Possible links between the liquid-gas and deconfinement-hadronization phase transitions

It is commonly accepted that strongly interacting matter has several phase transitions in different domains of temperature and baryon density. In this contribution I discuss two most popular phase transitions which, in principle, can be accessed in nuclear collisions. One of them, the liquid-gas phase transition, is well established theoretically and studied experimentally in nuclear multifragmentation reactions at intermediate energies. The other one, the deconfinement-hadronization phase transition, is at the focus of present and future experimental studies with relativistic heavy-ion beams at SPS, RHIC and LHC. Possible links between these two phase transitions are identified from the viewpoint of their manifestation in violent nuclear collisions.     

Magnetization plateaus for spin-one bosons in optical lattices: Stern-Gerlach experiments with strongly correlated atoms

We consider insulating states of spin-one bosons in optical lattices in the presence of a weak magnetic field. For the states with more than one atom per lattice site we find a series of quantum phase transitions between states with fixed magnetization and a canted nematic phase. In the presence of a global confining potential, this unusual phase diagram leads to several novel phenomena, including the formation of magnetization plateaus. We discuss how these effects can be observed using spatially resolved spin polarization measurements.     

First stages of the deposition of bismuth on copper examined by LEED: II. The (111) substrate

Three ordered overlayer structures are observed after evaporation for different times onto the (111) substrate. They are interpreted as monolayers with different densities: I, adsorption in sites of high coordination; II, a dense pseudo-square arrangement of bismuth atoms; III, a compact hexagonal arrangement. Structure III is only observed at high coverage and above 245°C. A reversible transformation occurs between II and III for a limited range of coverage. When they exist alone both structures II and III show melting type transitions. A schematic surface phase diagram is established.     

Phase transitions in two-dimensional anisotropic chain systems: submonolayers of Sr adsorbed on Mo(112)

Ordered phases of Sr on Mo(112) and their phase transitions have been studied up to one physical monolayer as a function of both coverage and temperature using optical LEED. Starting at a coverage of 0.07, islands of a p(8×1) structure are formed at 100 K, which coexist with a disordered lattice gas. The formation of incommensurate structures with properties of floating solids starts already at coverages slightly above the completed p(8×1) commensurate structure (θ=0.125). The latter itself behaves like a floating solid and undergoes a depinning transition at T≈125 K, similar to the next commensurate structure, p(5×1), which is formed at θ=0.20. Floating solids are found in the whole coverage range between 0.12 and 0.23. At higher coverage coexistence between p(5×1) and c(2×2) structures is found, which melt by forming intermediate two-dimensional eutectics, i.e. coexistence regions with their melts, with an eutectic point at θ=0.37, T_eu=310 K. Close to a coverage of 0.5 a homogenous phase is formed, which disorders by a continuous phase transition, as explicitly tested by determination of the critical exponents β of the order parameter and ν of the correlation length. It is shown that the system belongs to the universality class of the Ising model. An incommensurate phase is again formed at higher coverage due to uniaxial compression of the layers. The behaviour at low coverages can be qualitatively understood assuming lateral interactions along the furrows mainly caused by dipole–dipole interactions and electrostatic screening of the adsorbate induced charge redistribution.     

Macroscopic description of the ferromagnetic superconductors

We present an improved analysis of the phase transitions in spin-triplet ferromagnetic superconductors within Ginzburg–Landau theory. We put special emphasis on the phase transitions from normal phase to the mixed phase of coexistence of ferromagnetism and unconventional superconductivity. We present a detailed analysis of the different phases that can occur and analyze the question under which conditions the phase transitions from normal phase to the mixed phase of coexistence of ferromagnetism and unconventional superconductivity are possible when compared to other phase transitions. The conditions for the phase transitions and the stability conditions are calculated. On the basis of this model, it is argued that the transition from normal phase to the mixed phase of coexistence is always of first order. It was observed from the theoretical calculations that the transition from the ferromagnetic phase to the coexistence phase can cross over from the first to the second order at the tricritical point.     

Hydrogen-induced reconstruction on W(100) and Mo(100) by surface infrared spectroscopy

Infrared absorption and low-energy electron-diffraction measurements of H adsorbed on W(100) and Mo(100) show that on each surface, distinct wavenumbers characterize the H-substrate stretching modes associated with the different long-range structures of the complicated T-θ phase diagram. Hydrogen is bonded at a two-fold bridge site at all temperatures and coverages investigated and the wavenumber of the symmetric stretch mode, v₁, is determined by the local geometry, i.e. the substrate dimer length. Analysis of the coverage dependence of the v₁ wavenumber shows that, at low coverages (θ ≲0.3), the effective H-H interactions are very different for the two substrates, leading to a uniform H layer on W(100) and to island formation on Mo(100). In general, the phase transitions are continuous on W(100), with regions of intermediate structures, and first order on Mo(100), with regions of coexisting phases.     

Step-by-step first order antiferroelectric-paraelectric transition induced by frustration and electric field

We show analytically that even not too strong frustrating next neighbor interaction strongly affects first order antiferroelectric-paraelectric transition in an external electric field. We apply mean-field Landau theory. In the electric field a single phase transition at T ₀ splits into a step-by-step staircase with a series of intermediate phases. Unexpectedly enough we found that the equilibrium structures of the phases differ substantially from structures formed at low temperature both without field and in field. Polarization of intermediate structures decreases with temperature in a stepwise manner. Similar step-by-step transitions can occur also in magnetic materials with frustrating interaction.     

Domain structure of double layer single crystal films of iron

The domain structures of multilayered films consisting of mutually parallel single crystal (001) Fe layers and an LiF intermediate layer were studied by Lorentz microscopy. Magnetic flux transitions from layer to layer and formation of extraordinary domain walls were observed in systems with magnetic layers approximately equal in thickness. The effect of the adjacent layer on the 180° wall structure was observed.Died November 3rd, 1969.     

Dynamics of a quantum phase transition

We present two approaches to the dynamics of a quench-induced phase transition in the quantum Ising model. One follows the standard treatment of thermodynamic second order phase transitions but applies it to the quantum phase transitions. The other approach is quantum, and uses Landau-Zener formula for transition probabilities in avoided level crossings. We show that predictions of the two approaches of how the density of defects scales with the quench rate are compatible, and discuss the ensuing insights into the dynamics of quantum phase transitions.     

The effect of surface reconstruction on desorption: H/Mo(100)

We have measured adsorption isobars for the system H/Mo(100) and from them we have extracted the energy of activation, E_d, and the frequency factor, ν, as functions of coverage from 0 to 2 ML along the isobar. This method allows the independent determination of each of these quantities. We have also obtained estimates of the partial molar entropy of adsorption as a function of coverage. We observe large changes in all of these quantities as functions of coverage. The strong correlation between the observed changes in these parameters and the structural phase transitions as observed by LEED and IR lead to the conclusion that surface reconstruction has a profound influence on the kinetics of desorption.     

The QCD vacuum and quark-gluon plasma

In this talk we consider present status in understanding of the QCD vacuum structure and the nature of phase transitions, separating hadronic matter from the quark-gluon plasma. We also briefly discuss the simplest signals for this phase transition in high energy collisions.     

Study of higher-energy core states in CdSe/CdS octapod nanocrystals by ultrafast spectroscopy

We present a study of the intermediate energy transitions in octapod CdSe/CdS nanocrystals accomplished by ultrafast pump probe spectroscopy (150 fs resolution) combined with effective mass calculations. The bleaching features revealed in the differential transmission spectrum indicate that intermediate transitions occur from higher-energy hole states confined in the core, to the few electron states mildly localized in the core by the weak geometrical confinement. The detection of bleaching features of the intermediate states at long time implies that electron-hole recombination is inhibited in these structures, meanwhile electrons are available for further transport along the nanostructures. This information indicates that such nanostructures could be promising for photovoltaic applications.     

Exactly solvable models of adaptive networks

A satisfiability-unsatisfiability (SAT-UNSAT) transition takes place for many optimization problems when the number of constraints, graphically represented by links between variables nodes, is brought above some threshold. If the network of constraints is allowed to adapt by redistributing its links, the SAT-UNSAT transition may be delayed and preceded by an intermediate phase where the structure self-organizes to satisfy the constraints. We present an analytic approach, based on the recently introduced cavity method for large deviations, which exactly describes the two phase transitions delimiting this adaptive intermediate phase. We give explicit results for random bond models subject to the connectivity or rigidity percolation transitions, and compare them with numerical simulations.     

Formation of the crystal structure of intermetallic compounds in mechanically activated Ni-Al and Ti-Al systems during self-propagating high-temperature synthesis

The dynamics of structural and phase transitions during heterogeneous reaction in mechanically activated mixtures has been investigated by X-ray diffraction, scanning electron microscopy, and dynamic synchrotron radiation diffraction. It is shown that the mechanisms of formation of the structure of reaction products are significantly different, depending on the temperature mode of the synthesis. Upon slow heating, the process is multistage and includes several intermediate crystalline phases. Upon fast heating, the transformation in the combustion wave occurs much faster, with only one intermediate phase observed.     

Virtual levels,mixed valence phase and electronic phase transitions in rare earth compounds

We discuss the influence of the Coulomb interaction between localized and conduction electrons on the properties of magnetic impurities in metals and on electronic phase transitions such as the γ—α—α' transitions in Ce and the insulator—metal transition in SmS. Due to excitonic pairing between ?-holes and s-electrons, similar to that in excitonic insulators, the virtual ?-levels in metals may acquire an extra width, which, in contrast to the width in the Anderson model, depends upon the position of the ?-level, the width being the largest when the ?-level crosses the Fermi-level. This effect stabilizes the intermediate valence phase. As a result, in the Falicov model we get either a gradual phase transition (like that found in SmTe), or a first order one, followed by the intermediate valence phase (SmS), or, which is most interesting, two successive jump-like transitions with a mixed valence in between, similar to the γ—α—α' transitions in Ce. The mixed valence phase is described here as a kind of an “excitonic insulator”. The theory also predicts the correct slopes of the phase equilibrium lines for both Ce and SmS.     

‘Phase transitions’ in bacteria – From structural transitions in free living bacteria to phenotypic transitions in bacteria within biofilms

Phase transitions are common in inanimate systems and have been studied extensively in natural sciences. Less explored are the rich transitions that take place at the micro- and nano-scales in biological systems. In conventional phase transitions, large-scale properties of the media change discontinuously in response to continuous changes in external conditions. Such changes play a significant role in the dynamic behaviours of organisms. In this review, we focus on some transitions in both free-living and biofilms of bacteria. Particular attention is paid to the transitions in the flagellar motors and filaments of free-living bacteria, in cellular gene expression during the biofilm growth, in the biofilm morphology transitions during biofilm expansion, and in the cell motion pattern transitions during the biofilm formation. We analyse the dynamic characteristics and biophysical mechanisms of these phase transition phenomena and point out the parallels between these transitions and conventional phase transitions. We also discuss the applications of some theoretical and numerical methods, established for conventional phase transitions in inanimate systems, in bacterial biofilms.     

Structural phase transitions in ZnS

X-ray diffraction techniques have been used to investigate structural phase transitions in ZnS between 20 and 1200°C. These measurements imply that the transition from the cubic 3C structure to the hexagonal 2H structure is a first-order phase transition while transitions between the 2H, 4H, and the 6H(33) hexagonal structures were found to obey the symmetry rules of second-order phase transitions. Direct transitions from the cubic 3C structure to the 4 or 6H hexagonal structures are not observed.     

Classification of Phase Transitions and Ensemble Inequivalence, in Systems with Long Range Interactions

Systems with long range interactions in general are not additive, which can lead to an inequivalence of the microcanonical and canonical ensembles. The microcanonical ensemble may show richer behavior than the canonical one, including negative specific heats and other non-common behaviors. We propose a classification of microcanonical phase transitions, of their link to canonical ones, and of the possible situations of ensemble inequivalence. We discuss previously observed phase transitions and inequivalence in self-gravitating, two-dimensional fluid dynamics and non-neutral plasmas. We note a number of generic situations that have not yet been observed in such systems.