Final Report Summary - MODPHYSFRICT (Modeling the Physics of Nano-Friction)
MODPHYSFRICT – modeling the physics of nanofriction -- pursued successfully four subprojects:
Sp1- Controlling nanofriction
Sp2- Quantum physics of live substrates and frictional dissipation
Sp3- Crystalline depinning in real and in laser controlled sliders
Sp4- Basic nanofriction theory
Sp1- Controlling nanofriction
We explored theoretically the nanofrictional effects at the surface of crystals hosting a bulk phase transition. We definitively established our originally proposed concept that nanofriction and mechanical nanodissipation may provide a novel form of “Braille spectroscopy”, i.e. revealing the bulk physics underneath without looking, intruding, or disturbing a solid. It follows, as a corollary, that controlling the bulk ordering by means of an external field will also control the friction. This prediction is now ready for experimental verification.
Sp2- Quantum physics of live substrates and frictional dissipation
The electronic structure and spin of electrons at a defect-riddled SrTiO3 surface has been used in this subproject to predict, then to understand, noncontact AFM dissipation peaks of clearly electronic origin. Another kind of quantum live substrate is one where a magnetic impurity and its Kondo effect at a metal surface can be quenched and de-quenched by a tip. The wasted Kondo energy reflects into a tip mechanical dissipation, sensitive to magnetic field and to temperature, and fully detectable.
Sp3- Crystalline depinning in real and in laser controlled sliders
The frictional pinning and depinning of 2D crystalline interfaces or islands that are incommensurate is a central issue in idealized friction experiments and optical lattice emulators. Realistic simulations and collaboration with Quartz Crystal Microbalance experiments established that the pinning of an incommensurate island is mainly due to its own edges. In emulators consisting of 2D charged colloids sliding over optical lattice potentials, three separate frictionally related phenomena were discovered: the Novaco twist angle, the Aubry pinning transition, and the Shapiro velocity steps. Equally striking, our predictions about detecting superlubricity and thermolubricity in 1D trapped cold ion chains were picked up and confirmed by an MIT experimental group.
Sp4- Basic nanofriction theory
The starting point being that there is no proper theory of friction beyond simulation, MODPHYSFRICT stood up to that challenge, with three important results. First, sliding friction between solids can be given a non-equilibrium formulation of the so-called Markov State Model, generally employed to describe only equilibrium evolutions, leading to bias-free identification of a handful of frictionally relevant variables. Second, effects of quantum mechanics of atomic motion have been uncovered for the first time. Third, it was discovered that satisfaction of the Jarzynski-Crooks identities, well known to require low sliding velocities and high temperatures, coincides exactly with conditions required for friction to be in the so-called thermolubric regime, where friction is low and linear with velocity. Like all proofs of equivalence between phenomena or descriptions previously believed to be unrelated, this coincidence will be fruitful in both areas.
Sp1- Controlling nanofriction
Sp2- Quantum physics of live substrates and frictional dissipation
Sp3- Crystalline depinning in real and in laser controlled sliders
Sp4- Basic nanofriction theory
Sp1- Controlling nanofriction
We explored theoretically the nanofrictional effects at the surface of crystals hosting a bulk phase transition. We definitively established our originally proposed concept that nanofriction and mechanical nanodissipation may provide a novel form of “Braille spectroscopy”, i.e. revealing the bulk physics underneath without looking, intruding, or disturbing a solid. It follows, as a corollary, that controlling the bulk ordering by means of an external field will also control the friction. This prediction is now ready for experimental verification.
Sp2- Quantum physics of live substrates and frictional dissipation
The electronic structure and spin of electrons at a defect-riddled SrTiO3 surface has been used in this subproject to predict, then to understand, noncontact AFM dissipation peaks of clearly electronic origin. Another kind of quantum live substrate is one where a magnetic impurity and its Kondo effect at a metal surface can be quenched and de-quenched by a tip. The wasted Kondo energy reflects into a tip mechanical dissipation, sensitive to magnetic field and to temperature, and fully detectable.
Sp3- Crystalline depinning in real and in laser controlled sliders
The frictional pinning and depinning of 2D crystalline interfaces or islands that are incommensurate is a central issue in idealized friction experiments and optical lattice emulators. Realistic simulations and collaboration with Quartz Crystal Microbalance experiments established that the pinning of an incommensurate island is mainly due to its own edges. In emulators consisting of 2D charged colloids sliding over optical lattice potentials, three separate frictionally related phenomena were discovered: the Novaco twist angle, the Aubry pinning transition, and the Shapiro velocity steps. Equally striking, our predictions about detecting superlubricity and thermolubricity in 1D trapped cold ion chains were picked up and confirmed by an MIT experimental group.
Sp4- Basic nanofriction theory
The starting point being that there is no proper theory of friction beyond simulation, MODPHYSFRICT stood up to that challenge, with three important results. First, sliding friction between solids can be given a non-equilibrium formulation of the so-called Markov State Model, generally employed to describe only equilibrium evolutions, leading to bias-free identification of a handful of frictionally relevant variables. Second, effects of quantum mechanics of atomic motion have been uncovered for the first time. Third, it was discovered that satisfaction of the Jarzynski-Crooks identities, well known to require low sliding velocities and high temperatures, coincides exactly with conditions required for friction to be in the so-called thermolubric regime, where friction is low and linear with velocity. Like all proofs of equivalence between phenomena or descriptions previously believed to be unrelated, this coincidence will be fruitful in both areas.