Disordered Flat Phase in a Solid on Solid Model of Fcc(110) Surfaces and Dimer States in Quantum Spin-1/2 Chains

We present a restricted solid on solid hamiltonian for fcc (110) surfaces. It is the simplest generalization of the exactly solvable BCSOS model which is able to describe a $(2\times 1)$ missing-row reconstructed surface. We study this model by mapping it onto a quantum spin-1/2 chain of the Heisenberg type, with second and third neighbor $S^z_iS^z_j$ couplings. The ground state phase diagram of the spin-chain model is studied by exact diagonalization of finite chains up to $N=28$ sites, as well as through analytical techniques. We find four phases in the phase diagram: two ordered phases in which the spins have a N\'eel-type of long range order (an unreconstructed and a missing-row reconstructed phase, in the surface language), a spin liquid phase (representing a rough surface), and an intermediate dimer phase which breaks translational invariance and has a doubly degenerate ground state, corresponding to a disordered flat surface. The transition from the $(2\times 1)$ reconstructed phase to the disordered flat phase belongs to the $2D$ Ising universality class. A critical (preroughening) line with varying exponents separates the unreconstructed phase from the disordered flat phase. The possible experimental signatures of the disordered flat phase are discussed.Comment: 20 pages (10 Figures available upon request), REVTEX, SISSA PREPRINT 1/94/CM/S

Interacting hard-core bosons and surface preroughening

The theory of the preroughening transition of an unreconstructed surface, and the ensuing disordered flat (DOF) phase, is formulated in terms of interacting steps. Finite terraces play a crucial role in the formulation. We start by mapping the statistical mechanics of interacting (up and down) steps onto the quantum mechanics of two species of one-dimensional hard-core bosons. The effect of finite terraces translates into a number-non-conserving term in the boson Hamiltonian, which does not allow a description in terms of fermions, but leads to a two-chain spin problem. The Heisenberg spin-1 chain is recovered as a special limiting case. The global phase diagram is rich. We find the DOF phase is stabilized by short-range repulsions of like steps. On-site repulsion of up-down steps is essential in producing a DOF phase, whereas an off-site attraction between them is favorable but not required. Step-step correlation functions and terrace width distributions can be directly calculated with this method.Comment: 15 pages, 13 figures, to appear on Phys. Rev.

Atomic spin sensitive dissipation on magnetic surfaces

We identify the mechanism of energy dissipation relevant to spin-sensitive nanomechanics including the recently introduced magnetic exchange force microscopy, where oscillating magnetic tips approach surface atomic spins. The tip-surface exchange couples spin and atom coordinates, leading to a spin-phonon problem with Caldeira-Leggett type dissipation. In the overdamped regime, that can lead to a hysteretic flip of the local spin with a large spin-dependent dissipation, even down to the very low experimental tip oscillation frequencies, describing recent observations for Fe tips on NiO. A phase transition to an underdamped regime with dramatic drop of magnetic tip dissipation should in principle be possible by tuning tip-surface distance.Comment: 4 pages, 4 figure

Line-Recovery by Programmable Particles

Shape formation has been recently studied in distributed systems of programmable particles. In this paper we consider the shape recovery problem of restoring the shape when $f$ of the $n$ particles have crashed. We focus on the basic line shape, used as a tool for the construction of more complex configurations. We present a solution to the line recovery problem by the non-faulty anonymous particles; the solution works regardless of the initial distribution and number $f<n-4$ of faults, of the local orientations of the non-faulty entities, and of the number of non-faulty entities activated in each round (i.e., semi-synchronous adversarial scheduler)

Effective thermal dynamics following a quantum quench in a spin chain

We study the nonequilibrium dynamics of the Quantum Ising Model following an abrupt quench of the transverse field. We focus on the on-site autocorrelation function of the order parameter, and extract the phase coherence time $\tau^{\phi}_Q$ from its asymptotic behavior. We show that the initial state determines $\tau^{\phi}_Q$ only through an effective temperature set by its energy and the final Hamiltonian. Moreover, we observe that the dependence of $\tau^{\phi}_Q$ on the effective temperature fairly agrees with that obtained in thermal equilibrium as a function of the equilibrium temperature.Comment: 4 pages, 4 figures. Published versio

Lavoro eterorganizzato, coordinato, agile e il telelavoro: un puzzle non facile da comporre in un’impresa in via di trasformazione = Heterorganized, coordinated, agile work and teleworking: a puzzle not easy to compose in a company undergoing transformation. WP C.S.D.L.E. “Massimo D’Antona”.IT – 327/2017

The investigation developed by S.P. identifies the boundary between collaborations organized by client and coordinated collaborations, organized by the independent contractor, of wich the art. 15 of the law ..... provides authentic interpretation. And after an examination of smart working the A. highlights the potential impact of this new form of subordinate work with co-ordinated collaborations because in both forms of work, parties determine by mutual agreement performance terms. It will not be easy to distinguish between them. On the other hand legislative amendments, concerning work organized by customer, coordinated work, smart working and teleworking, underline that it is outlining an enterprice configuration different from the fordist and hierarchical one, adopted by the code of 1942. And however, in the face of this different organizational set-up of the enterprise, it would be desirable and preferable, in comparison to the detailed legislative measures, such as those examined until now, to amend art. 2094 c.c

Sui lavoratori che operano mediante piattaforme anche digitali, sui riders e il ragionevole equilibrio della Cassazione 1663/2020 WP C.S.D.L.E. “Massimo D’Antona”.IT – 411/2020 = On workers who operate through digital platforms, on riders and the reasonable balance of Cassation 1663/2020. WP C.S.D.L.E. “Massimo D’Antona”.IT – 411/2020

The purpose of this work is to assess how art. 2, paragraph 1, of Legislative Decree no. 81/2015 determines, like art. 409 no. 3 c.p.c., a category of relationships of various origins characterised by a situation of social sub-protection imperatively and fully includes the discipline of salaried employment. Moreover, the article does not provide for a new legal type of employment, such as project work or even its own discipline. Furthermore, this work analyses the anti-avoidance function of art. 2, paragraph 1, and the extension of the scope of application of art. 2 paragraph 1 to weak self-employed workers. Coordination is, now, not a unilateral power but the result of an agreement between the parties pursuant to art. 15 of law no. 81/2017. For this reason, it is appropriate to analyse the regulatory differences between employer-organised work and coordination. In addition to this, according to art. 2 paragraph 2 only collective bargaining can identify a different discipline from salaried employment and not the theoretical and practical operator. Finally, this work addresses the ongoing issue of fixed and periodic riders in relation to the different applicable normative

Theory of Quantum Annealing of an Ising Spin Glass

Probing the lowest energy configuration of a complex system by quantum annealing was recently found to be more effective than its classical, thermal counterpart. Comparing classical and quantum Monte Carlo annealing protocols on the random two-dimensional Ising model we confirm the superiority of quantum annealing relative to classical annealing. We also propose a theory of quantum annealing, based on a cascade of Landau-Zener tunneling events. For both classical and quantum annealing, the residual energy after annealing is inversely proportional to a power of the logarithm of the annealing time, but the quantum case has a larger power which makes it fasterComment: RevTex, 8 pages, 3 figure