title: Brownian ratchet in a thermal bath driven by Coulomb friction.
abstract: The rectification of unbiased fluctuations, also known as the ratchet effect, is normally obtained under statistical nonequilibrium conditions. Here we propose a new ratchet mechanism where a thermal bath solicits the random rotation of an asymmetric wheel, which is also subject to Coulomb friction due to solid-on-solid contacts. Numerical simulations and analytical calculations demonstrate a net drift induced by friction. If the thermal bath is replaced by a granular gas, the well-known granular ratchet effect also intervenes, becoming dominant at high collision rates. For our chosen wheel shape the granular effect acts in the opposite direction with respect to the friction-induced torque, resulting in the inversion of the ratchet direction as the collision rate increases. We have realized a new granular ratchet experiment where both these ratchet effects are observed, as well as the predicted inversion at their crossover. Our discovery paves the way to the realization of micro and submicrometer Brownian motors in an equilibrium fluid, based purely upon nanofriction.
authors.affiliation: Istituto dei Sistemi Complessi-CNR, via del Fosso del Cavaliere 100, 00133 Rome, Italy and Istituto dei Sistemi Complessi-CNR and Dipartimento di Fisica, Università "Sapienza", Piazzale Aldo Moro 2, 00185 Rome, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Gnoli
authors.affiliation: Istituto dei Sistemi Complessi-CNR, via del Fosso del Cavaliere 100, 00133 Rome, Italy.
authors.forename: Alberto
authors.initials: A
authors.lastname: Petri
authors.affiliation: Istituto dei Sistemi Complessi-CNR, via del Fosso del Cavaliere 100, 00133 Rome, Italy.
authors.forename: Fergal
authors.initials: F
authors.lastname: Dalton
authors.affiliation: Istituto dei Sistemi Complessi-CNR, via del Fosso del Cavaliere 100, 00133 Rome, Italy.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Pontuale
authors.affiliation: Istituto dei Sistemi Complessi-CNR and Dipartimento di Fisica, Università "Sapienza", Piazzale Aldo Moro 2, 00185 Rome, Italy.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Gradenigo
authors.affiliation: Istituto dei Sistemi Complessi-CNR and Dipartimento di Fisica, Università "Sapienza", Piazzale Aldo Moro 2, 00185 Rome, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Sarracino
authors.affiliation: Istituto dei Sistemi Complessi-CNR and Dipartimento di Fisica, Università "Sapienza", Piazzale Aldo Moro 2, 00185 Rome, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Puglisi