Local phase transitions in driven colloidal suspensions

Using dynamical density functional theory and Brownian dynamics simulations, we investigate the influence of a driven tracer particle on the density distribution of a colloidal suspension at a thermodynamic state point close to the liquid side of the binodal. In bulk systems, we find that a localised region of the colloid-poor phase, a ‘cavitation bubble’, forms behind the moving tracer. The extent of the cavitation bubble is investigated as a function of both the size and velocity of the tracer. The addition of a confining boundary enables us to investigate the interaction between the local phase instability at the substrate and that at the particle surface. When both the substrate and tracer interact repulsively with the colloids we observe the formation of a colloid-poor bridge between the substrate and the tracer. When a shear flow is applied parallel to the substrate the bridge becomes distorted and, at sufficiently high shear-rates, disconnects from the substrate to form a cavitation bubble.     

BEC-BCS crossover, phase transitions and phase separation in polarized resonantly-paired superfluids

We study resonantly-paired s-wave superfluidity in a degenerate gas of two species (hyperfine states labeled by ↑, ↓) of fermionic atoms when the numbers N_↑ and N_↓ of the two species are unequal, i.e., the system is “polarized.” We find that the continuous crossover from the Bose-Einstein condensate (BEC) limit of tightly-bound diatomic molecules to the Bardeen-Cooper-Schrieffer (BCS) limit of weakly correlated Cooper pairs, studied extensively at equal populations, is interrupted by a variety of distinct phenomena under an imposed population difference ΔN ≡ N_↑ − N_↓. Our findings are summarized by a “polarization” (ΔN) versus Feshbach-resonance detuning (δ) zero-temperature phase diagram, which exhibits regions of phase separation, a periodic FFLO superfluid, a polarized normal Fermi gas and a polarized molecular superfluid consisting of a molecular condensate and a fully polarized Fermi gas. We describe numerous experimental signatures of such phases and the transitions between them, in particular focusing on their spatial structure in the inhomogeneous environment of an atomic trap.     

Formation of a polarized state in polydiethylsiloxane during structural phase transitions

The interrelation between structural rearrangements and a stable induced polarization state in polydiethylsiloxane (PDES) is studied. At the temperatures of crystallization and crystal-crystal transitions in PDES, thermally-induced polarization currents are observed whose temperature dependence is determined by the magnitude of the polarizing field and the choice of polarization temperature interval. This implies the existence of a mesophase state in PDES. Fiz. Tverd. Tela (St. Petersburg) 39, 377–381 (February 1997)     

A model for phase transitions in a system of rod-like colloidal suspensions

The present paper describes an extension of the Maier-Saupe theory of liquid crystals to a system of charged interacting rods and shows that nematic to isotropic transitions can also be induced by increasing the charge on the rods. The effects of length of rod, concentration of salt and the volume fraction on the phase diagram are described. The concept of the charge-induced isotropic phase is described, and it is argued that the structure is expected to be glassy. Evidence to support these conclusions from the existing literature is presented.     

New multiple histogram method for studying phase transitions

For temperature zero the effects of disorder for interacting bosons are considered. The disorder induced superfluid-insulator transition in thed-dimensional disordered Bogoliubov model is discussed. Results for a short-range and a long-range random potential are given. For short-range disorder we argue that ford<4 arbitrarily small disorder localizes the Bose condensate for vanishing interaction potential. Ford>4 a certain strength of the disorder potential is necessary in order to localize the condensate. For the three-dimensional Bogoliubov model our results are in agreement with a recent calculation. We compare our theoretical predictions with numerical experiments for a disordered boson Hubbard model.     

Glass transitions in quasi-two-dimensional suspensions of colloidal ellipsoids

We observed a two-step glass transition in monolayers of colloidal ellipsoids by video microscopy. The glass transition in the rotational degree of freedom was at a lower density than that in the translational degree of freedom. Between the two transitions, ellipsoids formed an orientational glass. Approaching the respective glass transitions, the rotational and translational fastest-moving particles in the supercooled liquid moved cooperatively and formed clusters with power-law size distributions. The mean cluster sizes diverge in power law as they approach the glass transitions. The clusters of translational and rotational fastest-moving ellipsoids formed mainly within pseudonematic domains and around the domain boundaries, respectively.     

Cosmic phase transitions

The sequence of phase transitions during the hot history of the universe is followed within a phenomenological framework. Particular emphasis is put on the QCD confinement transition, which is at reach under earth laboratory conditions. A tepid inflationary scenario on the GUT scale with bubble growth at moderate supercooling is discussed.     

量子相变

量子相变是一种发生在绝对零度,由量子涨落而非热涨落导致的相变现象,满足著名的海森堡不确定关系。通过零温量子临界点的研究,可获知物质系统更广泛范围的行为,包括稀土磁性绝缘体,高温超导体和二维电子气体等。     

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.     

Pressure-induced phase transitions in gypsum

Abstract

We report high-pressure Raman scattering spectroscopy and energy dispersive X-ray diffraction investigations on gypsum, CaSO₄ · 2H₂O, at room temperature in a diamond cell. With increasing pressure, measurements indicate that CaSO₄ · 2H₂O undergoes two stages of crystalline-state phase transitions at 5 and 9 GPa, and then converts to a disordered phase above 11 GPa. The structures of the three high-pressure phases of gypsum have not been determined yet. These phases are tentatively named as “post-gypsum-I” (PG-I), “post-gypsum-II” (PG-II) and “disordered” according to the sequence of their appearance with pressure.

Gypsum shows anisotropic compressibility along three crystallographic axes with b > c > a below 5 GPa. The difference in the behavior of the two OH stretching modes in gypsum is attributed to the different reduction rate in the hydrogen bonding distances by the anisotropic axial compressibility.     

Elastic phase transitions in plutonium

The rich phase diagram of plutonium with a large number of different transitions in a narrow temperature interval has been puzzling scientists for decades. We offer a theoretical proof that most of the structural transformations in plutonium at temperatures exceeding the Debye temperature are the elastic phase transitions. The proof is given in the framework of the Landau theory of phase transitions and space group theory taking into account the anomalously small value of the elastic shear constants related to tetragonal and orthorhombic lattice deformations.     

Isostructural phase transitions in solids

A model of electrons interacting with lattice vibrations is shown to exhibit an isostructural phase transition as a function of applied force by relating the Hamiltonian to that of an Ising model in magnetic field.     

Coarsening in fluid phase transitions

We review the understanding of the kinetics of fluid phase separation in various space dimensions. Morphological differences, percolating or disconnected domains, based on overall composition in a binary liquid or on density in a vapor–liquid system, are discussed. Depending upon the morphology, various possible mechanisms for domain growth are pointed out and discussions of corresponding theoretical predictions are provided. On the computational front, useful models and simulation methodologies are presented. Theoretically predicted growth laws have been tested via molecular dynamics simulations of vapor–liquid transitions. In the case of a disconnected structure, the mechanism has been confirmed directly.     

Singularities in first-order phase transitions

Several theories of phase transitions and their inter-relations have been criticized, focusing on the problem of whether z _c, the value of the fugacity corresponding to the point of condensation, is given by z _s, the smallest real positive singularity of the analytic function defined by the power series using volume-independent cluster integrals, or not. The present situation has been analysed and it is made clear that none of the existing theories can give the answer to this problem. Plausibility arguments for an affirmative or negative answer are discussed.     

Magnetic phase transitions in garnets

The phenomenological theory broadly applicable to magnetic transitions in ferrimagnetic garnets is discussed briefly. The experimental techniques, particularly nuclear magnetic resonance and Mössbauer effect spectroscopy, are then reviewed. Finally, there is a review of the results on specific garnets which undergo such transitions. Some remaining problems are pointed out.     

Stress-induced phase transitions in diamond

A phase transformation in diamond into an intermediate carbon phase (ICP) was revealed in regions of maximal shear stress of diamond anvils. The transition was stimulated by additional stresses supplied to the compressed anvils with torque by a rotation of the anvil around the anvil's axis; maximal shear stress approached 55 GPa during the rotation. Creation of an ICP is considered as a mechanism of the stress-induced stability loss of the diamond structure. The characteristic Raman bands of ICP near 250, 500, 650–850 and 1050–1390 cm^?1 were observed in the failure regions.