Erio Tosatti

Scuola Internazionale Superiore di Studi Avanzati di Trieste, Trst, Friuli Venezia Giulia, Italy

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Publications (587)2367.65 Total impact

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    ABSTRACT: The quantum well states of a film can be used to sample the electronic structure of the parent bulk material and determine its band parameters. We highlight the benefits of two-dimensional film band mapping, with respect to complex bulk analysis, in an angle-resolved photoemission spectroscopy study of the 5d states of Au(111). Discrete 5d-derived quantum well states of various orbital characters form in Au(111) films and span the width of the corresponding bulk bands. For sufficiently thick films, the dispersion of these states samples the bulk band edges, as confirmed by first-principles calculations, thus providing the positions of the critical points of bulk Au in agreement with previously determined values. In turn, this analysis identifies several d-like surface states and resonances with large spin splittings that originate from the strong spin-orbit coupling of the Au 5d atomic levels.
    No preview · Article · Jan 2016
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    Lorenzo Del Re · Michele Fabrizio · Erio Tosatti
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    ABSTRACT: We consider non-equilibrium phenomena in a very simple model that displays a zero-temperature first-order phase transition. The quantum Ising model with a four-spin exchange is adopted as a general representative of first-order quantum phase transitions that belong to the Ising universality class, such as for instance the order-disorder ferroelectric transitions, and possibly first-order T = 0 Mott transitions. In particular, we address quantum quenches in the exactly solvable limit of infinite connectivity and show that, within the coexistence region around the transition, the system can remain trapped in a metastable phase, as long as it is spatially homogeneous so that nucleation can be ignored. Motivated by the physics of nucleation, we then study in the same model static but inhomogeneous phenomena that take place at surfaces and interfaces. The first order nature implies that both phases remain locally stable across the transition, and with that the possibility of a metastable wetting layer showing up at the surface of the stable phase, even at T=0. We use mean-field theory plus quantum fluctuations in the harmonic approximation to study quantum surface wetting.
    Full-text · Article · Dec 2015
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    Davide Mandelli · Andrea Vanossi · Erio Tosatti

    Full-text · Dataset · Oct 2015
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    Davide Mandelli · Erio Tosatti
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    ABSTRACT: Cold ions sliding across periodic energy-potential patterns formed by lasers have been used to elucidate the physics of dry friction between crystals. Experiments with no more than six ions suffice to explore a vast domain of frictional forces.
    Full-text · Article · Oct 2015 · Nature
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    ABSTRACT: We investigate theoretically the possibility to observe dynamical mode locking, in the form of Shapiro steps, when a time-periodic potential or force modulation is applied to a two-dimensional (2D) lattice of colloidal particles that are dragged by an external force over an optically generated periodic potential. Here we present realistic molecular dynamics simulations of a 2D experimental setup, where the colloid sliding is realized through the motion of soliton lines between locally commensurate patches or domains, and where the Shapiro steps are predicted and analyzed. Interestingly, the jump between one step and the next is seen to correspond to a fixed number of colloids jumping from one patch to the next, across the soliton line boundary, during each AC cycle. In addition to ordinary "integer" steps, coinciding here with the synchronous rigid advancement of the whole colloid monolayer, our main prediction is the existence of additional smaller "subharmonic" steps due to localized solitonic regions of incommensurate layers executing synchronized slips, while the majority of the colloids remains pinned to a potential minimum. The current availability and wide parameter tunability of colloid monolayers makes these predictions potentially easy to access in an experimentally rich 2D geometrical configuration.
    Preview · Article · Aug 2015
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    ABSTRACT: Recent measurements suggest the possibility to exploit ionic liquids (ILs) as smart lubricants for nano-contacts, tuning their tribological and rheological properties by charging the sliding interfaces. Following our earlier theoretical study of charging effects on nanoscale confinement and squeezout of a model IL, we present here molecular dynamics simulations of the frictional and lubrication properties of that model under charging conditions.First we describe the case when two equally charged plates slide while being held together to a confinement distance of a few molecular layers.The shear sliding stress is found to rise as the number of IL layers decreases stepwise. However the shear stress shows, within each given number of layers, only a weak dependence upon the precise value of the normal load, a result in agreement with data extracted from recent experiments.We subsequently describe the case of opposite charging of the sliding plates, and follow the shear stress when the charging is slowly and adiabatically reversed in the course of time, under fixed load. Despite the fixed load, the number and structure of the confined IL layers changes with changing charge, and that in turn drives strong friction variations. The latter involve first of all charging-induced freezing of the IL film, followed by a discharging-induced melting, both made possible by the nanoscale confinement. Another mechanism for charging-induced frictional changes is a shift of the plane of maximum shear from mid-film to the plate-film interface, and viceversa. While these occurrences and results invariably depend upon the parameters of the model IL and upon its specific interaction with the plates, the present study helps identifying a variety of possible behavior, obtained under very simple assumptions, while connecting it to an underlying equilibrium thermodynamics picture.
    Full-text · Article · Aug 2015 · The Journal of Chemical Physics
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    ABSTRACT: Two-dimensional (2D) crystalline colloidal monolayers sliding over a laser-induced optical lattice recently emerged as a new tool for the study of friction between ideal crystal surfaces. Here we focus in particular on static friction, the minimal sliding force necessary to depin one lattice from the other. If the colloid and the optical lattices are mutually commensurate, the colloid sliding is always pinned by static friction; but when they are incommensurate the presence or absence of pinning can be expected to depend upon the system parameters. If a 2D analogy to the mathematically established Aubry transition of one-dimensional systems were to hold, an increasing periodic corrugation strength $U_0$ should turn an initially free-sliding monolayer into a pinned state through a well-defined dynamical phase transition. We address this problem by the simulated sliding of a realistic model 2D colloidal lattice, confirming the existence of a clear and sharp superlubric-pinned transition for increasing corrugation strength. Unlike the 1D Aubry transition which is continuous, the 2D transition exhibits a definite first-order character. With no change of symmetry, the transition entails a structural character, with a sudden increase of the colloid-colloid interaction energy, accompanied by a compensating downward jump of the colloid-corrugation energy. The transition value for the corrugation amplitude $U_0$ depends upon the misalignment angle $\theta$ between the optical and the colloidal lattices, superlubricity surviving until larger corrugations for angles away from the energetically favored orientation, which is itself generally slightly misaligned, as shown in recent work. The observability of the superlubric-pinned colloid transition is proposed and discussed.
    Full-text · Article · Aug 2015 · Physical Review B
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    ABSTRACT: The critical fluctuations at second order structural transitions in a bulk crystal may affect the dissipation of mechanical probes even if completely external to the crystal surface. Here, we show that noncontact force microscope dissipation bears clear evidence of the antiferrodistortive phase transition of SrTiO_{3}, known for a long time to exhibit a unique, extremely narrow neutron scattering "central peak." The noncontact geometry suggests a central peak linear response coupling connected with strain. The detailed temperature dependence reveals for the first time the intrinsic central peak width of order 80 kHz, 2 orders of magnitude below the established neutron upper bound.
    Full-text · Article · Jul 2015 · Physical Review Letters
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    ABSTRACT: The Kondo zero bias anomaly of Co adatoms probed by scanning tunneling microscopy is known to depend on the height of the tip above the surface, and this dependence is different on different low index Cu surfaces. On the (100) surface, the Kondo temperature first decreases then increases as the tip approaches the adatom, while on the (111) surface it is virtually unaffected. These trends are captured by combined density functional theory and numerical renormalization group (DFT+NRG) calculations. The adatoms are found to be described by an S = 1 Anderson model on both surfaces, and ab initio calculations help identify the symmetry of the active d orbitals. We correctly reproduce the Fano lineshape of the zero bias anomaly for Co/Cu(100) in the tunneling regime but not in the contact regime, where it is probably dependent on the details of the tip and contact geometry. The lineshape for Co/Cu(111) is presumably affected by the presence of surface states, which are not included in our method. We also discuss the role of symmetry, which is preserved in our model scattering geometry but most likely broken in experimental conditions.
    Full-text · Article · Jul 2015 · Physical Review B
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    ABSTRACT: The critical fluctuations at second order structural transitions in a bulk crystal may affect the dissipation of mechanical probes even if completely external to the crystal surface. Here we show that noncontact force microscope dissipation bears clear evidence of the antiferrodistortive phase transition of SrTiO3, known for a long time to exhibit a unique, extremely narrow neutron scattering "central peak". The noncontact geometry suggests a central peak linear response coupling connected with strain. The detailed temperature dependence reveals for the first time the intrinsic central peak width of order 80 kHz, two orders of magnitude below the established neutron upper bound.
    Full-text · Article · Jun 2015
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    ABSTRACT: The inertial sliding of physisorbed submonolayer islands on crystal surfaces contains unexpected information on the exceptionally smooth sliding state associated with incommensurate superlubricity and on the mechanisms of its disappearance. Here, in a joint quartz crystal microbalance and molecular dynamics simulation case study of Xe on Cu(111), we show how superlubricity emerges in the large size limit of naturally incommensurate Xe islands. As coverage approaches a full monolayer, theory also predicts an abrupt adhesion-driven two-dimensional density compression on the order of several per cent, implying a hysteretic jump from superlubric free islands to a pressurized commensurate immobile monolayer. This scenario is fully supported by the quartz crystal microbalance data, which show remarkably large slip times with increasing submonolayer coverage, signalling superlubricity, followed by a dramatic drop to zero for the dense commensurate monolayer. Careful analysis of this variety of island sliding phenomena will be essential in future applications of friction at crystal/adsorbate interfaces.
    Full-text · Article · May 2015 · Nature Nanotechnology
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    ABSTRACT: Solid CS$_{2}$ is superficially similar to CO$_{2}$, with the same $Cmca$ molecular crystal structure at low pressures, which has suggested similar phases also at high pressures. We carried out an extensive first principles evolutionary search in order to identify the zero temperature lowest enthalpy structures of CS$_{2}$ for increasing pressure up to 200\,GPa. Surprisingly, the molecular $Cmca$ phase does not evolve into $\beta$-cristobalite as in CO$_{2}$, but transforms instead into phases HP2 and HP1, both recently described in high pressure SiS$_{2}$. HP1 in particular, with a wide stability range, is a layered $P2_{1}/c$ structure characterized by pairs of edge-sharing tetrahedra, and theoretically more robust than all other CS$_{2}$ phases discussed so far. Its predicted Raman spectrum and pair correlation function agree with experiment better than those of $\beta$-cristobalite, and further differences are predicted between their respective IR spectra. The band gap of HP1-CS$_{2}$ is calculated to close under pressure yielding an insulator-metal transition near 50 GPa in agreement with experimental observations. However, the metallic density of states remains modest above this pressure, suggesting a different origin for the reported superconductivity.
    Full-text · Article · May 2015 · Physical Review B
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    ABSTRACT: Colloidal 2D monolayers sliding in an optical lattice are of recent importance as a frictional system. In the general case when the monolayer and optical lattices are incommensurate, we predict two important novelties, one in the static equilibrium structure, the other in the frictional behavior under sliding. Structurally, realistic simulations show that the colloid layer should possess in full equilibrium a small misalignment rotation angle relative to the optical lattice, an effect so far unnoticed but visible in some published experimental moir\'e patterns. Under sliding, this misalignment has the effect of boosting the colloid monolayer friction by a considerable factor over the hypothetical aligned case discussed so far. A frictional increase of similar origin must generally affect other incommensurate adsorbed monolayers and contacts, to be sought out case by case.
    Full-text · Article · Mar 2015 · Physical Review Letters
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    Full-text · Dataset · Mar 2015
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    [Show abstract] [Hide abstract]
    ABSTRACT: Colloidal two-dimensional monolayers sliding in an optical lattice are of recent importance as a frictional system. In the general case when the monolayer and optical lattices are incommensurate, we predict two important novelties, one in the static equilibrium structure, the other in the frictional behavior under sliding. Structurally, realistic simulations show that the colloid layer should possess in full equilibrium a small misalignment rotation angle relative to the optical lattice, an effect so far unnoticed but visible in some published experimental moiré patterns. Under sliding, this misalignment has the effect of boosting the colloid monolayer friction by a considerable factor over the hypothetical aligned case discussed so far. A frictional increase of similar origin must generally affect other incommensurate adsorbed monolayers and contacts, to be sought out case by case.
    Full-text · Article · Mar 2015 · Physical Review Letters
  • Andrea Vanossi · Nicola Manini · Erio Tosatti
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    ABSTRACT: Trapping and dragging colloidal monolayers in two-dimensional optical lattices is offering the possibility to mimic friction between crystals (or even quasicrystals) visualizing directly the intimate mechanisms of sliding friction, with the additional possibility to change parameters freely, and to compare directly experiment with theory. Realistic simulations, which we review here, make a number of predictions about static features and dynamic sliding and reproduce well recent observations. Together, they provide a first demonstration of the potential impact of colloid dynamics in nanotribology
    No preview · Article · Jan 2015 · NanoScience and Technology
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    R. Capozza · A. Vanossi · A. Benassi · E. Tosatti
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    ABSTRACT: Electrical charging of parallel plates confining a model ionic liquid down to nanoscale distances yields a variety of charge-induced changes in the structural features of the confined film. That includes even-odd switching of the structural layering and charging-induced solidification and melting, with important changes of local ordering between and within layers, and of squeezout behavior. By means of molecular dynamics simulations, we explore this variety of phenomena in the simplest charged Lennard-Jones coarse-grained model including or excluding the effect a neutral tail giving an anisotropic shape to one of the model ions. Using these models and open conditions permitting the flow of ions in and out of the interplate gap, we simulate the liquid squeezout to obtain the distance dependent structure and forces between the plates during their adiabatic appraoch under load. Simulations at fixed applied force illustrate an effective electrical pumping of the ionic liquid, from a thick nearly solid film that withstands the interplate pressure for high plate charge to complete squeezout following melting near zero charge. Effective enthalpy curves obtained by integration of interplate forces versus distance show the local minima that correspond to layering, and predict the switching between one minimum and another under squeezing and charging.
    Full-text · Article · Dec 2014 · The Journal of Chemical Physics
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    ABSTRACT: The static friction preventing the free sliding of nanosized rare gas solid islands physisorbed on incommensurate crystalline surfaces is not completely understood. Simulations modeled on Kr/Pb(111) highlights the importance and the scaling behavior of the island's edge contribution to static friction.
    Full-text · Article · Dec 2014 · Nanoscale
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    Oto Kohulák · Roman Martoňák · Erio Tosatti
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    ABSTRACT: The high pressure structural and electronic evolution of bulk MoS$_2$, an important transition metal layered dichalchogenide, is currently under active investigation. Recent theoretical and experimental work predicted and verified a 2H$_c \to$ 2H$_a$ layer sliding structural transition at 20 GPa and a band overlap semiconductor-semimetal transition in the same pressure range. The 2H$_a$ structure is known to persist up to pressure of 81 GPa but properties at higher pressures remain experimentally unknown. Here we predict, with a reliable first-principles evolutionary search, that major structural transformations should take place in equilibrium at higher pressures near 130-140 GPa. The main motif is a decomposition into MoS + S, also heralded in a small bimolecular cell by the appearance of a metastable non-layered metallic MoS$_2$ structure with space group \textit{P4/mmm}. Unlike semimetallic 2H$_a$-MoS$_2$, both this phase and sulphur in the fully phase separated system are fully metallic and superconducting with higher critical temperatures than alkali-intercalated MoS$_2$.
    Preview · Article · Dec 2014 · Physical Review B
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    ABSTRACT: Band splittings, chiral spin polarization and topological surface states generated by spin-orbit interactions at crystal surfaces are receiving a lot of attention for their potential device applications as well as fascinating physical properties. Most studies have focused on sp states near the Fermi energy, which are relevant for transport and have long lifetimes. Far less explored, though in principle stronger, are spin-orbit interaction effecs within d states, including those deep below the Fermi energy. Here, we report a joint photoemission/ab initio study of spin-orbit effects in the deep d orbital surface states of a 24-layer Au film grown on Ag(111) and a 24-layer Ag film grown on Au(111), singling out a conical intersection (Dirac cone) between two surface states in a large surface-projected gap at the time-reversal symmetric M points. Unlike the often isotropic dispersion at Gamma point Dirac cones, the M point cones are strongly anisotropic. An effective k.p Hamiltonian is derived to describe the anisotropic band splitting and spin polarization near the Dirac cone.
    Full-text · Article · Nov 2014 · Physical Review B

Publication Stats

14k Citations
2,367.65 Total Impact Points

Institutions

  • 1982-2016
    • Scuola Internazionale Superiore di Studi Avanzati di Trieste
      Trst, Friuli Venezia Giulia, Italy
  • 1972-2015
    • Italian National Research Council
      • Institute of Biophysics IBF
      Roma, Latium, Italy
  • 1977-2014
    • Abdus Salam International Centre for Theoretical Physics
      Trst, Friuli Venezia Giulia, Italy
  • 2009
    • Université Paris-Sud 11
      • Laboratoire de Physique des Solides
      Orsay, Île-de-France, France
  • 2007
    • Università degli Studi di Genova
      • Department of Physics
      Genova, Liguria, Italy
  • 2004
    • Pierre and Marie Curie University - Paris 6
      Lutetia Parisorum, Île-de-France, France
  • 2002
    • Sapienza University of Rome
      • Department of Physics
      Roma, Latium, Italy
    • University of Milan
      Milano, Lombardy, Italy
  • 2001
    • Università degli Studi di Messina
      • Dipartimento di Fisica e di Scienze della Terra
      Messina, Sicily, Italy
    • University of Naples Federico II
      • Department of Physical Sciences
      Napoli, Campania, Italy
  • 1970-2001
    • Scuola Normale Superiore di Pisa
      Pisa, Tuscany, Italy
  • 1978-2000
    • Università degli Studi di Trieste
      • Department of Physics
      Trst, Friuli Venezia Giulia, Italy
    • Stanford University
      Palo Alto, California, United States
  • 1994
    • University of Geneva
      • Department of Physical Chemistry
      Genève, Geneva, Switzerland
    • Forschungszentrum Jülich
      Jülich, North Rhine-Westphalia, Germany
  • 1972-1977
    • University of Rome Tor Vergata
      • Dipartimento di Fisica
      Roma, Latium, Italy
  • 1969
    • Università di Pisa
      Pisa, Tuscany, Italy