effect of applied voltage on adhesion, we rule out electronic excitations, electrostatic forces and changes in contact area as the reasons for the effect of resistive switching on friction. Instead, we argue that friction is limited by phonon relaxation times which are strongly coupled to the electronic degrees of freedom through distortions of the MnO6 octahedra. The concept of controlling friction forces by electric fields should be applicable to any materials where the field produces strong changes in phonon lifetimes.Friction is a complex phenomenon that occurs between two bodies at a sliding contact.Despite the fact that it often can be described by straight-forward empirical relations, its fundamental cause is by no means simple. With the advent of the atomic force microscope (AFM), understanding and controlling nanoscale friction has become one of the major interests in modern tribology. A promising direction is reported in several literature studies [1-8] which show a clear change in measured nanoscale friction force when the electronic state of the material is altered. Abrupt increases are observed in the non-contact dissipation of Nb [5] and the contact friction of YBCO [6] and Pb [1,8] as the materials are heated through their superconducting transitions. Contact friction measurements on Si [4] and GaAs [2] semiconductors demonstrate a strong dependence on the charge carrier density, while the contact friction of VO2 is strongly increased on heating through the metal-to-insulator transition (MIT) from the insulating to the metallic state [3,7].

Noncontact friction: Role of phonon damping and its nonuniversality

“…In this section, we quantitatively compare the analytic expressions in Eq. (19) with the numerical data obtained in simulations, in the limit of 𝜔 → 0.…”

“…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].…”

Polaronic Contributions to Friction in a Manganite Thin Film

“…[ 46–50 ] In addition to allowing systematic tests of the effects of electronic, magnetic, and phononic degrees of freedom on friction, the manganite films offer potential technological application since it has recently been shown that resistive switching of manganite films offers a practical tactic for controlling friction without having to vary the temperature. [ 54 ]…”

“…[46][47][48][49][50] In addition to allowing systematic tests of the effects of electronic, magnetic, and phononic degrees of freedom on friction, the manganite films offer potential technological application since it has recently been shown that resistive switching of manganite films offers a practical tactic for controlling friction without having to vary the temperature. [54] A 6 nm thick film of La 0.7 Sr 0.3 MnO 3 (x = 0.3 specimen) was fabricated on a buffered SrTiO 3 substrate by metal-organic aerosol deposition, [55] with a FM-PM transition at T C = 338 K and a metal-like to hopping small polaron conductivity transition at T MM = 330 K. A 70 nm thick film of La 0.8 Sr 0.2 MnO 3 (x = 0.2 specimen) was fabricated on SrTiO 3 by sputter deposition and exhibits a FM-PM transition at T C = 220 K and a metal-polaronic conductor transition at T MM = 187 K. The crystal structure is rhombohedral both above and below the transitions (R3c space group) and strained due to the epitaxial relation with the underlying substrates. [51] Measurements to determine crystal structure, film thickness, magnetic properties, and resistivity are summarized in the Supporting Information for both films (Figures S1-S10, Supporting Information).…”