Classical two-site fidelity and quantum phase transitions in the Ising model and the extended Hubbard model

In this Letter, the classical two-site-ground-state fidelity (CTGF) is exploited to identify quantum phase transitions (QPTs) for the transverse field Ising model (TFIM) and the one-dimensional extended Hubbard model (EHM). Our results show that the CTGF exhibits an abrupt change around the regions of criticality and can be used to identify QPTs in spin and fermionic systems. The method is especially convenient when it is connected with the density-matrix renormalization group (DMRG) algorithm. (C) 2008 Elsevier B.V. All rights reserved.

Density matrix Loschmidt echo and quantum phase transitions

We introduce the concept of the Loschmidt echo (LE) to the space of the reduced density matrix of spin and fermionic systems to study the density matrix LEs (DMLEs) of the one-dimensional extended Hubbard model and the transverse field Ising model. Our results show that the DMLEs are remarkably influenced by the criticality of the system, and the method is a convenient way to study quantum phase transitions.

Magnetic frustration induced quantum phase transitions in the S=1/2 vertically asymmetric diamond chain

This work was supported by the National Basic Research Program of China (973 Program) grant No. G2009CB929300 and the National Natural Science Foundation of China under Grant Nos. 60521001 and 60776061.

Surface phase separations of PMMA/SAN blends investigated by atomic force microscopy

The thin films of poly(methyl methacrylate) (PMMA), poly(styrene-co-acrylonitrile) (SAN) and their blends were prepared by means of spin-coating their corresponding solutions onto silicon wafers, followed by being annealed at different temperatures. The surface phase separations of PMMA/SAN blends were characterized by virtue of atomic force microscopy (AFM). By comparing the tapping mode AFM (TM-AFM) phase images of the pure components and their blends, surface phase separation mechanisms of the blends could be identified as the nucleation and growth mechanism or the spinodal decomposition mechanism. Therefore, the phase diagram of the PMMA/SAN system could be obtained by means of TM-AFM. Contact mode AFM was also used to study the surface morphologies of all the samples and the phase separations of the blends occurred by the spinodal decomposition mechanism could be ascertained. Moreover, X-ray photoelectron spectroscopy was used to characterize the chemical compositions on the surfaces of the samples and the miscibility principle of the PMMA/SAN system was discussed.

The phase transitions of hetero atoms substituted molecular sieves Me-VPI-5(Me=Mg, Ti, Sn, Si) and their influence on spectra structures of Eu(III) ion

The hetero atom substituted aluminophosphate molecular sieves Me-VPI-5(Me = Mgt Ti, Sn, Si) were synthesized hydrothermally. Rare earth ions are originally doped into these microporous materials by aqueous solution ion exchange procedures. The phase transitions of the microporous materials are investigated by high-temperature and high-pressure experimental techniques. The influence of the phase transitions on the rare earth ions' spectral structures is discussed, With the increase of temperature, Eu(II)Mg-VPI-5 is converted into Eu(II)Mg-AIPO(4)-8, then into tridymite phase. The pressure has a notable influence on Eu(II) ion's spectral structures. The spectral structures have changed regularly with the increase of pressure.

AN INFRARED SPECTROSCOPIC STUDY ON THE STRUCTURAL PHASE-TRANSITIONS OF LAURYLAMMONIUM CHLORIDE

Infrared spectroscopy was used to study the structural phase, transitions of laurylammonium chloride in the temperature range from 290 to 365K. It was shown that there is a solid-solid phase transition at 339 K with a pre-transition at 327 K. The infrared spectra indicated that virgin crystals at room temperature form a well-ordered phase with all-trans hydrocarbon chains, and the lengths of N-H...Cl hydrogen bonds are different. The spectra suggested that the gauche conformers begin to appear at temperature above 327 K. The spectra at high temperature over 339 K demonstrated that the interaction between the chains decreases, the partial ''melting'' of the chains is obvious, and the hydrogen bonds (N-H...Cl) have the same lengths. The main transition and pre-transition are mainly assigned to the intramolecular and intermolecular order-disorder changes, respectively.

Frequency-Dependent Phase Transitions in the Coordination of Human Bimanual Tasks

The 2-channel Ellias-Grossberg neural pattern generator of Cohen, Grossberg, and Pribe [1] is shown to simulate data from human bimanual coordination tasks in which anti-phase oscillations at low frequencies spontaneously switch to in-phase oscillations at high frequencies, in-phase oscillations can be performed at both low and high frequencies, phase fluctuations occur at the anti-phase to in-phase transition, and a "seagull effect" of larger errors occurs at intermediate phases.

First- and second-order phase transitions in the adlayer of biadipate on Au(111)

The adsorption of biadipate on Au(111) was studied by cyclic voltammetry and chronocoulometry. The biadipate adlayer undergoes a potential-driven phase transition. It is shown that the phase transition can be either of the first- or second-order depending on the biadipate concentration. At low surfactant concentrations, the first-order transition is characterised by a discontinuity in the charge density-potential curve and by the presence of very sharp peaks in the voltammetric response. At higher concentrations, these peaks are no longer observed but a discontinuity in the capacity curve is still noticeable, in agreement with a second-order transition. © the Owner Societies.

A reactive force field simulation of liquid-liquid phase transitions in phosphorus

A force field model of phosphorus has been developed based on density functional (DF) computations and experimental results, covering low energy forms of local tetrahedral symmetry and more compact (simple cubic) structures that arise with increasing pressure. Rules tailored to DF data for the addition, deletion, and exchange of covalent bonds allow the system to adapt the bonding configuration to the thermodynamic state. Monte Carlo simulations in the N-P-T ensemble show that the molecular (P-4) liquid phase, stable at low pressure P and relatively low temperature T, transforms to a polymeric (gel) state on increasing either P or T. These phase changes are observed in recent experiments at similar thermodynamic conditions, as shown by the close agreement of computed and measured structure factors in the molecular and polymer phases. The polymeric phase obtained by increasing pressure has a dominant simple cubic character, while the polymer obtained by raising T at moderate pressure is tetrahedral. Comparison with DF results suggests that the latter is a semiconductor, while the cubic form is metallic. The simulations show that the T-induced polymerization is due to the entropy of the configuration of covalent bonds, as in the polymerization transition in sulfur. The transition observed with increasing P is the continuation at high T of the black P to arsenic (A17) structure observed in the solid state, and also corresponds to a semiconductor to metal transition. (C) 2004 American Institute of Physics.

Phase transitions in epitaxial Ba0.5Sr0.5TiO3 thin films

Ba0.5Sr0.5TiO3 (BST) thin-film capacitor structures with various thicknesses, (50-1200 nm) and different strain conditions (on lanthanum strontium cobalt oxide La0.5Sr0.5CoO3 and strontium ruthenate SrRuO3 buffer layers) were made using pulsed laser deposition, and characterized by x-ray diffraction. The out-of-plane lattice parameter was followed as a function of temperature within the 100-300 K temperature interval. The phase sequence (cubic-tetragonal-orthorhombic-rhombohedral) known to exist in the bulk analog is shown to be strongly affected by both the stress conditions imposed by the buffer layer and the thickness of the BST film itself. Thus, no phase transition was found for the in-plane compressed BST films. On the stress-free BST films, on the contrary, more phase transitions were observed. It appeared that the complexity of structural phase transitions increased as the film thickness in this system was reduced.

Structural phase transitions in low-dimensional ion crystals

A chain of singly charged particles, confined by a harmonic potential, exhibits a sudden transition to a zigzag configuration when the radial potential reaches a critical value, depending on the particle number. This structural change is a phase transition of second order, whose order parameter is the crystal displacement from the chain axis. We study analytically the transition using Landau theory and find full agreement with numerical predictions by Schiffer [Phys. Rev. Lett. 70, 818 (1993)] and Piacente [Phys. Rev. B 69, 045324 (2004)]. Our theory allows us to determine analytically the system's behavior at the transition point.

Scaling of the entanglement spectrum near quantum phase transitions

The entanglement spectrum describing quantum correlations in many-body systems has been recently recognized as a key tool to characterize different quantum phases, including topological ones. Here we derive its analytically scaling properties in the vicinity of some integrable quantum phase transitions and extend our studies also to nonintegrable quantum phase transitions in one-dimensional spin models numerically. Our analysis shows that, in all studied cases, the scaling of the difference between the two largest nondegenerate Schmidt eigenvalues yields with good accuracy critical points and mass scaling exponents.