title: Quantum phase transition in the Frenkel-Kontorova chain: from pinned instanton glass to sliding phonon gas.
abstract: We study analytically and numerically the one-dimensional quantum Frenkel-Kontorova chain in the regime where the classical model is located in the pinned phase characterized by the gaped phonon excitations and devil's staircase. By extensive quantum Monte Carlo simulations, we show that for the effective Planck constant Planck smaller than the critical value Planck(c) the quantum chain is in the pinned instanton glass phase. In this phase, the elementary excitations have two branches: phonons, separated from zero energy by a finite gap, and instantons that have an exponentially small excitation energy. At Planck = Planck(c) the quantum phase transition takes place and for Planck > Planck(c) the pinned instanton glass is transformed into the sliding phonon gas with gapless phonon excitations. This transition is accompanied by the divergence of the spatial correlation length and appearance of sliding modes at Planck > Planck(c).
authors.affiliation: Budker Institute of Nuclear Physics, 630090 Novosibirsk, Russia. zhirov@inp.nsk.su
authors.forename: O V
authors.initials: OV
authors.lastname: Zhirov
authors.forename: G
authors.initials: G
authors.lastname: Casati
authors.forename: D L
authors.initials: DL
authors.lastname: Shepelyansky