WorldWideScience

Sample records for antiferromagnetic phase transition

  1. Quantum phase transitions in antiferromagnets and superfluids

    Science.gov (United States)

    Sachdev, Subir; Vojta, Matthias

    2000-05-01

    We present a general introduction to the non-zero temperature dynamic and transport properties of low-dimensional systems near a quantum phase transition. Basic results are reviewed in the context of experiments on the spin-ladder compounds, insulating two-dimensional antiferromagnets, and double-layer quantum Hall systems. Recent large N computations on an extended t- J model (Phys. Rev. Lett. 83 (1999) 3916) motivate a global scenario of the quantum phases and transitions in the high-temperature superconductors, and connections are made to numerous experiments.

  2. A Holographic Model for Paramagnetism/antiferromagnetism Phase Transition

    CERN Document Server

    Cai, Rong-Gen

    2014-01-01

    In this paper we build a holographic model of paramagnetism/antiferromagnetism phase transition, which is realized by introducing two real antisymmetric tensor fields coupling to the background gauge field strength and interacting with each other in a dyonic black brane background. In the case without external magnetic field and in low temperatures, the magnetic moments condense spontaneously in antiparallel manner with the same magnitude, which leads to an antiferromagnetic phase. In the case with weak external magnetic field, the magnetic susceptibility density has a peak at the critical temperature and satisfies the Curie-Weiss law in the paramagnetic phase of antiferromagnetism.

  3. Holographic model for the paramagnetism/antiferromagnetism phase transition

    Science.gov (United States)

    Cai, Rong-Gen; Yang, Run-Qiu

    2015-04-01

    In this paper we build a holographic model of paramagnetism/antiferromagnetism phase transition, which is realized by introducing two real antisymmetric tensor fields coupling to the background gauge field strength and interacting with each other in a dyonic black brane background. In the case without an external magnetic field and in low temperatures, the magnetic moments condense spontaneously in an antiparallel manner with the same magnitude and the time reversal symmetry is also broken spontaneously (if the boundary spatial dimension is more than 2, spatial rotational symmetry is broken spontaneously as well), which leads to an antiferromagnetic phase. In the case with the weak external magnetic field, the magnetic susceptibility density has a peak at the critical temperature and satisfies the Curie-Weiss law in the paramagnetic phase of antiferromagnetism. In the strong external magnetic field case, there is a critical magnetic field Bc in the antiferromagnetic phase: when the magnetic field reaches Bc, the system will return into the paramagnetic phase by a second order phase transition.

  4. Quantum Phase Transitions of Antiferromagnets and the Cuprate Superconductors

    Science.gov (United States)

    Sachdev, Subir

    I begin with a proposed global phase diagram of the cuprate superconductors as a function of carrier concentration, magnetic field, and temperature, and highlight its connection to numerous recent experiments. The phase diagram is then used as a point of departure for a pedagogical review of various quantum phases and phase transitions of insulators, superconductors, and metals. The bond operator method is used to describe the transition of dimerized antiferromagnetic insulators between magnetically ordered states and spin-gap states. The Schwinger boson method is applied to frustrated square lattice antiferromagnets: phase diagrams containing collinear and spirally ordered magnetic states, Z_2 spin liquids, and valence bond solids are presented, and described by an effective gauge theory of spinons. Insights from these theories of insulators are then applied to a variety of symmetry breaking transitions in d-wave superconductors. The latter systems also contain fermionic quasiparticles with a massless Dirac spectrum, and their influence on the order parameter fluctuations and quantum criticality is carefully discussed. I conclude with an introduction to strong coupling problems associated with symmetry breaking transitions in two-dimensional metals, where the order parameter fluctuations couple to a gapless line of fermionic excitations along the Fermi surface.

  5. Antiferromagnetic phase transition and spin correlations in NiO

    DEFF Research Database (Denmark)

    Chatterji, Tapan; McIntyre, G.J.; Lindgård, Per-Anker

    2009-01-01

    We have investigated the antiferromagnetic (AF) phase transition and spin correlations in NiO by high-temperature neutron diffraction below and above TN. We show that AF phase transition is a continuous second-order transition within our experimental resolution. The spin correlations manifested...... by the strong diffuse magnetic scattering persist well above TN530 K and could still be observed at T=800 K which is about 1.5TN. We argue that the strong spin correlations above TN are due to the topological frustration of the spins on a fcc lattice. The Néel temperature is substantially reduced...... by this process. We determined the critical exponents =0.328±0.002 and =0.64±0.03 and the Néel temperature TN=530±1 K. These critical exponents suggest that NiO should be regarded as a 3dXY system...

  6. Design of Co/ Pd multilayer system with antiferromagnetic-to-ferromagnetic phase transition

    OpenAIRE

    Thiele, Jan-Ulrich; Hauet, Thomas; Hellwig, Olav

    2008-01-01

    International audience Among the known magnetic material systems, most are either purely antiferromagnetic or purely ferromagnetic at temperatures up to their critical temperature. There are only very few examples of materials that undergo a temperature dependent phase transition from an antiferromagnetic to a ferromagnetic phase or vice versa, and of these, only the chemically ordered alloy FeRh exhibits this transition near room temperature. Here we present a perpendicular anisotropy mul...

  7. Pressure-induced antiferromagnetic transition and phase diagram in FeSe

    International Nuclear Information System (INIS)

    We report measurements of resistance and ac magnetic susceptibility on FeSe single crystals under high pressure up to 27.2 kbar. The structural phase transition is quickly suppressed with pressure, and the associated anomaly is not seen above ∼18 kbar. The superconducting transition temperature evolves nonmonotonically with pressure, showing a minimum at ∼12 kbar. We find another anomaly at 21.2 K at 11.6 kbar. This anomaly most likely corresponds to the antiferromagnetic phase transition found in μSR measurements. The antiferromagnetic and superconducting transition temperatures both increase with pressure up to ∼25 kbar and then level off. The width of the superconducting transition anomalously broadens in the pressure range where the antiferromagnetism coexists. (author)

  8. Barkhausen-like antiferromagnetic to ferromagnetic phase transition driven by spin polarized current

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, Ippei; Naito, Tomoyuki; Itoh, Mitsuru; Taniyama, Tomoyasu, E-mail: taniyama.t.aa@m.titech.ac.jp [Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan)

    2015-08-24

    We provide clear evidence for the effect of a spin polarized current on the antiferromagnetic to ferromagnetic phase transition of an FeRh wire at Co/FeRh wire junctions, where the antiferromagnetic ground state of FeRh is suppressed by injecting a spin polarized current. We find a discrete change in the current-voltage characteristics with increasing current density, which we attribute to the Barkhausen-like motion of antiferromagnetic/ferromagnetic interfaces within the FeRh wire. The effect can be understood via spin transfer, which exerts a torque to the antiferromagnetic moments of FeRh, together with non-equilibrium magnetic effective field at the interface. The conclusion is reinforced by the fact that spin unpolarized current injection from a nonmagnetic Cu electrode has no effects on the antiferromagnetic state of FeRh.

  9. Barkhausen-like antiferromagnetic to ferromagnetic phase transition driven by spin polarized current

    Science.gov (United States)

    Suzuki, Ippei; Naito, Tomoyuki; Itoh, Mitsuru; Taniyama, Tomoyasu

    2015-08-01

    We provide clear evidence for the effect of a spin polarized current on the antiferromagnetic to ferromagnetic phase transition of an FeRh wire at Co/FeRh wire junctions, where the antiferromagnetic ground state of FeRh is suppressed by injecting a spin polarized current. We find a discrete change in the current-voltage characteristics with increasing current density, which we attribute to the Barkhausen-like motion of antiferromagnetic/ferromagnetic interfaces within the FeRh wire. The effect can be understood via spin transfer, which exerts a torque to the antiferromagnetic moments of FeRh, together with non-equilibrium magnetic effective field at the interface. The conclusion is reinforced by the fact that spin unpolarized current injection from a nonmagnetic Cu electrode has no effects on the antiferromagnetic state of FeRh.

  10. Imaging the antiferromagnetic to ferromagnetic first order phase transition of FeRh

    OpenAIRE

    Mariager, S. O.; Guyader, L. Le; Buzzi, M.; Ingold, G.; Quitmann, C.

    2013-01-01

    The antiferromagnetic (AFM) to ferromagnetic (FM) first order phase transition of an epitaxial FeRh thin-film has been studied with x-ray magnetic circular dichroism using photoemission electron microscopy. The FM phase is magnetized in-plane due to shape anisotropy, but the magnetocrystalline anisotropy is negligible and there is no preferred in-plane magnetization direction. When heating through the AFM to FM phase transition the nucleation of the FM phase occurs at many independent nucleat...

  11. Field-induced phase transitions in antiferromagnetic systems

    International Nuclear Information System (INIS)

    Neutron scattering experiments and magnetization measurements are carried out on cobalt bromide hexahydrate, of which 48% of the water molecules are replaced by deuterium oxide molecules. Results were compared with data obtained from non-deuterated cobalt bromide hexahydrate. Neutron scattering experiments showed the importance of the deuterium fraction. Interplay exists between the crystallographic system and the magnetic system, which is influenced by changing the deuterium fraction. Neutron scattering and magnetization experiments on partially deuterated RbFeCl3.2H2O and CsFeCl3.2H2O were performed to study the magnetic phase transitions in these quasi one-dimensional Ising compounds. The observed behaviour in the various phases can be described by the nucleation theory of chain reversals. (Auth.)

  12. Antiferromagnet-long-period structure phase transition in RMn2O5 oxides

    Science.gov (United States)

    Men'shenin, V. V.; Nikolaev, V. V.; Dmitriev, A. V.

    2011-07-01

    An analysis of the magnetic phase transition from an antiferromagnetic into an incommensurate phase in oxides RMn2O5 has been performed. It has been shown that this is a second-order phase transition and that it can occur through one of complete irreducible representations of the space group Pbam, i.e., without a decrease in the symmetry of the crystal lattice. It has been established that the decrease in the electric polarization of the oxides in this transition is due to the development of long-period magnetic ordering.

  13. Quantum Phase Transition in Quasi-two-dimensional Heisenberg Antiferromagnet with Single-Ion Anisotropy

    Institute of Scientific and Technical Information of China (English)

    JI An-Chun; TIAN Guang-Shan

    2007-01-01

    In the present paper, we investigate the quantum phase transition in a spatially anisotropic antiferromagnetic Heisenberg model of S = 1 with single-ion energy anisotropy. By using the Schwinger boson representation, we calculate the Gaussian correction to the critical value Jc⊥ caused by quantum spin fluctuations. We find that, for the positive single-ion energy, a nonzero value of Jc⊥ is always needed to stabilize the antiferromagnetic long-range order in this model. It resolves a difference among literature and shows clearly that the effect of quantum fluctuations may qualitatively change a result obtained by the mean-field theories on lower-dimensional systems.

  14. Néel Temperature of Antiferromagnets for Phase Transitions Driven by Spin-wave Interactions

    OpenAIRE

    Ayuela, Andrés; Klein, Douglas J.; March, Norman H.

    2013-01-01

    In a recent article,1 a wide variety of phase transitions, with transition (t) temperature Tt , were shown to be usefully characterized by the form kBTt  Echar exp1/ λ  where λ measured the strength of the quasiparticle interactions driving the phase transition. The present article is concerned primarily with antiferromagnets (AFs) having Néel temperature TN. It is first argued that the characteristic energy Echar can be usefully represented by kBθ, where θ is the Curie-Weiss ...

  15. Static characterization of the antiferromagnetic-to-ferromagnetic phase transition of FeRh thin films

    Energy Technology Data Exchange (ETDEWEB)

    Ramm, Paul; Radu, Ilie; Weber, Alexander; Back, Christian [Institut fuer Angewandte und Experimentelle Physik, Universitaet Regensburg (Germany); Stamm, Christian; Kachel, Torsten; Pontius, Niko; Duerr, Hermann [BESSY GmbH, Berlin (Germany); Raabe, Joerg; Quitmann, Christoph; Joly, Luiic [Paul Scherrer Institut, Villigen PSI (Switzerland); Thiele, Jan-Ulrich [Hitachi Global Storage Technologies, San Jose Research Center (United States)

    2007-07-01

    The antiferromagnetic-to-ferromagnetic phase transition present on the FeRh thin film alloy is studied by employing static magneto-optic Kerr effect (MOKE), X-ray magnetic circular dichroism (XMCD) and X-ray photoemission electron microscopy (XPEEM) techniques, which give information on the average magnetization, the element-specific magnetic moments as well as the domain structure, respectively. The element-specific hysteresis provided by the XMCD measurements near the transition temperature reveal the growth of the Fe magnetic moment and development of the small but crucial induced Rh magnetic moment in the ferromagnetic phase. Using temperature dependent XPEEM in the vicinity of the phase transition we observe the formation and the partial reproducibility of the magnetic domain structure. The temperature hysteresis of the magnetic contrast deduced from the XPEEM data is in good agreement with the temperature dependent MOKE measurements.

  16. A holographic model for antiferromagnetic quantum phase transition induced by magnetic field

    CERN Document Server

    Cai, Rong-Gen; Kusmartsev, F V

    2015-01-01

    We propose a gravity dual of antiferromagnetic quantum phase transition (QPT) induced by magnetic field and study the criticality in the vicinity of quantum critical point (QCP). Results show the boundary critical theory is a strong coupling theory with dynamic exponent $z=2$. The hyperscaling law is violated and logarithmic corrections appear near the QCP. We compare our theoretical results with experimental data on variety of materials including low-dimensional magnet, BiCoPO$_5$ and pyrochlores, Er$_{2-2x}$Y$_{2x}$Ti$_2$O$_7$. Our model describes well the existing experiments and predicts QCP and other high field magnetic properties of these compounds.

  17. Critical Space-Time Networks and Geometric Phase Transitions from Frustrated Edge Antiferromagnetism

    CERN Document Server

    Trugenberger, Carlo A

    2015-01-01

    Recently I proposed a simple dynamical network model for discrete space-time which self-organizes as a graph with Hausdorff dimension d_H=4. The model has a geometric quantum phase transition with disorder parameter (d_H-d_s) where d_s is the spectral dimension of the dynamical graph. Self-organization in this network model is based on a competition between a ferromagnetic Ising model for vertices and an antiferromagnetic Ising model for edges. In this paper I solve a toy version of this model defined on a bipartite graph in the mean field approximation. I show that the geometric phase transition corresponds exactly to the antiferromagnetic transition for edges, the dimensional disorder parameter of the former being mapped to the staggered magnetization order parameter of the latter. The model has a critical point with long-range correlations between edges, where a continuum random geometry can be defined, exactly as in Kazakov's famed 2D random lattice Ising model but now in any number of dimensions.

  18. First Order Phase Transition of Plaquette Ordering in SU(4) Antiferromagnets

    Science.gov (United States)

    Mishra, Anup; Ma, Michael; Zhang, Fu-Chun

    2002-03-01

    Spin systems with orbital degeneracy may have an ideal limit with SU(4) degeneracy(Phys. Rev. Lett 81,3527 (1998)). Based on MFT and variational calculations, it was proposed that the ground state of the SU(4) system in 2D is a spin and orbital liquid. Finite-sized numerical calculations on square lattice further support this proposition(Eur. Phys. J. B17,367 (2000)). The numerical work also suggests the ground state to be 4-fold degenerate. We propose that the 4-fold degeneracy is due to spontaneous formation of plaquettes with alternating plaquettes of strong and weak correlations. Using fermion MFT on square and triangular lattice, we find at zero temperature that the ground state is a state of disconnected plaquettes. The discrete symmetry of plaquette ordering allows for a finite temperature phase transition from the disordered phase to the ordered phase even in 2D. Within MFT, the transition is found to be first order for both the square and triangular lattice. Nevertheless, there are important differences between the transitions on the two lattices.

  19. Electron doping evolution of structural and antiferromagnetic phase transitions in NaFe1 -xCoxAs iron pnictides

    Science.gov (United States)

    Tan, Guotai; Song, Yu; Zhang, Chenglin; Lin, Lifang; Xu, Zhuang; Hou, Tingting; Tian, Wei; Cao, Huibo; Li, Shiliang; Feng, Shiping; Dai, Pengcheng

    2016-07-01

    We use transport and neutron diffraction to study the electronic phase diagram of NaFe1 -xCoxAs . In the undoped state, NaFeAs exhibits a tetragonal-to-orthorhombic structural transition below Ts followed by a collinear antiferromagnetic (AF) order below TN. Upon codoping to form NaFe1 -xCoxAs ,Ts and TN are gradually suppressed, leading to optimal superconductivity near Co-doping x =0.025 . While transport experiments on these materials reveal an anomalous behavior suggesting the presence of a quantum critical point (QCP) near optimal superconductivity, our neutron diffraction results indicate that commensurate AF order becomes transversely incommensurate with TN>Tc before vanishing abruptly at optimal superconductivity. These results are remarkably similar to electron-doping and isovalent-doping evolution of the AF order in BaFe2 -xNixAs2 and BaFe2(As1 -xPx)2 , thus suggesting a universal behavior in the suppression of the magnetic order in iron pnictides as superconductivity is induced.

  20. Charge-regulation phase transition on surface lattices of titratable sites adjacent to electrolyte solutions: An analog of the Ising antiferromagnet in a magnetic field

    Science.gov (United States)

    Shore, Joel D.; Thurston, George M.

    2015-12-01

    We report a charge-patterning phase transition on two-dimensional square lattices of titratable sites, here regarded as protonation sites, placed in a low-dielectric medium just below the planar interface between this medium and a salt solution. We calculate the work-of-charging matrix of the lattice with use of a linear Debye-Hückel model, as input to a grand-canonical partition function for the distribution of occupancy patterns. For a large range of parameter values, this model exhibits an approximate inverse cubic power-law decrease of the voltage produced by an individual charge, as a function of its in-lattice separation from neighboring titratable sites. Thus, the charge coupling voltage biases the local probabilities of proton binding as a function of the occupancy of sites for many neighbors beyond the nearest ones. We find that even in the presence of these longer-range interactions, the site couplings give rise to a phase transition in which the site occupancies exhibit an alternating, checkerboard pattern that is an analog of antiferromagnetic ordering. The overall strength W of this canonical charge coupling voltage, per unit charge, is a function of the Debye length, the charge depth, the Bjerrum length, and the dielectric coefficients of the medium and the solvent. The alternating occupancy transition occurs above a curve of thermodynamic critical points in the (p H-p K ,W ) plane, the curve representing a charge-regulation analog of variation of the Néel temperature of an Ising antiferromagnet as a function of an applied, uniform magnetic field. The analog of a uniform magnetic field in the antiferromagnet problem is a combination of p H-p K and W , and 1 /W is the analog of the temperature in the antiferromagnet problem. We use Monte Carlo simulations to study the occupancy patterns of the titratable sites, including interactions out to the 37th nearest-neighbor category (a distance of √{74 } lattice constants), first validating simulations

  1. Tuning the antiferromagnetic to ferromagnetic phase transition in FeRh thin films by means of low-energy/low fluence ion irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Heidarian, A.; Bali, R.; Grenzer, J.; Wilhelm, R.A.; Heller, R.; Yildirim, O.; Lindner, J.; Potzger, K.

    2015-09-01

    Ion irradiation induced modifications of the thermomagnetic properties of equiatomic FeRh thin films have been investigated. The application of 20 keV Ne{sup +} ions at different fluencies leads to broadening of the antiferromagnetic to ferromagnetic phase transition as well as a shift of the transition temperature towards lower temperatures with increasing ion fluence. Moreover, the ferromagnetic background at low temperatures generated by the ion irradiation leads to pronounced saturation magnetisation at 5 K. Complete erasure of the transition, i.e. ferromagnetic ordering through the whole temperature regime was achieved at a Ne{sup +} fluence of 3 × 10{sup 14} ions/cm{sup 2}. It does not coincide with the complete randomization of the chemical ordering of the crystal lattice.

  2. Tuning the antiferromagnetic to ferromagnetic phase transition in FeRh thin films by means of low-energy/low fluence ion irradiation

    Science.gov (United States)

    Heidarian, A.; Bali, R.; Grenzer, J.; Wilhelm, R. A.; Heller, R.; Yildirim, O.; Lindner, J.; Potzger, K.

    2015-09-01

    Ion irradiation induced modifications of the thermomagnetic properties of equiatomic FeRh thin films have been investigated. The application of 20 keV Ne+ ions at different fluencies leads to broadening of the antiferromagnetic to ferromagnetic phase transition as well as a shift of the transition temperature towards lower temperatures with increasing ion fluence. Moreover, the ferromagnetic background at low temperatures generated by the ion irradiation leads to pronounced saturation magnetisation at 5 K. Complete erasure of the transition, i.e. ferromagnetic ordering through the whole temperature regime was achieved at a Ne+ fluence of 3 × 1014 ions/cm2. It does not coincide with the complete randomization of the chemical ordering of the crystal lattice.

  3. Magnetic phase diagrams of classical triangular and kagome antiferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Gvozdikova, M V [Department of Physics, Kharkov National University, 61077 Kharkov (Ukraine); Melchy, P-E; Zhitomirsky, M E, E-mail: mike.zhitomirsky@cea.fr [Service de Physique Statistique, Magnetisme et Supraconductivite, UMR-E9001 CEA-INAC/UJF, 17 rue des Martyrs, 38054 Grenoble (France)

    2011-04-27

    We investigate the effect of geometrical frustration on the H-T phase diagrams of the classical Heisenberg antiferromagnets on triangular and kagome lattices. The phase diagrams for the two models are obtained from large-scale Monte Carlo simulations. For the kagome antiferromagnet, thermal fluctuations are unable to lift degeneracy completely and stabilize translationally disordered multipolar phases. We find a substantial difference in the temperature scales of the order by disorder effect related to different degeneracy of the low- and the high-field classical ground states in the kagome antiferromagnet. In the low-field regime, the Kosterlitz-Thouless transition into a spin-nematic phase is produced by unbinding of half-quantum vortices.

  4. The Berezinskii-Kosterlitz-Thouless transition and correlations in the XY kagome antiferromagnet

    CERN Document Server

    Cherepanov, V B; Podivilov, E V

    2001-01-01

    The problem of the Berezinskii-Kosterlitz-Thouless transition in the highly frustrated XY antiferromagnetic is solved. The transition temperature is found. It is shown that the spin correlation function exponentially decays with distance even in the low-temperature phase, in contrast to the order parameter correlation function, which decays algebraically with distance

  5. Antiferromagnetic, metal-insulator, and superconducting phase transitions in underdoped cuprates: Slave-fermion t-J model in the hopping expansion

    Science.gov (United States)

    Shimizu, Akihiro; Aoki, Koji; Sakakibara, Kazuhiko; Ichinose, Ikuo; Matsui, Tetsuo

    2011-02-01

    We study a system of doped antiferromagnet in three dimensions at finite temperatures using the t-J model, a canonical model of strongly correlated electrons. We employ the slave-fermion representation of electrons, in which an electron is described as a composite of a charged spinless holon and a chargeless spinon. We introduce two kinds of U(1) gauge fields on links as auxiliary fields, one describing resonating valence bonds of antiferromagnetic nearest-neighbor spin pairs and the other for nearest-neighbor hopping amplitudes of holons and spinons in the ferromagnetic channel. To perform a numerical study of the system, we integrate out the fermionic holon field by using the hopping expansion in powers of the hopping amplitude, which is legitimate for the region in and near the insulating phase. The resultant effective model is described in terms of bosonic spinons, two U(1) gauge fields, and a collective field for hole pairs. We study this model by means of Monte Carlo simulations, calculating the specific heat, spin correlation functions, and instanton densities. We obtain a phase diagram in the hole concentration-temperature plane, which is in good agreement with that observed recently for clean and homogeneous underdoped samples.

  6. Phase transitions

    CERN Document Server

    Solé, Ricard V

    2011-01-01

    Phase transitions--changes between different states of organization in a complex system--have long helped to explain physics concepts, such as why water freezes into a solid or boils to become a gas. How might phase transitions shed light on important problems in biological and ecological complex systems? Exploring the origins and implications of sudden changes in nature and society, Phase Transitions examines different dynamical behaviors in a broad range of complex systems. Using a compelling set of examples, from gene networks and ant colonies to human language and the degradation o

  7. CoF2: a model system for magnetoelastic coupling and elastic softening mechanisms associated with paramagnetic ↔ antiferromagnetic phase transitions.

    Science.gov (United States)

    Thomson, R I; Chatterji, T; Carpenter, M A

    2014-04-01

    Resonant ultrasound spectroscopy has been used to monitor variations in the elastic and anelastic behaviour of polycrystalline CoF2 through the temperature interval 10-290 K and in the frequency range ∼0.4-2 MHz. Marked softening, particularly of the shear modulus, and a peak in attenuation occur as the Néel point (TN=39 K) is approached from both high and low temperatures. Although the effective thermodynamic behaviour can be represented semiquantitatively with a Bragg-Williams model for a system with spin 1/2, the magnetoelastic coupling follows a pattern which is closely analogous to that of a Landau tricritical transition which is co-elastic in character. Analysis of lattice parameter data from the literature confirms that linear spontaneous strains scale with the square of the magnetic order parameter and combine to give effective shear and volume strains on the order of 1‰. Softening of the shear modulus at T>TN is attributed to coupling of acoustic modes with dynamical local ordering of spins and can be represented by a Vogel-Fulcher expression. At Tmechanism is attributed to spin-lattice relaxations under the influence of externally applied dynamic shear stress. CoF2 provides a reference or end-member behaviour against which the likely antiferromagnetic component of magnetoelastic behaviour in more complex multiferroic materials, with additional displacive instabilities, Jahn-Teller effects and ferroelastic microstructures, can be compared.

  8. Field-driven transitions in the dipolar pyrochlore antiferromagnet Gd2Ti2O7

    Science.gov (United States)

    Cépas, Olivier; Shastry, B. Sriram

    2004-05-01

    We present a mean-field theory for magnetic-field-driven transitions in dipolar coupled gadolinium titanate Gd2Ti2O7 pyrochlore system. Low-temperature neutron scattering yields a phase that can be regarded as a eight sublattice antiferromagnet, in which long-ranged ordered moments and fluctuating moments coexist. Our theory gives parameter regions where such a phase is realized, and predicts several other phases, with transitions amongst them driven by magnetic field as well as temperature. We find several instances of local disorder parameters describing the transitions.

  9. Low temperature transformation from antiferromagnetic to ferromagnetic order in impurity system Ge:As near the insulator-metal phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Veinger, A. I.; Zabrodskii, A. G.; Tisnek, T. V.; Goloshchapov, S. I.; Semenikhin, P. V. [Ioffe Institute, 194021 St. Petersburg (Russian Federation); Makarova, T. L. [Ioffe Institute, 194021 St. Petersburg, Russia and Umea University, Universitetomradet 90187, Umea (Sweden)

    2014-08-20

    The low-temperature transformation from antiparallel to parallel spin orientation in a nonmagnetic compensated system Ge:As semiconductor near the metal-insulator phase transition has been experimentally observed. This effect is manifested in the temperature dependences of the impurity magnetic susceptibility obtained by integration of the spin resonance absorption line. These dependences show that the spin density falls in the medium temperature range (10-100 K) and grows at low temperatures. The effect is confirmed by the specific temperature features of the g-factor and inverse magnetic susceptibility. As the relative content of a compensating impurity (gallium) is made lower than 0.7, the transition temperature begins to decrease and, at a degree of compensation < 0.3, falls outside the temperature range under study (i.e., below 2 K)

  10. Magnetic correlations and quantum criticality in the insulating antiferromagnetic, insulating spin liquid, renormalized Fermi liquid, and metallic antiferromagnetic phases of the Mott system V2O3

    International Nuclear Information System (INIS)

    Magnetic correlations in all four phases of pure and doped vanadium sesquioxide (V2O3) have been examined by magnetic thermal-neutron scattering. Specifically, we have studied the antiferromagnetic and paramagnetic phases of metallic V2-yO3, the antiferromagnetic insulating and paramagnetic metallic phases of stoichiometric V2O3, and the antiferromagnetic and paramagnetic phases of insulating V1.944Cr0.056O3. While the antiferromagnetic insulator can be accounted for by a localized Heisenberg spin model, the long-range order in the antiferromagnetic metal is an incommensurate spin-density wave, resulting from a Fermi surface nesting instability. Spin dynamics in the strongly correlated metal are dominated by spin fluctuations with a open-quotes single lobeclose quotes spectrum in the Stoner electron-hole continuum. Furthermore, our results in metallic V2O3 represent an unprecedentedly complete characterization of the spin fluctuations near a metallic quantum critical point, and provide quantitative support for the self-consistent renormalization theory for itinerant antiferromagnets in the small moment limit. Dynamic magnetic correlations for ℎωBT in the paramagnetic insulator carry substantial magnetic spectral weight. However, they are extremely short-ranged, extending only to the nearest neighbors. The phase transition to the antiferromagnetic insulator, from the paramagnetic metal and the paramagnetic insulator, introduces a sudden switching of magnetic correlations to a different spatial periodicity which indicates a sudden change in the underlying spin Hamiltonian. To describe this phase transition and also the unusual short-range order in the paramagnetic state, it seems necessary to take into account the orbital degrees of freedom associated with the degenerate d orbitals at the Fermi level in V2O3. copyright 1998 The American Physical Society

  11. Elastic instabilities in an antiferromagnetically ordered phase of the orbitally frustrated spinel GeCo2O4

    Science.gov (United States)

    Watanabe, Tadataka; Hara, Shigeo; Ikeda, Shin-Ichi; Tomiyasu, Keisuke

    2011-07-01

    Ultrasound velocity measurements of the orbitally frustrated spinel GeCo2O4 reveal unique elastic anomalies within the antiferromagnetic phase. Temperature dependence of shear moduli exhibits a minimum within the antiferromagnetic phase, suggesting the coupling of shear acoustic phonons to molecular spin-orbit excitations. Magnetic-field dependence of elastic moduli exhibits diplike anomalies, being interpreted as magnetic-field-induced metamagnetic and structural transitions. These elastic anomalies suggest that the survival of geometrical frustration, and the interplay of spin, orbital, and lattice degrees of freedom evoke a set of phenomena in the antiferromagnetic phase.

  12. Physical properties of FeRh alloys: The antiferromagnetic to ferromagnetic transition

    Science.gov (United States)

    Kudrnovský, J.; Drchal, V.; Turek, I.

    2015-01-01

    The electronic, magnetic, thermodynamical, and transport properties of FeRh alloys are studied from first principles. We present a unified approach to the phase stability, an estimate of exchange interactions in various magnetic phases, and transport properties including the effect of temperature which are all based on the same electronic-structure model. Emphasis is put on the transition between the ferromagnetic (FM) and antiferromagnetic (AFM) phases. Such a study is motivated by a recent suggestion of FeRh as a room-temperature antiferromagnetic memory resistor. The theory predicts the order-disorder transformation from the hypothetical disordered bcc phase into ordered B2 phase. Comparison of exchange interactions in the magnetically ordered FM and AFM phases with corresponding spin-disordered counterparts allows us to identify relevant interactions which are precursors of magnetically ordered phases. The most important result is the explanation of a dramatic decrease of the resistivity accompanying the AFM to FM phase transition which is due to the spin disorder present in the system. The study of the anisotropic magnetoresistance in the AFM phase found recently experimentally is extended also to finite temperatures.

  13. Surface antiferromagnetism and incipient metal-insulator transition in strained manganite films

    KAUST Repository

    Cossu, F.

    2013-06-21

    Using first-principles calculations, we show that the (001) surface of the ferromagnet La0.7Sr0.3MnO3 under an epitaxial compressive strain favors antiferromagnetic (AF) order in the surface layers, coexisting with ferromagnetic (FM) bulk order. Surface antiferromagnetism is accompanied by a very marked surface-related spectral pseudogap, signaling an incomplete metal-insulator transition at the surface. The different relaxation and rumpling of the MnO2 and LaO surface planes in the two competing magnetic phases cause distinct work-function changes, which are of potential diagnostic use. The AF phase is recognized as an extreme surface-assisted case of the combination of in-plane AF super-exchange and vertical FM double-exchange couplings that rules magnetism in manganites under in-plane compression.

  14. Magnetization processes and transitions between two antiferromagnetic spin configurations in single-crystalline MnSn2

    Science.gov (United States)

    Duan, T. F.; Ren, W. J.; Liu, W.; Zhang, Z. D.

    2016-08-01

    The magnetic structure of MnSn2 and magnetic phase transitions in this compound have been investigated by magnetic measurements on single crystals. The results show that two antiferromagnetic (AFM) states exist below 325 K and that a transition between these two phases occurs at 74 K. Applying a magnetic field (H) has great influence on the transition temperature. An anomalous magnetization process at low fields occurs when the magnetic field applied along the [110] direction, which is ascribed to the contribution of the basal anisotropy. Based on the data for the magnetization processes and the phase transition of the present single crystal, the H-T phase diagram has been established.

  15. Spin waves in the block checkerboard antiferromagnetic phase

    Institute of Scientific and Technical Information of China (English)

    Lu Feng; Dai Xi

    2012-01-01

    Motivated by the discovery of a new family of 122 iron-based superconductors,we present the theoretical results on the ground state phase diagram,spin wave,and dynamic structure factor obtained from the extended J1-J2 Heisenberg model.In the reasonable physical parameter region of K2Fe4Ses,we find that the block checkerboard antiferromagnetic order phase is stable.There are two acoustic spin wave branches and six optical spin wave branches in the block checkerboard antiferromagnetic phase,which have analytic expressions at the high-symmetry points.To further compare the experimental data on neutron scattering,we investigate the saddlepoint structure of the magnetic excitation spectrum and the inelastic neutron scattering pattern based on linear spin wave theory.

  16. Quantum phase transition between disordered and ordered states in the spin-1/2 kagome lattice antiferromagnet (Rb1-xCsx) 2Cu3SnF12

    Science.gov (United States)

    Katayama, Kazuya; Kurita, Nobuyuki; Tanaka, Hidekazu

    2015-06-01

    We have systematically investigated the variation of the exchange parameters and the ground state in the S =1/2 kagome-lattice antiferromagnet (Rb1 -xCsx )2Cu3SnF12 via magnetic measurements using single crystals. One of the parent compounds, Rb2Cu3SnF12 , which has a distorted kagome lattice accompanied by four sorts of nearest-neighbor exchange interaction, has a disordered ground state described by a pinwheel valence-bond-solid state. The other parent compound, Cs2Cu3SnF12 , which has a uniform kagome lattice at room temperature, has an ordered ground state with the q =0 spin structure. The analysis of magnetic susceptibilities shows that with increasing cesium concentration x , the exchange parameters increase with the tendency to be uniform. It was found that the ground state is disordered for x 0.53 . The pseudogap observed for x 0.53 approach zero at xc≃0.53 . This is indicative of the occurrence of a quantum phase transition at xc.

  17. Transition from the Z2 spin liquid to antiferromagnetic order: Spectrum on the torus

    Science.gov (United States)

    Whitsitt, Seth; Sachdev, Subir

    2016-08-01

    We describe the finite-size spectrum in the vicinity of the quantum critical point between a Z2 spin liquid and a coplanar antiferromagnet on the torus. We obtain the universal evolution of all low-lying states in an antiferromagnet with global SU(2) spin rotation symmetry, as it moves from the fourfold topological degeneracy in a gapped Z2 spin liquid to the Anderson "tower-of-states" in the ordered antiferromagnet. Due to the existence of nontrivial order on either side of this transition, this critical point cannot be described in a conventional Landau-Ginzburg-Wilson framework. Instead, it is described by a theory involving fractionalized degrees of freedom known as the O (4) * model, whose spectrum is altered in a significant way by its proximity to a topologically ordered phase. We compute the spectrum by relating it to the spectrum of the O (4 ) Wilson-Fisher fixed point on the torus, modified with a selection rule on the states, and with nontrivial boundary conditions corresponding to topological sectors in the spin liquid. The spectrum of the critical O (2 N ) model is calculated directly at N =∞ , which then allows a reconstruction of the full spectrum of the O (2N ) * model at leading order in 1 /N . This spectrum is a unique characteristic of the vicinity of a fractionalized quantum critical point, as well as a universal signature of the existence of proximate Z2 topological and antiferromagnetically ordered phases, and can be compared with numerical computations on quantum antiferromagnets on two-dimensional lattices.

  18. Cascade of field-induced magnetic transitions in a frustrated antiferromagnetic metal

    OpenAIRE

    Coldea, A. I.; Seabra, L.; McCollam, A.; Carrington, A.; Malone, L.; Bangura, A. F.; Vignolles, D.; van Rhee, P.G.; McDonald, R. D.; Sorgel, T.; Jansen, M.; Shannon, N; Coldea, R.

    2014-01-01

    Frustrated magnets can exhibit many novel forms of order when exposed to high magnetic fields, however, much less is known about materials where frustration occurs in the presence of itinerant electrons. Here we report thermodynamic and transport measurements on micron-sized single crystals of the triangular-lattice metallic antiferromagnet 2H-AgNiO2, in magnetic fields of up to 90 T and temperatures down to 0.35 K. We observe a cascade of magnetic phase transitions at 13.5 20, 28 and 39T in ...

  19. Magnetic and calorimetric studies of antiferromagnetic transitions in erbium sesquisulfide

    Energy Technology Data Exchange (ETDEWEB)

    Wang, C.R.; Chen, Y.Y.; Yao, Y.D.; Lin, Y.S.; Ou, M.N.; Taher, S.M.A.; Hamdeh, H.H.; Zhang, X.; Ho, J.C. E-mail: james.ho@wichita.edu; Gruber, J.B.John B

    2004-03-01

    Magnetic measurements reveal an antiferromagnetic transition in erbium sesquisulfide ErS{sub 1.5} (Er{sub 2}S{sub 3}). The Neel temperature T{sub N} decreases from approximately 3 K at low fields to below 1.8 K at 9000 G. A Curie-Weiss fit to the low-field data between 100 and 300 K yields an effective magnetic moment of 9.65 {mu}{sub B} per Er{sup 3+}. Zero-field calorimetric measurements between 0.7 and 8 K also show a corresponding specific heat peak at T{sub N}. Not expected, however, is the presence of a lower-temperature specific heat shoulder near 2 K. An entropy analysis indicates that both anomalies provide a total of R ln 2 as expected for the Er{sup 3+} ordering, suggesting that the two non-equivalent Er{sup 3+} sites in the monoclinic lattice have different transition temperatures near 3 and 2 K, respectively.

  20. The phase-separated states in antiferromagnetic semiconductors with polarizable lattice

    OpenAIRE

    Nagaev, E. L.

    2000-01-01

    The possibility of the slab or stripe phase separation (alternating ferromagnetic highly- conductive and insulating antiferromagnetic layers) is proved for isotropic degenerate antiferromagnetic semiconductors. This type of phase separation competes with the droplet phase separation (ferromagnetic droplets in the antiferromagnetic host or vice versa). The interaction of electrons with optical phonons alone cannot cause phase-separated state with alternating highly-conductive and insulating re...

  1. Revealing novel quantum phases in quantum antiferromagnets on random lattices

    Directory of Open Access Journals (Sweden)

    R. Yu

    2009-01-01

    Full Text Available Quantum magnets represent an ideal playground for the controlled realization of novel quantum phases and of quantum phase transitions. The Hamiltonian of the system can be indeed manipulated by applying a magnetic field or pressure on the sample. When doping the system with non-magnetic impurities, novel inhomogeneous phases emerge from the interplay between geometric randomness and quantum fluctuations. In this paper we review our recent work on quantum phase transitions and novel quantum phases realized in disordered quantum magnets. The system inhomogeneity is found to strongly affect phase transitions by changing their universality class, giving the transition a novel, quantum percolative nature. Such transitions connect conventionally ordered phases to unconventional, quantum disordered ones - quantum Griffiths phases, magnetic Bose glass phases - exhibiting gapless spectra associated with low-energy localized excitations.

  2. Coupling-induced ferromagnetic transitions in ferroelectromagnets of weak antiferromagnetic order

    Institute of Scientific and Technical Information of China (English)

    LI Qichang; LIU Junming

    2006-01-01

    A Monte-Carlo simulation on phase transitions in ferroelectromagnets (FEMs) in which a weak antiferromagnetic ordering occurs at the Neel point TN far below the ferroelectric ordering point TE was performed. It is revealed that an intrinsic coupling between spins and electric-dipoles ( mp -coupling) does result in a weak ferromagnetic transition from the paramagnetic state at a temperature far above TN, as long as the coupling is strong enough. The magnetoelectric properties as a function of temperature, mp -coupling strength and external electric and magnetic fields were investigated. A mean-field calculation based on the Heisenberg model was performed and a rough consistency between the simulated and calculated ferromagnetic transitions was shown.

  3. On Julia sets concerning phase transitions

    Institute of Scientific and Technical Information of China (English)

    QIAO; Jianyong(乔建永)

    2003-01-01

    The sets of the points corresponding to the phase transitions of the Potts model on the diamondhierarchical lattice for antiferromagnetic coupling are studied. These sets are the Julia sets of a family ofrational mappings. It is shown that they may be disconnected sets. Furthermore, the topological structures ofthese sets are described completely.

  4. Phase Diagram of Antiferromagnetically Exchange-Coupled Bilayer

    Institute of Scientific and Technical Information of China (English)

    GUO Guang-Hua; ZHANG Guang-Fu; SUN Li-Yuan; Peter A. J. de Groot

    2008-01-01

    Magnetic hysteresis properties of antiferromagnetically exchange-coupled bilayer structures, in which the two magnetic layers have different magnetic parameters and thicknesses, are studied within the framework of the Stoner-Wohifarth model. Analytical expressions for the switching fields corresponding to the linear magnetic states are obtained. By adjusting the magnetic parameters or thicknesses of layers, nine different types of easyaxis hysteresis loops may exist. The phase diagram of easy-axis hysteresis loops is mapped in the k,1 and k,2 plane, where k,1 and k,2 are the ratios of magnetic anisotropy to the interlayer exchange coupling of the two magnetic layers, respectively.

  5. Hubbard one-particle Green function in the antiferromagnetic phase

    International Nuclear Information System (INIS)

    An analytic approach is presented of electronic one-particle spectra of the one-band Hubbard model at half filling in the antiferromagnetic phase. Starting from the strong-coupling regime U>t, a projection technique is used to set up self-consistent coupled equations for the electron Green function, which are valid down to values U∼t. The self-consistent equation for the hole propagator is a direct generalization of the one found from the t-J model. This gives further support to the open-quotes stringclose quotes picture, where propagation of holes creates strings of overturned spins with which the holes interact. Hopping of holes (or electrons) with up spin on the down sublattice is also taken into acount, as well as transitions between the lower and upper Hubbard bands. These are shown to change significantly the incoherent part of the t-J model spectra, by smearing out the shake-off peaks, reminiscent of higher bound string states due to multispin scattering. Coherent (quasiparticle) peaks exist at the band edges, on both sides of the insulating gap. With decreasing U the quasiparticle concept loses its meaning for wave vectors at the center of the magnetic Brillouin zone (MBZ). For large values of U the dispersion of the quasiparticle is found to scale with its band width, which is of order J. Extrema are always found at k=(π/2,π/2). The weight of the quasiparticle at this k value decreases logarithmically with increasing U. In the strong-coupling limit the spectrum tends to be symmetric, i.e., to become an even function of the frequency around the chemical potential, for any wave vector. For small values of U the dispersion at the edge of the MBZ flattens away. The spectral function in this regime, for wave vectors away from the edge of the MBZ, is concentrated mainly on one side of the chemical potential. copyright 1996 The American Physical Society

  6. High Resolution Far Infrared Study of Antiferromagnetic Resonance Transitions in α-Fe2O3 (hematite)

    Science.gov (United States)

    Chou, Shin Grace; Plusquellic, David F.; Stutzman, Paul E.; Wang, Shuangzhen; Garboczi, Edward J.; Egelhoff, William F.

    2012-02-01

    In this study, we report high resolution optical measurements of the temperature dependence of the antiferromagnetic (AFM) transition in α-Fe2O3 (hematite) between (0.5 and 10) cm-1. The absorption peak position, over a large temperature range, is found to be in agreement with a modified spin-wave model at both the high and low temperature phases, where the temperature is above and below the Morin transition temperature, respectively. The high spectral resolution optical measurements as demonstrated in this study allow unprecedented zero-field spectral analysis of the zone center AFM magnon in a previously challenging spectral region, giving insights into the role of temperature and strain on the exchange and anisotropy interactions in the system. The results also suggest that the frequency-resolved measurement platform could be extended for room-temperature non-destructive examination and imaging applications for antiferromagnetic materials and devices.

  7. Cosmological phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Kolb, E.W. [Fermi National Accelerator Lab., Batavia, IL (United States)]|[Chicago Univ., IL (United States)

    1993-10-01

    If modern ideas about the role of spontaneous symmetry breaking in fundamental physics are correct, then the Universe should have undergone a series of phase transitions early in its history. The study of cosmological phase transitions has become an important aspect of early-Universe cosmology. In this lecture I review some very recent work on three aspects of phase transitions: the electroweak transition, texture, and axions.

  8. Cluster dynamical mean field theory study of antiferromagnetic transition in the square-lattice Hubbard model: Optical conductivity and electronic structure

    Science.gov (United States)

    Sato, Toshihiro; Tsunetsugu, Hirokazu

    2016-08-01

    We numerically study optical conductivity σ (ω ) near the "antiferromagnetic" phase transition in the square-lattice Hubbard model at half filling. We use a cluster dynamical mean field theory and calculate conductivity including vertex corrections and, to this end, we have reformulated the vertex corrections in the antiferromagnetic phase. We find that the vertex corrections change various important details in temperature and ω dependencies of conductivity in the square lattice, and this contrasts sharply the case of the Mott transition in the frustrated triangular lattice. Generally, the vertex corrections enhance variations in the ω dependence, and sharpen the Drude peak and a high-ω incoherent peak in the paramagnetic phase. They also enhance the dip in σ (ω ) at ω =0 in the antiferromagnetic phase. Therefore, the dc conductivity is enhanced in the paramagnetic phase and suppressed in the antiferromagnetic phase, but this change occurs slightly below the transition temperature. We also find a temperature region above the transition temperature in which the dc conductivity shows an insulating behavior but σ (ω ) retains the Drude peak, and this region is stabilized by the vertex corrections. We also investigate which fluctuations are important in the vertex corrections and analyze momentum dependence of the vertex function in detail.

  9. Interface Coupling Transition in a Thin EpitaxialAntiferromagnetic Film Interacting with a Ferromagnetic Substrate

    Energy Technology Data Exchange (ETDEWEB)

    Finazzi, M.; Brambilla, A.; Biagioni, P.; Graf, J.; Gweon, G.-H.; Scholl, A.; Lanzara, A.; Duo, L.

    2006-09-07

    We report experimental evidence for a transition in theinterface coupling between an antiferromagnetic film and a ferromagneticsubstrate. The transition is observed in a thin epitaxial NiO film grownon top of Fe(001) as the film thickness is increased. Photoemissionelectron microscopy excited with linearly polarized x rays shows that theNiO film is antiferromagnetic at room temperature with in-plane uniaxialmagnetic anisotropy. The anisotropy axis is perpendicular to the Fesubstrate magnetization when the NiO thickness is less than about 15A,but rapidly becomes parallel to the Fe magnetization for a NiO coveragehigher than 25 A.

  10. Symmetry origin of the phase transitions and phase separation in manganites at low doping

    OpenAIRE

    Wang, ZD; Zhong, F

    1999-01-01

    We analyze the symmetry changes of paramagnetic to A-type antiferromagnetic and to ferromagnetic phase transitions in undoped and moderately doped LaMnO 3, respectively. We show that in orthorhombic-distorted perovskite manganites the phase separation at low doping is associated with the noncollinear nature of the magnetic orders permitted by symmetry. A simple model for the competition between the two phase transitions is put forward within the framework of the Landau theory of phase transit...

  11. Canted antiferromagnetic phase of the ν=0 quantum Hall state in bilayer graphene.

    Science.gov (United States)

    Kharitonov, Maxim

    2012-07-27

    Motivated to understand the nature of the strongly insulating ν=0 quantum Hall state in bilayer graphene, we develop the theory of the state in the framework of quantum Hall ferromagnetism. The generic phase diagram, obtained in the presence of the isospin anisotropy, perpendicular electric field, and Zeeman effect, consists of the spin-polarized ferromagnetic (F), canted antiferromagnetic (CAF), and partially (PLP) and fully (FLP) layer-polarized phases. We address the edge transport properties of the phases. Comparing our findings with the recent data on suspended dual-gated devices, we conclude that the insulating ν=0 state realized in bilayer graphene at lower electric field is the CAF phase. We also predict a continuous and a sharp insulator-metal phase transition upon tilting the magnetic field from the insulating CAF and FLP phases, respectively, to the F phase with metallic edge conductance 2e(2)/h, which could be within the reach of available fields and could allow one to identify and distinguish the phases experimentally.

  12. Magnetic phase transitions in layered intermetallic compounds

    Science.gov (United States)

    Mushnikov, N. V.; Gerasimov, E. G.; Rosenfeld, E. V.; Terent'ev, P. B.; Gaviko, V. S.

    2012-10-01

    Magnetic, magnetoelastic, and magnetotransport properties have been studied for the RMn2Si2 and RMn6Sn6 (R is a rare earth metal) intermetallic compounds with natural layered structure. The compounds exhibit wide variety of magnetic structures and magnetic phase transitions. Substitution of different R atoms allows us to modify the interatomic distances and interlayer exchange interactions thus providing the transition from antiferromagnetic to ferromagnetic state. Near the boundary of this transition the magnetic structures are very sensitive to the external field, temperature and pressure. The field-induced transitions are accompanied by considerable change in the sample size and resistivity. It has been shown that various magnetic structures and magnetic phase transitions observed in the layered compounds arise as a result of competition of the Mn-Mn and Mn-R exchange interactions.

  13. Dynamic selective switching in antiferromagnetically-coupled bilayers close to the spin reorientation transition

    Energy Technology Data Exchange (ETDEWEB)

    Fernández-Pacheco, A., E-mail: af457@cam.ac.uk; Mansell, R.; Petit, D.; Lee, J. H.; Cowburn, R. P. [Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Ummelen, F. C.; Swagten, H. J. M. [Department of Applied Physics, Center for NanoMaterials, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (Netherlands)

    2014-09-01

    We have designed a bilayer synthetic antiferromagnet where the order of layer reversal can be selected by varying the sweep rate of the applied magnetic field. The system is formed by two ultra-thin ferromagnetic layers with different proximities to the spin reorientation transition, coupled antiferromagnetically using Ruderman-Kittel-Kasuya-Yosida interactions. The different dynamic magnetic reversal behavior of both layers produces a crossover in their switching fields for field rates in the kOe/s range. This effect is due to the different effective anisotropy of both layers, added to an appropriate asymmetric antiferromagnetic coupling between them. Field-rate controlled selective switching of perpendicular magnetic anisotropy layers as shown here can be exploited in sensing and memory applications.

  14. Martensitic phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Petry, W.; Neuhaus, J. [Techn. Universitaet Muenchen, Physik Department E13, Munich (Germany)

    1996-11-01

    Many elements transform from a high temperature bcc phase to a more dense packed temperature phase. The great majority of these transitions are of 1st order, displacive and reconstructive. The lattice potentials which govern these martensitic transitions can be probed by inelastic neutron scattering, thereby answering fundamental questions like : Will the transition be announced by dynamical or static fluctuations? What are the trajectories for the displacements needed for the transformation? Does the vibrational entropy stabilize the high temperature phase? Are the unusual transport properties in these materials related to their ability to transform? (author) 17 figs., 1 tab., 46 refs.

  15. Magneto-elastic coupling across the first-order transition in the distorted kagome lattice antiferromagnet Dy3Ru4Al12

    Science.gov (United States)

    Henriques, M. S.; Gorbunov, D. I.; Kriegner, D.; Vališka, M.; Andreev, A. V.; Matěj, Z.

    2016-02-01

    Structural changes through the first-order paramagnetic-antiferromagnetic phase transition of Dy3Ru4Al12 at 7 K have been studied by means of X-ray diffraction and thermal expansion measurements. The compound crystallizes in a hexagonal crystal structure of Gd3Ru4Al12 type (P63/mmc space group), and no structural phase transition has been found in the temperature interval between 2.5 and 300 K. Nevertheless, due to the spin-lattice coupling the crystal volume undergoes a small orthorhombic distortion of the order of 2×10-5 as the compound enters the antiferromagnetic state. We propose that the first-order phase transition is not driven by the structural changes but rather by the exchange interactions present in the system.

  16. Phase transitions modern applications

    CERN Document Server

    Gitterman, Moshe

    2014-01-01

    This book provides a comprehensive review of the theory of phase transitions and its modern applications, based on the five pillars of the modern theory of phase transitions i.e. the Ising model, mean field, scaling, renormalization group and universality. This expanded second edition includes, along with a description of vortices and high temperature superconductivity, a discussion of phase transitions in chemical reaction and moving systems. The book covers a close connection between phase transitions and small world phenomena as well as scale-free systems such as the stock market and the Internet. Readership: Scientists working in different fields of physics, chemistry, biology and economics as well as teaching material for undergraduate and graduate courses.

  17. The SAT phase transition

    Institute of Scientific and Technical Information of China (English)

    许可; 李未

    1999-01-01

    Phase transition is an important feature of SAT problem. For random k-SAT model, it is proved that as r(ratio of clauses to variables) increases, the structure of solutions will undergo a sudden change like satisfiability phase transition when r reaches a threshold point (r=rcr). This phenomenon shows that the satisfying truth assignments suddenly shift from being relatively different from each other to being very similar to each other.##属性不符

  18. Interplay of D-wave Superconductivity and Antiferromagnetism in the Cuprate Superconductors: Phase Separation and the Pseudogap Phase Diagram

    OpenAIRE

    Su, W. P.

    2005-01-01

    To understand the interplay of d-wave superconductivity and antiferromagnetism in the cuprates, we consider a two-dimensional extended Hubbard model with nearest neighbor attractive interaction. Free energy of the homogeneous (coexisting superconducting and antiferromagnetic) state calculated a s a function of the band filling shows a region of of phase separation. The phase separation caused by the intersite attractive force leads to novel insights into salient features of the pseudogap phas...

  19. Multiple charge density wave transitions in the antiferromagnets R NiC2 (R =Gd ,Tb)

    Science.gov (United States)

    Shimomura, S.; Hayashi, C.; Hanasaki, N.; Ohnuma, K.; Kobayashi, Y.; Nakao, H.; Mizumaki, M.; Onodera, H.

    2016-04-01

    X-ray scattering and electrical resistivity measurements were performed on GdNiC2 and TbNiC2. We found a set of satellite peaks characterized by q1=(0.5 ,η ,0 ) below T1, at which the resistivity shows a sharp inflection, suggesting the charge density wave (CDW) formation. The value of η decreases with decreasing temperature below T1, and then a transition to a commensurate phase with q1 C=(0.5 ,0.5 ,0 ) takes place. The diffuse scattering observed above T1 indicates the presence of soft phonon modes associated with CDW instabilities at q1 and q2=(0.5 ,0.5 ,0.5 ) . The long-range order given by q2 is developed in addition to that given by q1 C in TbNiC2, while the short-range correlation with q2 persists even at 6 K in GdNiC2. The amplitude of the q1 C lattice modulation is anomalously reduced below an antiferromagnetic transition temperature TN in GdNiC2. In contrast, the q2 order vanishes below TN in TbNiC2. We demonstrate that R NiC2 (R = rare earth) compounds exhibit similarities with respect to their CDW phenomena, and discuss the effects of magnetic transitions on CDWs. We offer a possible displacement pattern of the modulated structure characterized by q1 C and q2 in terms of frustration.

  20. Magnetization behavior of nanocrystalline systems combining ferromagnetic and antiferromagnetic phases

    Energy Technology Data Exchange (ETDEWEB)

    Loeffler, J.; Wagner, W.; Svygenhoven, H. van [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Meier, J.; Doudin, B.; Ansermet, J.P. [Ecole Polytechnique Federale, Lausanne (Switzerland)

    1997-09-01

    The magnetic properties of nanostructured materials on the basis of Fe and Ni have been investigated with a SQUID magnetometer, complementary to the small-angle neutron scattering study reported in the same volume. Measurements of the coercive field in a temperature range from 5 to 300 K confirm the validity of the random anisotropy model for our nanostructured systems. Furthermore, we obtain information about the presence and distribution of the antiferromagnetic oxides, joining the ferromagnetic grains. (author) 2 figs., 3 refs.

  1. Lifshitz transitions in magnetic phases of the periodic Anderson model

    International Nuclear Information System (INIS)

    We investigate the reconstruction of a Fermi surface, which is called a Lifshitz transition, in magnetically ordered phases of the periodic Anderson model on a square lattice with a finite Coulomb interaction between f electrons. We apply the variational Monte Carlo method to the model by using the Gutzwiller wavefunctions for the paramagnetic, antiferromagnetic, ferromagnetic, and charge-density-wave states. We find that an antiferromagnetic phase is realized around half-filling and a ferromagnetic phase is realized when the system is far away from half-filling. In both magnetic phases, Lifshitz transitions take place. By analyzing the electronic states, we conclude that the Lifshitz transitions to large ordered-moment states can be regarded as itinerant-localized transitions of the f electrons. (author)

  2. Lifshitz Transitions in Magnetic Phases of the Periodic Anderson Model

    Science.gov (United States)

    Kubo, Katsunori

    2015-09-01

    We investigate the reconstruction of a Fermi surface, which is called a Lifshitz transition, in magnetically ordered phases of the periodic Anderson model on a square lattice with a finite Coulomb interaction between f electrons. We apply the variational Monte Carlo method to the model by using the Gutzwiller wavefunctions for the paramagnetic, antiferromagnetic, ferromagnetic, and charge-density-wave states. We find that an antiferromagnetic phase is realized around half-filling and a ferromagnetic phase is realized when the system is far away from half-filling. In both magnetic phases, Lifshitz transitions take place. By analyzing the electronic states, we conclude that the Lifshitz transitions to large ordered-moment states can be regarded as itinerant-localized transitions of the f electrons.

  3. INFLUENCE OF Ge ON THE ANTIFERROMAGNETIC TRANSITION AND γ → ε MARTENSITIC TRANSFORMATION OF Fe-24Mn ALLOYS

    Institute of Scientific and Technical Information of China (English)

    B. Zhang; X. Lu; Z.X. Qin; H.B. Chang; X.Y. Ruan

    2002-01-01

    The aims of the work were to study the effect of Ge (0-6wt. %) on the paramagnetic-antiferromagnetic transition and martensitic transformation of Fe-Mn alloy using the susceptibility, microstructure examination, X-ray diffraction (XRD) and lattice parameter measurement. Ge lowers the Neel temperature, TN, and enhances the mag-netic susceptibility X, changing the Pauli paramagnetism above TN to paramagnetism state obeying the Curie Weiss law, which is essentially similar to that of γ-Fe-Mn alloys containing Al or Si; Ge depresses γ → ε martensitic transformation, which attribute to Ge increasing the stacking fault energy; Moreover, Ge increases the lat-tice parameter of 7 phase, and low content Ge increases the lattice parameter of γphase more than that of high Ge content. Comparing Ge(4s2 4p2 ) with Si(3s2 3p2 ) and Al(3s2 3p1), which have the same outer-shell of electron structures, we found that their effects on the martensitic transformation of Fe-Mn alloy are completely different. The result suggests the outer-shell of electron is not the main factor of governing the Ms temperature of Fe-Mn alloy although it is essential in the alloy's antiferromagnetic transition. The relation among the Ms temperature, stacking fault energy and lattice parameter of austenite, has been discussed in brief.

  4. Magnetic thermal hysteresis due to paramagnetic-antiferromagnetic transition in Fe-24.4Mn-5.9Si-5.1Cr alloy

    Directory of Open Access Journals (Sweden)

    L. Wang

    2013-08-01

    Full Text Available Magnetic thermal hysteresis (MTH associated with a paramagnetic (PM-antiferromagnetic (AFM phase transition was found in an Fe-24.4Mn-5.9Si-5.1Cr shape-memory alloy. Aside from the magnetic field (H, the driving rate (v can also tune the critical temperature of the magnetic transition and cause an increase in MTH. The magnetic phase diagram obtained is discussed. The equation for MTH was deduced based on the Landau model for a PM-AFM transition that includes H and v dependence, which gives a reasonable account of the experimental results.

  5. Finite-size effect of antiferromagnetic transition and electronic structure in LiFePO4

    OpenAIRE

    Shu, G. J.; Wu, M. W.; Chou, F. C.

    2012-01-01

    The finite-size effect on the antiferromagnetic (AF) transition and electronic configuration of iron has been observed in LiFePO4. Determination of the scaling behavior of the AF transition temperature (TN) versus the particle-size dimension (L) in the critical regime 1-TN(L)/TN(XTL)\\simL^-1 reveals that the activation nature of the AF ordering strongly depends on the surface energy. In addition, the effective magnetic moment that reflects the electronic configuration of iron in LiFePO4 is fo...

  6. Superfluid and antiferromagnetic phases in ultracold fermionic quantum gases

    International Nuclear Information System (INIS)

    In this thesis several models are treated, which are relevant for ultracold fermionic quantum gases loaded onto optical lattices. In particular, imbalanced superfluid Fermi mixtures, which are considered as the best way to realize Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states experimentally, and antiferromagnetic states, whose experimental realization is one of the next major goals, are examined analytically and numerically with the use of appropriate versions of the Hubbard model. The usual Bardeen-Cooper-Schrieffer (BCS) superconductor is known to break down in a magnetic field with a strength exceeding the size of the superfluid gap. A spatially inhomogeneous spin-imbalanced superconductor with a complex order parameter known as FFLO-state is predicted to occur in translationally invariant systems. Since in ultracold quantum gases the experimental setups have a limited size and a trapping potential, we analyze the realistic situation of a non-translationally invariant finite sized Hubbard model for this purpose. We first argue analytically, why the order parameter should be real in a system with continuous coordinates, and map our statements onto the Hubbard model with discrete coordinates defined on a lattice. The relevant Hubbard model is then treated numerically within mean field theory. We show that the numerical results agree with our analytically derived statements and we simulate various experimentally relevant systems in this thesis. Analogous calculations are presented for the situation at repulsive interaction strength where the N'eel state is expected to be realized experimentally in the near future. We map our analytical results obtained for the attractive model onto corresponding results for the repulsive model. We obtain a spatially invariant unit vector defining the direction of the order parameter as a consequence of the trapping potential, which is affirmed by our mean field numerical results for the repulsive case. Furthermore, we observe

  7. Elastically controlled magnetic phase transition in Ga-FeRh/BaTiO3(001) heterostructure

    Science.gov (United States)

    Suzuki, Ippei; Itoh, Mitsuru; Taniyama, Tomoyasu

    2014-01-01

    We demonstrate elastically induced ferromagnetic to antiferromagnetic phase transition of Ga-substituted FeRh thin films on BaTiO3(001). It is found that two abrupt changes of magnetization occur at the successive phase transitions from the tetragonal to orthorhombic and the orthorhombic to rhombohedral phases of BaTiO3. Magnetization and magnetoresistance together clearly reveal that a ferromagnetic to antiferromagnetic phase transition is induced due to the compressive lattice strain accompanied by the orthorhombic to rhombohedral structural phase transition, while the tetragonal to orthorhombic phase transition causes a change in the symmetry of the magnetic anisotropy in the ferromagnetic phase of FeRh.

  8. The effect of surface and interface on Neel transition temperature of low-dimensional antiferromagnetic materials

    International Nuclear Information System (INIS)

    Incorporating the bond order-length-strength (BOLS) notion with the Ising premise, we have modeled the size dependence of the Neel transition temperature (TN) of antiferromagnetic nanomaterials. Reproduction of the size trends reveals that surface atomic undercoordination induces bond contraction, and interfacial hetero-coordination induces bond nature alteration. Both surface and interface of nanomaterials modulate the TN by adjusting the atomic cohesive energy. The TN is related to the atomic cohesive/exchange energy that is lowered by the coordination number (CN) imperfection of the undercoordinated atoms near the surface and altered by the changed bond nature of epitaxial interface. A numerical match between predictions and measurements reveals that the TN of antiferromagnetic nanomaterials declines with reduced size and increases with both the strengthening of heterogeneous bond and the increase of the bond number

  9. Photoinduced phase transitions

    CERN Document Server

    Nasu, K

    2004-01-01

    A new class of insulating solids was recently discovered. Whenirradiated by a few visible photons, these solids give rise to amacroscopic excited domain that has new structural and electronicorders quite different from the starting ground state. This occurrenceis called "photoinduced phase transition", and this multi-authoredbook reviews recent theoretical and experimental studies of this newphenomenon.

  10. Superfluid and antiferromagnetic phases in ultracold fermionic quantum gases

    Energy Technology Data Exchange (ETDEWEB)

    Gottwald, Tobias

    2010-08-27

    In this thesis several models are treated, which are relevant for ultracold fermionic quantum gases loaded onto optical lattices. In particular, imbalanced superfluid Fermi mixtures, which are considered as the best way to realize Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states experimentally, and antiferromagnetic states, whose experimental realization is one of the next major goals, are examined analytically and numerically with the use of appropriate versions of the Hubbard model. The usual Bardeen-Cooper-Schrieffer (BCS) superconductor is known to break down in a magnetic field with a strength exceeding the size of the superfluid gap. A spatially inhomogeneous spin-imbalanced superconductor with a complex order parameter known as FFLO-state is predicted to occur in translationally invariant systems. Since in ultracold quantum gases the experimental setups have a limited size and a trapping potential, we analyze the realistic situation of a non-translationally invariant finite sized Hubbard model for this purpose. We first argue analytically, why the order parameter should be real in a system with continuous coordinates, and map our statements onto the Hubbard model with discrete coordinates defined on a lattice. The relevant Hubbard model is then treated numerically within mean field theory. We show that the numerical results agree with our analytically derived statements and we simulate various experimentally relevant systems in this thesis. Analogous calculations are presented for the situation at repulsive interaction strength where the N'eel state is expected to be realized experimentally in the near future. We map our analytical results obtained for the attractive model onto corresponding results for the repulsive model. We obtain a spatially invariant unit vector defining the direction of the order parameter as a consequence of the trapping potential, which is affirmed by our mean field numerical results for the repulsive case. Furthermore, we observe

  11. Emergence and Phase Transitions

    Science.gov (United States)

    Sikkema, Arnold

    2006-05-01

    Phase transitions are well defined in physics through concepts such as spontaneous symmetry breaking, order parameter, entropy, and critical exponents. But emergence --- also exhibiting whole-part relations (such as top-down influence), unpredictability, and insensitivity to microscopic detail --- is a loosely-defined concept being used in many disciplines, particularly in psychology, biology, philosophy, as well as in physics[1,2]. I will review the concepts of emergence as used in the various fields and consider the extent to which the methods of phase transitions can clarify the usefulness of the concept of emergence both within the discipline of physics and beyond.1. Robert B. Laughlin, A Different Universe: Reinventing Physics from the Bottom Down (New York: Basic Books, 2005). 2. George F.R. Ellis, ``Physics and the Real World'', Physics Today, vol. 58, no. 7 (July 2005) pp. 49-54.

  12. Understanding quantum phase transitions

    CERN Document Server

    Carr, Lincoln

    2010-01-01

    Quantum phase transitions (QPTs) offer wonderful examples of the radical macroscopic effects inherent in quantum physics: phase changes between different forms of matter driven by quantum rather than thermal fluctuations, typically at very low temperatures. QPTs provide new insight into outstanding problems such as high-temperature superconductivity and display fundamental aspects of quantum theory, such as strong correlations and entanglement. Over the last two decades, our understanding of QPTs has increased tremendously due to a plethora of experimental examples, powerful new numerical meth

  13. Quantum phase diagram of a frustrated antiferromagnet on the bilayer honeycomb lattice

    Science.gov (United States)

    Zhang, Hao; Lamas, Carlos A.; Arlego, Marcelo; Brenig, Wolfram

    2016-06-01

    We study the spin-1/2 Heisenberg antiferromagnet on a bilayer honeycomb lattice including interlayer frustration. Using a set of complementary approaches, namely, Schwinger bosons, dimer series expansion, bond operators, and exact diagonalization, we map out the quantum phase diagram. Analyzing ground-state energies and elementary excitation spectra, we find four distinct phases, corresponding to three collinear magnetic long-range ordered states, and one quantum disordered interlayer dimer phase. We detail that the latter phase is adiabatically connected to an exact singlet product ground state of the bilayer, which exists along a line of maximum interlayer frustration. The order within the remaining three phases will be clarified.

  14. Room temperature write-read operations in antiferromagnetic memory

    OpenAIRE

    Moriyama, Takahiro; Matsuzaki, Noriko; Kim, Kab-Jin; Suzuki, Ippei; Taniyama, Tomoyasu; Ono, Teruo

    2015-01-01

    B2-ordered FeRh has been known to exhibit antiferromagnetic-ferromagnetic (AF-F) phase transitions in the vicinity of room temperature. Manipulation of the N\\'eel order via AF-F phase transition and recent experimental observation of the anisotropic magnetoresistance in antiferromagnetic FeRh has proven that FeRh is a promising candidate for antiferromagnetic memory material. In this work, we demonstrate sequential write and read operations in antiferromagnetic memory resistors made of B2-ord...

  15. The disordered-free-moment phase: a low-field disordered state in spin-gap antiferromagnets with site dilution

    OpenAIRE

    Yu, Rong; Roscilde, Tommaso; Haas, Stephan

    2006-01-01

    Site dilution of spin-gapped antiferromagnets leads to localized free moments, which can order antiferromagnetically in two and higher dimensions. Here we show how a weak magnetic field drives this order-by-disorder state into a novel disordered-free-moment phase, characterized by the formation of local singlets between neighboring moments and by localized moments aligned antiparallel to the field. This disordered phase is characterized by the absence of a gap, as it is the case in a Bose gla...

  16. Learning phase transitions by confusion

    CERN Document Server

    van Nieuwenburg, Evert P L; Huber, Sebastian D

    2016-01-01

    Classifying phases of matter is a central problem in physics. For quantum mechanical systems, this task can be daunting owing to the exponentially large Hilbert space. Thanks to the available computing power and access to ever larger data sets, classification problems are now routinely solved using machine learning techniques. Here, we propose to use a neural network based approach to find phase transitions depending on the performance of the neural network after training it with deliberately incorrectly labelled data. We demonstrate the success of this method on the topological phase transition in the Kitaev chain, the thermal phase transition in the classical Ising model, and the many-body-localization transition in a disordered quantum spin chain. Our method does not depend on order parameters, knowledge of the topological content of the phases, or any other specifics of the transition at hand. It therefore paves the way to a generic tool to identify unexplored phase transitions.

  17. Quantum phase transition in space

    Energy Technology Data Exchange (ETDEWEB)

    Damski, Bogdan [Los Alamos National Laboratory; Zurek, Wojciech H [Los Alamos National Laboratory

    2008-01-01

    A quantum phase transition between the symmetric (polar) phase and the phase with broken symmetry can be induced in a ferromagnetic spin-1 Bose-Einstein condensate in space (rather than in time). We consider such a phase transition and show that the transition region in the vicinity of the critical point exhibits scalings that reflect a compromise between the rate at which the transition is imposed (i.e., the gradient of the control parameter) and the scaling of the divergent healing length in the critical region. Our results suggest a method for the direct measurement of the scaling exponent {nu}.

  18. Anomaly in the phase diagram of the spin quantum 1/2 anisotropic Heisenberg antiferromagnet model with Dzyaloshinskii-Moriya interaction: A low temperature analysis

    Science.gov (United States)

    Parente, Walter E. F.; Pacobahyba, J. T. M.; Araújo, Ijanílio G.; Neto, Minos A.; Ricardo de Sousa, J.

    2015-11-01

    We will study phase diagram the quantum spin-1/2 anisotropic Heisenberg antiferromagnet model in the presence of a Dzyaloshinskii-Moriya interaction (D) and a uniform longitudinal (H) magnetic field, where we have observed an anomaly at low temperatures. Using the effective-field theory with a finite cluster N=2 spin (EFT-2) we calculate the phase diagram in the H - D plane on a simple cubic lattice (z=6). We analyzed the cases: anisotropic Heisenberg - case I: (Δ = 1), anisotropic Heisenberg - case II: (Δ = 0.5) and anisotropic Heisenberg - case III: (Δ = 0), where only second order phase transitions are observed.

  19. Phase Diagram in a Random Mixture of Two Antiferromagnets with Competing Spin Anisotropies. I

    Science.gov (United States)

    Someya, Yoshiko

    1981-12-01

    The phase diagram of a random mixture of two antiferromagnets with competing spin anisotropies (A1-xBx) has been analyzed by extending the theory of Matsubara and Inawashiro, and Oguchi and Ishikawa. In the model assumed, the anisotropy energies are expressed by the anisotropic exchange interactions. According to this formulation, it has been shown that the concentration dependence of TN becomes a function of \\includegraphics{dummy.eps}, where P, Q=A, B; SP is a magnitude of P-spin, and JPQη is a η component of exchange integral between P- and Q-spin). Further, the phase boundary between an AF phase and an OAF (oblique antiferromagnetic) phase at T{=}0 K has been shown to be determined by α({\\equiv}SB/SA), if \\includegraphics{dummy.eps} are given. The obtained phase diagrams for Fe1-xCoxCl2, K2Mn1-xFexF4 and Fe1-xCoxCl2\\cdot2H2O are compared with the experimental ones.

  20. Sequential write-read operations in FeRh antiferromagnetic memory

    Science.gov (United States)

    Moriyama, Takahiro; Matsuzaki, Noriko; Kim, Kab-Jin; Suzuki, Ippei; Taniyama, Tomoyasu; Ono, Teruo

    2015-09-01

    B2-ordered FeRh has been known to exhibit antiferromagnetic-ferromagnetic (AF-F) phase transitions in the vicinity of room temperature. Manipulation of the Néel order via AF-F phase transition and recent experimental observation of the anisotropic magnetoresistance in antiferromagnetic FeRh has proven that FeRh is a promising candidate for antiferromagnetic memory material. In this work, we demonstrate sequential write and read operations in antiferromagnetic memory resistors made of B2-orderd FeRh thin films by a magnetic field and electric current only, which open a realistic pathway towards operational antiferromagnetic memory devices.

  1. Spin-current probe for phase transition in an insulator

    Science.gov (United States)

    Qiu, Zhiyong; Li, Jia; Hou, Dazhi; Arenholz, Elke; N'diaye, Alpha T.; Tan, Ali; Uchida, Ken-Ichi; Sato, Koji; Okamoto, Satoshi; Tserkovnyak, Yaroslav; Qiu, Z. Q.; Saitoh, Eiji

    2016-08-01

    Spin fluctuation and transition have always been one of the central topics of magnetism and condensed matter science. Experimentally, the spin fluctuation is found transcribed onto scattering intensity in the neutron-scattering process, which is represented by dynamical magnetic susceptibility and maximized at phase transitions. Importantly, a neutron carries spin without electric charge, and therefore it can bring spin into a sample without being disturbed by electric energy. However, large facilities such as a nuclear reactor are necessary. Here we show that spin pumping, frequently used in nanoscale spintronic devices, provides a desktop microprobe for spin transition; spin current is a flux of spin without an electric charge and its transport reflects spin excitation. We demonstrate detection of antiferromagnetic transition in ultra-thin CoO films via frequency-dependent spin-current transmission measurements, which provides a versatile probe for phase transition in an electric manner in minute devices.

  2. Spin-current probe for phase transition in an insulator.

    Science.gov (United States)

    Qiu, Zhiyong; Li, Jia; Hou, Dazhi; Arenholz, Elke; N'Diaye, Alpha T; Tan, Ali; Uchida, Ken-Ichi; Sato, Koji; Okamoto, Satoshi; Tserkovnyak, Yaroslav; Qiu, Z Q; Saitoh, Eiji

    2016-01-01

    Spin fluctuation and transition have always been one of the central topics of magnetism and condensed matter science. Experimentally, the spin fluctuation is found transcribed onto scattering intensity in the neutron-scattering process, which is represented by dynamical magnetic susceptibility and maximized at phase transitions. Importantly, a neutron carries spin without electric charge, and therefore it can bring spin into a sample without being disturbed by electric energy. However, large facilities such as a nuclear reactor are necessary. Here we show that spin pumping, frequently used in nanoscale spintronic devices, provides a desktop microprobe for spin transition; spin current is a flux of spin without an electric charge and its transport reflects spin excitation. We demonstrate detection of antiferromagnetic transition in ultra-thin CoO films via frequency-dependent spin-current transmission measurements, which provides a versatile probe for phase transition in an electric manner in minute devices. PMID:27573443

  3. Magnetic resonance of phase transitions

    CERN Document Server

    Owens, Frank J; Farach, Horacio A

    1979-01-01

    Magnetic Resonance of Phase Transitions shows how the effects of phase transitions are manifested in the magnetic resonance data. The book discusses the basic concepts of structural phase and magnetic resonance; various types of magnetic resonances and their underlying principles; and the radiofrequency methods of nuclear magnetic resonance. The text also describes quadrupole methods; the microwave technique of electron spin resonance; and the Mössbauer effect. Phase transitions in various systems such as fluids, liquid crystals, and crystals, including paramagnets and ferroelectrics, are also

  4. Neutron diffraction and electrical transport studies on the incommensurate magnetic phase transition in holmium at high pressures

    Energy Technology Data Exchange (ETDEWEB)

    Thomas, Sarah [University of Alabama, Birmingham; Uhoya, Walter [University of Alabama, Birmingham; Tsoi, Georgiy [University of Alabama, Birmingham; Wenger, Lowell E [University of Alabama, Birmingham; Vohra, Yogesh [University of Alabama, Birmingham; Chesnut, Gary Neal [University of Alabama, Birmingham; Weir, S. T. [Lawrence Livermore National Laboratory (LLNL); Tulk, Christopher A [ORNL; Moreira Dos Santos, Antonio F [ORNL

    2012-01-01

    Neutron diffraction and electrical transport measurements have been made on the heavy rare earth metal holmium at high pressures and low temperatures in order to elucidate its transition from a paramagnetic (PM) to a helical antiferromagnetic (AFM) ordered phase as a function of pressure. The electrical resistance measurements show a change in the resistance slope as the temperature is lowered through the antiferromagnetic Neel temperature. The temperature of this antiferromagnetic transition decreases from approximately 122 K at ambient pressure at a rate of -4.9 K GPa(-1) up to a pressure of 9 GPa, whereupon the PM-to-AFM transition vanishes for higher pressures. Neutron diffraction measurements as a function of pressure at 89 and 110 K confirm the incommensurate nature of the phase transition associated with the antiferromagnetic ordering of the magnetic moments in a helical arrangement and that the ordering occurs at similar pressures as determined from the resistance results for these temperatures.

  5. Magnetic Phase Transitions of CeSb. II: Effects of Applied Magnetic Fields

    DEFF Research Database (Denmark)

    Meier, G.; Fischer, P.; Hälg, W.;

    1978-01-01

    For pt.I see ibid., vol.11, p.345 (1978). The metamagnetic phase transition and the associated phase diagram of the anomalous antiferromagnet CeSb were determined in a neutron diffraction study of the magnetic ordering of CeSb single crystals in applied magnetic fields parallel to the (001) and (...

  6. Multiobjective Optimization and Phase Transitions

    CERN Document Server

    Seoane, Luís F

    2015-01-01

    Many complex systems obey to optimality conditions that are usually not simple. Conflicting traits often interact making a Multi Objective Optimization (MOO) approach necessary. Recent MOO research on complex systems report about the Pareto front (optimal designs implementing the best trade-off) in a qualitative manner. Meanwhile, research on traditional Simple Objective Optimization (SOO) often finds phase transitions and critical points. We summarize a robust framework that accounts for phase transitions located through SOO techniques and indicates what MOO features resolutely lead to phase transitions. These appear determined by the shape of the Pareto front, which at the same time is deeply related to the thermodynamic Gibbs surface. Indeed, thermodynamics can be written as an MOO from where its phase transitions can be parsimoniously derived; suggesting that the similarities between transitions in MOO-SOO and Statistical Mechanics go beyond mere coincidence.

  7. First-order superfluid-to-Mott-insulator phase transitions in spinor condensates

    Science.gov (United States)

    Jiang, J.; Zhao, L.; Wang, S.-T.; Chen, Z.; Tang, T.; Duan, L.-M.; Liu, Y.

    2016-06-01

    We observe evidence of first-order superfluid-to-Mott-insulator quantum phase transitions in a lattice-confined antiferromagnetic spinor Bose-Einstein condensate. The observed signatures include the hysteresis effect, significant heatings across the phase transitions, and changes in spin populations due to the formation of spin singlets in the Mott-insulator phase. The nature of the phase transitions is found to strongly depend on the ratio of the quadratic Zeeman energy to the spin-dependent interaction. Our observations are qualitatively understood by the mean field theory and suggest tuning the quadratic Zeeman energy is a new approach to realize superfluid-to-Mott-insulator phase transitions.

  8. In-situ microscopy of the first-order magnetic phase transition in FeRh thin films

    OpenAIRE

    Baldasseroni, Chloe

    2013-01-01

    Simple ferromagnetic (FM) and antiferromagnetic (AF) materials such as Fe and Cr become paramagnetic when heated above some critical temperature, in what is known as a second-order phase transition. Less usual magnetic transitions are found in the magnetic world, for example a first-order magnetic phase transition from AF to FM with increasing temperature. Equiatomic FeRh has been known to exhibit such a transition for over 50 years, with a transition temperature slightly above room tempera...

  9. Phase Transitions in QCD

    OpenAIRE

    H. Satz(University of Bielefeld)

    2000-01-01

    At high temperatures or densities, hadronic matter shows different forms of critical behaviour: colour deconfinement, chiral symmetry restoration, and diquark condensation. I first discuss the conceptual basis of these phenomena and then consider the description of colour deconfinement in terms of symmetry breaking, through colour screening and as percolation transition.

  10. Phenomenology of cosmic phase transitions

    International Nuclear Information System (INIS)

    The evolution of the cosmic matter from Planck temperature to the atomic combination temperature is considered from a phenomenological point of view. Particular emphasis is devoted to the sequence of cosmic phase transitions. The inflationary era at the temperature of the order of the grand unification energy scale and the quantum chromodynamic confinement transition are dealt with in detail. (author) 131 refs.; 26 figs

  11. Physical properties of antiferromagnetic Mn doped ZnO samples: Role of impurity phase

    International Nuclear Information System (INIS)

    Structural, morphological, optical, and magnetic properties of nanocrystalline Zn1−xMnxO samples (x=0.01, 0.02, 0.04, 0.06, 0.08 and 0.10) prepared by the sol–gel route are studied by X-ray diffraction (XRD), Scanning electron microscopy (SEM), UV–visible absorption spectroscopy, Superconducting quantum interference device (SQUID) magnetometry and positron annihilation lifetime spectroscopy (PALS). XRD confirms formation of wurzite structure in all the Mn-substituted samples. A systematic increase in lattice constants and decrease in grain size have been observed with increase in manganese doping concentration up to 6 at% in the ZnO structure. An impurity phase (ZnMnO3) has been detected when percentage of Mn concentration is 6 at% or higher. The optical band gap of the Mn-substituted ZnO samples decrease with increase in doping concentration of manganese whereas the width of the localized states increases. The antiferromagnetic exchange interaction is strong in the samples for 2 and 4 at% of Mn doping but it reduces when the doping level increases from 6 at% and further. Positron life time components τ1 and τ2 are found to decrease when concentration of the dopant exceeds 6 at%. The changes in magnetic properties as well as positron annihilation parameters at higher manganese concentration have been assigned as due to the formation of impurity phase. - highlights: • Single phase structure has been observed up to 6 at% of Mn doping. • Impurity phase has been developed above 6 at% of Mn doping. • Antiferromagnetic and paramagnetic interactions are present in the samples. • Defect parameters show sharp fall as Mn concentration above 6 at%. • The magnetic and defect properties are modified by the formation of impurity phase

  12. Field-induced transition of the magnetic ground state from A-type antiferromagnetic to ferromagnetic order in CsCo2Se2

    Science.gov (United States)

    von Rohr, Fabian; Krzton-Maziopa, Anna; Pomjakushin, Vladimir; Grundmann, Henrik; Guguchia, Zurab; Schnick, Wolfgang; Schilling, Andreas

    2016-07-01

    We report on the magnetic properties of CsCo2Se2 with ThCr2Si2 structure, which we have characterized through a series of magnetization and neutron diffraction measurements. We find that CsCo2Se2 undergoes a phase transition to an antiferromagnetically ordered state with a Néel temperature of {{T}\\text{N}}≈ 66 K. The nearest neighbour interactions are ferromagnetic as observed by the positive Curie-Weiss temperature of \\Theta≈ 51.0 K. We find that the magnetic structure of CsCo2Se2 consists of ferromagnetic sheets, which are stacked antiferromagnetically along the tetragonal c-axis, generally referred to as A-type antiferromagnetic order. The observed magnitude of the ordered magnetic moment at T  =  1.5 K is found to be only 0.20(1){μ\\text{Bohr}}  / Co. Already in comparably small magnetic fields of {μ0}H{{}\\text{MM}}(5~K)≈ 0.3 T, we observe a metamagnetic transition that can be attributed to spin-rearrangements of CsCo2Se2, with the moments fully ferromagnetically saturated in a magnetic field of {μ0}{{H}\\text{FM}}(5~K)≈ 6.4 T. We discuss the entire experimentally deduced magnetic phase diagram for CsCo2Se2 with respect to its unconventionally weak magnetic coupling. Our study characterizes CsCo2Se2, which is chemically and electronically posed closely to the A x Fe2-y Se2 superconductors, as a host of versatile magnetic interactions.

  13. Optical investigation of magneto-structural phase transition in FeRh

    OpenAIRE

    Saidl, V.; Brajer, M.; Horak, L.; Reichlova, H.; Vyborny, K.; Veis, M.; Janda, T.; Trojanek, F.; Fina, I.; Marti, X.; Jungwirth, T.; Nemec, P.

    2015-01-01

    Magneto-structural phase transition in FeRh epitaxial layers was studied optically. It is shown that the transition between the low-temperature antiferromagnetic phase and the high-temperature ferromagnetic phase is accompanied by a rather large change of the optical response in the visible and near infrared spectral ranges. This phenomenon was used to measure the phase transition temperature in FeRh films with thicknesses from 6 to 100 nm and it was observed that the hysteretic transition re...

  14. Structural and magnetic phase transitions in NdCoAsO under high pressures

    International Nuclear Information System (INIS)

    We have investigated structural and magnetic phase transitions under high pressures in a quaternary rare-earth transition-metal arsenide oxide NdCoAsO compound that is isostructural to the high temperature superconductor parent phase NdFeAsO. The four-probe electrical resistance measurements carried out in a designer diamond anvil cell show that the ferromagnetic Curie temperature and antiferromagnetic Neel temperature increase with an increase in pressure. High pressure x-ray diffraction studies using a synchrotron source show a structural phase transition from a tetragonal phase to a new crystallographic phase at a pressure of 23 GPa at 300 K. The NdCoAsO sample remained antiferromagnetic and non-superconducting down to 10 K and up to the highest pressure achieved in this experiment, 53 GPa. A P-T phase diagram for NdCoAsO is presented from ambient conditions to P = 53 GPa and T = 10 K.

  15. Structural and magnetic phase transitions in NdCoAsO under high pressures

    Energy Technology Data Exchange (ETDEWEB)

    Uhoya, Walter; Tsoi, Georgiy M.; Vohra, Yogesh K.; McGuire, Michael A.; Sefat, Athena S.; Sales, Brian C.; Mandrus, David; Weir, Samuel T. (UAB); (ORNL); (LLNL)

    2010-05-04

    We have investigated structural and magnetic phase transitions under high pressures in a quaternary rare-earth transition-metal arsenide oxide NdCoAsO compound that is isostructural to the high temperature superconductor parent phase NdFeAsO. The four-probe electrical resistance measurements carried out in a designer diamond anvil cell show that the ferromagnetic Curie temperature and antiferromagnetic Neel temperature increase with an increase in pressure. High pressure x-ray diffraction studies using a synchrotron source show a structural phase transition from a tetragonal phase to a new crystallographic phase at a pressure of 23 GPa at 300 K. The NdCoAsO sample remained antiferromagnetic and non-superconducting down to 10 K and up to the highest pressure achieved in this experiment, 53 GPa. A P-T phase diagram for NdCoAsO is presented from ambient conditions to P = 53 GPa and T = 10 K.

  16. Structural and magnetic phase transitions in NdCoAsO under high pressures

    Energy Technology Data Exchange (ETDEWEB)

    Uhoya, Walter [University of Alabama, Birmingham; Tsoi, Georgiy [University of Alabama, Birmingham; Vohra, Y. K. [University of Alabama, Birmingham; McGuire, Michael A [ORNL; Sefat, A. S. [Oak Ridge National Laboratory (ORNL); Sales, Brian C [ORNL; Mandrus, David [ORNL; Weir, S. T. [Lawrence Livermore National Laboratory (LLNL)

    2010-01-01

    We have investigated structural and magnetic phase transitions under high pressures in a quaternary rare-earth transition-metal arsenide oxide NdCoAsO compound that is isostructural to the high temperature superconductor parent phase NdFeAsO. The four-probe electrical resistance measurements carried out in a designer diamond anvil cell show that the ferromagnetic Curie temperature and antiferromagnetic Neel temperature increase with an increase in pressure. High pressure x-ray diffraction studies using a synchrotron source show a structural phase transition from a tetragonal phase to a new crystallographic phase at a pressure of 23 GPa at 300 K. The NdCoAsO sample remained antiferromagnetic and non-superconducting down to 10 K and up to the highest pressure achieved in this experiment, 53 GPa. A P-T phase diagram for NdCoAsO is presented from ambient conditions to P = 53 GPa and T = 10 K.

  17. Quantum Phase Transition, Dissipation, and Measurement

    OpenAIRE

    Chakravarty, Sudip

    2009-01-01

    A selected set of topics in quantum phase transition is discussed. It includes dissipative quantum phase transitions, the role of disorder, and the relevance of quantum phase transition to measurement theory in quantum mechanics.

  18. Phase transitions in field theory

    International Nuclear Information System (INIS)

    By means of an example for which the effective potential is explicitly calculable (up to the one loop approximation), it is discussed how a phase transition takes place as the temperature is increased and pass from spontaneously broken symmetry to a phase in which the symmetry is restored. (Author)

  19. Incommensurate phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Currat, R. [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)

    1996-11-01

    We review the characteristic aspects of modulated crystals from the point of view of inelastic neutron scattering. We discuss the phenomenological Landau theory of the normal-to-incommensurate displacive instability and its predictions concerning the fluctuation spectrum of the modulated phase. General results on the form of the normal-mode eigenvectors and on the inelastic scattering channels through which they couple to the probe are established using the superspace approach. We illustrate these results on a simple discrete model symmetry and we review available inelastic neutron scattering data on several displacively modulated compounds. (author) 21 figs., 73 refs.

  20. Quantum magnetic phase transition in square-octagon lattice

    Science.gov (United States)

    Bao, An; Tao, Hong-Shuai; Liu, Hai-Di; Zhang, Xiaozhong; Liu, Wu-Ming

    2014-11-01

    Quantum magnetic phase transition in square-octagon lattice was investigated by cellular dynamical mean field theory combining with continuous time quantum Monte Carlo algorithm. Based on the systematic calculation on the density of states, the double occupancy and the Fermi surface evolution of square-octagon lattice, we presented the phase diagrams of this splendid many particle system. The competition between the temperature and the on-site repulsive interaction in the isotropic square-octagon lattice has shown that both antiferromagnetic and paramagnetic order can be found not only in the metal phase, but also in the insulating phase. Antiferromagnetic metal phase disappeared in the phase diagram that consists of the anisotropic parameter λ and the on-site repulsive interaction U while the other phases still can be detected at T = 0.17. The results found in this work may contribute to understand well the properties of some consuming systems that have square-octagon structure, quasi square-octagon structure, such as ZnO.

  1. Magnetic phase diagram of the antiferromagnetic pyrochlore Gd2 Ti2 O7

    Science.gov (United States)

    Petrenko, O. A.; Lees, M. R.; Balakrishnan, G.; Paul, D. Mck

    2004-07-01

    Gd2Ti2O7 is a highly frustrated antiferromagnet on a pyrochlore lattice, where apart from the Heisenberg exchange the spins also interact via dipole-dipole forces. We report on low-temperature specific heat measurements performed on single crystals of Gd2Ti2O7 for three different directions of an applied magnetic field. The measurements reveal the strongly anisotropic behavior of Gd2Ti2O7 in a magnetic field despite the apparent absence of a significant single-ion anisotropy for Gd3+ . The H-T phase diagrams are constructed for H∥[111] , H∥[110] , and H∥[112] . The results indicate that further theoretical work beyond a simple mean-field model is required.

  2. Field-Dependent Magnetic Phase Transitions in Mixed-Valent TmSe

    DEFF Research Database (Denmark)

    Bjerrum Møller, Hans; Shapiro, S. M.; Birgenau, R. J.

    1977-01-01

    A neutron diffraction study of the field-dependent magnetic ordering in TmSe is reported. The magnetic strucutre in zero field is antiferromagnetic fcc type I with TN=3.2 K. The magnetic phase diagram may be understood as a successive domain reorientation and metamagnetic transitions for T...

  3. Phase transition in evolutionary games

    CERN Document Server

    Cao, Z J; Cao, Zhen; Hwa, Rudolph C

    1995-01-01

    The evolution of cooperative behaviour is studied in the deterministic version of the Prisoners' Dilemma on a two-dimensional lattice. The payoff parameter is set at the critical region 1.8 < b < 2.0 , where clusters of cooperators are formed in all spatial sizes. Using the factorial moments developed in particle and nuclear physics for the study of phase transition, the distribution of cooperators is studied as a function of the bin size covering varying numbers of lattice cells. From the scaling behaviour of the moments a scaling exponent is determined and is found to lie in the range where phase transitions are known to take place in physical systems. It is therefore inferred that when the payoff parameter is increased through the critical region the biological system of cooperators undergoes a phase transition to defectors. The universality of the critical behaviour is thus extended to include also this particular model of evolution dynamics.

  4. Quantum phase transition in dimerised spin-1/2 chains

    Science.gov (United States)

    Das, Aparajita; Bhadra, Sreeparna; Saha, Sonali

    2015-11-01

    Quantum phase transition in dimerised antiferromagnetic Heisenberg spin chain has been studied. A staircase structure in the variation of concurrence within strongly coupled pairs with that of external magnetic field has been observed indicating multiple critical (or critical like) points. Emergence of entanglement due to external magnetic field or magnetic entanglement is observed for weakly coupled spin pairs too in the same dimer chain. Though closed dimerised isotropic XXX Heisenberg chains with different dimer strengths were mainly explored, analogous studies on open chains as well as closed anisotropic (XX interaction) chains with tilted external magnetic field have also been studied.

  5. Interaction of optical phonons with magnons in orthorhombic crystals. Effect of a magnetic field on structural phase transitions

    Science.gov (United States)

    Men'shenin, V. V.

    2007-05-01

    Interaction of polar optical phonons with magnons in manganates RMn2O5 (where R is a rare-earth ion) has been studied in the approximation of collinear antiferromagnetic ordering of manganese sublattices. It is shown that such interaction takes place only in multisublattice antiferromagnets in which exchange magnetic structures exist that are both even and odd with respect to space inversion. Effect of a magnetic field on the structural phase transitions in these oxides is analyzed.

  6. Phase transitions in finite systems

    Energy Technology Data Exchange (ETDEWEB)

    Chomaz, Ph. [Grand Accelerateur National d' Ions Lourds (GANIL), DSM-CEA / IN2P3-CNRS, 14 - Caen (France); Gulminelli, F. [Caen Univ., 14 (France). Lab. de Physique Corpusculaire

    2002-07-01

    In this series of lectures we will first review the general theory of phase transition in the framework of information theory and briefly address some of the well known mean field solutions of three dimensional problems. The theory of phase transitions in finite systems will then be discussed, with a special emphasis to the conceptual problems linked to a thermodynamical description for small, short-lived, open systems as metal clusters and data samples coming from nuclear collisions. The concept of negative heat capacity developed in the early seventies in the context of self-gravitating systems will be reinterpreted in the general framework of convexity anomalies of thermo-statistical potentials. The connection with the distribution of the order parameter will lead us to a definition of first order phase transitions in finite systems based on topology anomalies of the event distribution in the space of observations. Finally a careful study of the thermodynamical limit will provide a bridge with the standard theory of phase transitions and show that in a wide class of physical situations the different statistical ensembles are irreducibly inequivalent. (authors)

  7. Symmetry structure and phase transitions

    Indian Academy of Sciences (India)

    Ashok Goyal; Meenu Dahiya; Deepak Chandra

    2003-05-01

    We study chiral symmetry structure at finite density and temperature in the presence of external magnetic field and gravity, a situation relevant in the early Universe and in the core of compact stars. We then investigate the dynamical evolution of phase transition in the expanding early Universe and possible formation of quark nuggets and their survival.

  8. Artificiality of multifractal phase transitions

    OpenAIRE

    Wolf, Martin; Schmiegel, Jürgen; Greiner, Martin

    1999-01-01

    A multifractal phase transition is associated to a nonanalyticity in the generalised dimensions. We show that its occurrence is an artifact of the asymptotic scaling behaviour of integral moments and that it is not observed in an analysis based on differential n-point correlation densities.

  9. Phase transitions in quantum chromodynamics

    CERN Document Server

    Meyer-Ortmanns, H

    1996-01-01

    The current understanding of finite temperature phase transitions in QCD is reviewed. A critical discussion of refined phase transition criteria in numerical lattice simulations and of analytical tools going beyond the mean-field level in effective continuum models for QCD is presented. Theoretical predictions about the order of the transitions are compared with possible experimental manifestations in heavy-ion collisions. Various places in phenomenological descriptions are pointed out, where more reliable data for QCD's equation of state would help in selecting the most realistic scenario among those proposed. Unanswered questions are raised about the relevance of calculations which assume thermodynamic equilibrium. Promising new approaches to implement nonequilibrium aspects in the thermodynamics of heavy-ion collisions are described.

  10. Magnetoresistive study of the antiferromagnetic-weak ferromagnetic transition in single-crystal La2CuO4+δ

    Science.gov (United States)

    Belevtsev, B. I.; Dalakova, N. V.; Savitsky, V. N.; Panfilov, A. S.; Braude, I. S.; Bondarenko, A. V.

    2004-05-01

    Resistive measurements were made to study the magnetic field-induced antiferromagnetic (AF)—weak ferromagnetic (WF) transition in the La2CuO4 single crystal. The magnetic field (dc or pulsed) was applied normally to the CuO2 layers. The transition manifested itself in a drastic decrease of the resistance in critical fields of 5-7 T. The study is the first to display the effect of the AF-WF transition on the conductivity of the La2CuO4 single crystal in the direction parallel to the CuO2 layers. The results provide support for the three-dimensional nature of the hopping conduction of this layered oxide.

  11. Phase transitions and critical phenomena

    CERN Document Server

    Domb, Cyril

    2001-01-01

    The field of phase transitions and critical phenomena continues to be active in research, producing a steady stream of interesting and fruitful results. It has moved into a central place in condensed matter studies.Statistical physics, and more specifically, the theory of transitions between states of matter, more or less defines what we know about 'everyday' matter and its transformations.The major aim of this serial is to provide review articles that can serve as standard references for research workers in the field, and for graduate students and others wishing to obtain reliable in

  12. Magnetic phase transition in iron-rhodium thin films probed by ferromagnetic resonance

    Science.gov (United States)

    Mancini, E.; Pressacco, F.; Haertinger, M.; Fullerton, E. E.; Suzuki, T.; Woltersdorf, G.; Back, C. H.

    2013-06-01

    We report the results of ferromagnetic (FMR) resonance measurements on epitaxial FeRh/MgO(0 0 1) samples across the phase transition from the antiferromagnetic (AF) state of FeRh to its ferromagnetic (F) state. From temperature-dependent measurements of position, width and amplitude of the FMR line the phase transition is studied in detail. Our measurements indicate that the AF to F phase transition of FeRh is first order in nature. In addition, the angular and frequency-dependent FMR measurements are used to determine the anisotropy constants and the Gilbert damping parameter of the epitaxial FeRh films.

  13. Field driven ferromagnetic phase nucleation and propagation from the domain boundaries in antiferromagnetically coupled perpendicular anisotropy films

    Energy Technology Data Exchange (ETDEWEB)

    Hauet, Thomas; Gunther, Christian M.; Hovorka, Ondrej; Berger, Andreas; Im, Mi-Young; Fischer, Peter; Hellwig, Olav

    2008-12-09

    We investigate the reversal process in antiferromagnetically coupled [Co/Pt]{sub X-1}/{l_brace}Co/Ru/[Co/Pt]{sub X-1}{r_brace}{sub 16} multilayer films by combining magnetometry and Magnetic soft X-ray Transmission Microscopy (MXTM). After out-of-plane demagnetization, a stable one dimensional ferromagnetic (FM) stripe domain phase (tiger-tail phase) for a thick stack sample (X=7 is obtained), while metastable sharp antiferromagnetic (AF) domain walls are observed in the remanent state for a thinner stack sample (X=6). When applying an external magnetic field the sharp domain walls of the thinner stack sample transform at a certain threshold field into the FM stripe domain wall phase. We present magnetic energy calculations that reveal the underlying energetics driving the overall reversal mechanisms.

  14. Phase Transitions in the Universe

    CERN Document Server

    Gleiser, Marcello

    1998-01-01

    During the past two decades, cosmologists turned to particle physics in order to explore the physics of the very early Universe. The main link between the physics of the smallest and largest structures in the Universe is the idea of spontaneous symmetry breaking, familiar from condensed matter physics. Implementing this mechanism into cosmology leads to the interesting possibility that phase transitions related to the breaking of symmetries in high energy particle physics took place during the early history of the Universe. These cosmological phase transitions may help us understand many of the challenges faced by the standard hot Big Bang model of cosmology, while offering a unique window into the very early Universe and the physics of high energy particle interactions.

  15. Structural dynamics in FeRh during a laser-induced metamagnetic phase transition

    Science.gov (United States)

    Quirin, Florian; Vattilana, Michael; Shymanovich, Uladzimir; El-Kamhawy, Abd-Elmoniem; Tarasevitch, Alexander; Hohlfeld, Julius; von der Linde, Dietrich; Sokolowski-Tinten, Klaus

    2012-01-01

    Time-resolved x-ray diffraction with ultrashort x-ray pulses from a laser-produced plasma is used to study the lattice response of FeRh during a femtosecond laser-induced antiferromagnetic (AFM) to ferromagnetic (FM) phase transition. Pump-probe measurements at initial sample temperatures below as well as above the AFM-to-FM transition temperature and for different laser pump fluences allowed to disentangle the various contributions driving lattice expansion. In particular, the data reveal that the structural changes associated with the magnetic phase transition occur on a time scale of a hundred picoseconds.

  16. Phase Transition in Tensor Models

    CERN Document Server

    Delepouve, Thibault

    2015-01-01

    Generalizing matrix models, tensor models generate dynamical triangulations in any dimension and support a $1/N$ expansion. Using the intermediate field representation we explicitly rewrite a quartic tensor model as a field theory for a fluctuation field around a vacuum state corresponding to the resummation of the entire leading order in $1/N$ (a resummation of the melonic family). We then prove that the critical regime in which the continuum limit in the sense of dynamical triangulations is reached is precisely a phase transition in the field theory sense for the fluctuation field.

  17. Phase transitions and critical phenomena

    CERN Document Server

    Domb, Cyril

    2000-01-01

    The field of phase transitions and critical phenomena continues to be active in research, producing a steady stream of interesting and fruitful results. No longer an area of specialist interest, it has acquired a central focus in condensed matter studies. The major aim of this serial is to provide review articles that can serve as standard references for research workers in the field, and for graduate students and others wishing to obtain reliable information on important recent developments.The two review articles in this volume complement each other in a remarkable way. Both deal with what m

  18. Light scattering near phase transitions

    CERN Document Server

    Cummins, HZ

    1983-01-01

    Since the development of the laser in the early 1960's, light scattering has played an increasingly crucial role in the investigation of many types of phase transitions and the published work in this field is now widely dispersed in a large number of books and journals.A comprehensive overview of contemporary theoretical and experimental research in this field is presented here. The reviews are written by authors who have actively contributed to the developments that have taken place in both Eastern and Western countries.

  19. Study of the Static and Dynamic Magnetization across the First Order Phase Transition in FeRh Thin Films

    OpenAIRE

    Heidarian, Alireza

    2016-01-01

    The equiatomic FeRh alloy undergoes a first-order phase transition from an antiferromagnetic (AFM) to a ferromagnetic (FM) state at about 370 K with a small thermal hysteresis of about 10 K around the phase transition. The transition is accompanied by a unit cell volume expansion about 1% in the c lattice parameter. During the transition the new phase nucleates in the matrix of the original phase by reaching the critical temperature followed by a growth in size upon increasing temperature fur...

  20. Effects of strain and surfaces on the antiferromagnetic and ferromagnetic phases of thin film FeRh

    Science.gov (United States)

    Hellman, Frances; Bordel, Catherine; Baldasseroni, Chloe; Antonakos, Cory; Schneider, Oliver; Pal, Gunar; Valencia, Sergio; Unal, Akin; Kronast, Florian; Nemsak, Slavo; Fadley, Chuck; Borchers, Julie; Maranville, Brian

    2014-03-01

    FeRh undergoes an unusual antiferromagnetic (AFM) to ferromagnetic (FM) first order transition just above room temperature. This transition can be tuned by pressure, magnetic field, composition, and strain. The underlying source of the transition is still under much discussion, but it is clear from a variety of measurements that electronic structure, lattice, and magnetic excitations all play roles in contributing the underlying entropy difference and hence the competition between AFM and FM states. The surface and bottom interface of thin films are often found to be FM even while the bulk of the film is AFM. The source of this effect, along with the dependence of strain on both anisotropy and transition temperature will be presented and discussed. Thanks to DOE BES LBNL magnetism program for support.

  1. Structural and Magnetic Dynamics of a Laser Induced Phase Transition in FeRh

    Science.gov (United States)

    Mariager, S. O.; Pressacco, F.; Ingold, G.; Caviezel, A.; Möhr-Vorobeva, E.; Beaud, P.; Johnson, S. L.; Milne, C. J.; Mancini, E.; Moyerman, S.; Fullerton, E. E.; Feidenhans'L, R.; Back, C. H.; Quitmann, C.

    2012-02-01

    We use time-resolved x-ray diffraction and magneto-optical Kerr effect to study the laser-induced antiferromagnetic to ferromagnetic phase transition in FeRh. The structural response is given by the nucleation of independent ferromagnetic domains (τ1˜30ps). This is significantly faster than the magnetic response (τ2˜60ps) given by the subsequent domain realignment. X-ray diffraction shows that the two phases coexist on short time scales and that the phase transition is limited by the speed of sound. A nucleation model describing both the structural and magnetic dynamics is presented.

  2. Structural and magnetic dynamics of a laser induced phase transition in FeRh

    OpenAIRE

    Mariager, S. O.; Pressacco, F.; Ingold, G.; Mancini, E; Caviezel, A.; Möhr-Vorobeva, E.; Beaud, P.; Johnson, S. L.; Milne, C. J.; Moyerman, S.; Fullerton, E.; Feidenhans'l, R.; Back, C.H.; Quitmann, C.

    2011-01-01

    We use time-resolved x-ray diffraction and magnetic optical Kerr effect to study the laser induced antiferromagnetic to ferromagnetic phase transition in FeRh. The structural response is given by the nucleation of independent ferromagnetic domains (\\tau_1 ~ 30ps). This is significantly faster than the magnetic response (\\tau_2 ~ 60ps) given by the subsequent domain realignment. X-ray diffraction shows that the two phases co-exist on short time-scales and that the phase transition is limited b...

  3. Interacting Weyl fermions: Phases, phase transitions and global phase diagram

    CERN Document Server

    Roy, Bitan; Juricic, Vladimir

    2016-01-01

    We study the effects of short-range interactions on a generalized three-dimensional Weyl semimetal, where the band touching points act as the (anti)monopoles of Abelian Berry curvature of strength $n$. We show that any local interaction has a \\emph{negative} scaling dimension $-2/n$. Consequently all Weyl semimetals are stable against weak short-range interactions. For sufficiently strong interactions, we demonstrate that the Weyl semimetal either undergoes a first order transition into a band insulator or a continuous transition into a symmetry breaking phase. A translational symmetry breaking axion insulator and a rotational symmetry breaking semimetal are two prominent candidates for the broken symmetry phase. At one loop level, the correlation length exponent for continuous transitions is $\

  4. QCD Phase Transitions, Volume 15

    Energy Technology Data Exchange (ETDEWEB)

    Schaefer, T.; Shuryak, E.

    1999-03-20

    The title of the workshop, ''The QCD Phase Transitions'', in fact happened to be too narrow for its real contents. It would be more accurate to say that it was devoted to different phases of QCD and QCD-related gauge theories, with strong emphasis on discussion of the underlying non-perturbative mechanisms which manifest themselves as all those phases. Before we go to specifics, let us emphasize one important aspect of the present status of non-perturbative Quantum Field Theory in general. It remains true that its studies do not get attention proportional to the intellectual challenge they deserve, and that the theorists working on it remain very fragmented. The efforts to create Theory of Everything including Quantum Gravity have attracted the lion share of attention and young talent. Nevertheless, in the last few years there was also a tremendous progress and even some shift of attention toward emphasis on the unity of non-perturbative phenomena. For example, we have seen some efforts to connect the lessons from recent progress in Supersymmetric theories with that in QCD, as derived from phenomenology and lattice. Another example is Maldacena conjecture and related development, which connect three things together, string theory, super-gravity and the (N=4) supersymmetric gauge theory. Although the progress mentioned is remarkable by itself, if we would listen to each other more we may have chance to strengthen the field and reach better understanding of the spectacular non-perturbative physics.

  5. Colossal magnetic phase transition asymmetry in mesoscale FeRh stripes

    Science.gov (United States)

    Uhlíř, V.; Arregi, J. A.; Fullerton, E. E.

    2016-10-01

    Coupled order parameters in phase-transition materials can be controlled using various driving forces such as temperature, magnetic and electric field, strain, spin-polarized currents and optical pulses. Tuning the material properties to achieve efficient transitions would enable fast and low-power electronic devices. Here we show that the first-order metamagnetic phase transition in FeRh films becomes strongly asymmetric in mesoscale structures. In patterned FeRh stripes we observed pronounced supercooling and an avalanche-like abrupt transition from the ferromagnetic to the antiferromagnetic phase, while the reverse transition remains nearly continuous over a broad temperature range. Although modest asymmetry signatures have been found in FeRh films, the effect is dramatically enhanced at the mesoscale. The activation volume of the antiferromagnetic phase is more than two orders of magnitude larger than typical magnetic heterogeneities observed in films. The collective behaviour upon cooling results from the role of long-range ferromagnetic exchange correlations that become important at the mesoscale and should be a general property of first-order metamagnetic phase transitions.

  6. Colossal magnetic phase transition asymmetry in mesoscale FeRh stripes

    Science.gov (United States)

    Uhlíř, V.; Arregi, J. A.; Fullerton, E. E.

    2016-01-01

    Coupled order parameters in phase-transition materials can be controlled using various driving forces such as temperature, magnetic and electric field, strain, spin-polarized currents and optical pulses. Tuning the material properties to achieve efficient transitions would enable fast and low-power electronic devices. Here we show that the first-order metamagnetic phase transition in FeRh films becomes strongly asymmetric in mesoscale structures. In patterned FeRh stripes we observed pronounced supercooling and an avalanche-like abrupt transition from the ferromagnetic to the antiferromagnetic phase, while the reverse transition remains nearly continuous over a broad temperature range. Although modest asymmetry signatures have been found in FeRh films, the effect is dramatically enhanced at the mesoscale. The activation volume of the antiferromagnetic phase is more than two orders of magnitude larger than typical magnetic heterogeneities observed in films. The collective behaviour upon cooling results from the role of long-range ferromagnetic exchange correlations that become important at the mesoscale and should be a general property of first-order metamagnetic phase transitions. PMID:27725642

  7. Cloud regimes as phase transitions

    Science.gov (United States)

    Stechmann, Samuel N.; Hottovy, Scott

    2016-06-01

    Clouds are repeatedly identified as a leading source of uncertainty in future climate predictions. Of particular importance are stratocumulus clouds, which can appear as either (i) closed cells that reflect solar radiation back to space or (ii) open cells that allow solar radiation to reach the Earth's surface. Here we show that these clouds regimes -- open versus closed cells -- fit the paradigm of a phase transition. In addition, this paradigm characterizes pockets of open cells as the interface between the open- and closed-cell regimes, and it identifies shallow cumulus clouds as a regime of higher variability. This behavior can be understood using an idealized model for the dynamics of atmospheric water as a stochastic diffusion process. With this new conceptual viewpoint, ideas from statistical mechanics could potentially be used for understanding uncertainties related to clouds in the climate system and climate predictions.

  8. Random exchange interaction effects on the phase transitions in frustrated classical Heisenberg model

    Energy Technology Data Exchange (ETDEWEB)

    Li, W. C.; Song, X.; Feng, J. J.; Zeng, M.; Gao, X. S.; Qin, M. H., E-mail: qinmh@scnu.edu.cn [Institute for Advanced Materials and Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou 510006 (China); Jia, X. T. [School of Physics and Chemistry, Henan Polytechnic University, Jiaozuo 454000 (China)

    2015-07-07

    In this work, the effects of the random exchange interaction on the phase transitions and phase diagrams of classical frustrated Heisenberg model are investigated by Monte Carlo simulation in order to simulate the chemical doping effect in real materials. It is observed that the antiferromagnetic transitions shift toward low temperature with the increasing magnitude of the random exchange interaction, which can be qualitatively understood from the competitions among local spin states. This study is related to the magnetic properties in the doped iron-based superconductors.

  9. Itinerant-Localized Transitions in Magnetic Phases of the Periodic Anderson Model

    Science.gov (United States)

    Kubo, Katsunori

    To clarify the characteristics of Fermi-surface reconstruction, called Lifshitz transitions, in magnetic phases of f-electron materials, we investigate magnetically ordered states of the periodic Anderson model by applying the variational Monte Carlo method. As variational wavefunctions, we use the Gutzwiller wavefunctions for the paramagnetic, antiferromagnetic, and ferromagnetic states. Around half-filling, we find an antiferromagnetic phase, and far away from half-filling, we find a ferromagnetic phase as the ground state. Inside both magnetic phases, Lifshitz transitions take place. At the Lifshitz transitions, the sizes of the ordered moments change. In order to understand the Lifshitz transitions further, we also analyze the f -electron contribution to the Fermi surface by evaluating the jump in the momentum distribution function at the Fermi momentum. Then, we find that, in the large ordered-moment states, the f -electron contribution to the Fermi surface becomes small. This observation clearly shows that these Lifshitz transitions are itinerant-localized transitions of the f electrons.

  10. Magnetic Phase Transition in FeRh

    OpenAIRE

    Gu, R. Y.; Antropov, V.P.

    2005-01-01

    Density functional calculations are performed to investigate the phase transition in FeRh alloy. The effective exchange coupling, the critical temperature of magnetic phase transition and the adiabatic spin wave spectrum have been obtained. Different contributions to the free energy of different phases are estimated. It has been found that the antiferro-ferromagnetic transition in FeRh occurs mostly due to the spin wave excitations.

  11. Phase transition and thermodynamic properties of BiFeO3 from first-principles calculations

    Institute of Scientific and Technical Information of China (English)

    Li Qiang; Huang Duo-Hui; Cao Qi-Long; Wang Fan-Hou

    2013-01-01

    The first-principles projector-augmented wave method employing the quasi-harmonic Debye model,is applied to investigate the thermodynamic properties and the phase transition between the trigonal R3c structure and the orthorhombic Pnma structure.It is found that at ambient temperature,the phase transition from the trigonal R3c phase to the orthorhombic Pnma phase is a first-order antiferromagnetic-nonmagnetic and insulator-metal transition,and occurs at 10.56 GPa,which is in good agreement with experimental data.With increasing temperature,the transition pressure decreases almost linearly.Moreover,the thermodynamic properties including Grüineisen parameter,heat capacity,entropy,and the dependences of thermal expansion coefficient on temperature and pressure are also obtained.

  12. Phase-matched sum frequency generation of antiferromagnetic film in THz frequency field

    International Nuclear Information System (INIS)

    We report on a way to obtain a new source in THz frequency field based on sum frequency (SF) generation of an antiferromagnetic film (AFF). The continuous SF output windows versus the infrared signal wave frequencies are shown. We found that the highest SF outputs can be induced when the frequencies of the two signal waves are both situated at the vicinity of the same resonant frequency of AFF. In addition, the incident angles are in the smaller angle regions. An optimum interact length is defined which should be necessary for the choice of AFF thickness in the experiments. Finally, the frequencies of highest SF outputs can be modulated by controlling the external magnetic field strength. - Highlights: • SF generation of antiferromagnetic film. • New source available with the SF generation method in THz field. • SF conversion efficiency affected by incident frequencies, angles and thickness film

  13. Magnetism and phase transitions in LaCoO3

    Science.gov (United States)

    Durand, A. M.; Belanger, D. P.; Booth, C. H.; Ye, F.; Chi, S.; Fernandez-Baca, J. A.; Bhat, M.

    2013-09-01

    Neutron scattering and magnetometry measurements have been used to study phase transitions in LaCoO3 (LCO). For H ≤ 100 Oe, evidence for a ferromagnetic (FM) transition is observed at Tc ≈ 87 K. For 1 kOe ≤ H ≤ 60 kOe, no transition is apparent. For all H, Curie-Weiss analysis shows predominantly antiferromagnetic (AFM) interactions for T > Tc, but the lack of long-range AFM order indicates magnetic frustration. We argue that the weak ferromagnetism in bulk LCO is induced by lattice strain, as is the case with thin films and nanoparticles. The lattice strain is present at the bulk surfaces and at the interfaces between the LCO and a trace cobalt oxide phase. The ferromagnetic ordering in the LCO bulk is strongly affected by the Co-O-Co angle (γ), in agreement with recent band calculations which predict that ferromagnetic long-range order can only take place above a critical value, γC. Consistent with recent thin film estimations, we find γC = 162.8°. For γ > γC, we observe power-law behavior in the structural parameters. γ decreases with T until the critical temperature, To ≈ 37 K below To the rate of change becomes very small. For T < To, FM order appears to be confined to regions close to the surfaces, likely due to the lattice strain keeping the local Co-O-Co angle above γC.

  14. Magnetism and phase transitions in LaCoO3

    Energy Technology Data Exchange (ETDEWEB)

    Belanger, David P [University of California, Santa Cruz; Durand, Alice M [University of California, Santa Cruz; Booth, C [Lawrence Berkeley National Laboratory (LBNL); Ye, Feng [ORNL; Chi, Songxue [ORNL; Fernandez-Baca, Jaime A [ORNL; Bhat, M [Castilleja School

    2013-01-01

    Neutron scattering and magnetometry measurements have been used to study phase transitions in LaCoO3 (LCO). For H 100 Oe, evidence for a ferromagnetic (FM) transition is observed at Tc 87 K. For 1 kOe H 60 kOe, no transition is apparent. For all H, Curie Weiss analysis shows predominantly antiferromagnetic (AFM) interactions for T > Tc, but the lack of long-range AFM order indicates magnetic frustration. We argue that the weak ferromagnetism in bulk LCO is induced by lattice strain, as is the case with thin films and nanoparticles. The lattice strain is present at the bulk surfaces and at the interfaces between the LCO and a trace cobalt oxide phase. The ferromagnetic ordering in the LCO bulk is strongly affected by the Co O Co angle ( ), in agreement with recent band calculations which predict that ferromagnetic long-range order can only take place above a critical value, C. Consistent with recent thin film estimations, we find C D 162:8. For > C, we observe power-law behavior in the structural parameters. decreases with T until the critical temperature, To 37 K; below To the rate of change becomes very small. For T < To, FM order appears to be confined to regions close to the surfaces, likely due to the lattice strain keeping the local Co O Co angle above C.

  15. Phase transitions in semidefinite relaxations.

    Science.gov (United States)

    Javanmard, Adel; Montanari, Andrea; Ricci-Tersenghi, Federico

    2016-04-19

    Statistical inference problems arising within signal processing, data mining, and machine learning naturally give rise to hard combinatorial optimization problems. These problems become intractable when the dimensionality of the data is large, as is often the case for modern datasets. A popular idea is to construct convex relaxations of these combinatorial problems, which can be solved efficiently for large-scale datasets. Semidefinite programming (SDP) relaxations are among the most powerful methods in this family and are surprisingly well suited for a broad range of problems where data take the form of matrices or graphs. It has been observed several times that when the statistical noise is small enough, SDP relaxations correctly detect the underlying combinatorial structures. In this paper we develop asymptotic predictions for several detection thresholds, as well as for the estimation error above these thresholds. We study some classical SDP relaxations for statistical problems motivated by graph synchronization and community detection in networks. We map these optimization problems to statistical mechanics models with vector spins and use nonrigorous techniques from statistical mechanics to characterize the corresponding phase transitions. Our results clarify the effectiveness of SDP relaxations in solving high-dimensional statistical problems. PMID:27001856

  16. Structural and magnetic properties of ferrimagnetic ε-phase Mn4N and antiferromagnetic ζ-phase Mn10N thin films on MgO(001)

    Science.gov (United States)

    Foley, Andrew; Corbett, Joseph; Richard, Andrea L.; Alam, Khan; Ingram, David C.; Smith, Arthur R.

    2016-07-01

    Single phase ε-Mn4N and ζ-Mn10N thin films are grown on MgO(001) using molecular beam epitaxy. The films are identified and characterized using reflection high-energy electron diffraction, x-ray diffraction, back scattered electron scanning electron microscopy, atomic/magnetic force microscopy and Rutherford backscattering spectrometry. These films are found to be highly smooth with root-mean-squared roughnesses 3.39 nm and below. The quality of ε-Mn4N grown is strongly dependent on substrate temperature during growth. Epitaxial growth of substantial grains composed of the antiferromagnetic η-phase Mn3N2 side by side with ferrimagnetic ε-phase grains is observed when growth temperature is below 480 °C. Ising domains isolated within areas roughly 0.5 μm across are observed in the ferrimagnetic ε-phase grains of samples consisting of a mix of η- and ε-phase grains. Magnetic domains following semi-continuous paths, which are 0.7-7.2 μm across, are observed in single phase ε-Mn4N. Measurements of the ζ-phase detail the structure and magnetism of the material as high Mn content γ-type ζ-phase with a regular surface corrugation along the [100]-direction and antiferromagnetic.

  17. The Structural Phase Transition in Solid DCN

    DEFF Research Database (Denmark)

    Dietrich, O. W.; Mackenzie, Gordon A.; Pawley, G. S.

    1976-01-01

    Neutron scattering measurements on deuterated hydrogen cyanide have shown that the structural phase transition from a tetragonal to an orthorhombic form at 160 K is a first order transition. A transverse acoustic phonon mode, which has the symmetry of the transition was observed at very low energ...

  18. Quantum Phase Transitions in a Finite System

    CERN Document Server

    Leviatan, A

    2006-01-01

    A general procedure for studying finite-N effects in quantum phase transitions of finite systems is presented and applied to the critical-point dynamics of nuclei undergoing a shape-phase transition of second-order (continuous), and of first-order with an arbitrary barrier.

  19. Magnetization dynamics across the first order phase transition in FeRh thin films

    Energy Technology Data Exchange (ETDEWEB)

    Pressacco, Federico

    2014-08-01

    The metallic alloy FeRh undergoes a phase transition from an antiferromagnetic phase (AFP) to a ferromagnetic phase (FP) when heated above 400 K. The change in magnetic order results in a change in the net magnetization of the system from zero up to 1.2 kA/m after increasing the system temperature. This is an uncommon characteristic for a magnetic material since usually one observes a decrease of the magnetization upon heating. This discloses the possibility to apply FeRh to Heat-Assisted Magnetic Recording (HAMR) devices.

  20. Magnetization dynamics across the first order phase transition in FeRh thin films

    OpenAIRE

    Pressacco, Federico

    2014-01-01

    The metallic alloy FeRh undergoes a phase transition from an antiferromagnetic phase (AFP) to a ferromagnetic phase (FP) when heated above 400 K. The change in the magnetic order results in a change in the net magnetization of the system from zero up to 1.2 kA/m after increasing the system temperature. This is an uncommon character for a magnetic material since usually one observes a decrease of the magnetization upon heating. This discloses the possibility to apply FeRh to Heat-Assisted Magn...

  1. Supercooling transition in phase separated manganite thin films: An electrical transport study

    Science.gov (United States)

    Singh, Sandeep; Kumar, Pawan; Siwach, P. K.; Tyagi, Pawan Kumar; Singh, H. K.

    2014-05-01

    The impact of variation in the relative fractions of the ferromagnetic metallic and antiferromagnetic/charge ordered insulator phases on the supercooling/superheating transition in strongly phase separated system, La5/8-yPryCa3/8MnO3 (y ≈ 0.4), has been studied employing magnetotransport measurements. Our study clearly shows that the supercooling transition temperature is non-unique and strongly depends on the magneto-thermodynamic path through which the low temperature state is accessed. In contrast, the superheating transition temperature remains constant. The thermo-magnetic hysteresis, the separation of the two transitions and the associated resistivity, all are functions of the relative fraction of the coexisting phases.

  2. Instability of the rhodium magnetic moment as origin of the metamagnetic phase transition in alpha-FeRh

    OpenAIRE

    Gruner, M. E.; Hoffmann, E.; Entel, P.

    2002-01-01

    Based on ab initio total energy calculations we show that two magnetic states of rhodium atoms together with competing ferromagnetic and antiferromagnetic exchange interactions are responsible for a temperature induced metamagnetic phase transition, which experimentally is observed for stoichiometric alpha-FeRh. A first-principle spin-based model allows to reproduce this first-order metamagnetic transition by means of Monte Carlo simulations. Further inclusion of spacial variation of exchange...

  3. Switchable thermal antenna by phase transition

    CERN Document Server

    Ben-Abdallah, Philippe; Besbes, Mondher

    2013-01-01

    We introduce a thermal antenna which can be actively switched by phase transition. The source makes use of periodically patterned vanadium dioxide, a metal-insulator phase transition material which supports a surface phonon-polariton (SPP) in the infrared range in its crystalline phase. Using electrodes properly registred with respect to the pattern, the phase transition of VO2 can be localy triggered within few microseconds and the SPP can be diffracted making the thermal emission highly directionnal. This switchable antenna could find broad applications in the domain of active thermal coatings or in those of infrared spectroscopy and sensing.

  4. Inhomogeneous nucleation in quark hadron phase transition

    CERN Document Server

    Shukla, P K; Sen-Gupta, S K; Gleiser, Marcello; Gleiser, Marcelo

    2000-01-01

    The effect of subcritical hadron bubbles on a first-order quark-hadron phase transition is studied. These subcritical hadron bubbles created due to thermal fluctuations introduce a finite amount of phase mixing (quark phase mixed with hadron phase) even at and above the critical temperature. For sufficiently strong transitions, as is expected to be the case for the quark-hadron transition, we show that the amount of phase mixing at the critical temperature remains much below the percolation threshold. Thus, as the system cools below the critical temperature, the transition proceeds through the nucleation of critical-size hadron bubbles from a metastable quark-gluon phase (QGP) within an inhomogeneous background populated by an equilibrium distribution of subcritical hadron bubbles. The inhomogenity of the medium is incorporated consistently by modelling the subcritical bubbles as Gaussian fluctuations, resulting in a large reduction of the nucleation barrier for the critical bubbles. Using the corrected nucle...

  5. Intersubband-transition-induced phase matching

    OpenAIRE

    Almogy, Gilad; Segev, Mordechai; Yariv, Amnon

    1994-01-01

    We suggest the use of the refractive-index changes associated with the intersubband transitions in quantum wells for phase matching in nonlinear materials. An improvement in the conversion efficiency of mid-IR second-harmonic generation by almost 2 orders of magnitude over non-phase-matched bulk GaAs is predicted. We also show that the linear phase contributions of intersubband transitions used for resonant enhancement of second-harmonic generation must be considered, as they could limit the ...

  6. Field driven phases in the geometrically frustrated dipolar Heisenberg pyrochlore antiferromagnet Gd2Ti2O7

    Science.gov (United States)

    Enjalran, Matthew; Del Maestro, Adrian; Gingras, Michel J. P.

    2008-03-01

    The rare-earth pyrochlore gadolinium titanate, Gd2Ti2O7, represents an excellent experimental realization of a Heisenberg antiferromagnet (AFM) in a frustrated geometry with weak long-range dipole-dipole interactions (approximately 20% of nearest neighbor AFM exchange). Experiments on Gd2Ti2O7 in a magnetic field reveal a complex phase diagram associated with the breaking of spatial symmetries of the pyrochlore lattice as the field is applied along select symmetry directions. We study a model of classical Heisenberg spins (O(3) symmetry) on a pyrochlore lattice with exchange and dipolar interactions within mean-field theory. Using parameters relevant to the material system, we develop phase diagrams in finite magnetic fields. Our results our compared to experiments on Gd2Ti2O7 (and Gd2Sn2O7).

  7. Pressure induced magneto-structural phase transitions in layered RMn2X2 compounds (invited)

    Science.gov (United States)

    Kennedy, Shane; Wang, Jianli; Campbell, Stewart; Hofmann, Michael; Dou, Shixue

    2014-05-01

    We have studied a range of pseudo-ternaries derived from the parent compound PrMn2Ge2, substituting for each constituent element with a smaller one to contract the lattice. This enables us to observe the magneto-elastic transitions that occur as the Mn-Mn nearest neighbour distance is reduced and to assess the role of Pr on the magnetism. Here, we report on the PrMn2Ge2-xSix, Pr1-xYxMn2Ge2, and PrMn2-xFexGe2 systems. The pressure produced by chemical substitution in these pseudo-ternaries is inherently non-uniform, with local pressure variations dependent on the local atomic distribution. We find that concentrated chemical substitution on the R or X site (e.g., in Pr0.5Y0.5Mn2Ge2 and PrMn2Ge0.8Si1.2) can produce a separation into two distinct magnetic phases, canted ferromagnetic and canted antiferromagnetic, with a commensurate phase gap in the crystalline lattice. This phase gap is a consequence of the combination of phase separation and spontaneous magnetostriction, which is positive on transition to the canted ferromagnetic phase and negative on transition to the canted antiferromagnetic phase. Our results show that co-existence of canted ferromagnetic and antiferromagnetic phases depends on chemical pressure from the rare earth and metalloid sites, on local lattice strain distributions and on applied magnetic field. We demonstrate that the effects of chemical pressure bear close resemblance to those of mechanical pressure on the parent compound.

  8. Interplay between chiral and deconfinement phase transitions

    Directory of Open Access Journals (Sweden)

    Mukherjee T.K.

    2011-04-01

    Full Text Available By using the dressed Polyakov loop or dual chiral condensate as an equivalent order parameter of the deconfinement phase transition, we investigate the relation between the chiral and deconfinement phase transitions at finite temperature and density in the framework of three-flavor Nambu-Jona-Lasinio (NJL model. It is found that in the chiral limit, the critical temperature for chiral phase transition coincides with that of the dressed Polyakov loop in the whole (T,µ plane. In the case of explicit chiral symmetry breaking, it is found that the phase transitions are flavor dependent. For each flavor, the transition temperature for chiral restoration $T^{mathcal{X}}_c$ is smaller than that of the dressed Polyakov loop $T^{mathcal{D}}_c$ in the low baryon density region where the transition is a crossover, and, the two critical temperatures coincide in the high baryon density region where the phase transition is of first order. Therefore, there are two critical end points, i.e, $T^{u,d}_{CEP}$ and $T^{s}_{CEP}$ at finite density. We also explain the feature of $T^{mathcal{X}}_c$ = $T^{mathcal{D}}_c$ in the case of 1st and 2nd order phase transitions, and $T^{mathcal{X}}_c$ < $T^{mathcal{D}}_c$ in the case of crossover, and expect this feature is general and can be extended to full QCD theory.

  9. Detection of para–antiferromagnetic transition in Bi{sub 2}Fe{sub 4}O{sub 9} powders by means of microwave absorption measurements

    Energy Technology Data Exchange (ETDEWEB)

    Alvarez, G., E-mail: memodin@yahoo.com [Escuela Superior de Física y Matemáticas del Instituto Politécnico Nacional, U.P.A.L.M, Edificio 9, Av. Instituto Politécnico Nacional S/N, San Pedro Zacatenco, México DF 07738 (Mexico); Contreras, J. [Facultad de Química de la Universidad Nacional Autónoma de México, Cd. Universitaria, México DF 04510 (Mexico); Conde-Gallardo, A. [Departamento de Física, CINVESTAV-IPN, A.P. 14-740, México DF 07360 (Mexico); Montiel, H., E-mail: herlinda_m@yahoo.com [Centro de Ciencias Aplicadas y Desarrollo Tecnológico de la Universidad Nacional Autónoma de México, Cd. Universitaria, A.P. 70-186, México DF 04510 (Mexico); Zamorano, R. [Escuela Superior de Física y Matemáticas del Instituto Politécnico Nacional, U.P.A.L.M, Edificio 9, Av. Instituto Politécnico Nacional S/N, San Pedro Zacatenco, México DF 07738 (Mexico)

    2013-12-15

    An electron paramagnetic resonance (EPR) study of Bi{sub 2}Fe{sub 4}O{sub 9} powders is carried out in X-band (8.8–9.8 GHz) and the 200–350 K temperature range. For all the temperatures, the EPR spectra show a single broad line attributable to Fe{sup 3+} (S=5/2) ions. The onset of the para–antiferromagnetic transition has been determined from the temperature dependence of the parameters deduced from EPR spectra: the peak-to-peak linewidth (ΔH{sub pp}) and the resonant field (H{sub res}); a weak ferromagnetism is also observed at low temperature and it is attributed to canting of Fe{sup 3+} ion sublattices in the antiferromagnetic matrix. The magnetically modulated microwave absorption spectroscopy (MAMMAS) and the low-field microwave absorption (LFMA) are used to give further information on this material. These techniques give evidence of the magnetic transition, suggesting a weak ferromagnetism at low temperature. - Highlights: • The changes in lineshape of the EPR spectra in Bi{sub 2}Fe{sub 4}O{sub 9} powders are studied. • The onset of the para–antiferromagnetic transition is detected. • A weak ferromagnetism is also observed in this material. • MAMMAS and LFMA techniques are used to give a further knowledge on the bismuth ferrite.

  10. Phase transitions in QCD and string theory

    International Nuclear Information System (INIS)

    We develop a unified effective field theory approach to the high-temperature phase transitions in QCD and string theory, incorporating winding modes (time-like Polyakov loops, vortices) as well as low-mass states (pseudoscalar mesons and glueballs, matter and dilaton supermultiplets). Anomalous scale invariance and the Z3 structure of the centre of SU(3) decree a first-order phase transition with simultaneous deconfinement and Polyakov loop condensation in QCD, whereas string vortex condensation is a second-order phase transition breaking a Z2 symmetry. We argue that vortex condensation is accompanied by a dilaton phase transition to a strong coupling regime, and comment on the possible role of soliton degrees of freedom in the high-temperature string phase. (orig.)

  11. Chiral Magnetic Effect and Chiral Phase Transition

    Institute of Scientific and Technical Information of China (English)

    FU Wei-Jie; LIU Yu-Xin; WU Yue-Liang

    2011-01-01

    We study the influence of the chiral phase transition on the chiral magnetic effect.The azimuthal chargeparticle correlations as functions of the temperature are calculated.It is found that there is a pronounced cusp in the correlations as the temperature reaches its critical value for the QCD phase transition.It is predicted that there will be a drastic suppression of the charge-particle correlations as the collision energy in RHIC decreases to below a critical value.We show then the azimuthal charge-particle correlations can be the signal to identify the occurrence of the QCD phase transitions in RHIC energy scan experiments.

  12. Dynamics of weak first order phase transitions

    CERN Document Server

    Gleiser, Marcello

    1994-01-01

    The dynamics of weak vs. strong first order phase transitions is investigated numerically for 2+1 dimensional scalar field models. It is argued that the change from a weak to a strong transition is itself a (second order) phase transition, with the order parameter being the equilibrium fractional population difference between the two phases at the critical temperature, and the control parameter being the coefficient of the cubic coupling in the free-energy density. The critical point is identified, and a power law controlling the relaxation dynamics at this point is obtained. Possible applications are briefly discussed.

  13. Pressure-induced transition from localized electron toward band antiferromagnetism in LaMnO(3).

    Science.gov (United States)

    Zhou, J-S; Goodenough, J B

    2002-08-19

    The temperature dependence of the ac susceptibility under pressure has been used to track the Néel temperature T(N) of the Mott insulators LaMnO3, CaMnO3, and YCrO3. Bloch's rule relating T(N) to volume V, viz., alpha=dlog(T(N)/dlog(V=-3.3, is obeyed in YCrO3 and CaMnO3; it fails in LaMnO3. This breakdown is interpreted to be due to a sharp increase in the factor [U(-1)+(2Delta)(-1)] entering the superexchange perturbation formula. A first-order change at 7 kbar indicates that the transition from localized-electron to band magnetism is not smooth.

  14. The AFM-FM phase transition in FeRh investigated using XMCD

    Energy Technology Data Exchange (ETDEWEB)

    Stamm, Christian; Duerr, Hermann A.; Eberhardt, Wolfgang [BESSY, Albert-Einstein-Str. 15, 12489 Berlin (Germany); Back, Christian [Institut fuer Experimentelle und Angewandte Physik, Universitaet Regensburg, Universitaetsstr. 31, 93040 Regensburg (Germany); Radu, Ilie [BESSY, Albert-Einstein-Str. 15, 12489 Berlin (Germany); Institut fuer Experimentelle und Angewandte Physik, Universitaet Regensburg, Universitaetsstr. 31, 93040 Regensburg (Germany); Thiele, Jan-Ulrich [Hitachi Global Storage Technologies, 3403 Yerba Buena Road, San Jose, CA 95135 (United States)

    2008-07-01

    The phase transition from antiferromagnetic to ferromagnetic ordering in FeRh is investigated in an element specific way by means of X-ray absorption spectroscopy. Dichroism sum rules allow us to determine spin and orbital moments of the two elements. Increasing the temperature from 300 to 450 Kelvin, the magnetic moments in Fe and Rh both evolve from zero to their final value, while the ratio of Rh to Fe moments stays constant. We attribute this to a coexistence of the AFM and FM phases.

  15. Elastic anomalies at the magnetic phase transitions of TbTe3

    Science.gov (United States)

    Saint-Paul, M.; Guttin, C.; Lejay, P.; Leynaud, O.; Monceau, P.

    2016-08-01

    We report sound velocity and ultrasonic attenuation measurements in the vicinity of the successive magnetic phase transitions Tmag1~6.5 K, Tmag2~5.8 K and Tmag3~5.3 K in the charge density wave TbTe3 compound. A detailed investigation of the critical contributions to the temperature dependences of the sound velocity and ultrasonic attenuation is presented. Anisotropic stress dependences ∂Tmag1 / ∂σ found at the antiferromagnetic phase transition Tmag1 is associated with the layered structure of this compound. An abrupt step-like increase in the velocity and a sharp peak in the attenuation are observed with the longitudinal and shear modes at the lock-in magnetic phase transition Tmag3=5.3 K. The critical velocity and attenuation behaviors in the high temperature paramagnetic above Tmag1 are described in terms of a phenomenological dynamic scaling expression.

  16. Electrochemical control of the phase transition of ultrathin FeRh films

    Science.gov (United States)

    Jiang, M.; Chen, X. Z.; Zhou, X. J.; Cui, B.; Yan, Y. N.; Wu, H. Q.; Pan, F.; Song, C.

    2016-05-01

    We investigate the electrical manipulation of the phase transition in ultrathin FeRh films through a combination of ionic liquid and oxide gating. The 5 nm-thick FeRh films show an antiferromagnetic-ferromagnetic transition at around 275 K with in-plane magnetic field of 70 kOe. A negative gate voltage seriously suppresses the transition temperature to ˜248 K, while a positive gate voltage does the opposite but with a smaller tuning amplitude. The formation of electric double layer associated with a large electric field induces the migration of oxygen ions between the oxide gate and the FeRh layer, producing the variation of Fe moments in antiferromagnetic FeRh accompanied by the modulation of the transition temperature. Such a modulation only occurs within several nanometers thick scale in the vicinity of FeRh surface. The reversible control of FeRh phase transition by electric field might pave the way for non-volatile memories with low power consumption.

  17. Modelling of phase transitions: do it yourself

    International Nuclear Information System (INIS)

    We present the basics of a powerful contemporary statistical mechanical technique that can be used by students to explore first-order phase transitions by themselves and for models of their own construction. The technique is a generalization of the well-known Peierls argument and is applicable to various models on a lattice. We illustrate the technique with the help of two simple models that were recently used to simulate phase transitions on surfaces. (paper)

  18. Desynchronization transitions in nonlinearly coupled phase oscillators

    OpenAIRE

    Burylko, Oleksandr; Pikovsky, Arkady

    2011-01-01

    We consider the nonlinear extension of the Kuramoto model of globally coupled phase oscillators where the phase shift in the coupling function depends on the order parameter. A bifurcation analysis of the transition from fully synchronous state to partial synchrony is performed. We demonstrate that for small ensembles it is typically mediated by stable cluster states, that disappear with creation of heteroclinic cycles, while for a larger number of oscillators a direct transition from full sy...

  19. Thin film dynamics with surfactant phase transition

    OpenAIRE

    Köpf, M. H.; Gurevich, S. V.; Friedrich, R.

    2009-01-01

    A thin liquid film covered with an insoluble surfactant in the vicinity of a first-order phase transition is discussed. Within the lubrication approximation we derive two coupled equations to describe the height profile of the film and the surfactant density. Thermodynamics of the surfactant is incorporated via a Cahn-Hilliard type free-energy functional which can be chosen to describe a transition between two stable phases of different surfactant density. Within this model, a linear stabilit...

  20. Interplay between chiral and deconfinement phase transitions

    CERN Document Server

    Xu, Fukun; Chen, Huan; Huang, Mei

    2011-01-01

    By using the dressed Polyakov loop or dual chiral condensate as an equivalent order parameter of the deconfinement phase transition, we investigate the relation between the chiral and deconfinement phase transitions at finite temperature and density in the framework of three-flavor Nambu--Jona-Lasinio (NJL) model. It is found that in the chiral limit, the critical temperature for chiral phase transition coincides with that of the dressed Polyakov loop in the whole $(T,\\mu)$ plane. In the case of explicit chiral symmetry breaking, it is found that the phase transitions are flavor dependent. For each flavor, the transition temperature for chiral restoration $T_c^{\\chi}$ is smaller than that of the dressed Polyakov loop $T_c^{{\\cal D}}$ in the low baryon density region where the transition is a crossover, and, the two critical temperatures coincide in the high baryon density region where the phase transition is of first order. Therefore, there are two critical end points, i.e, $T_{CEP}^{u,d}$ and $T_{CEP}^{s}$ a...

  1. Phase transitions in two dimensions

    International Nuclear Information System (INIS)

    Although a two-dimensional solid with long-range translational order cannot existin the thermodynamic limit (N → ∞, V →∞, N/V finite) macroscopic samples of two-dimensional solids can exist. In this work, stability of the phase was determined by the usuar method of equating the pressure and chemical potential of the phases. (A.C.A.S.)

  2. Molecular markers of phase transition in locusts

    Institute of Scientific and Technical Information of China (English)

    ARNOLD DE LOOF; ILSE CLAEYS; GERT SIMONET; PETER VERLEYEN; TIM VANDERSMISSEN; FILIP SAS; JURGEN HUYBRECHTS

    2006-01-01

    The changes accompanying the transition from the gregarious to the solitary phase state in locusts are so drastic that for a long time these phases were considered as distinct species. It was Boris Uvarov who introduced the concept of polyphenism. Decades of research revealed that phase transition implies changes in morphometry, the color of the cuticle, behavior and several aspects of physiology. In particular, in the recent decade, quite a number of molecular studies have been undertaken to uncover phase-related differences.They resulted in novel insights into the role of corazonin, neuroparsins, some protease inhibitors, phenylacetonitrile and so on. The advent of EST-databases of locusts (e.g. Kang et al., 2004) is a most encouraging novel development in physiological and behavioral locust research. Yet, the answer to the most intriguing question, namely whether or not there is a primordial molecular inducer of phase transition, is probably not within reach in the very near future.

  3. Thermal phase mixing during first order phase transitions

    CERN Document Server

    Borrill, J; Borrill, Julian; Gleiser, Marcelo

    1995-01-01

    The dynamics of first order phase transitions are studied in the context of (3+1)-dimensional scalar field theories. Particular attention is paid to the question of quantifying the strength of the transition, and how `weak' and `strong' transitions have different dynamics. We propose a model with two available low temperature phases separated by an energy barrier so that one of them becomes metastable below the critical temperature T_c. The system is initially prepared in this phase and is coupled to a thermal bath. Investigating the system at its critical temperature, we find that `strong' transitions are characterized by the system remaining localized within its initial phase, while `weak' transitions are characterized by considerable phase mixing. Always at T_c, we argue that the two regimes are themselves separated by a (second order) phase transition, with an order parameter given by the fractional population difference between the two phases and a control parameter given by the strength of the scalar fi...

  4. An absorbing phase transition from a structured active particle phase

    Energy Technology Data Exchange (ETDEWEB)

    Lopez, Cristobal [Instituto Mediterraneo de Estudios Avanzados IMEDEA (CSIC-UIB), Campus de la Universidad de las Islas Baleares, E-07122 Palma de Mallorca (Spain); Ramos, Francisco [Departamento de Electromagnetismo y Fisica de la Materia and Instituto de Fisica Teorica y Computacional Carlos I, Facultad de Ciencias, Universidad de Granada, 18071 Granada (Spain); Hernandez-GarcIa, Emilio [Instituto Mediterraneo de Estudios Avanzados IMEDEA (CSIC-UIB), Campus de la Universidad de las Islas Baleares, E-07122 Palma de Mallorca (Spain)

    2007-02-14

    In this work we study the absorbing state phase transition of a recently introduced model for interacting particles with neighbourhood-dependent reproduction rates. The novelty of the transition is that as soon as the active phase is reached by increasing a control parameter a periodically arranged structure of particle clusters appears. A numerical study in one and two dimensions shows that the system falls into the directed percolation universality class.

  5. The Structural Phase Transition in Solid DCN

    DEFF Research Database (Denmark)

    Dietrich, O. W.; Mackenzie, Gordon A.; Pawley, G. S.

    1975-01-01

    Neutron scattering measurements on deuterated hydrogen cyanide have shown that the structural phase change from a tetragonal to an orthorhombic form at 160K is a first-order transition. A transverse acoustic phonon mode, which has the symmetry of the phase change, was observed at very low energie...

  6. Numerical Study of Phase Transition in Thermoviscoelasticity

    Institute of Scientific and Technical Information of China (English)

    ShaoqingTANG

    1997-01-01

    We study the spatially periodic problem of thermoviscoelasticity with nonmonotone structure relations.By pseudo-spectral method.we demosnstrate numerically phase transitions for certain symmetric initial data.Without symmetry,the simulations show that a translation occurs for the phase boundary.

  7. Magnetic phase transitions in low dimension quantum spin systems

    International Nuclear Information System (INIS)

    In this PhD thesis, three low dimensional spin systems are studied by means of elastic and inelastic neutron scattering. Macroscopic measurements in the DMACuCl3 compound indicate the coexistence of two kinds of dimers: antiferromagnetic and ferromagnetic. The magnetic structure determined by our neutron diffraction survey at H = 0 shows irrevocably the existence of these two kinds of dimers. It has been shown that the Ising-like compound BaCo2V2O8 should be the first realization of a system in which a longitudinal spin density wave (LSDW) magnetic order occurs when a magnetic field is applied. In a first time, we have determined the magnetic structure in zero magnetic field. Then, we focused on the effect of a magnetic field on the propagation vector, showing an entrance in the LSDW phase at Hc = 3.9 T. The magnetic structure refined above this critical field confirms that BaCo2V2O8 is the first compound in which occurs a LSDW phase. In the organic compound DF5PNN, it has been shown that this compound is well described at low temperature by spin chains with alternating couplings. However, the crystallographic structure determined at room temperature implies that the interactions are uniform. By means of neutron diffraction, we characterized a structural transition at low temperature (Tc = 450 mK) making the system evolve from C2/c space group to Pc. This transition explains the alternating behavior of the interactions. We have also evidenced a field-induced structural transition (Hc = 1.1 T). Above this field, the system is back to the C2/c space group, implying that the interactions are back to uniform. We have confirmed this by studying the magnetic excitations. (author)

  8. Phase Transition in the Simplest Plasma Model

    CERN Document Server

    Iosilevskiy, Igor

    2009-01-01

    We have investigated the phase transition of the gas-liquid type, with an upper critical point, in a variant of the One Component Plasma model (OCP) that has a uniform but compressible compensating background. We have calculated the parameters of the critical and triple points, spinodals, and two-phase coexistence curves (binodals). We have analyzed the connection of this simplest plasma phase transition with anomalies in the spatial charge profiles of equilibrium non-uniform plasma in the local-density approximations of Thomas-Fermi or Poisson-Boltzmann-type.

  9. End point of the electroweak phase transition

    CERN Document Server

    Csikor, Ferenc; Heitger, J; Aoki, Y; Ukawa, A

    1999-01-01

    We study the hot electroweak phase transition (EWPT) by 4-dimensional lattice simulations on lattices with symmetric and asymmetric lattice spacings and give the phase diagram. A continuum extrapolation is done. We find first order phase transition for Higgs-boson masses $m_H<66.5 \\pm 1.4$ GeV. Above this end point a rapid cross-over occurs. Our result agrees with that of the dimensional reduction approach. It also indicates that the fermionic sector of the Standard Model (SM) may be included perturbatively. We get for the SM end point $72.4 the SM.

  10. Thermochromic phase transitions in two aromatic tetrachlorocuprates

    Science.gov (United States)

    Mostafa, M. Fareed; Abdel-Kader, M. M.; Arafat, S. S.; Kandeel, E. M.

    1991-06-01

    Bis(para-toluidinium)2 tetrachlorocuprate and bis(para-chloroanilinium)2 tetrachlorocuprate crystallize in a perovskite-related layer structure. The former crystallizes in an orthorhombic unit cell with a = 6.911 Å, b = 7.052 Å and c = 33.182 Å. It undergoes a thermochromic first order phase transition from a yellow low temperature phase to a dark orange high temperature phase at T = 300 ± 3K with a 10° thermal hysteresis. The latter compound undergoes two thermochromic transitions expressed by the relation. Orange Phase (I) rightleftarrows294 K Yellow Phase (II) rightleftarrows214K Green Phase (III). Both compounds are ferromagnetic at low temperture with exchange interactions J/k = 17.5° and 20° for the two compounds respectively.

  11. Phase transitions and entropies for synchronizing oscillators.

    Science.gov (United States)

    Bier, Martin; Lisowski, Bartosz; Gudowska-Nowak, Ewa

    2016-01-01

    We study a generic model of coupled oscillators. In the model there is competition between phase synchronization and diffusive effects. For a model with a finite number of states we derive how a phase transition occurs when the coupling parameter is varied. The phase transition is characterized by a symmetry breaking and a discontinuity in the first derivative of the order parameter. We quantitatively account for how the synchronized pulse is a low-entropy structure that facilitates the production of more entropy by the system as a whole. For a model with many states we apply a continuum approximation and derive a potential Burgers' equation for a propagating pulse. No phase transition occurs in that case. However, positive entropy production by diffusive effects still exceeds negative entropy production by the shock formation. PMID:26871059

  12. Quantum trajectory phase transitions in the micromaser.

    Science.gov (United States)

    Garrahan, Juan P; Armour, Andrew D; Lesanovsky, Igor

    2011-08-01

    We study the dynamics of the single-atom maser, or micromaser, by means of the recently introduced method of thermodynamics of quantum jump trajectories. We find that the dynamics of the micromaser displays multiple space-time phase transitions, i.e., phase transitions in ensembles of quantum jump trajectories. This rich dynamical phase structure becomes apparent when trajectories are classified by dynamical observables that quantify dynamical activity, such as the number of atoms that have changed state while traversing the cavity. The space-time transitions can be either first order or continuous, and are controlled not just by standard parameters of the micromaser but also by nonequilibrium "counting" fields. We discuss how the dynamical phase behavior relates to the better known stationary-state properties of the micromaser. PMID:21928957

  13. Phase Transition Induced Fission in Lipid Vesicles

    CERN Document Server

    Leirer, C; Myles, V M; Schneider, M F

    2010-01-01

    In this work we demonstrate how the first order phase transition in giant unilamellar vesicles (GUVs) can function as a trigger for membrane fission. When driven through their gel-fluid phase transition GUVs exhibit budding or pearl formation. These buds remain connected to the mother vesicle presumably by a small neck. Cooling these vesicles from the fluid phase (T>Tm) through the phase transition into the gel state (T

  14. Closure Phase Signatures of Planet Transit Events

    CERN Document Server

    Van Belle, G T

    2008-01-01

    Planet transit events present as attractive targets for the ultra-high-resolution capabilities afforded by optical interferometers. Herein is presented an evaluation of the possibility of detection of such events through measurement of high-precision closure phases with the MIRC instrument on the CHARA Array. Recovery of the transit position angle upon the sky appears readily achievable with the existing capabilities of the instrument, along with characterization of other system parameters, such as stellar radius, planet radius, and other parameters of the transit event. This technique is the only one presently available that can provide a transiting planet's orbital plane position angle, and can directly determine the planet's radius independent of any outside observations, appearing able to improve substantially upon other determinations of that radius. Additional directly observed parameters - also not dependent upon transit photometry or spectroscopy - include impact parameter, transit ingress time, trans...

  15. Phase Transitions in Operational Risk

    OpenAIRE

    Kartik Anand; Reimer K\\"uhn

    2006-01-01

    In this paper we explore the functional correlation approach to operational risk. We consider networks with heterogeneous a-priori conditional and unconditional failure probability. In the limit of sparse connectivity, self-consistent expressions for the dynamical evolution of order parameters are obtained. Under equilibrium conditions, expressions for the stationary states are also obtained. The consequences of the analytical theory developed are analyzed using phase diagrams. We find co-exi...

  16. Classical and quantum anisotropic Heisenberg antiferromagnets

    Directory of Open Access Journals (Sweden)

    W. Selke

    2009-01-01

    Full Text Available We study classical and quantum Heisenberg antiferromagnets with exchange anisotropy of XXZ-type and crystal field single-ion terms of quadratic and quartic form in a field. The magnets display a variety of phases, including the spin-flop (or, in the quantum case, spin-liquid and biconical (corresponding, in the quantum lattice gas description, to supersolid phases. Applying ground-state considerations, Monte Carlo and density matrix renormalization group methods, the impact of quantum effects and lattice dimension is analysed. Interesting critical and multicritical behaviour may occur at quantum and thermal phase transitions.

  17. PT phase transition in multidimensional quantum systems

    CERN Document Server

    Bender, Carl M

    2012-01-01

    Non-Hermitian PT-symmetric quantum-mechanical Hamiltonians generally exhibit a phase transition that separates two parametric regions, (i) a region of unbroken PT symmetry in which the eigenvalues are all real, and (ii) a region of broken PT symmetry in which some of the eigenvalues are complex. This transition has recently been observed experimentally in a variety of physical systems. Until now, theoretical studies of the PT phase transition have generally been limited to one-dimensional models. Here, four nontrivial coupled PT-symmetric Hamiltonians, $H=p^2/2+x^2/2+q^2/2+y^2/2+igx^2y$, $H=p^2/2+x^2/2+q^2/2+y^2+igx^2y$, $H=p^2/2+x^2/2+q^2/2+y^2/2+r^2/2+z^2/2+igxyz$, and $H=p^2/2+x^2/2+q^2/2+y^2+r^2/2+3z^2/2+igxyz$ are examined. Based on extensive numerical studies, this paper conjectures that all four models exhibit a phase transition. The transitions are found to occur at $g\\approx 0.1$, $g\\approx 0.04$, $g\\approx 0.1$, and $g\\approx 0.05$. These results suggest that the PT phase transition is a robust phen...

  18. Magnetization studies of first-order magnetostructural phase transition in polycrystalline FeRh thin films

    Science.gov (United States)

    Lu, Wei; Huang, Ping; Chen, Zhe; He, Chenchong; Wang, Yuxin; Yan, Biao

    2012-10-01

    The nucleation and growth of the transformed phase in the matrix of the original phase played an important role in the progress of magnetic transition. In spite of extensive investigations in B2 ordered FeRh alloy systems, until now few studies have been conducted for clarifying the nucleation and growth mechanism of the antiferromagnetic-ferromagnetic phase transition in FeRh alloys. In this work, B2 ordered polycrystalline FeRh thin films were fabricated on glass substrates by a sputtering technique and subsequent heat treatment. The as-deposited film shows a nonmagnetic property because of its face centred cubic structure. After annealing, the polycrystalline FeRh thin films show a clear first-order magnetostructural phase transition. The FeRh thin film shows an overall activation energy of about 228.6 kJ mol-1 for the entire first-order magnetostructural phase transition process. Results suggest that the first-order magnetostructural phase transition in ordered FeRh thin films follows the Johnson-Mehl-Avrami model with characteristic exponent n in the range 1-4, indicating that the phase transition process is a multi-step process characterized by different nucleation and growth mechanisms of the new ferromagnetic phase. The results obtained in this study will shed light on the underlying physics of the first-order magnetostructural phase transition of ordered FeRh alloys. The applicability of the concepts used in this study to the FeRh system shows universality and can be applied to other material systems where there is a first-order magnetostructural phase transition such as in manganites.

  19. Phase transitions in warm, asymmetric nuclear matter

    International Nuclear Information System (INIS)

    A relativistic mean-field model of nuclear matter with arbitrary proton fraction is studied at finite temperature. An analysis is performed of the liquid-gas phase transition in a system with two conserved charges (baryon number and isospin) using the stability conditions on the free energy, the conservation laws, and Gibbs' criteria for phase equilibrium. For a binary system with two phases, the coexistence surface (binodal) is two dimensional. The Maxwell construction through the phase-separation region is discussed, and it is shown that the stable configuration can be determined uniquely at every density. Moreover, because of the greater dimensionality of the binodal surface, the liquid-gas phase transition is continuous (second order by Ehrenfest's definition), rather than discontinuous (first order), as in familiar one-component systems. Using a mean-field equation of state calibrated to the properties of nuclear matter and finite nuclei, various phase-separation scenarios are considered. The model is then applied to the liquid-gas phase transition that may occur in the warm, dilute matter produced in energetic heavy-ion collisions. In asymmetric matter, instabilities that produce a liquid-gas phase separation arise from fluctuations in the proton concentration (chemical instability), rather than from fluctuations in the baryon density (mechanical instability)

  20. Simple explanation for the reentrant magnetic phase transition in Pr0.5Sr0.41Ca0.09MnO3 perovskite

    Indian Academy of Sciences (India)

    B T Cong; P N A Huy; N H Long; D D Long

    2003-01-01

    The reentrant magnetic phase transition in Pr0.5Sr0.41Ca0.09MnO3 perovskite is explained using the Ising spin model on the square lattice with mixed ferromagnetic and antiferromagnetic exchange interactions. It is shown using numerical calculations that this effect is strongly affected by the external magnetic field and lattice disorder.

  1. Critical behavior in the electroweak phase transition

    CERN Document Server

    Gleiser, Marcello

    1993-01-01

    We examine the behavior of the standard-model electroweak phase transition in the early Universe. We argue that close to the critical temperature it is possible to estimate the {\\it effective} infrared corrections to the 1-loop potential using well known $\\varepsilon$-expansion results from the theory of critical phenomena in 3 spatial dimensions. The theory with the $\\varepsilon$-corrected potential exhibits much larger fluctuations in the spatial correlations of the order parameter, considerably weakening the strength of the transition.

  2. Quantum phase transitions with dynamical flavors

    CERN Document Server

    Bea, Yago; Ramallo, Alfonso V

    2016-01-01

    We study the properties of a D6-brane probe in the ABJM background with smeared massless dynamical quarks in the Veneziano limit. Working at zero temperature and non-vanishing charge density, we show that the system undergoes a quantum phase transition in which the topology of the brane embedding changes from a black hole to a Minkowski embedding. In the unflavored background the phase transition is of second order and takes place when the charge density vanishes. We determine the corresponding critical exponents and show that the scaling behavior near the quantum critical point has multiplicative logarithmic corrections. In the background with dynamical quarks the phase transition is of first order and occurs at non-zero charge density. In this case we compute the discontinuity of several physical quantities as functions of the number $N_f$ of unquenched quarks of the background.

  3. The diamagnetic phase transition in Magnetars

    CERN Document Server

    Wang, Zhaojun; Zhu, Chunhua; Wu, Baoshan

    2016-01-01

    Neutron stars are ideal astrophysical laboratories for testing theories of the de Haas-van Alphen (dHvA) effect and diamagnetic phase transition which is associated with magnetic domain formation. The "magnetic interaction" between delocalized magnetic moments of electrons (the Shoenberg effect), can result in an effect of the diamagnetic phase transition into domains of alternating magnetization (Condon's domains). Associated with the domain formation are prominent magnetic field oscillation and anisotropic magnetic stress which may be large enough to fracture the crust of magnetar with a super-strong field. Even if the fracture is impossible as in "low-field" magnetar, the depinning phase transition of domain wall motion driven by low field rate (mainly due to the Hall effect) in the randomly perturbed crust can result in a catastrophically variation of magnetic field. This intermittent motion, similar to the avalanche process, makes the Hall effect be dissipative. These qualitative consequences about magne...

  4. Non-equilibrium dynamics and phase transitions

    CERN Document Server

    Janik, Romuald A; Soltanpanahi, Hesam

    2015-01-01

    We study the poles of the retarded Green's functions of strongly coupled field theories exhibiting a variety of phase structures from a crossover up to a first order phase transition. These theories are modeled by a dual gravitational description. The poles of the holographic Green's functions appear at the frequencies of the quasinormal modes of the dual black hole background. We establish that near the transition, in all cases considered, the applicability of a hydrodynamic description breaks down already at lower momenta than in the conformal case. We establish the appearance of the spinodal region in the case of the first order phase transition at temperatures for which the speed of sound squared is negative. An estimate of the preferential scale attained by the unstable modes is also given. We additionally observe a novel diffusive regime for sound modes for a range of wavelengths.

  5. Magnetization reversal of giant perpendicular magnetic anisotropy at the magnetic-phase transition in FeRh films on MgO

    Science.gov (United States)

    Odkhuu, Dorj

    2016-02-01

    Based on first-principles calculations, we demonstrate that substitutions of transition metals Ru and Ir, neighboring and same group elements in the periodic table, for the Rh site in the vicinity of surface can induce a substantially large perpendicular magnetic anisotropy (PMA), up to an order of magnitude of 20 erg /cm2 , in FeRh films on MgO. The main driving mechanism for this huge PMA is the interplay between the dx y and dx2-y2 orbital states of the substitutional 4 d and 5 d transition metal atoms with large spin-orbit coupling. Further investigations demonstrate that magnetization direction of PMA undergoes a transition into an in-plane magnetization at the antiferromagnet → ferromagnet phase transition, which provides a viable route for achieving large and switchable PMA associated with the magnetic-phase transition in antiferromagnet spintronics.

  6. Some phase transition studies under shock waves

    International Nuclear Information System (INIS)

    Experimental studies on pressure-induced phase transitions are generally conducted using both static- and shock-loading techniques. Comparison of these results is interesting as the presence of shear and high strain rate under shock compression may alter the mechanism of a transition and also its onset pressure. Recently we have carried out an gas-gun experiments to study phase transitions in GeO2, Ti and Zr. In Ti and Zr, our objective has been to understand the causes of the reported scatter in the pressure of shock induced α -> ω transition (6.0 - 11.9 GPa). Our experiments on Zr show that the initial oxygen content of the sample has a large influence on the transition pressure. For example no α to ω transition is seen up to 11 GPa in Zr samples containing oxygen concentration above 1600 ppm. Unlike that in static experiments, the effect of shear is found to be small up to 9 GPa in inclined impact experiments in Ti. The microscopic nature of the α -> ω transition in Zr has also been examined using selected area electron diffraction measurements

  7. Queueing phase transition: theory of translation

    OpenAIRE

    Romano, M. Carmen; Thiel, Marco; Stansfield, Ian; Grebogi, Celso

    2009-01-01

    We study the current of particles on a lattice, where to each site a different hopping probability has been associated and the particles can move only in one direction. We show that the queueing of the particles behind a slow site can lead to a first-order phase transition, and derive analytical expressions for the configuration of slow sites for this to happen. We apply this stochastic model to describe the translation of mRNAs. We show that the first-order phase transition, uncovered in thi...

  8. Scaling Concepts in Describing Continuous Phase Transitions

    Indian Academy of Sciences (India)

    2016-10-01

    Phase transitions, like the boiling of water upon increasingtemperature, are a part of everyday experience and are yet,upon closer inspection, unusual phenomena, and reveal a hostof fascinating features. Comprehending key aspects of phasetransitions has lead to the uncovering of new ways of describingmatter composed of large numbers of interacting elements,which form a dominant way of analysis in contemporarystatistical mechanics and much else. An introductorydiscussion is presented here of the concepts of scaling, universalityand renormalization, which forms the foundation ofthe study of continuous phase transitions, such as the spontaneousmagnetization of ferromagnetic substances.

  9. Exceptional Points and Dynamical Phase Transitions

    Directory of Open Access Journals (Sweden)

    I. Rotter

    2010-01-01

    Full Text Available In the framework of non-Hermitian quantum physics, the relation between exceptional points,dynamical phase transitions and the counter intuitive behavior of quantum systems at high level density is considered. The theoretical results obtained for open quantum systems and proven experimentally some years ago on a microwave cavity, may explain environmentally induce deffects (including dynamical phase transitions, which have been observed in various experimental studies. They also agree(qualitatively with the experimental results reported recently in PT symmetric optical lattices.

  10. Phase Transition in Loop Quantum Gravity

    OpenAIRE

    Mäkelä, Jarmo

    2016-01-01

    We point out that with a specific counting of states loop quantum gravity implies that black holes perform a phase transition at a certain characteristic temperature $T_C$. In this phase transition the punctures of the spin network on the stretched horizon of the black hole jump, in effect, from the vacuum to the excited states. The characteristic temperature $T_C$ may be regarded as the lowest possible temperature of the hole. From the point of view of a distant observer at rest with respect...

  11. Network traffic behaviour near phase transition point

    Science.gov (United States)

    Lawniczak, A. T.; Tang, X.

    2006-03-01

    We explore packet traffic dynamics in a data network model near phase transition point from free flow to congestion. The model of data network is an abstraction of the Network Layer of the OSI (Open Systems Interconnect) Reference Model of packet switching networks. The Network Layer is responsible for routing packets across the network from their sources to their destinations and for control of congestion in data networks. Using the model we investigate spatio-temporal packets traffic dynamics near the phase transition point for various network connection topologies, and static and adaptive routing algorithms. We present selected simulation results and analyze them.

  12. Phase Transition in Loop Quantum Gravity

    CERN Document Server

    Mäkelä, Jarmo

    2016-01-01

    We point out that with a specific counting of states loop quantum gravity implies that black holes perform a phase transition at a certain characteristic temperature $T_C$. In this phase transition the punctures of the spin network on the stretched horizon of the black hole jump, in effect, from the vacuum to the excited states. The characteristic temperature $T_C$ may be regarded as the lowest possible temperature of the hole. From the point of view of a distant observer at rest with respect to the hole the characteristic temperature $T_C$ corresponds to the Hawking temperature of the hole.

  13. Phase transition in loop quantum gravity

    Science.gov (United States)

    Mäkelä, Jarmo

    2016-04-01

    We point out that with a specific counting of states loop quantum gravity implies that black holes perform a phase transition at a certain characteristic temperature TC . In this phase transition the punctures of the spin network on the stretched horizon of the black hole jump, in effect, from the vacuum to the excited states. The characteristic temperature TC may be regarded as the lowest possible temperature of the hole. From the point of view of a distant observer at rest with respect to the hole, the characteristic temperature TC corresponds to the Hawking temperature of the hole.

  14. Exploring the Fragile Antiferromagnetic Superconducting Phase in CeCoIn5

    DEFF Research Database (Denmark)

    Blackburn, E.; Das, P.; Eskildsen, M.R.;

    2010-01-01

    CeCoIn5 is a heavy fermion type-II superconductor showing clear signs of Pauli-limited superconductivity. A variety of measurements give evidence for a transition at high magnetic fields inside the superconducting state, when the field is applied either parallel to or perpendicular to the c axis...

  15. PHASE TRANSITION IN SEQUENCE UNIQUE RECONSTRUCTION

    Institute of Scientific and Technical Information of China (English)

    Li XIA; Chan ZHOU

    2007-01-01

    In this paper,sequence unique reconstruction refers to the property that a sequence is uniquely reconstructable from all its K-tuples.We propose and study the phase transition behavior of the probability P(K)of unique reconstruction with regard to tuple size K in random sequences (iid model).Based on Monte Carlo experiments,artificial proteins generated from iid model exhibit a phase transition when P(K)abruptly jumps from a low value phase(e.g.<0.1)to a high value phase (e.g.>0.9).With a generalization to any alphabet,we prove that for a random sequence of length L,as L is large enough,P(K)undergoes a sharp phase transition when P≤0.1015 where p=P(two random letters match).Besides,formulas are derived to estimate the transition points,which may be of practical use in sequencing DNA by hybridization.Concluded from our study,most proteins do not deviate greatly from random sequences in the sense of sequence unique reconstruction,while there are some "stubborn" proteins which only become uniquely reconstructable at a very large K and probably have biological implications.

  16. Abrupt transition from ferromagnetic to antiferromagnetic of interfacial exchange in perpendicularly magnetized L1(0)-MnGa/FeCo tuned by Fermi level position.

    Science.gov (United States)

    Ma, Q L; Mizukami, S; Kubota, T; Zhang, X M; Ando, Y; Miyazaki, T

    2014-04-18

    An abrupt transition of the interfacial exchange coupling from ferromagnetic to antiferromagnetic was observed in the interface of perpendicularly magnetized L10-MnGa/Fe1-xCox epitaxial bilayers when x was around 25%. By considering the special band structure of the MnGa alloy, we present a model explaining this transition by the spin-polarization reversal of Fe1-xCox alloys due to the rise of the Fermi level as the Co content increases. The effect of interfacial exchange coupling on the coercive force (Hc) and the spin-dependent tunneling effect in perpendicular magnetic tunnel junctions (pMTJs) based on the coupled composite were also studied. Changes from the normal spin valve to inverted magnetoresistance loops corresponding to the coupling transition were observed in pMTJs with MnGa/Fe1-xCox as an electrode. PMID:24785068

  17. Transition to turbulence in pipe flow as a phase transition

    Science.gov (United States)

    Vasudevan, Mukund; Hof, Björn

    2015-11-01

    In pipe flow, turbulence first arises in the form of localized turbulent patches called puffs. The flow undergoes a transition to sustained turbulence via spatio-temporal intermittency, with puffs splitting, decaying and merging in the background laminar flow. However, the due to mean advection of the puffs and the long timescales involved (~107 advective time units), it is not possible to study the transition in typical laboratory set-ups. So far, it has only been possible to indirectly estimate the critical point for the transition. Here, we exploit the stochastic memoryless nature of the puff decay and splitting processes to construct a pipe flow set-up, that is periodic in a statistical sense. It then becomes possible to study the flow for sufficiently long times and characterize the transition in detail. We present measurements of the turbulent fraction as a function of Reynolds number which in turn allows a direct estimate of the critical point. We present evidence that the transition has features of a phase transition of second order.

  18. Deconfinement phase transition in neutron star matter

    Institute of Scientific and Technical Information of China (English)

    LI Ang; PENG Guang-Xiong; Lombardo U

    2009-01-01

    The transition from hadron phase to strange quark phase in dense matter is investigated. Instead of using the conventional bag model in quark sect, we achieve the confinement by a density-dependent quark mass derived from in-medium chiral condensates, with a thermodynamic problem improved. In nuclear slot,we adopt the equation of state from Brueckner-Bethe-Goldstone approach with three-body force. It is found that the mixed phase can occur, for reasonable confinement parameter, near the normal saturation density,and transit to pure quark matter at 4-5 times the saturation, which is quite different from the previous results from other quark models that pure quark phase can not appear at neutron-star densities.

  19. Magnetic Bose glass phases of coupled antiferromagnetic dimers with site dilution

    OpenAIRE

    Yu, Rong; Nohadani, Omid; Haas, Stephan; Roscilde, Tommaso

    2010-01-01

    We numerically investigate the phase diagram of two-dimensional site-diluted coupled dimer systems in an external magnetic field. We show that this phase diagram is characterized by the presence of an extended Bose glass, not accessible to mean-field approximation, and stemming from the localization of two distinct species of bosonic quasiparticles appearing in the ground state. On the one hand, non-magnetic impurities doped into the dimer-singlet phase of a weakly coupled dimer system are kn...

  20. Some neutron scattering studies on magnetic and molecular phase transitions

    International Nuclear Information System (INIS)

    In this thesis neutron-scattering investigations on two different systems are described. The first study is concerned with the magnetic ordering phenomena in pseudo two-dimensional (d = 2), two-component antiferromagnets K2Mnsub(1-x)Msub(x)F4 (M = Fe, Co), as a function of the composition x and temperature T. For one of the samples in this series, K2Musub(0.978)Fesub(0.022)F4, the influence of an external magnetic field on the ordering characteristics was studied in addition. The second study deals with the rotational motions of the NH4+ groups in NH4ZnF3 in relation with the structural phase transition at Tsub(c) = 115.1 K. The experimental techniques were chosen according to the requirements of each of these two subjects. The former study was carried out by observing the elastic magnetic neutron scattering with a double-axis diffractometer, whereas for the latter study time-of-flight (TOF) techniques were applied to observe the inelastic and quasi-elastic incoherent neutron scattering by the protons of the rotating NH4+ groups. (Auth.)

  1. Liquid gas phase transition in hypernuclei

    CERN Document Server

    Mallik, S

    2016-01-01

    The fragmentation of excited hypernuclear system formed in heavy ion collisions has been described by the canonical thermodynamical model extended to three component systems. The multiplicity distribution of the fragments has been analyzed in detail and it has been observed that the hyperons have the tendency to get attached to the heavier fragments. Another important observation is the phase coexistence of the hyperons, a phenomenon which is linked to liquid gas phase transition in strange matter.

  2. Phase transition to a commensurate magnetic structure in PrMn{sub 2}O{sub 5} oxide

    Energy Technology Data Exchange (ETDEWEB)

    Men’shenin, V. V., E-mail: menshenin@imp.uran.ru [Russian Academy of Sciences, Mikheev Institute of Metal Physics, Ural Branch (Russian Federation)

    2015-06-15

    On the basis of the experimentally obtained structure of the magnetic phase of the PrMn{sub 2}O{sub 5} oxide, it is found that in the temperature interval from 18 to 25 K, a transition to this phase should be analytically described by a two-component order parameter and that the effective Hamiltonian of the system should contain two independent fourth-order invariants with respect to the components of this parameter. With the use of the results of renormalization group analysis of phase transitions with this effective Hamiltonian, which are known from the literature, it is established that a second-order transition occurs. It is shown that the commensurate antiferromagnetic phase resulting from this transition has no electric polarization because this polarization is forbidden by the symmetry of the system.

  3. Coupled magnetic, structural, and electronic phase transitions in FeRh

    Science.gov (United States)

    Lewis, L. H.; Marrows, C. H.; Langridge, S.

    2016-08-01

    The B2-ordered intermetallic magnetic compound FeRh exhibits a thermodynamically first-order phase transition in the vicinity of room temperature that makes it a highly intriguing subject for both fundamental and applied study. On heating through the transition the magnetic character changes from antiferromagnetic to ferromagnetic order with an accompanying large increase in the electrical conductivity and an abrupt expansion in the lattice structure. Accompanying these effects is a very large entropy change comprising both magnetic and lattice contributions. As well as being driven by temperature, these coupled phase transitions may be driven by the application or removal of a magnetic field, or, because of the extremely strong lattice-spin interactions present in this compound, by an applied strain (pressure), and combinations thereof. In addition to these driving factors, the transition temperature can also be tuned by both compositional and finite size effects. Building from historical work on bulk forms of FeRh, the effects of extrinsic and intrinsic parameter variation on the coupled magnetic, structural, and electronic phase transitions are reviewed here, with special attention directed to phenomena that manifest themselves in thin films. Overall, the rich manner in which the physical properties of FeRh change at the phase transition has potential for a wide range of technological applications in areas such as thermally-assisted magnetic recording media, CFC-free magnetic cooling, sensors for energy management, and novel spintronic devices.

  4. The Structural Phase Transition in Octaflournaphtalene

    DEFF Research Database (Denmark)

    Mackenzie, Gordon A.; Arthur, J. W.; Pawley, G. S.

    1977-01-01

    The phase transition in octafluoronaphthalene has been investigated by Raman scattering and neutron powder diffraction. The weight of the experimental evidence points to a unit cell doubling in the a direction, but with no change in space group symmetry. Lattice dynamics calculations support...

  5. Supersymmetric Kosterlitz-Thouless phase transition

    International Nuclear Information System (INIS)

    Supersymmetry is introduced in the Coulomb gas, namely the statistical theory for a set of interacting vortices and antivortices. The equivalence of this theory to the supersymmetric Sine-Gordon model is established. Mean-field considerations applied to this supersymmetric Coulomb gas lead to a phase transition of the kind described by Kosterlitz and Thouless. 12 references

  6. QCD phase transition and primordial density perturbations

    CERN Document Server

    Ignatius, J; Schwarz, Dominik J.

    2000-01-01

    We analyze the effect of primordial density perturbations on the cosmic QCD phase transition. According to our results hadron bubbles nucleate at the cold perturbations. We call this mechanism inhomogeneous nucleation. We find the typical distance between bubble centers to be a few meters. This exceeds the estimates from homogeneous nucleation by two orders of magnitude. The resulting baryon inhomogeneities may affect primordial nucleosynthesis.

  7. Hysteresis in the phase transition of chocolate

    Science.gov (United States)

    Ren, Ruilong; Lu, Qunfeng; Lin, Sihua; Dong, Xiaoyan; Fu, Hao; Wu, Shaoyi; Wu, Minghe; Teng, Baohua

    2016-01-01

    We designed an experiment to reproduce the hysteresis phenomenon of chocolate appearing in the heating and cooling process, and then established a model to relate the solidification degree to the order parameter. Based on the Landau-Devonshire theory, our model gave a description of the hysteresis phenomenon in chocolate, which lays the foundations for the study of the phase transition behavior of chocolate.

  8. Neutrino Oscillation Induced by Chiral Phase Transition

    Institute of Scientific and Technical Information of China (English)

    MU Cheng-Fu; SUN Gao-Feng; ZHUANG Peng-Fei

    2009-01-01

    Electric charge neutrality provides a relationship between chiral dynamics and neutrino propagation in compact stars.Due to the sudden drop of the electron density at the first-order chiral phase transition,the oscillation for low energy neutrinos is significant and can be regarded as a signature of chiral symmetry restoration in the core of compact stars.

  9. Passive Supporters of Terrorism and Phase Transitions

    CERN Document Server

    August, Friedrich; Delitzscher, Sascha; Hiller, Gerald; Krueger, Tyll

    2010-01-01

    We discuss some social contagion processes to describe the formation and spread of radical opinions. The dynamics of opinion spread involves local threshold processes as well as mean field effects. We calculate and observe phase transitions in the dynamical variables resulting in a rapidly increasing number of passive supporters. This strongly indicates that military solutions are inappropriate.

  10. Black Hole Phase Transition in Massive Gravity

    Science.gov (United States)

    Ning, Shou-Li; Liu, Wen-Biao

    2016-07-01

    In massive gravity, some new phenomena of black hole phase transition are found. There are more than one critical points under appropriate parameter values and the Gibbs free energy near critical points also has some new properties. Moreover, the Maxwell equal area rule is also investigated and the coexistence curve of the black hole is given.

  11. Vol. 3: Statistical Physics and Phase Transitions

    International Nuclear Information System (INIS)

    Problems of modern physics and the situation with physical research in Ukraine are considered. Programme of the conference includes scientific and general problems. Its proceedings are published in 6 volumes. The papers presented in this volume refer to statistical physics and phase transition theory

  12. The transition to chaotic phase synchronization

    DEFF Research Database (Denmark)

    Mosekilde, E.; Laugesen, J. L.; Zhusubaliyev, Zh. T.

    2012-01-01

    The transition to chaotic phase synchronization for a periodically driven spiral-type chaotic oscillator is known to involve a dense set of saddle-node bifurcations. By following the synchronization transition through the cascade of period-doubling bifurcations in a forced Ro¨ssler system......, this paper describes how these saddle-node bifurcations arise and how their characteristic cyclic organisation develops. We identify the cycles that are involved in the various saddle-node bifurcations and describe how the formation of multi-layered resonance cycles in the synchronization domain is related...... varying arterial blood pressure. The paper finally discusses how an alternative transition to chaotic phase synchronization may occur in the mutual synchronization of two chaotically oscillating period-doubling systems....

  13. Finite temperature field theory and phase transitions

    International Nuclear Information System (INIS)

    These lectures review phases and phase transitions of the Standard Model, with emphasis on those aspects which are amenable to a first principle study. Model calculations and theoretical idea of practical applicability are discussed as well. Contents: 1. Overview; 2. Field Theory at Finite Temperature and Density; 3. Critical Phenomena; 4. Electroweak Interactions at Finite Temperature; 5. Thermodynamics of Four Fermions models; 6. The Phases of QCD; 7. QCD at Finite Temperature, μB = 0; 8. QCD at Finite Temperature, μB ≠ 0. (author)

  14. Phase transition to QGP matter : confined vs deconfined matter

    CERN Multimedia

    Maire, Antonin

    2015-01-01

    Simplified phase diagram of the nuclear phase transition, from the regular hadronic matter to the QGP phase. The sketch is meant to describe the transition foreseen along the temperature axis, at low baryochemical potential, µB.

  15. Phase transitions in Pareto optimal complex networks

    CERN Document Server

    Seoane, Luís F

    2015-01-01

    The organization of interactions in complex systems can be described by networks connecting different units. These graphs are useful representations of the local and global complexity of the underlying systems. The origin of their topological structure can be diverse, resulting from different mechanisms including multiplicative processes and optimization. In spatial networks or in graphs where cost constraints are at work, as it occurs in a plethora of situations from power grids to the wiring of neurons in the brain, optimization plays an important part in shaping their organization. In this paper we study network designs resulting from a Pareto optimization process, where different simultaneous constraints are the targets of selection. We analyze three variations on a problem finding phase transitions of different kinds. Distinct phases are associated to different arrangements of the connections; but the need of drastic topological changes does not determine the presence, nor the nature of the phase transit...

  16. Phase transitions in a lattice population model

    International Nuclear Information System (INIS)

    We introduce a model for a population on a lattice with diffusion and birth/death according to 2A→3A and A→Φ for a particle A. We find that the model displays a phase transition from an active to an absorbing state which is continuous in 1 + 1 dimensions and of first-order in higher dimensions in agreement with the mean field equation. For the (1 + 1)-dimensional case, we examine the critical exponents and a scaling function for the survival probability and show that it belongs to the universality class of directed percolation. In higher dimensions, we look at the first-order phase transition by plotting a histogram of the population density and use the presence of phase coexistence to find an accurate value for the critical point in 2 + 1 dimensions

  17. Magnetic phase transitions of spin-1 ultracold bosons in a cubic optical lattice

    Science.gov (United States)

    Li, Yongqiang; He, Liang; Hofstetter, Walter

    2016-03-01

    We investigate strongly correlated spin-1 ultracold bosons with antiferromagnetic interactions in a cubic optical lattice, based on bosonic dynamical mean-field theory. Rich phase diagrams of the system are mapped out at both zero and finite temperature, and in particular the existence of a spin-singlet condensate is established. Interestingly, at finite temperature, we find that the superfluid can be heated into a Mott insulator with even (odd) filling via a first- (second-) order phase transition, analogous to the Pomeranchuk effect in 3He. Moreover, for typical experimental setups, we estimate the critical temperature (entropy) for different ordered phases and our results suggest that direct experimental observation of these phases is promising.

  18. Universal space-time scaling symmetry in the dynamics of bosons across a quantum phase transition

    CERN Document Server

    Clark, Logan W; Chin, Cheng

    2016-01-01

    The dynamics of many-body systems spanning condensed matter, cosmology, and beyond is hypothesized to be universal when the systems cross continuous phase transitions. The universal dynamics is expected to satisfy a scaling symmetry of space and time with the crossing rate, inspired by the Kibble-Zurek mechanism. We test this symmetry based on Bose condensates in a shaken optical lattice. Shaking the lattice drives condensates across an effectively ferromagnetic quantum phase transition. After crossing the critical point, the condensates manifest delayed growth of spin fluctuations and develop anti-ferromagnetic spatial correlations resulting from sub-Poisson generation of topological defects. The characteristic times and lengths scale as power-laws of the crossing rate, yielding the temporal exponent 0.50(2) and the spatial exponent 0.26(2), consistent with theory. Furthermore, the fluctuations and correlations are invariant in scaled space-time coordinates, in support of the scaling symmetry of quantum crit...

  19. Ultrafast lattice dynamics in FeRh during a laser-induced magnetic phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Quirin, Florian; Vattilana, Michael; Shymanovich, Uladzimir; El-Kamhawy, Abd-Elmonien; Nicoul, Matthieu; Tarasevitch, Alexander; Linde, Dietrich von der; Sokolowski-Tinten, Klaus [Universitaet Duisburg-Essen, Duisburg (Germany)

    2011-07-01

    FeRh exhibits an anti-ferromagnetic to ferromagnetic phase transition upon heating to temperatures above 353 K, which is accompanied by an iso-structural increase in volume of about 1%. Recent results of time-resolved magneto-optical experiments gave indication that after intense optical excitation ferromagnetic order starts to build up on sub-ps time-scales. We have used time-resolved X-ray diffraction with fs X-ray pulses from a laser-produced plasma to directly follow the lattice response of FeRh after optical excitation. From experimental data obtained at different starting temperatures below and above the phase transition temperature we have to conclude that the fast changes of the magnetic properties do not lead to the corresponding structural changes as under equilibrium conditions.

  20. The comfortable driving model revisited: Traffic phases and phase transitions

    CERN Document Server

    Knorr, Florian

    2013-01-01

    We study the spatiotemporal patterns resulting from different boundary conditions for a microscopic traffic model and contrast it with empirical results. By evaluating the time series of local measurements, the local traffic states are assigned to the different traffic phases of Kerner's three-phase traffic theory. For this classification we use the rule-based FOTO-method, which provides `hard' rules for this assignment. Using this approach, our analysis shows that the model is indeed able to reproduce three qualitatively different traffic phases: free flow (F), synchronized traffic (S), and wide moving jams (J). In addition, we investigate the likelihood of transitions between the three traffic phases. We show that a transition from free flow (F) to a wide moving jam (J) often involves an intermediate transition; first from free flow F to synchronized flow S and then from synchronized flow to a wide moving jam. This is supported by the fact that the so called F->S transition (from free flow to synchronized t...

  1. Paramagnetism and antiferromagnetic interactions in single-phase Fe-implanted ZnO

    CERN Document Server

    Pereira, Lino Miguel da Costa; Correia, João Guilherme; Van Bael, M J; Temst, Kristiaan; Vantomme, André; Araújo, João Pedro

    2013-01-01

    As the intrinsic origin of the high temperature ferromagnetism often observed in wide-gap dilute magnetic semiconductors becomes increasingly debated, there is a growing need for comprehensive studies on the single-phase region of the phase diagram of these materials. Here we report on the magnetic and structural properties of Fe-doped ZnO prepared by ion implantation of ZnO single crystals. A detailed structural characterization shows that the Fe impurities substitute for Zn in ZnO in a wurtzite Zn$_{1−x}$Fe$_{x}$O phase which is coherent with the ZnO host. In addition, the density of beam-induced defects is progressively decreased by thermal annealing up to 900$^{\\circ}$C, from highly disordered after implantation to highly crystalline upon subsequent annealing. Based on a detailed analysis of the magnetometry data, we demonstrate that isolated Fe impurities occupying Zn substitutional sites behave as localized paramagnetic moments down to 2$^{\\circ}$K, irrespective of the Fe concentration and the density...

  2. The Phase Transition to Eternal Inflation

    OpenAIRE

    Creminelli, Paolo; Dubovsky, Sergei; Nicolis, Alberto; Senatore, Leonardo; Zaldarriaga, Matias

    2008-01-01

    For slow-roll inflation we study the phase transition to the eternal regime. Starting from a finite inflationary volume, we consider the volume of the universe at reheating as order parameter. We show that there exists a critical value for the classical inflaton speed, \\dot\\phi^2/H^4 = 3/(2 \\pi^2), where the probability distribution for the reheating volume undergoes a sharp transition. In particular, for sub-critical inflaton speeds all distribution moments become infinite. We show that at t...

  3. Long range anti-ferromagnetic spin model for prebiotic evolution

    Energy Technology Data Exchange (ETDEWEB)

    Nokura, Kazuo [Shonan Institute of Technology, Fujisawa 251-8511 (Japan)

    2003-11-28

    I propose and discuss a fitness function for one-dimensional binary monomer sequences of macromolecules for prebiotic evolution. The fitness function is defined by the free energy of polymers in the high temperature random coil phase. With repulsive interactions among the same kind of monomers, the free energy in the high temperature limit becomes the energy function of the one-dimensional long range anti-ferromagnetic spin model, which is shown to have a dynamical phase transition and glassy states.

  4. Long range anti-ferromagnetic spin model for prebiotic evolution

    International Nuclear Information System (INIS)

    I propose and discuss a fitness function for one-dimensional binary monomer sequences of macromolecules for prebiotic evolution. The fitness function is defined by the free energy of polymers in the high temperature random coil phase. With repulsive interactions among the same kind of monomers, the free energy in the high temperature limit becomes the energy function of the one-dimensional long range anti-ferromagnetic spin model, which is shown to have a dynamical phase transition and glassy states

  5. Phase transitions in Pareto optimal complex networks.

    Science.gov (United States)

    Seoane, Luís F; Solé, Ricard

    2015-09-01

    The organization of interactions in complex systems can be described by networks connecting different units. These graphs are useful representations of the local and global complexity of the underlying systems. The origin of their topological structure can be diverse, resulting from different mechanisms including multiplicative processes and optimization. In spatial networks or in graphs where cost constraints are at work, as it occurs in a plethora of situations from power grids to the wiring of neurons in the brain, optimization plays an important part in shaping their organization. In this paper we study network designs resulting from a Pareto optimization process, where different simultaneous constraints are the targets of selection. We analyze three variations on a problem, finding phase transitions of different kinds. Distinct phases are associated with different arrangements of the connections, but the need of drastic topological changes does not determine the presence or the nature of the phase transitions encountered. Instead, the functions under optimization do play a determinant role. This reinforces the view that phase transitions do not arise from intrinsic properties of a system alone, but from the interplay of that system with its external constraints.

  6. Low-temperature specific heat of YMn{sub 2} in the paramagnetic and antiferromagnetic phases

    Energy Technology Data Exchange (ETDEWEB)

    Fisher, R.A.; Emerson, J.P.; Phillips, N.E. [Lawrence Berkeley Lab., CA (United States); Ballou, R.; Lelievre-Berna, E. [Centre National de la Recherche Scientifique (CNRS), 38 - Grenoble (France). Lab. Louis Neel

    1992-07-01

    The low-temperature specific heat of YMn{sub 2} has been measured at applied pressures of 0 to 7.7 kbar. A paramagnetic state is stabilized for moderate values of the applied pressure (of the order of 1.6 kbar). A large linear term in the specific heat, which decreases regularly with increasing pressure, is observed in this phase. It is ascribed to giant spin fluctuations associated with a magnetic-non magnetic instability and a strong geometrical spin frustration.

  7. Low-temperature specific heat of YMn sub 2 in the paramagnetic and antiferromagnetic phases

    Energy Technology Data Exchange (ETDEWEB)

    Fisher, R.A.; Emerson, J.P.; Phillips, N.E. (Lawrence Berkeley Lab., CA (United States)); Ballou, R.; Lelievre-Berna, E. (Centre National de la Recherche Scientifique (CNRS), 38 - Grenoble (France). Lab. Louis Neel)

    1992-07-01

    The low-temperature specific heat of YMn{sub 2} has been measured at applied pressures of 0 to 7.7 kbar. A paramagnetic state is stabilized for moderate values of the applied pressure (of the order of 1.6 kbar). A large linear term in the specific heat, which decreases regularly with increasing pressure, is observed in this phase. It is ascribed to giant spin fluctuations associated with a magnetic-non magnetic instability and a strong geometrical spin frustration.

  8. Hydrogenation-controlled phase transition on two-dimensional transition metal dichalcogenides and their unique physical and catalytic properties

    Science.gov (United States)

    Qu, Yuanju; Pan, Hui; Kwok, Chi Tat

    2016-09-01

    Two-dimensional (2D) transition metal dichalcogenides (TMDs) have been widely used from nanodevices to energy harvesting/storage because of their tunable physical and chemical properties. In this work, we systematically investigate the effects of hydrogenation on the structural, electronic, magnetic, and catalytic properties of 33 TMDs based on first-principles calculations. We find that the stable phases of TMD monolayers can transit from 1T to 2H phase or vice versa upon the hydrogenation. We show that the hydrogenation can switch their magnetic and electronic states accompanying with the phase transition. The hydrogenation can tune the magnetic states of TMDs among non-, ferro, para-, and antiferro-magnetism and their electronic states among semiconductor, metal, and half-metal. We further show that, out of 33 TMD monolayers, 2H-TiS2 has impressive catalytic ability comparable to Pt in hydrogen evolution reaction in a wide range of hydrogen coverages. Our findings would shed the light on the multi-functional applications of TMDs.

  9. Hydrogenation-controlled phase transition on two-dimensional transition metal dichalcogenides and their unique physical and catalytic properties

    Science.gov (United States)

    Qu, Yuanju; Pan, Hui; Kwok, Chi Tat

    2016-01-01

    Two-dimensional (2D) transition metal dichalcogenides (TMDs) have been widely used from nanodevices to energy harvesting/storage because of their tunable physical and chemical properties. In this work, we systematically investigate the effects of hydrogenation on the structural, electronic, magnetic, and catalytic properties of 33 TMDs based on first-principles calculations. We find that the stable phases of TMD monolayers can transit from 1T to 2H phase or vice versa upon the hydrogenation. We show that the hydrogenation can switch their magnetic and electronic states accompanying with the phase transition. The hydrogenation can tune the magnetic states of TMDs among non-, ferro, para-, and antiferro-magnetism and their electronic states among semiconductor, metal, and half-metal. We further show that, out of 33 TMD monolayers, 2H-TiS2 has impressive catalytic ability comparable to Pt in hydrogen evolution reaction in a wide range of hydrogen coverages. Our findings would shed the light on the multi-functional applications of TMDs. PMID:27686869

  10. Thermalon mediated phase transitions in Gauss-Bonnet gravity

    CERN Document Server

    Hennigar, Robie A; Mbarek, Saoussen

    2015-01-01

    Thermalons can mediate phase transitions between different vacua in higher curvature gravity, potentially changing the asymptotic structure of the spacetime. Treating the cosmological constant as a dynamical parameter, we study these phase transitions in the context of extended thermodynamic phase space. We find that in addition to the AdS to dS phase transitions previously studied, thermal AdS space can undergo a phase transition to an asymptotically flat black hole geometry. In the context of AdS to AdS transitions, we comment on the similarities and differences between thermalon transitions and the Hawking-Page transition.

  11. Phase Transitions in Models of Bird Flocking

    CERN Document Server

    Christodoulidi, H; Bountis, T

    2013-01-01

    The aim of the present paper is to elucidate the transition from collective to random behavior exhibited by various mathematical models of bird flocking. In particular, we compare Vicsek's model [Viscek et al., Phys. Rev. Lett. 75, 1226 -- 1229 (1995)] with one based on topological considerations. The latter model is found to exhibit a first order phase transition from flocking to decoherence, as the 'noise parameter' of the problem is increased, whereas Viscek's model gives a second order transition. Refining the topological model in such a way that birds are influenced mostly by the birds in front of them, less by the ones at their sides and not at all by those behind them (because they do not see them), we find a behavior that lies in between the two models. Finally, we propose a novel mechanism for preserving the flock's cohesion, without imposing artificial boundary conditions or attracting forces.

  12. The Next Generation Transit Survey - Prototyping Phase

    CERN Document Server

    McCormac, James; Wheatley, Peter; West, Richard; Walker, Simon; Bento, Joao; Skillen, Ian; Faedi, Francesca; Burleigh, Matt; Casewell, Sarah; Chazelas, Bruno; Genolet, Ludovic; Gibson, Neale; Goad, Mike; Lawrie, Katherine; Ryans, Robert; Todd, Ian; Udry, Stephan; Watson, Christopher

    2016-01-01

    We present the prototype telescope for the Next Generation Transit Survey, which was built in the UK in 2008/09 and tested on La Palma in the Canary Islands in 2010. The goals for the prototype system were severalfold: to determine the level of systematic noise in an NGTS-like system; demonstrate that we can perform photometry at the (sub) millimagnitude level on transit timescales across a wide field; show that it is possible to detect transiting super-Earth and Neptune-sized exoplanets and prove the technical feasibility of the proposed planet survey. We tested the system for around 100 nights and met each of the goals above. Several key areas for improvement were highlighted during the prototyping phase. They have been subsequently addressed in the final NGTS facility which was recently commissioned at ESO Cerro Paranal, Chile.

  13. Effects of gauge boson mass on chiral and deconfinement phase transitions in QED$_{3}$

    CERN Document Server

    Yin, Pei-Lin; Feng, Hong-Tao; Zong, Hong-Shi

    2016-01-01

    Based on the experimental observation that there is a coexisting region between the antiferromagnetic (AF) and $\\textit{d}$-wave superconducting ($\\textit{d}$SC) phases, the influences of gauge boson mass $m_{a}$ on chiral symmetry restoration and deconfinement phase transitions in QED$_{3}$ are investigated simultaneously within a unified framework, i.e., Dyson-Schwinger equations. The results show that the chiral symmetry restoration phase transition in the presence of the gauge boson mass $m_{a}$ is a typical second-order phase transition; the chiral symmetry restoration and deconfinement phase transitions are coincident; the critical number of fermion flavors $N^{c}_{f}$ decreases as the gauge boson mass $m_{a}$ increases and there exists a boundary that separates the $N^{c}_{f}$-$m_{a}$ plane into chiral symmetry breaking/confinement region for ($N_{f}^{c}$, $m_{a}$) below the boundary and chiral symmetry restoration/deconfinement region for ($N_{f}^{c}$, $m_{a}$) above it.

  14. A nonequilibrium phase transition in immune response

    Institute of Scientific and Technical Information of China (English)

    Zhang Wei; Qi An-Shen

    2004-01-01

    The dynamics of immune response correlated to signal transduction in immune thymic cells (T cells) is studied.In particular, the problem of the phosphorylation of the immune-receptor tyrosine-based activation motifs (ITAM) is explored. A nonlinear model is established on the basis of experimental observations. The behaviours of the model can be well analysed using the concepts of nonequilibrium phase transitions. In addition, the Riemann-Hugoniot cusp catastrophe is demonstrated by the model. Due to the application of the theory of nonequilibrium phase transitions,the biological phenomena can be clarified more precisely. The results can also be used to further explain the signal transduction and signal discrimination of an important type of immune T cell.

  15. Nonequilibrium phase transitions in biomolecular signal transduction

    Science.gov (United States)

    Smith, Eric; Krishnamurthy, Supriya; Fontana, Walter; Krakauer, David

    2011-11-01

    We study a mechanism for reliable switching in biomolecular signal-transduction cascades. Steady bistable states are created by system-size cooperative effects in populations of proteins, in spite of the fact that the phosphorylation-state transitions of any molecule, by means of which the switch is implemented, are highly stochastic. The emergence of switching is a nonequilibrium phase transition in an energetically driven, dissipative system described by a master equation. We use operator and functional integral methods from reaction-diffusion theory to solve for the phase structure, noise spectrum, and escape trajectories and first-passage times of a class of minimal models of switches, showing how all critical properties for switch behavior can be computed within a unified framework.

  16. Phase transitions: An overview with a view

    Energy Technology Data Exchange (ETDEWEB)

    Gleiser, M. [Dartmouth Coll., Hanover, NH (United States)

    1997-10-01

    The dynamics of phase transitions plays a crucial role in the so- called interface between high energy particle physics and cosmology. Many of the interesting results generated during the last fifteen years or so rely on simplified assumptions concerning the complex mechanisms typical of nonequilibrium field theories. After reviewing well-known results concerning the dynamics of first and second order phase transitions, I argue that much is yet to be understood, in particular in situations where homogeneous nucleation theory does not apply. I present a method to deal with departures from homogeneous nucleation, and compare its efficacy with numerical simulations. Finally, I discuss the interesting problem of matching numerical simulations of stochastic field theories with continuum models.

  17. Extracellular ice phase transitions in insects.

    Science.gov (United States)

    Hawes, T C

    2014-01-01

    At temperatures below their temperature of crystallization (Tc), the extracellular body fluids of insects undergo a phase transition from liquid to solid. Insects that survive the transition to equilibrium (complete freezing of the body fluids) are designated as freeze tolerant. Although this phenomenon has been reported and described in many Insecta, current nomenclature and theory does not clearly delineate between the process of transition (freezing) and the final solid phase itself (the frozen state). Thus freeze tolerant insects are currently, by convention, described in terms of the temperature at which the crystallization of their body fluids is initiated, Tc. In fact, the correct descriptor for insects that tolerate freezing is the temperature of equilibrium freezing, Tef. The process of freezing is itself a separate physical event with unique physiological stresses that are associated with ice growth. Correspondingly there are a number of insects whose physiological cryo-limits are very specifically delineated by this transitional envelope. The distinction also has considerable significance for our understanding of insect cryobiology: firstly, because the ability to manage endogenous ice growth is a fundamental segregator of cryotype; and secondly, because our understanding of internal ice management is still largely nascent.

  18. Quantum Phase Transitions in the BKL Universe

    CERN Document Server

    D'Odorico, Giulio

    2015-01-01

    We study quantum corrections to the classical Bianchi I and Bianchi IX universes. The modified dynamics is well-motivated from the asymptotic safety program where the short-distance behavior of gravity is governed by a non-trivial renormalization group fixed point. The correction terms induce a phase transition in the dynamics of the model, changing the classical, chaotic Kasner oscillations into a uniform approach to a point singularity. The resulting implications for the microscopic structure of spacetime are discussed.

  19. Phase transitions in Nowak Sznajd opinion dynamics

    Science.gov (United States)

    Wołoszyn, Maciej; Stauffer, Dietrich; Kułakowski, Krzysztof

    2007-05-01

    The Nowak modification of the Sznajd opinion dynamics model on the square lattice assumes that with probability β the opinions flip due to mass-media advertising from down to up, and vice versa. Besides, with probability α the Sznajd rule applies that a neighbour pair agreeing in its two opinions convinces all its six neighbours of that opinion. Our Monte Carlo simulations and mean-field theory find sharp phase transitions in the parameter space.

  20. Unprovability and phase transitions in Ramsey theory

    OpenAIRE

    De Smet, Michiel

    2011-01-01

    The first mathematically interesting, first-order arithmetical example of incompleteness was given in the late seventies and is know as the Paris-Harrington principle. It is a strengthened form of the finite Ramsey theorem which can not be proved, nor refuted in Peano Arithmetic. In this dissertation we investigate several other unprovable statements of Ramseyan nature and determine the threshold functions for the related phase transitions. Chapter 1 sketches out the historical development...

  1. Quantum phase transitions in constrained Bose systems

    OpenAIRE

    Bonnes, Lars

    2011-01-01

    This doctoral thesis studies low dimensional quantum systems that can be realized in recent cold atom experiments. From the viewpoint of quantum statistical mechanics, the main emphasis is on the detailed study of the different quantum and thermal phases and their transitions using numerical methods, such as quantum Monte Carlo and the Tensor Network Renormalization Group. The first part of this work deals with a lattice Boson model subject to strong three-body losses. In a quantum-Zeno li...

  2. Chirality effects on 2D phase transitions

    DEFF Research Database (Denmark)

    Scalas, E.; Brezesinski, G.; Möhwald, H.;

    1996-01-01

    investigated pressures. However, at both temperatures, there is a sharp phase transition from a low-pressure phase, in which the molecules are tilted towards nearest neighbours (NN) and the distortion azimuth also points towards NN, to a high-pressure phase, in which the molecules are tilted towards next......Monolayers of the racemate and pure enantiomers of 1-hexadecyl-glycerol were investigated by grazing incidence X-ray diffraction (GID) at 5 and 20 degrees C on compression from 0 mN m(-1) to pressures greater than 30 mN m(-1). The racemate Lattice is centred-rectangular for both temperatures at all......-nearest neighbours (NNN) and an NNN-distorted lattice is observed. At 5 degrees C, the transition pressure is 15 mN m(-1), whereas at 20 degrees C it is 18 mN m(-1). Chirality destroys this transition: the pure enantiomer always exhibits an oblique lattice with tilted molecules, and the azimuths of tilt...

  3. Phase Transitions in Model Active Systems

    Science.gov (United States)

    Redner, Gabriel S.

    The amazing collective behaviors of active systems such as bird flocks, schools of fish, and colonies of microorganisms have long amazed scientists and laypeople alike. Understanding the physics of such systems is challenging due to their far-from-equilibrium dynamics, as well as the extreme diversity in their ingredients, relevant time- and length-scales, and emergent phenomenology. To make progress, one can categorize active systems by the symmetries of their constituent particles, as well as how activity is expressed. In this work, we examine two categories of active systems, and explore their phase behavior in detail. First, we study systems of self-propelled spherical particles moving in two dimensions. Despite the absence of an aligning interaction, this system displays complex emergent dynamics, including phase separation into a dense active solid and dilute gas. Using simulations and analytic modeling, we quantify the phase diagram and separation kinetics. We show that this nonequilibrium phase transition is analogous to an equilibrium vapor-liquid system, with binodal and spinodal curves and a critical point. We also characterize the dense active solid phase, a unique material which exhibits the structural signatures of a crystalline solid near the crystal-hexatic transition point, as well as anomalous dynamics including superdiffusive motion on intermediate timescales. We also explore the role of interparticle attraction in this system. We demonstrate that attraction drastically changes the phase diagram, which contains two distinct phase-separated regions and is reentrant as a function of propulsion speed. We interpret this complex situation with a simple kinetic model, which builds from the observed microdynamics of individual particles to a full description of the macroscopic phase behavior. We also study active nematics, liquid crystals driven out of equilibrium by energy-dissipating active stresses. The equilibrium nematic state is unstable in these

  4. On Dynamical Systems and Phase Transitions for q + 1-state p-adic Potts Model on the Cayley Tree

    Energy Technology Data Exchange (ETDEWEB)

    Mukhamedov, Farrukh, E-mail: far75m@yandex.ru [International Islamic University Malaysia, Department of Computational and Theoretical Sciences, Faculty of Science (Malaysia)

    2013-03-15

    In the present paper, we study a new kind of p-adic measures for q + 1-state Potts model, called p-adic quasi Gibbs measure. For such a model, we derive a recursive relations with respect to boundary conditions. Note that we consider two mode of interactions: ferromagnetic and antiferromagnetic. In both cases, we investigate a phase transition phenomena from the associated dynamical system point of view. Namely, using the derived recursive relations we define a fractional p-adic dynamical system. In ferromagnetic case, we establish that if q is divisible by p, then such a dynamical system has two repelling and one attractive fixed points. We find basin of attraction of the fixed point. This allows us to describe all solutions of the nonlinear recursive equations. Moreover, in that case there exists the strong phase transition. If q is not divisible by p, then the fixed points are neutral, and this yields that the existence of the quasi phase transition. In antiferromagnetic case, there are two attractive fixed points, and we find basins of attraction of both fixed points, and describe solutions of the nonlinear recursive equation. In this case, we prove the existence of a quasi phase transition.

  5. Effect of Carbon on the Paramagnetic-Antiferromagnetic Transition and γ→ε Martensitic Transformation of Fe-24Mn Alloys

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The effect of C content (0.014~0.39 wt pct) on the paramagnetic-antiferromagnetic transition and γ -→ ε martensitic transformation of Fe-24Mn alloys has been investigated by the resistivity,dilation, tensile properties measurement and microstructure examination. The results have shown that C decreases TN; increases the thermal expansion coefficients both above and below the TN; increases the resistivity above the TN and antiferromagnetic scattering resistivity below TN. It strongly depresses the γ→ε martensitic transformation and reduces the Ms of Fe-24Mn alloys.Moreover, it increases the lattice parameter of austenite, enhances the tensile ductility, but almost does not affect the tensile strength. With increasing C content from 0.014 to 0.19 wt pct, theyield strength of Fe-24Mn alloy decreases obviously arising from the decreasing of preexisting εmartensite, but it increases from 0.19 to 0.39 wt pct C due to the solution hardening of C.

  6. Capturing the Magnetic and Structural Phase Transition of Ferh using Extreme Ultraviolet Light

    Science.gov (United States)

    Zusin, Dmitriy; Grychtol, Patrik; Gentry, Christian; Murnane, Margaret; Kapteyn, Henry; Canton, Sophie; Knut, Ronny; Shaw, Justin; Nembach, Hans; Silva, Thomas; Ceballos, Alejandro; Bordel, Catherine; Fischer, Peter; Hellman, Frances

    2015-03-01

    The temperature dependent transition from the anti-ferromagnetic to the ferromagnetic phase in FeRh is accompanied by a modification of its crystal lattice. The interplay between the magnetic and the structural transition is a matter of strong debate. It is important to better understand the mechanism(s) of the transition since it can be induced by femtosecond laser pulses and, unlike slower (nanosecond) magnetic phase transitions, does not seem to be limited by heat transfer. In this work, we use extreme ultraviolet light generated by a tabletop high harmonics source to perform element-selective investigations of the temperature-dependent magneto-optical response of a thin film FeRh sample. We study the optically induced phase transition using two ultrafast pump-probe spectroscopy approaches: by monitoring the time-resolved transversal magneto-optical Kerr effect (T-MOKE) and the transient change in reflectivity. PF acknowledges support from BES MSD DOE # DE-AC02-05-CH11231 and LFRIR program (# 2012K1A4A3053565) through NRF Korea funded by MEST, and JILA from DOE # DE-FG02-09ER4665.

  7. Berry Phases, Quantum Phase Transitions and Chern Numbers

    OpenAIRE

    Contreras, H. A.; Reyes-Lega, A. F.

    2007-01-01

    We study the relation between Chern numbers and Quantum Phase Transitions (QPT) in the XY spin-chain model. By coupling the spin chain to a single spin, it is possible to study topological invariants associated to the coupling Hamiltonian. These invariants contain global information, in addition to the usual one (obtained by integrating the Berry connection around a closed loop). We compute these invariants (Chern numbers) and discuss their relation to QPT. In particular we show that Chern nu...

  8. Stability and Existence of Multidimensional Subsonic Phase Transitions

    Institute of Scientific and Technical Information of China (English)

    Ya-Guang Wang; Zhouping Xin

    2003-01-01

    The purpose of this paper is to prove the uniform stability of multidimensional subsonic phase transitions satisfying the viscosity-capillarity criterion in a van der Waals fluid, and further to establish the local existence of phase transition solutions.

  9. Phase transitions of ε-HNIW in compound systems

    Directory of Open Access Journals (Sweden)

    Jing-yuan Zhang

    2016-05-01

    Full Text Available The heat-induced phase transitions of ε-HNIW, both neat and coated with various additives used in plastic bonded explosives, were investigated using powder X-ray diffraction and differential scanning calorimetry. It was found that ε-HNIW, after being held at 70°C for 60h, remained in the ε-phase. Applying other conditions, various phase transition parameters were determined, including Tc (the critical phase transition temperature, T50 (the temperature at which 50% of the phase transition is complete and T180 (the percentage of γ-HNIW present in samples heated to 180°C. According to the above three parameters, additives were divided into three categories: those that delay phase transition, those that raise the critical temperature and the transition rate, and those that promote the phase transition. Based on the above data, a phase transition mechanism is proposed.

  10. Phase transitions and dark matter problems

    International Nuclear Information System (INIS)

    The possible relationships between phase transitions in the early universe and dark matter problems are discussed. It is shown that there are at least 3 distinct cosmological dark matter problems 1) halos; 2) galaxy formation and clustering; and 3) Ω = 1, each emphasizing different attributes for the dark matter. At least some of the dark matter must by baryonic but if problems 2 and 3 are real they seem to also require non-baryonic material. However, if seeds are generated at the quark-hadron-chiral symmetry transition then alternatives to the standard scenarios may occur. At present no simple simultaneous solution (neither ''hot'', ''warm'', nor ''cold'') exists for all 3 problems, but non-standard solutions with strings, decaying particles or light not tracing to mass may work. An alternative interpretation of the relationship of the cluster-cluster and galaxy-galaxy correlation functions using renormalized scaling is mentioned. In this interpretation galaxies are more strongly correlated and the cluster-cluster function is not expected to go negative until > or approx. 200 Mpc. Possible phase transition origins for the cluster-cluster renormalized scale are presented as ways to obtain a dimension 1.2 fractal. (orig.)

  11. Holography and the Electroweak Phase Transition

    CERN Document Server

    Creminelli, P; Rattazzi, Riccardo; Creminelli, Paolo; Nicolis, Alberto; Rattazzi, Riccardo

    2002-01-01

    We study through holography the compact Randall-Sundrum (RS) model at finite temperature. In the presence of radius stabilization, the system is described at low enough temperature by the RS solution. At high temperature it is described by the AdS-Schwarzshild solution with an event horizon replacing the TeV brane. We calculate the transition temperature T_c between the two phases and we find it to be somewhat smaller than the TeV scale. Assuming that the Universe starts out at T >> T_c and cools down by expansion, we study the rate of the transition to the RS phase. We find that the transition is too slow and the Universe ends up in an old inflation scenario unless tight bounds are satisfied by the model parameters. In particular we find that the AdS curvature must be comparable to the 5D Planck mass and that the radius stabilization mechanism must lead to a sizeable distortion of the basic RS metric.

  12. Second-order phase transitions of pure substances

    NARCIS (Netherlands)

    Schaftenaar, H.P.C.

    2009-01-01

    In this report we are dealing with the thermodynamic theory of second-order phase transitions or continuous transitions of unary systems. The first classification of these phase transitions is due to Ehrenfest (1933), based on chemical potentials. First-order transitions are changes in which the der

  13. Phase transitions in systems of magnetic dipoles on a square lattice with quenched disorder

    Energy Technology Data Exchange (ETDEWEB)

    Alonso, Juan J., E-mail: jjalonso@uma.e [Departamento de Fisica Aplicada I, Universidad de Malaga, 29071-Malaga (Spain)

    2010-05-15

    We study by Monte Carlo simulations the effect of quenched orientational disorder in systems of interacting classical dipoles on a square lattice. Each dipole can lie along any of the two perpendicular axes that form an angle psi with the principal axes of the lattice. We choose psi at random and without bias from the interval [-DELTA,DELTA] for each site of the lattice. For 0<=DELTA<=pi/4 we find a thermally driven second order transition between a paramagnetic and a dipolar antiferromagnetic order phase and critical exponents that change continuously with DELTA. Near the case of maximum disorder DELTAapproxpi/4 we still find a second order transition at a finite temperature T{sub c} but our results point to weak instead of strong long-ranged dipolar order for temperatures below T{sub c}.

  14. Magnetic and Ising quantum phase transitions in a model for isoelectronically tuned iron pnictides

    Science.gov (United States)

    Wu, Jianda; Si, Qimiao; Abrahams, Elihu

    2016-03-01

    Considerations of the observed bad-metal behavior in Fe-based superconductors led to an early proposal for quantum criticality induced by isoelectronic P for As doping in iron arsenides, which has since been experimentally confirmed. We study here an effective model for the isoelectronically tuned pnictides using a large-N approach. The model contains antiferromagnetic and Ising-nematic order parameters appropriate for J1-J2 exchange-coupled local moments on an Fe square lattice, and a damping caused by coupling to itinerant electrons. The zero-temperature magnetic and Ising transitions are concurrent and essentially continuous. The order-parameter jumps are very small, and are further reduced by the interplane coupling; consequently, quantum criticality occurs over a wide dynamical range. Our results reconcile recent seemingly contradictory experimental observations concerning the quantum phase transition in the P-doped iron arsenides.

  15. Diffraction studies of ordered phases and phase transitions

    International Nuclear Information System (INIS)

    Two investigations are reported here. First, monolayers of CF4 physisorbed on the (001) face of graphite have been studied by means of X-ray diffraction experiments carried out at the electron storage ring DORIS in Hamburg. The exfoliated graphite substrate UCAR-ZYX was used in order to obtain a large area for adsorption and hence a large sample. Four two-dimensional solid phases of the CF4 films were seen, including a structure which is 2x2 commensurate relative to the substrate. On compression (by variation of coverage or temperature), this phase transforms to a uniaxially compressed structure ('stripe' phase). Further, at higher coverages a hexagonal structure was seen, incommensurate relative to the substrate, and at low temperatures and coverages, a complicated structure emerged, giving three close diffraction peaks in the powder pattern. Data are presented characterizing the meltings and commensurate to incommensurate transitions. Complementary to the synchrotron X-ray data, a presentation of the theory of synchrotron radiation is given. The second investigation was of the ferromagnetic phase transitions in the randomly diluted, dipolar coupled uniaxial ferromagnets LiTbsub(.3)Ysub(.7)F4 and LiHosub(.3)Ysub(.7)F4 by neutron diffraction at the RIS0 DR 3 reactor. (orig.)

  16. Phase transition in SONFIS&SORST

    CERN Document Server

    Owladeghaffari, Hamed

    2008-01-01

    In this study, we introduce general frame of MAny Connected Intelligent Particles Systems (MACIPS). Connections and interconnections between particles get a complex behavior of such merely simple system (system in system).Contribution of natural computing, under information granulation theory, are the main topics of this spacious skeleton. Upon this clue, we organize two algorithms involved a few prominent intelligent computing and approximate reasoning methods: self organizing feature map (SOM), Neuro- Fuzzy Inference System and Rough Set Theory (RST). Over this, we show how our algorithms can be taken as a linkage of government-society interaction, where government catches various fashions of behavior: solid (absolute) or flexible. So, transition of such society, by changing of connectivity parameters (noise) from order to disorder is inferred. Add to this, one may find an indirect mapping among finical systems and eventual market fluctuations with MACIPS. Keywords: phase transition, SONFIS, SORST, many con...

  17. Collective flow and QCD phase transition

    CERN Document Server

    Sorge, H

    1999-01-01

    In the first part I discuss the sensitivity of collective matter expansion in ultrarelativistic heavy-ion collisions to the transition between quark and hadronic matter (physics of the softest point of the Equation of State). A kink in the centrality dependence of elliptic flow has been suggested as a signature for the phase transition in hot QCD matter. Indeed, preliminary data of NA49 presented at this conference show first indications for the predicted kink. In the second part I have a look at the present theories of heavy-ion reactions. These remarks may also be seen as a critical comment to B. Mueller's summary talk (nucl-th/9906029) presented at this conference.

  18. Locating phase transitions in computationally hard problems

    Indian Academy of Sciences (India)

    B Ashok; T K Patra

    2010-09-01

    We discuss how phase-transitions may be detected in computationally hard problems in the context of anytime algorithms. Treating the computational time, value and utility functions involved in the search results in analogy with quantities in statistical physics, we indicate how the onset of a computationally hard regime can be detected and the transit to higher quality solutions be quantified by an appropriate response function. The existence of a dynamical critical exponent is shown, enabling one to predict the onset of critical slowing down, rather than finding it after the event, in the specific case of a travelling salesman problem (TSP). This can be used as a means of improving efficiency and speed in searches, and avoiding needless computations.

  19. Phase transitions in paradigm shift models.

    Directory of Open Access Journals (Sweden)

    Huiseung Chae

    Full Text Available Two general models for paradigm shifts, deterministic propagation model (DM and stochastic propagation model (SM, are proposed to describe paradigm shifts and the adoption of new technological levels. By defining the order parameter m based on the diversity of ideas, Δ, it is studied when and how the phase transition or the disappearance of a dominant paradigm occurs as a cost C in DM or an innovation probability α in SM increases. In addition, we also investigate how the propagation processes affect the transition nature. From analytical calculations and numerical simulations m is shown to satisfy the scaling relation m=1-f(C/N for DM with the number of agents N. In contrast, m in SM scales as m=1-f(α(aN.

  20. Dynamical phase transitions in quantum mechanics

    Directory of Open Access Journals (Sweden)

    Rotter Ingrid

    2012-02-01

    Full Text Available The nucleus is described as an open many-body quantum system with a non-Hermitian Hamilton operator the eigenvalues of which are complex, in general. The eigenvalues may cross in the complex plane (exceptional points, the phases of the eigenfunctions are not rigid in approaching the crossing points and the widths bifurcate. By varying only one parameter, the eigenvalue trajectories usually avoid crossing and width bifurcation occurs at the critical value of avoided crossing. An analog spectroscopic redistribution takes place for discrete states below the particle decay threshold. By this means, a dynamical phase transition occurs in the many-level system starting at a critical value of the level density. Hence the properties of the low-lying nuclear states (described well by the shell model and those of highly excited nuclear states (described by random ensembles differ fundamentally from one another. The statement of Niels Bohr on the collective features of compound nucleus states at high level density is therefore not in contradiction to the shell-model description of nuclear (and atomic states at low level density. Dynamical phase transitions are observed experimentally in different quantum mechanical systems by varying one or two parameters.

  1. Phases and phase transitions in the algebraic microscopic shell model

    Directory of Open Access Journals (Sweden)

    Georgieva A. I.

    2016-01-01

    Full Text Available We explore the dynamical symmetries of the shell model number conserving algebra, which define three types of pairing and quadrupole phases, with the aim to obtain the prevailing phase or phase transition for the real nuclear systems in a single shell. This is achieved by establishing a correspondence between each of the pairing bases with the Elliott’s SU(3 basis that describes collective rotation of nuclear systems. This allows for a complete classification of the basis states of different number of particles in all the limiting cases. The probability distribution of the SU(3 basis states within theirs corresponding pairing states is also obtained. The relative strengths of dynamically symmetric quadrupole-quadrupole interaction in respect to the isoscalar, isovector and total pairing interactions define a control parameter, which estimates the importance of each term of the Hamiltonian in the correct reproduction of the experimental data for the considered nuclei.

  2. Temperature controlled motion of an antiferromagnet- ferromagnet interface within a dopant-graded FeRh epilayer

    OpenAIRE

    Le Graët, C; Charlton, T. R.; Mclaren, M.; Loving, M; Morley, S.A.; Kinane, C.J.; Brydson, R.M.D.; Lewis, L. H.; Langridge, S.; Marrows, C. H.

    2015-01-01

    Chemically ordered B2 FeRh exhibits a remarkable antiferromagnetic-ferromagnetic phase transition that is first order. It thus shows phase coexistence, usually by proceeding though nucleation at random defect sites followed by propagation of phase boundary domain walls. The transition occurs at a temperature that can be varied by doping other metals onto the Rh site. We have taken advantage of this to yield control over the transition process by preparing an epilayer with oppositely directed ...

  3. Critical Behavior at the Chiral Phase Transition

    CERN Document Server

    Bernard, C W; DeTar, C E; Gottlieb, S; Heller, U M; Hetrick, J E; Jegerlehner, B; Rummukainen, K; Sugar, R L; Toussaint, D; Wingate, M; Jegerlehner, Beat

    1998-01-01

    Quantum chromodynamics with two zero mass flavors is expected to exhibit a phase transition with O(4) critical behavior. Fixing the universality class is important for phenomenology and for facilitating the extrapolation of simulation data to physical quark mass values. At Lattice '96 the Tsukuba and Bielefeld groups reported results from new simulations with dynamical staggered quarks at $N_t = 4$, which suggested a departure from the expected critical behavior. We report observations of similar deviations and discuss efforts in progress to understand this phenomenon.

  4. Chiral phase transition from string theory.

    Science.gov (United States)

    Parnachev, Andrei; Sahakyan, David A

    2006-09-15

    The low energy dynamics of a certain D-brane configuration in string theory is described at weak t'Hooft coupling by a nonlocal version of the Nambu-Jona-Lasinio model. We study this system at finite temperature and strong t'Hooft coupling, using the string theory dual. We show that for sufficiently low temperatures chiral symmetry is broken, while for temperatures larger then the critical value, it gets restored. We compute the latent heat and observe that the phase transition is of the first order.

  5. Melonic phase transition in group field theory

    CERN Document Server

    Baratin, Aristide; Oriti, Daniele; Ryan, James P; Smerlak, Matteo

    2013-01-01

    Group field theories have recently been shown to admit a 1/N expansion dominated by so-called `melonic graphs', dual to triangulated spheres. In this note, we deepen the analysis of this melonic sector. We obtain a combinatorial formula for the melonic amplitudes in terms of a graph polynomial related to a higher dimensional generalization of the Kirchhoff tree-matrix theorem. Simple bounds on these amplitudes show the existence of a phase transition driven by melonic interaction processes. We restrict our study to the Boulatov-Ooguri models, which describe topological BF theories and are the basis for the construction of four dimensional models of quantum gravity.

  6. Deconfining phase transition in lattice QCD

    International Nuclear Information System (INIS)

    We present the first results obtained from the sixteen-processor version of the parallel supercomputer being built at Columbia. The color-deconfining phase transition has been studied fo pure SU(3) gauge theory on lattices with a spatial volume of 163 sites and temporal sizes of 10, 12, and 14 sites. The values found for the critical coupling are 6.07, 6.26, and 6.36, respectively. These results are in agreement with the perturbative predictions of the renormalization group, suggesting that lattice QCD calculations with the parameter β at least as large as 6.07 may approximate the continuum limit

  7. Evolutionary Phase Transitions in Random Environments

    Science.gov (United States)

    Skanata, Antun; Kussell, Edo

    2016-07-01

    We present analytical results for long-term growth rates of structured populations in randomly fluctuating environments, which we apply to predict how cellular response networks evolve. We show that networks which respond rapidly to a stimulus will evolve phenotypic memory exclusively under random (i.e., nonperiodic) environments. We identify the evolutionary phase diagram for simple response networks, which we show can exhibit both continuous and discontinuous transitions. Our approach enables exact analysis of diverse evolutionary systems, from viral epidemics to emergence of drug resistance.

  8. Berry phase transition in twisted bilayer graphene

    Science.gov (United States)

    Rode, Johannes C.; Smirnov, Dmitri; Schmidt, Hennrik; Haug, Rolf J.

    2016-09-01

    The electronic dispersion of a graphene bilayer is highly dependent on rotational mismatch between layers and can be further manipulated by electrical gating. This allows for an unprecedented control over electronic properties and opens up the possibility of flexible band structure engineering. Here we present novel magnetotransport data in a twisted bilayer, crossing the energetic border between decoupled monolayers and coupled bilayer. In addition a transition in Berry phase between π and 2π is observed at intermediate magnetic fields. Analysis of Fermi velocities and gate induced charge carrier densities suggests an important role of strong layer asymmetry for the observed phenomena.

  9. A Note on Holography and Phase Transitions

    Directory of Open Access Journals (Sweden)

    Marc Bellon

    2011-01-01

    Full Text Available Focusing on the connection between the Landau theory of second-order phase transitions and the holographic approach to critical phenomena, we study diverse field theories in an anti de Sitter black hole background. Through simple analytical approximations, solutions to the equations of motion can be obtained in closed form which give rather good approximations of the results obtained using more involved numerical methods. The agreement we find stems from rather elementary considerations on perturbation of Schrödinger equations.

  10. Dependence of phase transitions on small changes

    Science.gov (United States)

    Stoop, R.

    1993-06-01

    In this contribution, the generalized thermodynamic formalism is applied to a nonhyperbolic dynamical system in two comparable situations. The change from one situation to the other is small in the sense that the grammar and the singularities of the system are preserved. For the discussion of the effects generated by this change, the generalized entropy functions are calculated and the sets of the specific scaling functions which reflect the phase transition of the system are investigated. It is found that even under mild variations, this set is not invariant.

  11. Phase transitions and structures of methylammonium compounds

    International Nuclear Information System (INIS)

    The structures of CD3ND3Cl, CD3ND3I, CD3ND3BF4, (CD3ND3)2SnCl6, and CD3ND3SnBr3 crystals were studied with time-of-flight type high-resolution powder diffractometers using spallation pulsed neutron sources. The orientations of the CD3ND3 cations, including the positions of the D atoms, were determined at all the room temperature phases and at the low temperature phases of CD3ND3I and (CD3ND3)2SnCl6. The heat capacity experiments were also performed for both protonated and deuterated analogs of these compounds. From both structural and thermodynamic points of view, it was found that the transitions are mainly associated with the order-disorder change of the orientations of the CD3ND3 cations. (author)

  12. Topological phase transitions in superradiance lattices

    CERN Document Server

    Wang, Da-Wei; Yuan, Luqi; Liu, Ren-Bao; Zhu, Shi-Yao

    2015-01-01

    The discovery of the quantum Hall effect (QHE) reveals a new class of matter phases, topological insulators (TI's), which have been extensively studied in solid-state materials and recently in photonic structures, time-periodic systems and optical lattices of cold atoms. All these topological systems are lattices in real space. Our recent study shows that Scully's timed Dicke states (TDS) can form a superradiance lattice (SL) in momentum space. Here we report the discovery of topological phase transitions in a two-dimensional SL in electromagnetically induced transparency (EIT). By periodically modulating the three EIT coupling fields, we can create a Haldane model with in-situ tunable topological properties. The Chern numbers of the energy bands and hence the topological properties of the SL manifest themselves in the contrast between diffraction signals emitted by superradiant TDS. The topological superradiance lattices (TSL) provide a controllable platform for simulating exotic phenomena in condensed matte...

  13. Magnetostructural phase transitions in NiO and MnO: Neutron diffraction data

    Science.gov (United States)

    Balagurov, A. M.; Bobrikov, I. A.; Sumnikov, S. V.; Yushankhai, V. Yu.; Mironova-Ulmane, N.

    2016-07-01

    Structural and magnetic phase transitions in NiO and MnO antiferromagnets have been studied by high-precision neutron diffraction. The experiments have been performed on a high-resolution Fourier diffractometer (pulsed reactor IBR-2), which has the record resolution for the interplanar distance and a high intensity in the region of large interplanar distances; as a result, the characteristics of both transitions have been determined simultaneously. It has been shown that the structural and magnetic transitions in MnO occur synchronously and their temperatures coincide within the experimental errors: T str ≈ T mag ≈ (119 ± 1) K. The measurements for NiO have been performed with powders with different average sizes of crystallites (~1500 nm and ~138 nm). It has been found that the transition temperatures differ by ~50 K: T str = (471 ± 3) K, T mag = (523 ± 2) K. It has been argued that a unified mechanism of the "unsplit" magnetic and structural phase transition at a temperature of T mag is implemented in MnO and NiO. Deviation from this scenario in the behavior of NiO is explained by the quantitative difference—a weak coupling between the magnetic and secondary structural order parameters.

  14. Phase transitions in fluids and biological systems

    Science.gov (United States)

    Sipos, Maksim

    metric to 16S rRNA metagenomic studies of 6 vertebrate gastrointestinal microbiomes and find that they assembled through a highly non-neutral process. I then consider a phase transition that may occur in nutrient-poor environments such as ocean surface waters. In these systems, I find that the experimentally observed genome streamlining, specialization and opportunism may well be generic statistical phenomena.

  15. On Phase Transition of Compressed Sensing in the Complex Domain

    CERN Document Server

    Yang, Zai; Xie, Lihua

    2011-01-01

    The phase transition is a performance measure of the sparsity-undersampling tradeoff in compressed sensing (CS). This letter reports, for the first time, the existence of an exact phase transition for the $\\ell_1$ minimization approach to the complex valued CS problem. This discovery is not only a complementary result to the known phase transition of the real valued CS but also shows considerable superiority of the phase transition of complex valued CS over that of the real valued CS. The results are obtained by extending the recently developed ONE-L1 algorithms to complex valued CS and applying their optimal and iterative solutions to empirically evaluate the phase transition.

  16. Nuclear binding near a quantum phase transition

    CERN Document Server

    Elhatisari, Serdar; Rokash, Alexander; Alarcón, Jose Manuel; Du, Dechuan; Klein, Nico; Lu, Bing-nan; Meißner, Ulf-G; Epelbaum, Evgeny; Krebs, Hermann; Lähde, Timo A; Lee, Dean; Rupak, Gautam

    2016-01-01

    How do protons and neutrons bind to form nuclei? This is the central question of ab initio nuclear structure theory. While the answer may seem as simple as the fact that nuclear forces are attractive, the full story is more complex and interesting. In this work we present numerical evidence from ab initio lattice simulations showing that nature is near a quantum phase transition, a zero-temperature transition driven by quantum fluctuations. Using lattice effective field theory, we perform Monte Carlo simulations for systems with up to twenty nucleons. For even and equal numbers of protons and neutrons, we discover a first-order transition at zero temperature from a Bose-condensed gas of alpha particles (4He nuclei) to a nuclear liquid. Whether one has an alpha-particle gas or nuclear liquid is determined by the strength of the alpha-alpha interactions, and we show that the alpha-alpha interactions depend on the strength and locality of the nucleon-nucleon interactions. The existence of the nearby first-order ...

  17. Electronic phase transitions in ultrathin magnetite films

    International Nuclear Information System (INIS)

    Magnetite (Fe3O4) shows singular electronic and magnetic properties, resulting from complex electron–electron and electron–phonon interactions that involve the interplay of charge, orbital and spin degrees of freedom. The Verwey transition is a manifestation of these interactions, with a puzzling connection between the low temperature charge ordered state and the dynamic charge fluctuations still present above the transition temperature. Here we explore how these rich physical phenomena are affected by thin film geometries, particularly focusing on the ultimate size limit defined by thicknesses below the minimum bulk unit cell. On one hand, we address the influence of extended defects, such as surfaces or antiphase domains, on the novel features exhibited by thin films. On the other, we try to isolate the effect of the reduced thickness on the electronic and magnetic properties. We will show that a distinct phase diagram and novel charge distributions emerge under reduced dimensions, while holding the local high magnetic moments. Altogether, thin film geometries offer unique possibilities to understand the complex interplay of short- and long-range orders in the Verwey transition. Furthermore, they arise as interesting candidates for the exploitation of the rich physics of magnetite in devices that demand nanoscale geometries, additionally offering novel functionalities based on their distinct properties with respect to the bulk form. (topical review)

  18. Nuclear Binding Near a Quantum Phase Transition

    Science.gov (United States)

    Elhatisari, Serdar; Li, Ning; Rokash, Alexander; Alarcón, Jose Manuel; Du, Dechuan; Klein, Nico; Lu, Bing-nan; Meißner, Ulf-G.; Epelbaum, Evgeny; Krebs, Hermann; Lähde, Timo A.; Lee, Dean; Rupak, Gautam

    2016-09-01

    How do protons and neutrons bind to form nuclei? This is the central question of ab initio nuclear structure theory. While the answer may seem as simple as the fact that nuclear forces are attractive, the full story is more complex and interesting. In this work we present numerical evidence from ab initio lattice simulations showing that nature is near a quantum phase transition, a zero-temperature transition driven by quantum fluctuations. Using lattice effective field theory, we perform Monte Carlo simulations for systems with up to twenty nucleons. For even and equal numbers of protons and neutrons, we discover a first-order transition at zero temperature from a Bose-condensed gas of alpha particles (4He nuclei) to a nuclear liquid. Whether one has an alpha-particle gas or nuclear liquid is determined by the strength of the alpha-alpha interactions, and we show that the alpha-alpha interactions depend on the strength and locality of the nucleon-nucleon interactions. This insight should be useful in improving calculations of nuclear structure and important astrophysical reactions involving alpha capture on nuclei. Our findings also provide a tool to probe the structure of alpha cluster states such as the Hoyle state responsible for the production of carbon in red giant stars and point to a connection between nuclear states and the universal physics of bosons at large scattering length.

  19. Phase transition in the ABC model.

    Science.gov (United States)

    Clincy, M; Derrida, B; Evans, M R

    2003-06-01

    Recent studies have shown that one-dimensional driven systems can exhibit phase separation even if the dynamics is governed by local rules. The ABC model, which comprises three particle species that diffuse asymmetrically around a ring, shows anomalous coarsening into a phase separated steady state. In the limiting case in which the dynamics is symmetric and the parameter q describing the asymmetry tends to one, no phase separation occurs and the steady state of the system is disordered. In the present work, we consider the weak asymmetry regime q=exp(-beta/N), where N is the system size, and study how the disordered state is approached. In the case of equal densities, we find that the system exhibits a second-order phase transition at some nonzero beta(c). The value of beta(c)=2pi square root 3 and the optimal profiles can be obtained by writing the exact large deviation functional. For nonequal densities, we write down mean-field equations and analyze some of their predictions. PMID:16241312

  20. Phase transitions in Thirring’s model

    Science.gov (United States)

    Campa, Alessandro; Casetti, Lapo; Latella, Ivan; Pérez-Madrid, Agustín; Ruffo, Stefano

    2016-07-01

    In his pioneering work on negative specific heat, Walter Thirring introduced a model that is solvable in the microcanonical ensemble. Here, we give a complete description of the phase-diagram of this model in both the microcanonical and the canonical ensemble, highlighting the main features of ensemble inequivalence. In both ensembles, we find a line of first-order phase transitions which ends in a critical point. However, neither the line nor the point have the same location in the phase-diagram of the two ensembles. We also show that the microcanonical and canonical critical points can be analytically related to each other using a Landau expansion of entropy and free energy, respectively, in analogy with what has been done in (Cohen and Mukamel 2012 J. Stat. Mech. P12017). Examples of systems with certain symmetries restricting the Landau expansion have been considered in this reference, while no such restrictions are present in Thirring’s model. This leads to a phase diagram that can be seen as a prototype for what happens in systems of particles with kinematic degrees of freedom dominated by long-range interactions.

  1. Aspects of the cosmological electroweak phase transition

    International Nuclear Information System (INIS)

    We study the decay of the metastable symmetric phase in the standard model at finite temperature. For the SU(2)-Higgs model the two wave function correction terms Zφ(φ2,T) and Zχ(φ2,T) of Higgs and Goldstone boson fields are calculated to one-loop order. We find that the derivative expansion of the effective action is reliable for Higgs masses smaller than the W-boson mass. We propose a new procedure to evaluate the decay rate by first integrating out the vector field and the components of the scalar fields with non-zero Matsubara frequencies. The static part of the scalar field is treated in the saddle point approximation. As a by-product we obtain a formula for the decay rate of a homogeneous unstable state. The course of the cosmological electroweak phase transition is evaluated numerically for different Higgs boson masses and non-vanishing magnetic mass of the gauge boson. For Higgs masses above ∼ 60 GeV the latent heat can reheat the system to the critical temperature, which qualitatively changes the nature of the transition. (orig.)

  2. Stress induced phase transitions in silicon

    Science.gov (United States)

    Budnitzki, M.; Kuna, M.

    2016-10-01

    Silicon has a tremendous importance as an electronic, structural and optical material. Modeling the interaction of a silicon surface with a pointed asperity at room temperature is a major step towards the understanding of various phenomena related to brittle as well as ductile regime machining of this semiconductor. If subjected to pressure or contact loading, silicon undergoes a series of stress-driven phase transitions accompanied by large volume changes. In order to understand the material's response for complex non-hydrostatic loading situations, dedicated constitutive models are required. While a significant body of literature exists for the dislocation dominated high-temperature deformation regime, the constitutive laws used for the technologically relevant rapid low-temperature loading have severe limitations, as they do not account for the relevant phase transitions. We developed a novel finite deformation constitutive model set within the framework of thermodynamics with internal variables that captures the stress induced semiconductor-to-metal (cd-Si → β-Si), metal-to-amorphous (β-Si → a-Si) as well as amorphous-to-amorphous (a-Si → hda-Si, hda-Si → a-Si) transitions. The model parameters were identified in part directly from diamond anvil cell data and in part from instrumented indentation by the solution of an inverse problem. The constitutive model was verified by successfully predicting the transformation stress under uniaxial compression and load-displacement curves for different indenters for single loading-unloading cycles as well as repeated indentation. To the authors' knowledge this is the first constitutive model that is able to adequately describe cyclic indentation in silicon.

  3. Preon model and cosmological quantum-hyperchromodynamic phase transition

    Science.gov (United States)

    Nishimura, H.; Hayashi, Y.

    1987-05-01

    From the cosmological viewpoint, we investigate whether or not recent preon models are compatible with the picture of the first-order phase transition from the preon phase to the composite quark-lepton phase. It is shown that the current models accepting the 't Hooft anomaly-matching condition together with quantum hyperchromodynamics are consistent with the cosmological first-order phase transition.

  4. Quark-hadron phase transition in massive gravity

    Science.gov (United States)

    Atazadeh, K.

    2016-11-01

    We study the quark-hadron phase transition in the framework of massive gravity. We show that the modification of the FRW cosmological equations leads to the quark-hadron phase transition in the early massive Universe. Using numerical analysis, we consider that a phase transition based on the chiral symmetry breaking after the electroweak transition, occurred at approximately 10 μs after the Big Bang to convert a plasma of free quarks and gluons into hadrons.

  5. Unconventional exchange bias effect driven by phase separation in basically antiferromagnetic Sm0.1Ca0.6Sr0.3MnO3

    International Nuclear Information System (INIS)

    Highlights: • Sm0.1Ca0.6Sr0.3MnO3 displays negative exchange bias (NEB) effect at low temperatures. • The NEB increases rapidly with increasing Hcool up to 100 Oe, but is almost Hcool independent at H > 0.5 kOe. • The sign of the EB changes with temperature from NEB at T < 40 K to a positive one at T ⩾ 40 K. • The atypical magnetic properties are related to two different interfaces appearing between coexisting magnetic phases. - Abstract: Magnetic investigations, focused on the uncommon behavior of the exchange bias (EB) effect, have been performed for basically antiferromagnetic (AFM) electron doped manganite Sm0.1Ca0.6Sr0.3MnO3. The studied system in the ground state exhibits a heterogeneous spin configuration consisting of the C-type antiferromagnetic phase with the Néel temperature TN-C ≈ 150 K, the G-type AFM phase with the Néel temperature TN-G ≈ 70 K, and a FM-like phase with very weak spontaneous magnetic moment. The phase separation, into two different AFM phases and a FM-like phase at the temperatures below TN-G, leads to unusual magnetic properties, such as: narrowing of magnetic hysteresis loops in field cooling process, unconventional EB effect associated with spontaneous magnetization at temperatures below TN-C, strong magnetic field dependence of the negative exchange bias at fields below 100 Oe turning into practically field independent one for fields above 0.5 kOe, significant shift of EB with temperature with a change of the sign from negative at 10 K to positive above 40 K. The atypical magnetic properties are discussed and related to two different interfaces appearing between coexisting magnetic phases

  6. Phase transitions in high excited nuclear matter

    International Nuclear Information System (INIS)

    This work is a study of the mechanism of thermal multifragmentation, which takes place in collisions of light relativistic projectiles with heavy targets. This is a new multibody decay process of very hot nuclei (target spectator) with emission of a number of intermediate mass fragments (IMF, 2 4He and 12C with Au. The main results are the following: - The mean IMF multiplicity () saturates at 2.2 ± 0.2.This fact cannot be rendered by the traditional approach with the intranuclear cascade (INC) followed by Statistical Multifragmentation Models (SMM). Considering the expansion phase between two parts of the calculations, the excitation energies and the residual masses are empirically modified to obtain agreement with the measured IMF- multiplicities. The mean excitation energy is found to be around 500 MeV for the beam energies above 5 GeV. This modified model is denoted as INC + α + SMM where α indicates the preequilibrium processes. - The expansion is driven by the thermal pressure. It is larger for 4He and 12C induced collisions because of higher initial temperature. The kinetic energy spectra of IMF become harder and the expansion flow is visible. The total flow energy of the system is estimated to be around 115 MeV both for the He and the carbon beams. - The analysis of the data reveals very interesting information on the fragment space distribution inside the break-up volume. Heavier IMF are formed predominately in the interior of the fragmenting nucleus possibly due to a density gradient. This conclusion is in contrast to the predictions of the Statistical Multifragmentation Model (SMM). - This study of the multifragmentation using a range of projectiles demonstrates a transition from pure '' thermal decay '' (for p + Au collisions) to disintegration '' completed by '' the onset of a collective flow for the heavier projectiles. Nevertheless, in case of reaction caused by fast protons the decay mechanism should be considered as a thermal multifragmentation

  7. Critical Behaviour of a Two-Dimensional Random Antiferromagnet

    DEFF Research Database (Denmark)

    Als-Nielsen, Jens Aage; Birgeneau, R. J.; Guggenheim, H. J.;

    1976-01-01

    A neutron scattering study of the order parameter, correlation length and staggered susceptibility of the two-dimensional random antiferromagnet Rb2Mn0.5Ni0.5F4 is reported. The system is found to exhibit a well-defined phase transition with critical exponents identical to those of the isomorphou...... pure materials K2NiF4 and K2MnF4. Thus, in these systems, which have the asymptotic critical behaviour of the two-dimensional Ising model, randomness has no measurable effect on the phase-transition behaviour....

  8. Dynamical phase transitions in the two-dimensional ANNNI model

    Energy Technology Data Exchange (ETDEWEB)

    Barber, M.N.; Derrida, B.

    1988-06-01

    We study the phase diagram of the two-dimensional anisotropic next-nearest neighbor Ising (ANNNI) model by comparing the time evolution of two distinct spin configurations submitted to the same thermal noise. We clearly se several dynamical transitions between ferromagnetic, paramagnetic, antiphase, and floating phases. These dynamical transitions seem to occur rather close to the transition lines determined previously in the literature.

  9. Scaling theory of topological phase transitions.

    Science.gov (United States)

    Chen, Wei

    2016-02-10

    Topologically ordered systems are characterized by topological invariants that are often calculated from the momentum space integration of a certain function that represents the curvature of the many-body state. The curvature function may be Berry curvature, Berry connection, or other quantities depending on the system. Akin to stretching a messy string to reveal the number of knots it contains, a scaling procedure is proposed for the curvature function in inversion symmetric systems, from which the topological phase transition can be identified from the flow of the driving energy parameters that control the topology (hopping, chemical potential, etc) under scaling. At an infinitesimal operation, one obtains the renormalization group (RG) equations for the driving energy parameters. A length scale defined from the curvature function near the gap-closing momentum is suggested to characterize the scale invariance at critical points and fixed points, and displays a universal critical behavior in a variety of systems examined. PMID:26790004

  10. MAGNETIC FIELDS FROM QCD PHASE TRANSITIONS

    Energy Technology Data Exchange (ETDEWEB)

    Tevzadze, Alexander G. [Faculty of Exact and Natural Sciences, Javakhishvili Tbilisi State University, 1 Chavchavadze Avenue, Tbilisi 0128 (Georgia); Kisslinger, Leonard; Kahniashvili, Tina [McWilliams Center for Cosmology and Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213 (United States); Brandenburg, Axel, E-mail: aleko@tevza.org [Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm (Sweden)

    2012-11-01

    We study the evolution of QCD phase transition-generated magnetic fields (MFs) in freely decaying MHD turbulence of the expanding universe. We consider an MF generation model that starts from basic non-perturbative QCD theory and predicts stochastic MFs with an amplitude of the order of 0.02 {mu}G and small magnetic helicity. We employ direct numerical simulations to model the MHD turbulence decay and identify two different regimes: a 'weakly helical' turbulence regime, when magnetic helicity increases during decay, and 'fully helical' turbulence, when maximal magnetic helicity is reached and an inverse cascade develops. The results of our analysis show that in the most optimistic scenario the magnetic correlation length in the comoving frame can reach 10 kpc with the amplitude of the effective MF being 0.007 nG. We demonstrate that the considered model of magnetogenesis can provide the seed MF for galaxies and clusters.

  11. Scaling theory of topological phase transitions.

    Science.gov (United States)

    Chen, Wei

    2016-02-10

    Topologically ordered systems are characterized by topological invariants that are often calculated from the momentum space integration of a certain function that represents the curvature of the many-body state. The curvature function may be Berry curvature, Berry connection, or other quantities depending on the system. Akin to stretching a messy string to reveal the number of knots it contains, a scaling procedure is proposed for the curvature function in inversion symmetric systems, from which the topological phase transition can be identified from the flow of the driving energy parameters that control the topology (hopping, chemical potential, etc) under scaling. At an infinitesimal operation, one obtains the renormalization group (RG) equations for the driving energy parameters. A length scale defined from the curvature function near the gap-closing momentum is suggested to characterize the scale invariance at critical points and fixed points, and displays a universal critical behavior in a variety of systems examined.

  12. Information Dynamics at a Phase Transition

    CERN Document Server

    Sowinski, Damian

    2016-01-01

    We propose a new way of investigating phase transitions in the context of information theory. We use an information-entropic measure of spatial complexity known as configurational entropy (CE) to quantify both the storage and exchange of information in a lattice simulation of a Ginzburg-Landau model with a scalar order parameter coupled to a heat bath. The CE is built from the Fourier spectrum of fluctuations around the mean-field and reaches a minimum at criticality. In particular, we investigate the behavior of CE near and at criticality, exploring the relation between information and the emergence of ordered domains. We show that as the temperature is increased from below, the CE displays three essential scaling regimes at different spatial scales: scale free, turbulent, and critical. Together, they offer an information-entropic characterization of critical behavior where the storage and processing of information is maximized at criticality.

  13. The phase transition of Axelrod's model revisited

    CERN Document Server

    Reia, Sandro M

    2016-01-01

    Axelrod's model with $F=2$ cultural features, where each feature can assume $k$ states drawn from a Poisson distribution of parameter $q$, exhibits a continuous nonequilibrium phase transition in the square lattice. Here we use extensive Monte Carlo simulations and finite size scaling to study the critical behavior of the order parameter $\\rho$, which is the fraction of sites that belong to the largest domain of an absorbing configuration averaged over many runs. We find that it vanishes as $\\rho \\sim \\left (q_c^0 - q \\right)^\\beta$ with $\\beta \\approx 0.25$ at the critical point $q_c^0 \\approx 3.10$ and that the exponent that measures the width of the critical region is $\

  14. Phase Transitions in Networks of Memristive Elements

    Science.gov (United States)

    Sheldon, Forrest; di Ventra, Massimiliano

    The memory features of memristive elements (resistors with memory), analogous to those found in biological synapses, have spurred the development of neuromorphic systems based on them (see, e.g.,). In turn, this requires a fundamental understanding of the collective dynamics of networks of memristive systems. Here, we study an experimentally-inspired model of disordered memristive networks in the limit of a slowly ramped voltage and show through simulations that these networks undergo a first-order phase transition in the conductivity for sufficiently high values of memory, as quantified by the memristive ON/OFF ratio. We provide also a mean-field theory that reproduces many features of the transition and particularly examine the role of boundary conditions and current- vs. voltage-controlled networks. The dynamics of the mean-field theory suggest a distribution of conductance jumps which may be accessible experimentally. We finally discuss the ability of these networks to support massively-parallel computation. Work supported in part by the Center for Memory and Recording Research at UCSD.

  15. Mott insulating states and quantum phase transitions of correlated SU(2 N ) Dirac fermions

    Science.gov (United States)

    Zhou, Zhichao; Wang, Da; Meng, Zi Yang; Wang, Yu; Wu, Congjun

    2016-06-01

    The interplay between charge and spin degrees of freedom in strongly correlated fermionic systems, in particular of Dirac fermions, is a long-standing problem in condensed matter physics. We investigate the competing orders in the half-filled SU (2 N ) Hubbard model on a honeycomb lattice, which can be accurately realized in optical lattices with ultracold large-spin alkaline-earth fermions. Employing large-scale projector determinant quantum Monte Carlo simulations, we have explored quantum phase transitions from the gapless Dirac semimetals to the gapped Mott insulating phases in the SU(4) and SU(6) cases. Both of these Mott insulating states are found to be columnar valence bond solid (cVBS) and to be absent of the antiferromagnetic Néel ordering and the loop current ordering. Inside the cVBS phases, the dimer ordering is enhanced by increasing fermion components and behaves nonmonotonically as the interaction strength increases. Although the transitions generally should be of first order due to a cubic invariance possessed by the cVBS order, the coupling to gapless Dirac fermions can soften the transitions to second order through a nonanalytic term in the free energy. Our simulations provide important guidance for the experimental explorations of novel states of matter with ultracold alkaline-earth fermions.

  16. Studies on magnetic-field-induced first-order transitions

    Indian Academy of Sciences (India)

    P Chaddah

    2006-07-01

    We shall discuss magnetization and transport measurements in materials exhibiting a broad first-order transition. The phase transitions would be caused by varying magnetic field as well as temperature, and we concentrate on ferro- to antiferromagnetic transitions in magnetic materials. We distinguish between metastable supercooled phases and metastable glassy phase.

  17. Quantum phase transition and Coulomb blockade effect in triangular quantum dots with interdot capacitive and tunnel couplings

    Institute of Scientific and Technical Information of China (English)

    熊永臣; 王为忠; 杨俊涛; 黄海铭

    2015-01-01

    The quantum phase transition and the electronic transport in triangular quantum dot system are investigated using the numerical renormalization group method. We concentrate on the interplay between the interdot capacitive coupling V and the interdot tunnel coupling t . For small t , three dots form a local spin doublet. As t increases, due to the competition between V and t , there exist two first-order transitions with phase sequence spin-doublet-magnetic frustration phase-orbital spin singlet. When t is absent, the evolutions of the total charge on the dots and the linear conductance are of the typical Coulomb-blockade features with increasing gate voltage. While for sufficient t , the antiferromagnetic spin correlation between dots is enhanced, and the conductance is strongly suppressed for the bonding state is almost doubly occupied.

  18. Antiferromagnetic spin Seebeck effect.

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Stephen M.; Zhang, Wei; KC, Amit; Borisov, Pavel; Pearson, John E.; Jiang, J. Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand

    2016-03-03

    We report on the observation of the spin Seebeck effect in antiferromagnetic MnF2. A device scale on-chip heater is deposited on a bilayer of MnF2 (110) (30nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF2(110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF2 through the inverse spin Hall effect. The low temperature (2–80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9T) are applied parallel to the easy axis of the MnF2 thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.

  19. Phase transitions in a gas of anyons

    CERN Document Server

    MacKenzie, R; Paranjape, M B; Richer, J

    2010-01-01

    We continue our numerical Monte Carlo simulation of a gas of closed loops on a 3 dimensional lattice, however now in the presence of a topological term added to the action corresponding to the total linking number between the loops. We compute the linking number using certain notions from knot theory. Adding the topological term converts the particles into anyons. Using the correspondence that the model is an effective theory that describes the 2+1-dimensional Abelian Higgs model in the asymptotic strong coupling regime, the topological linking number simply corresponds to the addition to the action of the Chern-Simons term. We find the following new results. The system continues to exhibit a phase transition as a function of the anyon mass as it becomes small \\cite{mnp}, although the phases do not change the manifestation of the symmetry. The Chern-Simons term has no effect on the Wilson loop, but it does affect the {\\rm '}t Hooft loop. For a given configuration it adds the linking number of the 't Hooft loo...

  20. Towards the nuclear matter - quark matter phase transition

    International Nuclear Information System (INIS)

    The conjectured first order phase transition from cold nuclear to cold quark matter is considered. It is found that non-perturbative effects due to instantons may have a 'smoothing-out' effect on the transition. (author)

  1. Non-equilibrium phase transitions in complex plasma

    NARCIS (Netherlands)

    Sutterlin, K. R.; Wysocki, A.; Rath, C.; Ivlev, A. V.; Thomas, H. M.; Khrapak, S.; Zhdanov, S.; Rubin-Zuzic, M.; W. J. Goedheer,; Fortov, V. E.; Lipaev, A. M.; Molotkov, V. I.; Petrov, O. F.; Morfill, G. E.; Lowen, H.

    2010-01-01

    Complex plasma being the 'plasma state of soft matter' is especially suitable for investigations of non-equilibrium phase transitions. Non-equilibrium phase transitions can manifest in dissipative structures or self-organization. Two specific examples are lane formation and phase separatio

  2. Pressure-induced phase transition in CrO2.

    Science.gov (United States)

    Alptekin, Sebahaddin

    2015-12-01

    The ab initio constant pressure molecular dynamics technique and density functional theory with generalized gradient approximation (GGA) was used to study the pressure-induced phase transition of CrO2. The phase transition of the rutile (P42/mnm) to the orthorhombic CaCl2 (Pnnm) structure at 30 GPa was determined successfully in a constant pressure simulation. This phase transition was analyzed from total energy calculations and, from the enthalpy calculation, occurred at around 17 GPa. Structural properties such as bulk modules, lattice parameters and phase transition were compared with experimental results. The phase transition at 12 ± 3 GPa was in good agreement with experimental results, as was the phase transition from the orthorhombic CaCl2 (Pnnm) to the monoclinic (P21/c) structure also found at 35 GPa.

  3. Tunable spin selective transport and quantum phase transition in parallel double dot system

    Science.gov (United States)

    Xiong, Yong-Chen; Wang, Wei-Zhong; Luo, Shi-Jun; Yang, Jun-Tao

    2016-02-01

    We study theoretically the spin selective transport and the quantum phase transition (QPT) in a double dot device by means of the numerical renormalization group technique. When the gate voltage ε is in the Kondo regime and the interdot hopping t is large enough, a first order QPT between local spin singlet and Sz=1 of the triplet is observed as the magnetic field B increases. Beyond the Kondo regime, the QPTs depend closely on ε and t, and perfect spin filter is found, where the effect of spin filtering could easily be manipulated by tuning external parameters. We show that the interplay between the Zeeman effect and the antiferromagnetic interdot hopping, and occupancy switching are responsible for the QPT and the spin selective transport.

  4. Phase-separation transitions in asymmetric lipid bilayers

    OpenAIRE

    Shimobayashi, Shunsuke F.; Ichikawa, Masatoshi; Taniguchi, Takashi

    2015-01-01

    Morphological transitions of phase separation associated with the asymmetry of lipid composition were investigated using micrometer-sized vesicles of lipid bilayers made from a lipid mixture. The complete macro-phase-separated morphology undergoes a transition to a micro-phase-separation-like morphology via a lorate morphology as a metastable state. The transition leads to the emergence of monodisperse nanosized domains through repeated domain scission events. Moreover, we have numerically co...

  5. Emergent Geometric Hamiltonian and Insulator-Superfluid Phase Transitions

    OpenAIRE

    Zhou, Fei

    2005-01-01

    I argue that certain bosonic insulator-superfluid phase transitions as an interaction constant varies are driven by emergent geometric properties of insulating states. The {\\em renormalized} chemical potential and distribution of disordered bosons define the geometric aspect of an effective low energy Hamiltonian which I employ to study various resonating states and quantum phase transitions. In a mean field approximation, I also demonstrate that the quantum phase transitions are in the unive...

  6. Primordial Magnetic Fields from Cosmological First Order Phase Transitions

    OpenAIRE

    Sigl, Guenter; Olinto, Angela; Jedamzik, Karsten

    1996-01-01

    We give an improved estimate of primordial magnetic fields generated during cosmological first order phase transitions. We examine the charge distribution at the nucleated bubble wall and its dynamics. We consider instabilities on the bubble walls developing during the phase transition. It is found that damping of these instabilities due to viscosity and heat conductivity caused by particle diffusion can be important in the QCD phase transition, but is probably negligible in the electroweak t...

  7. Discord under the influence of a quantum phase transition

    Institute of Scientific and Technical Information of China (English)

    Wang Lin-cheng; Shen Jian; Yi Xue-Xi

    2011-01-01

    This paper studies the discord of a bipartite two-level system coupling to an XY spin-chain environment in a transverse field and investigates the relationship between the discord property and the environment's quantum phase transition. The results show that the quantum discord is also able to characterize the quantum phase transitions. We also discuss the difference between discord and entanglement, and show that quantum discord may reveal more general information than quantum entanglement for characterizing the environment's quantum phase transition.

  8. Quantum phase transition and entanglement in Li atom system

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    By use of the exact diagonalization method, the quantum phase transition and en- tanglement in a 6-Li atom system are studied. It is found that entanglement appears before the quantum phase transition and disappears after it in this exactly solvable quantum system. The present results show that the von Neumann entropy, as a measure of entanglement, may reveal the quantum phase transition in this model.

  9. Phase transition of holographic entanglement entropy in massive gravity

    CERN Document Server

    Zeng, Xiao-Xiong; Li, Li-Fang

    2015-01-01

    The phase structure of holographic entanglement entropy is studied in massive gravity for the quantum systems with finite and infinite volumes, which in the bulk is dual to calculate the minimal surface area for a black hole and black brane respectively. In the entanglement entropy$-$temperature plane, we find for both the black hole and black brane there is a Van der Waals-like phase transition as the case in thermal entropy$-$temperature plane. That is, there is a first order phase transition for the small charge and a second order phase transition at the critical charge. For the first order phase transition, the equal area law is checked and for the second order phase transition, the critical exponent of the heat capacity is obtained. All the results show that the phase structure of holographic entanglement entropy is the same as that of thermal entropy regardless of the volume of the spacetime on the boundary.

  10. Phase transition of holographic entanglement entropy in massive gravity

    Directory of Open Access Journals (Sweden)

    Xiao-Xiong Zeng

    2016-05-01

    Full Text Available The phase structure of holographic entanglement entropy is studied in massive gravity for the quantum systems with finite and infinite volumes, which in the bulk is dual to calculating the minimal surface area for a black hole and black brane respectively. In the entanglement entropy–temperature plane, we find for both the black hole and black brane there is a Van der Waals-like phase transition as the case in thermal entropy–temperature plane. That is, there is a first order phase transition for the small charge and a second order phase transition at the critical charge. For the first order phase transition, the equal area law is checked and for the second order phase transition, the critical exponent of the heat capacity is obtained. All the results show that the phase structure of holographic entanglement entropy is the same as that of thermal entropy regardless of the volume of the spacetime on the boundary.

  11. Holographic phase transition probed by non-local observables

    CERN Document Server

    Zeng, Xiao-Xiong

    2016-01-01

    From the viewpoint of holography, the phase structure of a 5-dimensional Reissner-Nordstr\\"{o}m-AdS black hole is probed by the two point correlation function, Wilson loop, and entanglement entropy. As the case of thermal entropy, we find for all the probes, the black hole undergos a Hawking-Page phase transition, a first order phase transition and a second order phase transition successively before it reaches to a stable phase. In addition, for these probes, we find the equal area law for the first order phase transition is valid always and the critical exponent of the heat capacity for the second order phase transition coincides with that of the mean field theory regardless of the size of the boundary region.

  12. Mesoscale modeling of phase transition dynamics of thermoresponsive polymers

    CERN Document Server

    Li, Zhen; Li, Xuejin; Karniadakis, George Em

    2015-01-01

    We present a non-isothermal mesoscopic model for investigation of the phase transition dynamics of thermoresponsive polymers. Since this model conserves energy in the simulations, it is able to correctly capture not only the transient behavior of polymer precipitation from solvent, but also the energy variation associated with the phase transition process. Simulations provide dynamic details of the thermally induced phase transition and confirm two different mechanisms dominating the phase transition dynamics. A shift of endothermic peak with concentration is observed and the underlying mechanism is explored.

  13. Nonlinear piezoelectric coefficients of ferroelectrics in the phase transition region

    Energy Technology Data Exchange (ETDEWEB)

    Iushin, N.K.; Smirnov, S.I.; Turovets, A.G.; Linnik, V.G.; Agishev, B.A.

    1987-03-01

    Changes in the nonlinear piezoelectric coefficients in ferroelectrics in the phase transition region are investigated experimentally using triglycine sulfate, lead germanate, potassium-lithium tantalate, and cadmium pyroniobate crystals, characterized by phase transitions of the second kind, and also gadolinium and terbium molybdate crystals, characterized by a ferroelectric phase transition of the first kind. In the crystals studied, a significant increase in nonlinear piezoelectric coefficients is observed near the phase transition temperature, which makes these crystals attractive materials for use as the elements of nonlinear acoustoelectronic instruments. 9 references.

  14. Raman study of thermochromic phase transition in tungsten trioxide nanowires

    Science.gov (United States)

    Lu, Dong Yu; Chen, Jian; Chen, Huan Jun; Gong, Li; Deng, Shao Zhi; Xu, Ning Sheng; Liu, Yu Long

    2007-01-01

    Tungsten trioxide (WO3) nanowires were synthesized by thermal evaporation of tungsten powder in two steps: tungsten suboxide (WO3-x) nanowires were synthesized, and then oxidized in O2 ambient and transformed into WO3 nanowires. Raman spectroscopy was applied to study the thermochromic phase transition of one-dimensional WO3 nanowires. From the temperature dependence of the characteristic mode at 33cm-1 in WO3, the phase transition temperature was determined. It was found that the phase transition of WO3 nanowires was reversible and the phase transition temperatures were even lower than that of WO3 nanopowder.

  15. Ultrafast measurements of the magnetic and structural phase transition of FeRh in the extreme ultraviolet range

    Science.gov (United States)

    Zusin, Dmitriy; Grychtol, Patrik; Turgut, Emrah; Kapteyn, Henry; Murnane, Margaret; Knut, Ronny; Shaw, Justin; Nembach, Hans; Silva, Thomas; Ceballos, Alejandro; Bordel, Catherine; Fischer, Peter; Hellman, Frances

    2014-03-01

    The temperature dependent transition from the anti-ferromagnetic to the ferromagnetic phase in FeRh is accompanied by a modification of its crystal lattice. In spite of extensive investigations, the interplay between the magnetic and the structural transition is still a matter of strong debate. A better understanding of the phase transition mechanism(s) is important, since the transition can be induced by femtosecond laser pulses and does not seem to be limited by heat transfer, as is the case in magnetic phase transitions that occur on longer (nanosecond) time scales. In this work, we use extreme ultraviolet radiation generated by a tabletop high harmonics source to perform element-selective investigations of the temperature-dependent magneto-optical response of a thin film FeRh sample. We study the optically induced phase transition using two ultrafast pump-probe spectroscopy approaches: by monitoring the time-resolved transversal magneto-optical Kerr effect (T-MOKE) and the transient change in reflectivity. P.F. acknowledges support from BES MSD DOE # DE-AC02-05-CH11231 and JILA from DOE # DE-FG02-09ER4665.

  16. Ultrafast dynamics of the magnetic phase transition on FeRh

    Energy Technology Data Exchange (ETDEWEB)

    Radu, Ilie [Institut fuer Experimentelle Physik, Universitaet Regensburg (Germany); BESSY GmbH, Berlin (Germany); Weber, Alexander; Ramm, Paul; Back, Christian [Institut fuer Experimentelle Physik, Universitaet Regensburg (Germany); Stamm, Christian; Kachel, Torsten; Pontius, Niko; Duerr, Hermann [BESSY GmbH, Berlin (Germany); Thiele, Jan [Hitachi Global Storage Technologies, San Jose (United States)

    2007-07-01

    The laser-induced dynamics of the antiferromagnetic (AFM) to ferromagnetic (FM) phase transition of the FeRh alloy is studied by two complementary experimental techniques: the time-resolved magnetooptical Kerr effect (MOKE) and the time-resolved X-ray circular magnetic dichroism (XMCD). The transient MOKE data reveal an ultrafast onset of the FM ordering within 500 fs after femtosecond laser excitation. This result points to an electronically-driven AFM-FM transition since the lattice heating and the resulting lattice expansion evolve on a longer time scale. From the time-resolved XMCD spectra we obtain a similar dynamics for the Fe and Rh magnetic moments with a rise-time of 100 ps, which seems to contradict the dynamic MOKE data. The possible origin of this discrepancy will be discussed in terms of excitation and detection mechanisms in MOKE and XMCD. Due to the large magnetic moment of FeRh established in the FM state, one can use the ultrafast phase transition to trigger a coherent magnetization precession of a thin ferromagnetic film in contact with FeRh. Here, we present first pump-probe MOKE measurements of such a double layer system of CoPd/FeRh, that show two oscillatory components at 60 GHz and 80 GHz.

  17. Pressure induced phase transitions in ceramic compounds containing tetragonal zirconia

    Energy Technology Data Exchange (ETDEWEB)

    Sparks, R.G.; Pfeiffer, G.; Paesler, M.A.

    1988-12-01

    Stabilized tetragonal zirconia compounds exhibit a transformation toughening process in which stress applied to the material induces a crystallographic phase transition. The phase transition is accompanied by a volume expansion in the stressed region thereby dissipating stress and increasing the fracture strength of the material. The hydrostatic component of the stress required to induce the phase transition can be investigated by the use of a high pressure technique in combination with Micro-Raman spectroscopy. The intensity of Raman lines characteristic for the crystallographic phases can be used to calculate the amount of material that has undergone the transition as a function of pressure. It was found that pressures on the order of 2-5 kBar were sufficient to produce an almost complete transition from the original tetragonal to the less dense monoclinic phase; while a further increase in pressure caused a gradual reversal of the transition back to the original tetragonal structure.

  18. Phase transitions in a vortex gas

    CERN Document Server

    Shah, P A

    1994-01-01

    It has been shown recently that the motion of solitons at couplings around a critical coupling can be reduced to the dynamics of particles (the zeros of the Higgs field) on a curved manifold with potential. The curvature gives a velocity dependent force, and the magnitude of the potential is proportional to the distance from a critical coupling. In this paper we apply this approximation to determining the equation of state of a gas of vortices in the Abelian Higgs model. We derive a virial expansion using certain known integrals of the metric, and the second virial coefficient is calculated, determining the behaviour of the gas at low densities. A formula for determining higher order coefficients is given. At low densities and temperatures T \\gg \\l the equation of state is of the Van der Waals form (P+b\\frac{N^{2}}{A^{2}})(A-aN) = NT with a=4\\pi and b=-4.89\\pi\\l where \\l is a measure of the distance from critical coupling. It is found that there is no phase transition in a low density type-II gas, but there i...

  19. Swarms, Phase Transitions, and Collective Intelligence

    CERN Document Server

    Millonas, M M

    1993-01-01

    A spacially extended model of the collective behavior of a large number of locally acting organisms is proposed in which organisms move probabilistically between local cells in space, but with weights dependent on local morphogenetic substances, or morphogens. The morphogens are in turn are effected by the passage of an organism. The evolution of the morphogens, and the corresponding flow of the organisms constitutes the collective behavior of the group. Such models have various types of phase transitions and self-organizing properties controlled both by the level of the noise, and other parameters. The model is then applied to the specific case of ants moving on a lattice. The local behavior of the ants is inspired by the actual behavior observed in the laboratory, and analytic results for the collective behavior are compared to the corresponding laboratory results. It is hoped that the present model might serve as a paradigmatic example of a complex cooperative system in nature. In particular swarm models c...

  20. Phase transitions in models of human cooperation

    Science.gov (United States)

    Perc, Matjaž

    2016-08-01

    If only the fittest survive, why should one cooperate? Why should one sacrifice personal benefits for the common good? Recent research indicates that a comprehensive answer to such questions requires that we look beyond the individual and focus on the collective behavior that emerges as a result of the interactions among individuals, groups, and societies. Although undoubtedly driven also by culture and cognition, human cooperation is just as well an emergent, collective phenomenon in a complex system. Nonequilibrium statistical physics, in particular the collective behavior of interacting particles near phase transitions, has already been recognized as very valuable for understanding counterintuitive evolutionary outcomes. However, unlike pairwise interactions among particles that typically govern solid-state physics systems, interactions among humans often involve group interactions, and they also involve a larger number of possible states even for the most simplified description of reality. Here we briefly review research done in the realm of the public goods game, and we outline future research directions with an emphasis on merging the most recent advances in the social sciences with methods of nonequilibrium statistical physics. By having a firm theoretical grip on human cooperation, we can hope to engineer better social systems and develop more efficient policies for a sustainable and better future.

  1. Structural and Magnetic Phase Transitions in Manganese Arsenide Thin-Films Grown by Molecular Beam Epitaxy

    Science.gov (United States)

    Jaeckel, Felix Till

    that the evolution of electrical resistivity in the coexistence regime of alpha- and beta-phase can be understood in terms of a simple model. These measurements allow accurate extraction of the order-parameter "phase fraction" and thus permit us to study the hysteresis of the phase transition in detail. Major features in the hysteresis can be correlated to the ordering observed in the array of alpha- and beta-stripes. As the continuous ferromagnetic film breaks up into isolated stripes of alpha-phase, a hysteresis in the out-of-plane magnetization is detected from measurements of the anomalous Hall effect. The appearance of out-of-plane domains can be understood from simple shape-anisotropy arguments. Remarkably, an anomaly of the Hall effect at low fields persists far into the beta-phase. Signatures of the more elusive beta- to gamma-transition are found in the temperature-dependence of resistivity, the out-of-plane lattice constant, and reflectance difference spectra. The transition temperature is significantly lowered compared to the bulk, consistent with the strained state of the material. The negative temperature coefficient of resistivity, as well as its anisotropic changes, lend support to the idea of an antiferromagnetic order within the beta-phase.

  2. The Wilson Flow and the finite temperature phase transition

    OpenAIRE

    Wandelt, Michèle; Knechtli, Francesco; Günther, Michael

    2016-01-01

    We consider the determination of the finite temperature phase transition in the Yang--Mills SU(3) gauge theory. We compute the difference of the spatial and temporal energy density at a physical Wilson flow time. This difference is zero in the confined phase and becomes non zero in the deconfined phase. We locate the phase transition by using a new technique based on an exponential smoothing spline. This method is an alternative to the determination of the phase transition based on the Polyak...

  3. Highly birefringent crystal for Raman transitions with phase modulators

    Science.gov (United States)

    Arias, Nieves; Abediyeh, Vahide; Hamzeloui, Saeed; Jeronimo-Moreno, Yasser; Gomez, Eduardo

    2016-05-01

    We present a system to excite Raman transitions with minimum phase noise. The system uses a phase modulator to generate the phase locked beams required for the transition. We use a long calcite crystal to filter out one of the sidebands, avoiding the cancellation that appears at high detunings for phase modulation. The measured phase noise is limited by the quality of the microwave synthesizer. We use the calcite crystal a second time to produce a co-propagating Raman pair with perpendicular polarizations to drive velocity insensitive Raman transitions. Support from CONACYT and Fundacion Marcos Moshinsky.

  4. The Wilson Flow and the finite temperature phase transition

    CERN Document Server

    Wandelt, Michèle; Günther, Michael

    2016-01-01

    We consider the determination of the finite temperature phase transition in the Yang--Mills SU(3) gauge theory. We compute the difference of the spatial and temporal energy density at a physical Wilson flow time. This difference is zero in the confined phase and becomes non zero in the deconfined phase. We locate the phase transition by using a new technique based on an exponential smoothing spline. This method is an alternative to the determination of the phase transition based on the Polyakov loop susceptibility and can also be used with dynamical fermions.

  5. Van der Waals phase transition in the framework of holography

    CERN Document Server

    Zeng, Xiao-Xiong

    2015-01-01

    Phase structure of the quintessence Reissner-Nordstr\\"{o}m-AdS black hole is probed with the nonlocal observables such as holographic entanglement entropy and two point correlation function. Our result shows that, as the case of the thermal entropy, both the observables exhibit the similar Van der Waals-like phase transition. To reinforce the conclusion, we further check the equal area law for the first order phase transition and critical exponent of the heat capacity for the second order phase transition. We also discuss the effect of the state parameter on the phase structure of the nonlocal observables.

  6. Cosmological Consequences of QCD Phase Transition(s) in Early Universe

    CERN Document Server

    Tawfik, A

    2008-01-01

    We discuss the cosmological consequences of QCD phase transition(s) on the early universe. We argue that our recent knowledge about the transport properties of quark-gluon plasma (QGP) should throw additional lights on the actual time evolution of our universe. Understanding the nature of QCD phase transition(s), which can be studied in lattice gauge theory and verified in heavy ion experiments, provides an explanation for cosmological phenomenon stem from early universe.

  7. LETTER TO THE EDITOR: Phase transitions, partial disorder and multi-k structures in Gd2Ti2O7

    Science.gov (United States)

    Stewart, J. R.; Ehlers, G.; Wills, A. S.; Bramwell, S. T.; Gardner, J. S.

    2004-07-01

    The geometrically frustrated antiferromagnet Gd2Ti2O7 exhibits magnetic behaviour of such complexity that it poses a challenge to both experiment and theory. Magnetic ordering commences at TN = 1.1 K and there is a further magnetic phase transition at T^{\\prime }=0.7 K. Here we use neutron diffraction to definitively establish the nature of the phase transition at T^{\\prime } and the magnetic structure adopted below this temperature. Between T^{\\prime } and TN the structure is partly ordered, as previously reported. Below T^{\\prime } the remaining spins order, but only weakly. The magnetic structure in this temperature range is shown to be a 4-k structure, closely related to the 1-k structure previously suggested. The 4-k and 1-k variants of the structure are distinguished by analysis of the diffuse scattering, which we believe represents a new method of solving the 'multi-k' problem of magnetic structure determination.

  8. Liquid-Gas Phase Transition in Nuclear Equation of State

    CERN Document Server

    Lee, S J

    1997-01-01

    A canonical ensemble model is used to describe a caloric curve of nuclear liquid-gas phase transition. Allowing a discontinuity in the freeze out density from one spinodal density to another for a given initial temperature, the nuclear liquid-gas phase transition can be described as first order. Averaging over various freeze out densities of all the possible initial temperatures for a given total reaction energy, the first order characteristics of liquid-gas phase transition is smeared out to a smooth transition. Two experiments, one at low beam energy and one at high beam energy show different caloric behaviors and are discussed.

  9. Quantum phase transitions in Bose-Fermi systems

    CERN Document Server

    Petrellis, D; Iachello, F

    2011-01-01

    Quantum phase transitions in a system of N bosons with angular momentum L=0,2 (s,d) and a single fermion with angular momentum j are investigated both classically and quantum mechanically. It is shown that the presence of the odd fermion strongly influences the location and nature of the phase transition, especially the critical value of the control parameter at which the phase transition occurs. Experimental evidence for the U(5)-SU(3) (spherical to axially-deformed) transition in odd-even nuclei is presented.

  10. Impacts of first-order phase transition and phase coexistence on the universal behavior of inverse magnetocaloric effect

    Science.gov (United States)

    Biswas, Anis; Bingham, N. S.; Phan, T. L.; Dan, N. H.; Yu, S. C.; Phan, M. H.; Srikanth, H.

    2014-05-01

    A systematic study of the inverse magnetocaloric effect (IMCE) in Ni50Mn35.8Sn14.2 and Pr0.5Sr0.5MnO3 has been performed to understand the impacts of first-order phase transition (FOPT) and phase coexistence on the universality of the temperature-dependent magnetic entropy change, ΔSM(T). We show that for Ni50Mn35.8Sn14.2—a system exhibiting IMCE associated with FOPT—it is possible to construct a universal master curve to describe ΔSM(T) in different applied fields without rescaling a temperature axis. However, the universality of IMCE does not hold for Pr0.5Sr0.5MnO3—a system with coexisting ferromagnetic and antiferromagnetic phases. The proposed universal curve provides a simple method for extrapolating ΔSM in a wide range of fields and temperatures, thus giving useful guidance to the design of magnetocaloric materials for active magnetic refrigeration technology.

  11. Quantum Monte Carlo simulation of topological phase transitions

    CERN Document Server

    Yamamoto, Arata

    2016-01-01

    We study the electron-electron interaction effects on topological phase transitions by the ab-initio quantum Monte Carlo simulation. We analyze two-dimensional class A topological insulators and three-dimensional Weyl semimetals with the long-range Coulomb interaction. The direct computation of the Chern number shows the electron-electron interaction modifies or extinguishes topological phase transitions.

  12. Experimental and theoretical investigations on shock wave induced phase transitions

    Science.gov (United States)

    Gupta, Satish C.; Sikka, S. K.

    2001-06-01

    Shock wave loading of a material can cause variety of phase transitions, like polymorphism, amorphization, metallization and molecular dissociations. As the shocked state lasts only for a very short duration (about a few microseconds or less), in-situ microscopic measurements are very difficult. Although such studies are beginning to be possible, most of the shock-induced phase transitions are detected using macroscopic measurements. The microscopic nature of the transition is then inferred from comparison with static pressure data or interpreted by theoretical methods. For irreversible phase transitions, microscopic measurements on recovered samples, together with orientation relations determined from selected area electron diffraction and examination of the morphology of growth of the new phase can provide insight into mechanism of phase transitions. On theoretical side, the current ab initio band structure techniques based on density functional formalism provide capability for accurate computation of the small energy differences (a few mRy or smaller) between different plausible structures. Total energy calculation along the path of a phase transition can furnish estimates of activation barrier, which has implications for understanding kinetics of phase transitions. Molecular dynamics calculations, where the new structure evolves naturally, are becoming increasingly popular especially for understanding crystal to amorphous phase transitions. Illustrations from work at our laboratory will be presented.

  13. Nuclear Liquid-Gas Phase Transition: Experimental Signals

    Science.gov (United States)

    D'Agostino, M.; Bruno, M.; Gulminelli, F.; Cannata, F.; Chomaz, Ph.; Casini, G.; Geraci, E.; Gramegna, F.; Moroni, A.; Vannini, G.

    2005-03-01

    The connection between the thermodynamics of charged finite nuclear systems and the asymptotically measured partitions in heavy ion collisions is discussed. Different independent signals compatible with a liquid-to-gas-like phase transition are reported. In particular abnormally large fluctuations in the measured observables are presented as a strong evidence of a first order phase transition with negative heat capacity.

  14. Nuclear liquid-gas phase transition: Experimental signals

    Energy Technology Data Exchange (ETDEWEB)

    D' Agostino, M. [Dipartimento di Fisica and INFN, Bologna (Italy); Bruno, M. [Dipartimento di Fisica and INFN, Bologna (Italy); Gulminelli, F. [LPC Caen (IN2P3-CNRS/ISMRA et Universite), F-14050 Caen Cedex (France); Cannata, F. [Dipartimento di Fisica and INFN, Bologna (Italy); Chomaz, Ph. [GANIL, DSM-CEA/IN2P3-CNRS (France); Casini, G. [INFN Sezione di Firenze (Italy); Geraci, E. [Dipartimento di Fisica and INFN, Bologna (Italy); Gramegna, F. [INFN Laboratorio Nazionale di Legnaro (Italy); Moroni, A. [Dipartimento di Fisica and INFN, Milano (Italy); Vannini, G. [Dipartimento di Fisica and INFN, Bologna (Italy)

    2005-03-07

    The connection between the thermodynamics of charged finite nuclear systems and the asymptotically measured partitions in heavy ion collisions is discussed. Different independent signals compatible with a liquid-to-gas-like phase transition are reported. In particular abnormally large fluctuations in the measured observables are presented as a strong evidence of a first order phase transition with negative heat capacity.

  15. Multipartite entanglement characterization of a quantum phase transition

    OpenAIRE

    Costantini, G.; Facchi, P.; G. Florio; Pascazio, S.

    2006-01-01

    A probability density characterization of multipartite entanglement is tested on the one-dimensional quantum Ising model in a transverse field. The average and second moment of the probability distribution are numerically shown to be good indicators of the quantum phase transition. We comment on multipartite entanglement generation at a quantum phase transition.

  16. On the nature of phase transition in solid electrolytes

    International Nuclear Information System (INIS)

    An attempt is made to precisely measure the solid electrolyte RbAg4I5 conductivity in the vicinity of the phase transition at 208 deg K. Polycrystalline samples obtained by common technique have been used as well as single RbAg4I5 crystals grown from the acetone solution of AgI and RbI. The dependence of conductivity on inverse temperature is given for different samples. The phase transition of the single crystals is accompanied by a jump (approximately 12%) of conductivity. This transfer is reversible, since no hysteresis is found in the +-0.3 deg K vicinity of the phase transition temperature. Polycrystalline samples display no pronounces jump of conductivity, but the conductivity curve has two bends, i.e. the phase transition is ''diffused''. The activation energy before the transition differs from that after the transition

  17. Pressure-induced phase transitions and metallization in VO2

    Science.gov (United States)

    Bai, Ligang; Li, Quan; Corr, Serena A.; Meng, Yue; Park, Changyong; Sinogeikin, Stanislav V.; Ko, Changhyun; Wu, Junqiao; Shen, Guoyin

    2015-03-01

    We report the results of pressure-induced phase transitions and metallization in VO2 based on synchrotron x-ray diffraction, electrical resistivity, and Raman spectroscopy. Our isothermal compression experiments at room temperature and 383 K show that the room temperature monoclinic phase (M 1 ,P 21/c ) and the high-temperature rutile phase (R ,P 42/m n m ) of VO2 undergo phase transitions to a distorted M 1 monoclinic phase (M 1' ,P 21/c ) above 13.0 GPa and to an orthorhombic phase (CaCl2-like, P n n m ) above 13.7 GPa, respectively. Upon further compression, both high-pressure phases transform into a new phase (phase X ) above 34.3 and 38.3 GPa at room temperature and 383 K, respectively. The room temperature M 1 -M 1' phase transition structurally resembles the R -CaCl2 phase transition at 383 K, suggesting a second-order displacive type of transition. Contrary to previous studies, our electrical resistivity results, Raman measurements, as well as ab initio calculations indicate that the new phase X , rather than the M 1' phase, is responsible for the metallization under pressure. The metallization mechanism is discussed based on the proposed crystal structure.

  18. High pressure phase transitions for CdSe

    Indian Academy of Sciences (India)

    Bo Kong; Ti-Xian Zeng; Zhu-Wen Zhou; De-Liang Chen; Xiao-Wei Sun

    2014-05-01

    The structure and pressure-induced phase transitions for CdSe are investigated using first-principles calculations. The pressure-induced phase transition sequence WZ/ZB $\\to$ Rs $\\to$ $\\to$ CsCl for CdSe is drawn reasonably for the fist time, the corresponding transition pressures are 3.8, 29 and 107 GPa, respectively and the intermediate states between the structure and the CsCl structure should exist.

  19. Quantum Phase Transitions in Odd-Mass Nuclei

    CERN Document Server

    Leviatan, A; Iachello, F

    2011-01-01

    Quantum shape-phase transitions in odd-even nuclei are investigated in the framework of the interacting boson-fermion model. Classical and quantum analysis show that the presence of the odd fermion strongly influences the location and nature of the phase transition, especially near the critical point. Experimental evidence for the occurrence of spherical to axially-deformed transitions in odd-proton nuclei Pm, Eu and Tb (Z=61, 63, 65) is presented.

  20. Low Energy Dynamics in Spin-Liquid and Ordered Phases of S=1/2 Antiferromagnet Cs2CuCl4

    Science.gov (United States)

    Smirnov, A. I.; Povarov, K. Yu; Starykh, O. A.; Shapiro, A. Ya; Petrov, S. V.

    2012-12-01

    Cs2CuCl4 realizes spin-1/2 quantum antiferromagnet on a distorted triangular lattice. It remains in a quantum spin-liquid state far below Curie-Weiss temperature 4 K and exhibits an incommensurate spin ordering at TN=0.6 K. We studied Cs2CuCl4 by means of electron spin resonance (ESR) at temperatures down to 0.05 K in the frequency range 9crossover of the signal from the above spinon-type ESR toward a resonance of a spiral-AFM type. However, for higher frequency f>60 GHz, we observe that the above spinon-type ESR survives deep in the ordered phase. These novel phenomena are consequences of fractionalized spinon excitations of spin chains, which are effectively decoupled in Cs2CuCl4 due to strong geometric frustration.

  1. Phase transition of Bose—Einstein condensate under decoherence

    International Nuclear Information System (INIS)

    The effect of decoherence on the phase transition of a Bose—Einstein condensate in a symmetric double-well potential is determined by the mean atom number difference. It still has two phases, the tunneling phase and the self-trapping phase, even under decoherence. The density matrix and the operator fidelity also show very different behaviors in the two phases. This suggests that operator fidelity can be used to characterize the phase transition of this Bose—Einstein condensate model, even under decoherence. (condensed matter: structural, mechanical, and thermal properties)

  2. Pressure-induced phase transitions and metallization in VO2

    OpenAIRE

    Bai, Ligang; Li, Quan; Corr, Serena A; Meng, Yue; Park, Changyong; Sinogeikin, Stanislav V.; Ko, Changhyun; Wu, Junqiao; Shen, Guoyin

    2015-01-01

    We report the results of pressure-induced phase transitions and metallization in VO2 based on synchrotron x-ray diffraction, electrical resistivity, and Raman spectroscopy. Our isothermal compression experiments at room temperature and 383 K show that the room temperature monoclinic phase (M1,P21/c) and the high-temperature rutile phase (R,P42/mnm) of VO2 undergo phase transitions to a distorted M1 monoclinic phase (M1′,P21/c) above 13.0 GPa and to an orthorhombic phase (CaCl2-like, Pnnm) abo...

  3. Bilayer Quantum Hall Systems: Spin-Pseudospin Symmetry Breaking and Quantum Phase Transitions

    OpenAIRE

    Sarma, Sankar Das; Demler, Eugene

    2000-01-01

    We discuss and review recent advances in our understaning of quantum Hall systems where additional quantum numbers associated with spin and/or layer (pseudospin) indices play crucial roles in creating exotic quantum phases. Among the novel quantum phases we discuss are the recently discovered canted antiferromagnetic phase, the spontaneous interlayer coherent phase, and various spin Bose glass phases. We describe the theoretical models used in studying these novel phases and the various exper...

  4. Phase transition and PTCR effect in erbium doped BT ceramics

    International Nuclear Information System (INIS)

    Highlights: ► Erbium influence the dielectric response BaTiO3 ceramics. ► Features of the phase transition are not explained by phenomenological models. ► Relaxation parameters do not show influence on ferroelectric–paraelectric phase transition. ► Dielectric anomaly on BET phase transition is associated with the PTCR effect. - Abstract: In this work the dielectric behaviour and main features of the phase transition of BaTiO3 and Ba0.99Er0.01TiO3 ceramics were carefully investigated. The temperature and frequency dependences of the dielectric properties of erbium doped BaTiO3 ceramics were measured in the 25–225 °C and 100 Hz to 10 MHz ranges, respectively. From this study, a dielectric anomaly in the ferroelectric–paraelectric phase transition of the Ba0.99Er0.01TiO3 ceramic was observed. The features of the samples phase transition were analysed by using Curie–Weiss, Santos–Eiras’ and order parameter local phenomenological models. In the BaTiO3 system, all models showed a normal phase transition, while was not possible to establish the character of the phase transition in the Ba0.99Er0.01TiO3 system. The relaxation parameters of conductive processes for the study ferroelectric materials, analysed in the time domain, did not show any influence on the ferroelectric–paraelectric phase transition. Finally, it was demonstrated that the anomaly observed on the phase transition of the erbium doped BaTiO3 ceramics is associated with the processes that results in the PTCR effect.

  5. Phase transition and PTCR effect in erbium doped BT ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Leyet, Y. [Departamento de Fisica, Facultad de Ciencias Naturales, Universidad de Oriente, C.P. 90500 Santiago de Cuba (Cuba); Instituto Federal de Educacao Ciencia e Tecnologia (IFAM), Av. 7 de Setembro 1975, Centro, Manaus 69020-120, AM (Brazil); Pena, R.; Zulueta, Y. [Departamento de Fisica, Facultad de Ciencias Naturales, Universidad de Oriente, C.P. 90500 Santiago de Cuba (Cuba); Guerrero, F. [Departamento de Fisica, Facultad de Ciencias Naturales, Universidad de Oriente, C.P. 90500 Santiago de Cuba (Cuba); CESI, Universidade do Estado do Amazonas, Ave Mario Andreaza, Amazonas (Brazil); Anglada-Rivera, J. [CESI, Universidade do Estado do Amazonas, Ave Mario Andreaza, Amazonas (Brazil); Romaguera, Y. [INESC TEC, Rua do Campo Alegre, 687, 4169-007 Porto (Portugal); Perez de la Cruz, J., E-mail: jcruz@inescporto.pt [INESC TEC, Rua do Campo Alegre, 687, 4169-007 Porto (Portugal)

    2012-06-25

    Highlights: Black-Right-Pointing-Pointer Erbium influence the dielectric response BaTiO{sub 3} ceramics. Black-Right-Pointing-Pointer Features of the phase transition are not explained by phenomenological models. Black-Right-Pointing-Pointer Relaxation parameters do not show influence on ferroelectric-paraelectric phase transition. Black-Right-Pointing-Pointer Dielectric anomaly on BET phase transition is associated with the PTCR effect. - Abstract: In this work the dielectric behaviour and main features of the phase transition of BaTiO{sub 3} and Ba{sub 0.99}Er{sub 0.01}TiO{sub 3} ceramics were carefully investigated. The temperature and frequency dependences of the dielectric properties of erbium doped BaTiO{sub 3} ceramics were measured in the 25-225 Degree-Sign C and 100 Hz to 10 MHz ranges, respectively. From this study, a dielectric anomaly in the ferroelectric-paraelectric phase transition of the Ba{sub 0.99}Er{sub 0.01}TiO{sub 3} ceramic was observed. The features of the samples phase transition were analysed by using Curie-Weiss, Santos-Eiras' and order parameter local phenomenological models. In the BaTiO{sub 3} system, all models showed a normal phase transition, while was not possible to establish the character of the phase transition in the Ba{sub 0.99}Er{sub 0.01}TiO{sub 3} system. The relaxation parameters of conductive processes for the study ferroelectric materials, analysed in the time domain, did not show any influence on the ferroelectric-paraelectric phase transition. Finally, it was demonstrated that the anomaly observed on the phase transition of the erbium doped BaTiO{sub 3} ceramics is associated with the processes that results in the PTCR effect.

  6. In-situ microscopy of the first-order magnetic phase transition in FeRh thin films

    Science.gov (United States)

    Baldasseroni, Chloe

    Simple ferromagnetic (FM) and antiferromagnetic (AF) materials such as Fe and Cr become paramagnetic when heated above some critical temperature, in what is known as a second-order phase transition. Less usual magnetic transitions are found in the magnetic world, for example a first-order magnetic phase transition from AF to FM with increasing temperature. Equiatomic FeRh has been known to exhibit such a transition for over 50 years, with a transition temperature slightly above room temperature. Interest in this material has been renewed in the recent years due to its potential application for heat-assisted magnetic recording, as well as a test system for fundamental studies of the physics of magnetic phase transitions. Similarly to crystallization, this AF-FM transition is expected to proceed by nucleation of magnetic domains but the features of the first-order hysteretic transition have been difficult to study with macroscopic measurements and very few microscopic studies have been performed. In this work, FeRh thin films were synthesized by magnetron sputtering and structurally and magnetically characterized. A membrane-based heating device was designed to enable temperature-dependent microscopy measurements, providing a thermally uniform and well-controlled sample area. Synchrotron x-ray magnetic microscopy was used to study the temperature-driven AF-FM phase transition in epitaxial FeRh thin films in zero field. Using magnetic microscopy with x-ray magnetic circular dichroism, the different stages of nucleation, growth and coalescence of FM domains were observed across the transition and details of the nucleation were identified. The FM phase nucleates into single domain islands and the width of the transition of the individual nuclei upon heating is sharper than that of the macroscopic transition. Using magnetic microscopy with x-ray magnetic linear dichroism, the evolution of the AF phase was studied. Differences in the morphology of AF and FM phases were

  7. Quantum phase transitions of topological insulators without gap closing.

    Science.gov (United States)

    Rachel, Stephan

    2016-10-12

    We consider two-dimensional Chern insulators and time-reversal invariant topological insulators and discuss the effect of perturbations breaking either particle-number conservation or time-reversal symmetry. The appearance of trivial mass terms is expected to cause quantum phase transitions into trivial phases when such a perturbation overweighs the topological term. These phase transitions are usually associated with a bulk-gap closing. In contrast, the chiral Chern insulator is unaffected by particle-number breaking perturbations. Moreover, the [Formula: see text] topological insulator undergoes phase transitions into topologically trivial phases without bulk-gap closing in the presence of any of such perturbations. In certain cases, these phase transitions can be circumvented and the protection restored by another U(1) symmetry, e.g. due to spin conservation. These findings are discussed in the context of interacting topological insulators. PMID:27530509

  8. Electronic and vibrational Raman spectroscopy of Nd0.5Sr0.5MnO3 through the phase transitions

    Indian Academy of Sciences (India)

    Md Motin Seikh; A K Sood; Chandrabhas Narayana

    2005-01-01

    Raman scattering experiments have been carried out on single crystals of Nd0.5Sr0.5MnO3 as a function of temperature in the range of 320–50 K, covering the paramagnetic insulator–ferromagnetic metal transition at 250 K and the charge-ordering antiferromagnetic transition at 150 K. The diffusive electronic Raman scattering response is seen in the paramagnetic phase which continue to exist even in the ferromagnetic phase, eventually disappearing below 150 K. We understand the existence of diffusive response in the ferromagnetic phase to the coexistence of the different electronic phases. The frequency and linewidth of the phonons across the transitions show significant changes, which cannot be accounted for only by anharmonic interactions.

  9. Temperature controlled motion of an antiferromagnet- ferromagnet interface within a dopant-graded FeRh epilayer

    Directory of Open Access Journals (Sweden)

    C. Le Graët

    2015-04-01

    Full Text Available Chemically ordered B2 FeRh exhibits a remarkable antiferromagnetic-ferromagnetic phase transition that is first order. It thus shows phase coexistence, usually by proceeding though nucleation at random defect sites followed by propagation of phase boundary domain walls. The transition occurs at a temperature that can be varied by doping other metals onto the Rh site. We have taken advantage of this to yield control over the transition process by preparing an epilayer with oppositely directed doping gradients of Pd and Ir throughout its height, yielding a gradual transition that occurs between 350 K and 500 K. As the sample is heated, a horizontal antiferromagnetic-ferromagnetic phase boundary domain wall moves gradually up through the layer, its position controlled by the temperature. This mobile magnetic domain wall affects the magnetisation and resistivity of the layer in a way that can be controlled, and hence exploited, for novel device applications.

  10. Temperature controlled motion of an antiferromagnet- ferromagnet interface within a dopant-graded FeRh epilayer

    Science.gov (United States)

    Le Graët, C.; Charlton, T. R.; McLaren, M.; Loving, M.; Morley, S. A.; Kinane, C. J.; Brydson, R. M. D.; Lewis, L. H.; Langridge, S.; Marrows, C. H.

    2015-04-01

    Chemically ordered B2 FeRh exhibits a remarkable antiferromagnetic-ferromagnetic phase transition that is first order. It thus shows phase coexistence, usually by proceeding though nucleation at random defect sites followed by propagation of phase boundary domain walls. The transition occurs at a temperature that can be varied by doping other metals onto the Rh site. We have taken advantage of this to yield control over the transition process by preparing an epilayer with oppositely directed doping gradients of Pd and Ir throughout its height, yielding a gradual transition that occurs between 350 K and 500 K. As the sample is heated, a horizontal antiferromagnetic-ferromagnetic phase boundary domain wall moves gradually up through the layer, its position controlled by the temperature. This mobile magnetic domain wall affects the magnetisation and resistivity of the layer in a way that can be controlled, and hence exploited, for novel device applications.

  11. Possible double magnetic phase transition in Dy5CuPb3

    Science.gov (United States)

    Tran, V. H.; Gulay, L. D.

    2006-03-01

    We have investigated the magnetic and transport properties of Dy5CuPb3 by magnetic susceptibility, electrical resistivity, magnetoresistance and thermoelectric power measurements. The compound crystallises in the hexagonal Hf5CuSn3-type structure (space group P63/mcm) and probably undergoes two successive magnetic transitions at TC=45.0±0.5 K and TN=6.5±0.5 K. The experimental data are indicative of a ferri- and antiferromagnetic types of the transitions, respectively. We attribute the double magnetic phase transition and the reduction of the magnetisation values at low temperatures to associate with the two non-equivalent magnetic sublattices of the Dy ions. We observed a large magnetoresistance value of -24% at temperatures in between TN and TC. The investigated compound has a negative thermoelectric power of -17 μV/K at 300 K. We interpret the overall behaviour of the S(T)-curve to two different mechanisms: magnetic and charge carrier diffusion.

  12. Micellar structures in lyotropic liquid crystals and phase transitions

    Science.gov (United States)

    Saupe, A.; Xu, S. Y.; Plumley, Sulakshana; Zhu, Y. K.; Photinos, P.

    1991-05-01

    The formation of micellar nematics is discussed with emphasis on the transitions between nematic phases and nematic-smectic transitions. Phase diagrams for MTAB/l-decanol/D,O systems show a direct transition between uniaxial nematics. Electrical conductivity and birefringence measurements on a mixture of sodium decylsulfate. 1-decanol, D,O demonstrate, on the other hand, the existence of a biaxial nemantic range that separates the Uniaxial nematics. On a mixture of cesium perflouroctanoate and H 2O the electrical conductivity and rotational viscosity are used to discuss the relevant features of nematic-lamellar-smectic transitions. The formation of elongated ribbon-like micelles at the nematic-smectic transition is suggested. Transitions between different nematic phases in the MTAB system may be connected with a structural change from long micelles with a fairly circular cross section to similar micelles with a more elliptical cross section.

  13. Magnetism and electronic phase transitions in monoclinic transition metal dichalcogenides with transition metal atoms embedded

    Science.gov (United States)

    Lin, Xianqing; Ni, Jun

    2016-08-01

    First-principles calculations have been performed to study the energetic, electronic, and magnetic properties of substitutional 3d transition metal dopants in monoclinic transition metal dichalcogenides (TMDs) as topological insulators ( 1 T ' - MX 2 with M = (Mo, W) and X = (S, Se)). We find various favorite features in these doped systems to introduce magnetism and other desirable electronic properties: (i) The Mn embedded monoclinic TMDs are magnetic, and the doped 1 T ' - MoS 2 still maintains the semiconducting character with high concentration of Mn, while an electronic phase transition occurs in other Mn doped monoclinic TMDs with an increasing concentration of Mn. Two Mn dopants prefer the ferromagnetic coupling except for substitution of the nearest Mo atoms in 1 T ' - MoS 2 , and the strength of exchange interaction shows anisotropic behavior with dopants along one Mo zigzag chain having much stronger coupling. (ii) The substitutional V is a promising hole dopant, which causes little change to the energy dispersion around the conduction and valence band edges in most systems. In contrast, parts of the conduction band drop for the electron dopants Co and Ni due to the large structural distortion. Moreover, closing band gaps of the host materials are observed with increasing carrier concentration. (iii) Single Fe dopant has a magnetic moment, but it also dopes electrons. When two Fe dopants have a small distance, the systems turn into nonmagnetic semiconductors. (iv) The formation energies of all dopants are much lower than those in hexagonal TMDs and are all negative in certain growth conditions, suggesting possible realization of the predicted magnetism, electronic phase transitions as well as carrier doping in 1 T ' - MX 2 based topological devices.

  14. Primordial Magnetic Fields from Cosmological First Order Phase Transitions

    CERN Document Server

    Sigl, G; Jedamzik, K; Sigl, Guenter; Olinto, Angela; Jedamzik, Karsten

    1996-01-01

    We give an improved estimate of primordial magnetic fields generated during cosmological first order phase transitions. We examine the charge distribution at the nucleated bubble wall and its dynamics. We consider instabilities on the bubble walls developing during the phase transition. It is found that damping of these instabilities due to viscosity and heat conductivity caused by particle diffusion can be important in the QCD phase transition, but is probably negligible in the electroweak transition. We show how such instabilities together with the surface charge densities on bubble walls excite magnetic fields within a certain range of wavelengths. We discuss how these magnetic seed fields may be amplified by MHD effects in the turbulent fluid. The strength and spectrum of the primordial magnetic field at the present time for the cases where this mechanism was operative during the electroweak or the QCD phase transition are estimated. On a 10 Mpc comoving scale, field strengths of the order 10**(-29) G for...

  15. Dynamics of Phase Transitions by Hysteresis Methods I

    CERN Document Server

    Berg, B A; Meyer-Ortmanns, H; Velytsky, A; Berg, Bernd A.; Heller, Urs M.; Meyer-Ortmanns, Hildegard; Velytsky, Alexander

    2004-01-01

    In studies of the QCD deconfining phase transition or crossover by means of heavy ion experiments, one ought to be concerned about non-equilibrium effects due to heating and cooling of the system. Motivated by this, we look at hysteresis methods to study the dynamics of phase transitions. Our systems are temperature driven through the phase transition using updating procedures in the Glauber universality class. Hysteresis calculations are presented for a number of observables, including the (internal) energy, properties of Fortuin-Kasteleyn clusters and structure functions. We test the methods for 2d Potts models, which provide a rich collection of phase transitions with a number of rigorously known properties. Comparing with equilibrium configurations we find a scenario where the dynamics of the transition leads to a spinodal decomposition which dominates the statistical properties of the configurations. One may expect an enhancement of low energy gluon production due to spinodal decomposition of the Polyako...

  16. Chern-Simons diffusion rate across different phase transitions

    Science.gov (United States)

    Rougemont, Romulo; Finazzo, Stefano Ivo

    2016-05-01

    We investigate how the dimensionless ratio given by the Chern-Simons diffusion rate ΓCS divided by the product of the entropy density s and temperature T behaves across different kinds of phase transitions in the class of bottom-up nonconformal Einstein-dilaton holographic models originally proposed by Gubser and Nellore. By tuning the dilaton potential, one is able to holographically mimic a first order, a second order, or a crossover transition. In a first order phase transition, ΓCS/s T jumps at the critical temperature (as previously found in the holographic literature), while in a second order phase transition it develops an infinite slope. On the other hand, in a crossover, ΓCS/s T behaves smoothly, although displaying a fast variation around the pseudo-critical temperature. In all the cases, ΓCS/s T increases with decreasing T . The behavior of the Chern-Simons diffusion rate across different phase transitions is expected to play a relevant role for the chiral magnetic effect around the QCD critical end point, which is a second order phase transition point connecting a crossover band to a line of first order phase transition. Our findings in the present work add to the literature the first predictions for the Chern-Simons diffusion rate across second order and crossover transitions in strongly coupled nonconformal, non-Abelian gauge theories.

  17. Structural and magnetic phase transitions in CeCu6 -xTx (T =Ag ,Pd )

    Science.gov (United States)

    Poudel, L.; de la Cruz, C.; Payzant, E. A.; May, A. F.; Koehler, M.; Garlea, V. O.; Taylor, A. E.; Parker, D. S.; Cao, H. B.; McGuire, M. A.; Tian, W.; Matsuda, M.; Jeen, H.; Lee, H. N.; Hong, T.; Calder, S.; Zhou, H. D.; Lumsden, M. D.; Keppens, V.; Mandrus, D.; Christianson, A. D.

    2015-12-01

    The structural and the magnetic properties of CeCu6 -xAgx (0 ≤x ≤0.85 ) and CeCu6 -xPdx (0 ≤x ≤0.4 ) have been studied using neutron diffraction, resonant ultrasound spectroscopy (RUS), x-ray diffraction measurements, and first principles calculations. The structural and magnetic phase diagrams of CeCu6 -xAgx and CeCu6 -xPdx as a function of Ag/Pd composition are reported. The end member, CeCu6, undergoes a structural phase transition from an orthorhombic (P n m a ) to a monoclinic (P 21/c ) phase at 240 K. In CeCu6 -xAgx , the structural phase transition temperature (Ts) decreases linearly with Ag concentration and extrapolates to zero at xS ≈0.1 . The structural transition in CeCu6 -xPdx remains unperturbed with Pd substitution within the range of our study. The lattice constant b slightly decreases with Ag/Pd doping, whereas a and c increase with an overall increase in the unit cell volume. Both systems, CeCu6 -xAgx and CeCu6 -xPdx , exhibit a magnetic quantum critical point (QCP), at x ≈0.2 and x ≈0.05 , respectively. Near the QCP, long range antiferromagnetic ordering takes place at an incommensurate wave vector (δ10 δ2), where δ1˜0.62 ,δ2˜0.25 ,x =0.125 for CeCu6 -xPdx and δ1˜0.64 ,δ2˜0.3 ,x =0.3 for CeCu6 -xAgx . The magnetic structure consists of an amplitude modulation of the Ce moments which are aligned along the c axis of the orthorhombic unit cell.

  18. Deviatoric stress-induced phase transitions in diamantane

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Fan; Lin, Yu [Geological and Environmental Sciences, Stanford University, Stanford, California 94305 (United States); Dahl, Jeremy E. P.; Carlson, Robert M. K. [Stanford Institute for Materials and Energy Science, Stanford, California 94305 (United States); Mao, Wendy L. [Geological and Environmental Sciences, Stanford University, Stanford, California 94305 (United States); Stanford Institute for Materials and Energy Science, Stanford, California 94305 (United States); Photon Science, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States)

    2014-10-21

    The high-pressure behavior of diamantane was investigated using angle-dispersive synchrotron x-ray diffraction (XRD) and Raman spectroscopy in diamond anvil cells. Our experiments revealed that the structural transitions in diamantane were extremely sensitive to deviatoric stress. Under non-hydrostatic conditions, diamantane underwent a cubic (space group Pa3) to a monoclinic phase transition at below 0.15 GPa, the lowest pressure we were able to measure. Upon further compression to 3.5 GPa, this monoclinic phase transformed into another high-pressure monoclinic phase which persisted to 32 GPa, the highest pressure studied in our experiments. However, under more hydrostatic conditions using silicone oil as a pressure medium, the transition pressure to the first high-pressure monoclinic phase was elevated to 7–10 GPa, which coincided with the hydrostatic limit of silicone oil. In another experiment using helium as a pressure medium, no phase transitions were observed to the highest pressure we reached (13 GPa). In addition, large hysteresis and sluggish transition kinetics were observed upon decompression. Over the pressure range where phase transitions were confirmed by XRD, only continuous changes in the Raman spectra were observed. This suggests that these phase transitions are associated with unit cell distortions and modifications in molecular packing rather than the formation of new carbon-carbon bonds under pressure.

  19. High-pressure phase transitions - Examples of classical predictability

    Science.gov (United States)

    Celebonovic, Vladan

    1992-09-01

    The applicability of the Savic and Kasanin (1962-1967) classical theory of dense matter to laboratory experiments requiring estimates of high-pressure phase transitions was examined by determining phase transition pressures for a set of 19 chemical substances (including elements, hydrocarbons, metal oxides, and salts) for which experimental data were available. A comparison between experimental and transition points and those predicted by the Savic-Kasanin theory showed that the theory can be used for estimating values of transition pressures. The results also support conclusions obtained in previous astronomical applications of the Savic-Kasanin theory.

  20. Phase Transition Induced by Small Molecules in Confined Copolymer Films

    Institute of Scientific and Technical Information of China (English)

    ZHOU Ling

    2007-01-01

    We investigate the phase transition induced by small molecules in confined copolymer films by using density functional theory.It is found that the addition of small molecules can effectively promote the phase separation of copolymers.In a symmetric diblock copolymer film,the affinity and concentration of small molecules play an important role in the structure transjtions.The disordered-lamellar transitions lamellar-lamellar transitions and the re-entrant transitions of the same structures are observed.Our results have potential applications in the fabrication of new functional materials.

  1. Phase-separation transitions in asymmetric lipid bilayers

    CERN Document Server

    Shimobayashi, Shunsuke F; Taniguchi, Takashi

    2015-01-01

    Morphological transitions of phase separation associated with the asymmetry of lipid composition were investigated using micrometer-sized vesicles of lipid bilayers made from a lipid mixture. The complete macro-phase-separated morphology undergoes a transition to a micro-phase-separation-like morphology via a lorate morphology as a metastable state. The transition leads to the emergence of monodisperse nanosized domains through repeated domain scission events. Moreover, we have numerically confirmed the transitions using the time-dependent Ginzburg-Landau model describing phase separation and the bending elastic membrane, which is quantitatively consistent with experimental results by fixing one free parameter. Our findings suggest that the local spontaneous curvature due to the asymmetric composition plays an essential role in the thermodynamic stabilization of micro-phase separation in lipid bilayers.

  2. Photothermoelectric (PTE) Versus Photopyroelectric (PPE) Detection of Phase Transitions

    Science.gov (United States)

    Dadarlat, D.; Guilmeau, E.; Hadj Sahraoui, A.; Tudoran, C.; Surducan, V.; Bourgès, C.; Lemoine, P.

    2016-05-01

    The photopyroelectric (PPE) technique is one of the photothermal (PT) methods mostly used for phase transitions investigations. In this paper, we want to compare the PPE results with those obtained using another, recently developed PT method [the photothermoelectric (PTE) calorimetry] for the same purpose of detecting phase transitions. The well-known ferro-paraelectric phase transition of TGS, taking place at a convenient temperature (about 49 {}^{circ }hbox {C}), has been selected for demonstration. A comparison of the two PPE and PTE methods, both in the back detection configuration (in the special case of optically opaque sample and thermally thick regime for both sensors and sample) shows that they are equally suitable for phase transitions detection. Performing a proper calibration, the amplitude and phase of the signals can be used in order to obtain the critical behaviour of all sample's static and dynamic thermal parameters.

  3. Resonating Valence Bond states for low dimensional S=1 antiferromagnets

    Science.gov (United States)

    Liu, Zheng-Xin; Zhou, Yi; Ng, Tai-Kai

    2014-03-01

    We study S = 1 spin liquid states in low dimensions. We show that the resonating-valence-bond (RVB) picture of S = 1 / 2 spin liquid state can be generalized to S = 1 case. For S = 1 system, a many-body singlet (with even site number) can be decomposed into superposition of products of two-body singlets. In other words, the product states of two-body singlets, called the singlet pair states (SPSs), are over complete to span the Hilbert space of many-body singlets. Furthermore, we generalized fermionic representation and the corresponding mean field theory and Gutzwiller projected stats to S = 1 models. We applied our theory to study 1D anti-ferromagnetic bilinear-biquadratic model and show that both the ground states (including the phase transition point) and the excited states can be understood excellently well within the framework. Our method can be applied to 2D S = 1 antiferromagnets.

  4. Phase transitions in pure and dilute thin ferromagnetic films

    Science.gov (United States)

    Korneta, W.; Pytel, Z.

    1983-10-01

    The mean-field model of a thin ferromagnetic film where the nearest-neighbor exchange coupling in surface layers can be different from that inside the film is considered. The phase diagram, equations for the second-order phase-transition lines, and the spontaneous magnetization profiles near the phase transitions are given. It is shown that there is no extra-ordinary transition in a thin film. If the thickness of the film tends to infinity the well-known results for the mean-field model of a semi-infinite ferromagnet are obtained. The generalization for disordered dilute thin ferromagnetic films and semi-infinite ferromagnets is also given.

  5. Superradiant phase transitions with three-level systems

    CERN Document Server

    Baksic, Alexandre; Ciuti, Cristiano

    2013-01-01

    We determine the phase diagram of $N$ identical three-level systems interacting with a single photonic mode in the thermodynamical limit ($N \\to \\infty$) by accounting for the so-called diamagnetic term and the inequalities imposed by the Thomas-Reich-Kuhn (TRK) oscillator strength sum rule. The key role of transitions between excited levels and the occurrence of first-order phase transitions is discussed. We show that, in contrast to two-level systems, in the three-level case the TRK inequalities do not always prevent a superradiant phase transition in presence of a diamagnetic term.

  6. Role of multistability in the transition to chaotic phase synchronization

    DEFF Research Database (Denmark)

    Postnov, D.E.; Vadivasova, T.E.; Sosnovtseva, Olga;

    1999-01-01

    In this paper we describe the transition to phase synchronization for systems of coupled nonlinear oscillators that individually follow the Feigenbaum route to chaos. A nested structure of phase synchronized regions of different attractor families is observed. With this structure, the transition...... to nonsynchronous behavior is determined by the loss of stability for the most stable synchronous mode. It is shown that the appearance of hyperchaos and the transition from lag synchronization to phase synchronization are related to the merging of chaotic attractors from different families. Numerical examples...

  7. Weakly First Order Cosmological Phase Transitions and Fermion Production

    CERN Document Server

    Gleiser, Marcello; Gleiser, Marcelo; Trodden, Mark

    2001-01-01

    We study weakly first order cosmological phase transitions in finite temperature field theories. Focusing on the standard electroweak theory and its minimal supersymmetric extension, we identify the regimes of Higgs masses for which the phase transition in these models proceeds by significant phase mixing and the coarsening of the subsequent domain network. This dynamics is distinct from that for strongly first order transitions, which proceed by the nucleation and propagation of critical bubbles. We describe how electroweak baryogenesis might take place in these models, explaining how our new picture can relax the sphaleron washout bound of traditional scenarios.

  8. On the chiral phase transition in the linear sigma model

    International Nuclear Information System (INIS)

    The Cornwall- Jackiw-Tomboulis (CJT) effective action for composite operators at finite temperature is used to investigate the chiral phase transition within the framework of the linear sigma model as the low-energy effective model of quantum chromodynamics (QCD). A new renormalization prescription for the CJT effective action in the Hartree-Fock (HF) approximation is proposed. A numerical study, which incorporates both thermal and quantum effect, shows that in this approximation the phase transition is of first order. However, taking into account the higher-loop diagrams contribution the order of phase transition is unchanged. (author)

  9. GGA+U study on phase transition, optoelectronic and magnetic properties of AmO{sub 2} with spin–orbit coupling

    Energy Technology Data Exchange (ETDEWEB)

    Bendjedid, A.; Seddik, T. [Laboratoire de Physique Quantique et de Modélisation Mathématique, Université de Mascara, 29000 (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique et de Modélisation Mathématique, Université de Mascara, 29000 (Algeria); Baltache, H. [Laboratoire de Physique Quantique et de Modélisation Mathématique, Université de Mascara, 29000 (Algeria); Murtaza, G., E-mail: murtaza@icp.edu.pk [Materials Modeling Laboratory, Department of Physics, Islamia College University, Peshawar (Pakistan); Bouhemadou, A. [Laboratory for Developing New Materials and their Characterization, Department of Physics, Faculty of Science, University of Setif, 19000 Setif (Algeria); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Azam, Sikander; Khan, Saleem Ayaz [New Technologies-Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic)

    2015-12-15

    In this work, we have investigated the structural, phase transition, optoelectronic and magnetic properties of AmO{sub 2} using the full potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method. The exchange-correlation potential was treated with the generalized gradient approximation (GGA). Moreover, the GGA+U approximation (where U denotes the Hubbard Coulomb energy U term) is employed to treat the f electrons properly. The structurally stable AmO{sub 2} compound is the Fm3m phase and at a pressure between 40 and 60 GPa underwent a phase transition to the Pnma phase. Our present calculations have considered ferromagnetic and simple antiferromagnetic ground states and the AF state is favored. However, the experimental situation suggests a complex magnetic structure, perhaps involving multipolar ordering. Our band structure calculation with GGA and GGA+U predicted the metallic behavior of AmO{sub 2}; however, with the spin–orbit coupling (SOC) added to the Coulomb energy U term, semiconducting ground states with antiferromagnetism is correctly predicted. The projected density of states from the energy-band structure indicates that the band gap opening is governed by the partially filled Am “5f” state, and the calculated gap is approximately 1.29 eV. Moreover, the optical properties reveal strong response of AmO{sub 2} in the UV region. - Highlights: • AmO{sub 2} is antiferromagnetic and stable in the Fm3m phase under ambient conditions. • It makes structural transition from the Fm3m to the Pnma phase at 55.91 GPa. • Columbic repulsion parameter U correctly predicted the electronic state of AmO{sub 2}. • This compound absorbs strongly in the UV region.

  10. Theory of Coupled Phase Transitions: Phase Separation and Variation of Order Parameter

    OpenAIRE

    Zhong, Fan

    1998-01-01

    A simplified Ginzburg-Landau theory is presented to study generally a coupling of a first-order phase transition (FOPT) to a second-order phase transition (SOPT). We show analytically that, due to the coupling between the two phase transitions, the SOPT may exhibit a FOPT-like phase separation in which an ordered phase is separated from a disordered one. This phase separation results in a distinct behavior in the variation of the order parameter of the SOPT, namely, it is primarily the propor...

  11. Phase sensitive quantum interference on forbidden transition in ladder scheme

    CERN Document Server

    Koganov, Gennady A

    2014-01-01

    A three level ladder system is analyzed and the coherence of initially electric-dipole forbidden transition is calculated. Due to the presence of two laser fields the initially dipole forbidden transition becomes dynamically permitted due to ac Stark effect. It is shown that such transitions exhibit quantum-interference-related phenomena, such as electromagnetically induced transparency, gain without inversion and enhanced refractive index. Gain and dispersion characteristics of such transitions strongly depend upon the relative phase between the driving and the probe fields. Unlike allowed transitions, gain/absorption behavior of ac-Stark allowed transitions exhibit antisymmetric feature on the Rabi sidebands. It is found that absorption/gain spectra possess extremely narrow sub-natural resonances on these ac Stark allowed forbidden transitions. An interesting finding is simultaneous existence of gain and negative dispersion at Autler-Townes transition which may lead to both reduction of the group velocity a...

  12. A strictly hyperbolic equilibrium phase transition model

    Energy Technology Data Exchange (ETDEWEB)

    Allaire, G [Ecole Polytech, CNRS, CMAP, F-91128 Palaiseau (France); Faccanoni, G; Kokh, S. [CEA Saclay, DEN, DANS, DM2S, F-91191 Gif Sur Yvette, (France)

    2007-01-15

    This Note is concerned with the strict hyperbolicity of the compressible Euler equations equipped with an equation of state that describes the thermodynamical equilibrium between the liquid phase and the vapor phase of a fluid. The proof is valid for a very wide class of fluids. The argument only relies on smoothness assumptions and on the classical thermodynamical stability assumptions, that requires a definite negative Hessian matrix for each phase entropy as a function of the specific volume and internal energy. (authors)

  13. Effect of dimensionality on vapor-liquid phase transition

    Science.gov (United States)

    Singh, Sudhir Kumar

    2014-04-01

    Dimensionality play significant role on `phase transitions'. Fluids in macroscopic confinement (bulk or 3-Dimensional, 3D) do not show significant changes in their phase transition properties with extent of confinement, since the number of molecules away from the surrounding surfaces is astronomically higher than the number of molecules in close proximity of the confining surfaces. In microscopic confinement (quasi 3D to quasi-2D), however, the number of molecules away from the close proximity of the surface is not as high as is the case with macroscopic (3D) confinement. Hence, under the same thermodynamic conditions `phase transition' properties at microscopic confinement may not remain the same as the macroscopic or 3D values. Phase transitions at extremely small scale become very sensitive to the dimensions as well as the surface characteristics of the system. In this work our investigations reveal the effect of dimensionality on the phase transition from 3D to quasi-2D to 2D behavior. We have used grand canonical transition matrix Monte Carlo simulation to understand the vapor-liquid phase transitions from 3D to quasi-2D behavior. Such studies can be helpful in understanding and controlling the fluid film behaviour confined between solid surfaces of few molecular diameters, for example, in lubrication applications.

  14. Discontinuous structural phase transition of liquid metal and alloys (2)

    International Nuclear Information System (INIS)

    The diameter (df) of diffusion fluid cluster before and after phase transition has been calculated in terms of the paper ''Discontinuous structural phase transition of liquid metal and alloy (1)'' Physics Letters. A 326 (2004) 429-435, to verify quantitatively the discontinuity of structural phase transition; the phenomena of thermal contraction and thermal expansion during the phase transition, together with the evolution model of discontinuous structural phase transition are also discussed in this Letter to explore further the nature of structural transition; In addition, based on the viscosity experimental result mentioned in paper [Y. Waseda, The Structure of Non-Crystalline Materials--Liquids and Amorphous Solids, McGraw-Hill, New York, 1980], we present an approach to draw an embryo of the liquid-liquid (L-L) phase diagram for binary alloys above liquidus in the paper, expecting to guide metallurgy process so as to improve the properties of alloys. The idea that controls amorphous structure and its properties by means of the L-L phase diagram for alloys and by the rapid cooling technique to form the amorphous alloy has been brought forward in the end

  15. Phase transition in extended thermodynamic phase space and charged Horava-Lifshitz black holes

    OpenAIRE

    Poshteh, Mohammad Bagher Jahani; Riazi, Nematollah

    2016-01-01

    For charged black holes in Horava-Lifshitz gravity, it is shown that a second order phase transition takes place in extended phase space. We study the behavior of specific heat and free energy at the point of transition in canonical and grand canonical ensembles and show that the black hole falls into a state which is locally and globally stable. We relate the second order nature of phase transition to the fact that the phase transition occurs at a sharp temperature and not over a temperature...

  16. One-dimensional caricature of phase transition

    Science.gov (United States)

    Schonmann, Roberto H.; Tanaka, Nelson I.

    1990-10-01

    In the limit as the volume grows and the temperature vanishes, it is shown that the one-dimensional nearest neighbor ferromagnetic Ising model presents a sharp transition between two different regimes. Fluctuations are studied in one of these regimes and also in the critical case.

  17. Statistical Physics and Dynamical Systems: Models of Phase Transitions

    OpenAIRE

    Patwardhan, Ajay

    2007-01-01

    This paper explores the connection between dynamical system properties and statistical physics of ensembles of such systems. Simple models are used to give novel phase transitions; particularly for finite N particle systems with many physically interesting examples.

  18. Character of. pi. -condensate phase transition at finite temperature

    Energy Technology Data Exchange (ETDEWEB)

    Voskresenskii, D.N.; Mishustin, I.N.

    1978-10-05

    The results of analytic calculations of the critical temperature of pion condensation are presented. It follows from these results, in particular, that at sufficiently high temperature the pion condensation proceeds like a first-order phase transition.

  19. Foundations of Statistical Mechanics and Theory of Phase Transition

    CERN Document Server

    Belokolos, E D

    1997-01-01

    A new formulation of statistical mechanics is put forward according to which a random variable characterizing a macroscopic body is postulated to be infinitely divisible. It leads to a parametric representation of partition function of an arbitrary macroscopic body, a possibility to describe a macroscopic body under excitation by a gas of some elementary quasiparticles etc. A phase transition is defined as such a state of a macroscopic body that its random variable is stable in sense of Lévy. From this definition it follows by deduction all general properties of phase transitions: existence of the renormalization semigroup, the singularity classification for thermodynamic functions, the phase transition universality and universality classes. On this basis we has also built a 2-parameter scaling theory of phase transitions, a thermodynamic function for the Ising model etc.

  20. Dynamical symmetries and causality in non-equilibrium phase transitions

    CERN Document Server

    Henkel, Malte

    2015-01-01

    Dynamical symmetries are of considerable importance in elucidating the complex behaviour of strongly interacting systems with many degrees of freedom. Paradigmatic examples are cooperative phenomena as they arise in phase transitions, where conformal invariance has led to enormous progress in equilibrium phase transitions, especially in two dimensions. Non-equilibrium phase transitions can arise in much larger portions of the parameter space than equilibrium phase transitions. The state of the art of recent attempts to generalise conformal invariance to a new generic symmetry, taking into account the different scaling behaviour of space and time, will be reviewed. Particular attention will be given to the causality properties as they follow for co-variant $n$-point functions. These are important for the physical identification of n-point functions as responses or correlators.

  1. Integrability and Quantum Phase Transitions in Interacting Boson Models

    CERN Document Server

    Dukelsky, J; García-Ramos, J E; Pittel, S

    2003-01-01

    The exact solution of the boson pairing hamiltonian given by Richardson in the sixties is used to study the phenomena of level crossings and quantum phase transitions in the integrable regions of the sd and sdg interacting boson models.

  2. Gravitational waves from a very strong electroweak phase transition

    CERN Document Server

    Leitao, Leonardo

    2015-01-01

    We investigate the production of a stochastic background of gravitational waves in the electroweak phase transition. We consider a few extensions of the Standard Model which can give very strongly first-order phase transitions. We concentrate on the possibility that the phase transition fronts either propagate as detonations or run away. We compute the bubble wall velocity taking into account the friction and hydrodynamics due to the presence of the plasma, and we track the development of the phase transition up to the percolation time. We calculate the contribution to the gravitational wave spectrum from bubble collisions, magnetohydrodynamic turbulence, and sound waves. For the kinds of models we consider we find parameter regions for which the gravitational waves are potentially observable at the planned space-based interferometer eLISA. The sound waves are generally the strongest source. Since this mechanism is diminished in the presence of runaway walls, the models with the best prospects of detection at...

  3. Behavior of the Lyapunov Exponent and Phase Transition in Nuclei

    Institute of Scientific and Technical Information of China (English)

    WANG Nan; WU Xi-Zhen; LI Zhu-Xia; WANG Ning; ZHUO Yi-Zhong; SUN Xiu-Quan

    2000-01-01

    Based on the quantum molecular dynamics model, we investigate the dynamical behaviors of the excited nuclear system to simulate the latter stage of heavy ion reactions, which associate with a liquid-gas phase transition. We try to search a microscopic way to describe the phase transition in realnuclei. The Lyapunov exponent is employed and examined for our purpose. We find out that the Lyapunov exponent is one of good microscopic quantities to describe the phase transition in hot nuclei. Coulomb potential and the finite size effect may give a strong influence on the critical temperature. However, the collision term plays a minor role in the process of the liquid-gas phase transition in finite systems.

  4. Dynamical Symmetries and Causality in Non-Equilibrium Phase Transitions

    Directory of Open Access Journals (Sweden)

    Malte Henkel

    2015-11-01

    Full Text Available Dynamical symmetries are of considerable importance in elucidating the complex behaviour of strongly interacting systems with many degrees of freedom. Paradigmatic examples are cooperative phenomena as they arise in phase transitions, where conformal invariance has led to enormous progress in equilibrium phase transitions, especially in two dimensions. Non-equilibrium phase transitions can arise in much larger portions of the parameter space than equilibrium phase transitions. The state of the art of recent attempts to generalise conformal invariance to a new generic symmetry, taking into account the different scaling behaviour of space and time, will be reviewed. Particular attention will be given to the causality properties as they follow for co-variant n-point functions. These are important for the physical identification of n-point functions as responses or correlators.

  5. Quantum phase transitions in the interacting boson model

    CERN Document Server

    Cejnar, Pavel

    2008-01-01

    This review is focused on various properties of quantum phase transitions (QPTs) in the Interacting Boson Model (IBM) of nuclear structure. The model in its infinite-size limit exhibits shape-phase transitions between spherical, deformed prolate, and deformed oblate forms of the ground state. Finite-size precursors of such behavior are verified by robust variations of nuclear properties (nuclear masses, excitation energies, transition probabilities for low lying levels) across the chart of nuclides. Simultaneously, the model serves as a theoretical laboratory for studying diverse general features of QPTs in interacting many-body systems, which differ in many respects from lattice models of solid-state physics. We outline the most important fields of the present interest: (a) The coexistence of first- and second-order phase transitions supports studies related to the microscopic origin of the QPT phenomena. (b) The competing quantum phases are characterized by specific dynamical symmetries and novel symmetry r...

  6. Research for the energy turnaround. Phase transitions actively shape. Contributions

    International Nuclear Information System (INIS)

    The Annual Conference 2014 of the Renewable Energy Research Association was held in Berlin on 6 and 7 November 2014. This book documents the contributions of the conference on research for the energy turnaround, phase transitions actively shape. After an introduction and two contributions to the political framework, the contributions to the economic phases of the energy transition, the phase of the current turn, the phases of social energy revolution, the stages of heat turnaround (Waermewende), and the stages of the mobility turn deal with the stages of development of the energy system. Finally, the Research Association Renewable Energy is briefly presented.

  7. Phase Transitions in a Forest-Fire Model

    OpenAIRE

    Clar, Siegfried; Schenk, Klaus; Schwabl, Franz

    1997-01-01

    We investigate a forest-fire model with the density of empty sites as control parameter. The model exhibits three phases, separated by one first-order phase transition and one 'mixed' phase transition which shows critical behavior on only one side and hysteresis. The critical behavior is found to be that of the self-organized critical forest-fire model [B. Drossel and F. Schwabl, Phys. Rev. Lett. 69, 1629 (1992)], whereas in the adjacent phase one finds the spiral waves of the Bak et al. fore...

  8. Probing phase transitions of vortex matter by Josephson plasma resonance

    International Nuclear Information System (INIS)

    The Josephson plasma resonance is the most powerful means to study the vortex state in high-Tc superconductors. In this paper we report the detailed and quantitative study of the interlayer quantum phase coherence in the vortex liquid, Bragg glass and vortex glass phases of Bi2Sr2CaCu2O8+δ by the Josephson plasma resonance. We also provide a quantitative discussion on the nature of the phase transitions among these vortex phases. (author)

  9. Phase transition of bismuth telluride thin films grown by MBE

    DEFF Research Database (Denmark)

    Fülöp, Attila; Song, Yuxin; Charpentier, Sophie;

    2014-01-01

    A previously unreported phase transition between Bi2Te3 and Bi4Te3 in bismuth telluride grown by molecular beam epitaxy is recorded via XRD, AFM, and SIMS observations. This transition is found to be related to the Te/Bi beam equivalent pressure (BEP) ratio. BEP ratios below 17 favor the formatio...

  10. Phase transition in L-alaninium oxalate by photoacoustics

    Indian Academy of Sciences (India)

    M Sivabarathy; S Natarajan; S K Ramakrishnan; K Ramachandran

    2004-10-01

    Phase transition in L-alaninium oxalate is studied by using TG, DTA and photoacoustic spectroscopy. A sharp transition at 378 K by photoacoustics is observed whereas at the same temperature the endothermic energy change observed by TG and DTA is not very sharp. This is discussed in detail with reference to the other known data for the organic crystals.

  11. Ab initio theory of helix <-> coil phase transition

    DEFF Research Database (Denmark)

    Yakubovich, Alexander V.; Solov'yov, Ilia; Solov'yov, Andrey V.;

    2008-01-01

    In this paper, we suggest a theoretical method based on the statistical mechanics for treating the alpha-helix <-> random coil transition in alanine polypeptides. We consider this process as a first-order phase transition and develop a theory which is free of model parameters and is based solely ...

  12. Quantum Shape-Phase Transitions in Finite Nuclei

    CERN Document Server

    Leviatan, A

    2007-01-01

    Quantum shape-phase transitions in finite nuclei are considered in the framework of the interacting boson model. Critical-point Hamiltonians for first- and second-order transitions are identified by resolving them into intrinsic and collective parts. Suitable wave functions and finite-N estimates for observables at the critical-points are derived.

  13. On the theory of phase transitions in polypeptides

    DEFF Research Database (Denmark)

    Yakubovich, Alexander V.; Solov'yov, Ilia; Solov'yov, Andrey V.;

    2008-01-01

    We suggest a theoretical method based on the statistical mechanics for treating the alpha-helix random coil transition in polypeptides. This process is considered as a first-order-like phase transition. The developed theory is free of model parameters and is based solely on fundamental physical...

  14. Formation of Black Holes in First Order Phase Transitions

    OpenAIRE

    Khlopov, M. Yu.; R. V. Konoplich(Physics Dept.New York University, N.Y., USA); Rubin, S. G.; Sakharov, A. S.

    1998-01-01

    A new mechanism of black hole formation in a first order phase transition is proposed. In vacuum bubble collisions the interaction of bubble walls leads to the formation of nontrivial vacuum configuration. The consequent collapse of this vacuum configuration induces the black hole formation with high probability. Observational constraints on the spectrum of primordial black holes allow to obtain new nontrivial restrictions on parameters of inflation models with first order phase transitions.

  15. Baryogenesis via leptonic CP-violating phase transition

    CERN Document Server

    Pascoli, Silvia; Zhou, Ye-Ling

    2016-01-01

    We propose a new mechanism to generate a lepton asymmetry based on the vacuum CP-violating phase transition (CPPT). This approach differs from classical thermal leptogenesis as a specific seesaw model, and its UV completion, need not be specified. The lepton asymmetry is generated via the dynamically realised coupling of the Weinberg operator during the phase transition. This mechanism provides strong connections with low-energy neutrino experiments.

  16. Effect of disorder on first-order phase transitions

    OpenAIRE

    Bellafard, Arash

    2015-01-01

    Disorder is an inevitable part of any condensed matter system and therefore its study has always been of great importance. The effect of quenched randomness on a system that exhibits a continuous phase transition in the absence of any impurity has been studied in the past and the results are relatively well understood. However, the effect of quenched randomness on \\emph{first-order} phase transitions is still not well understood. In this dissertation, we study the effect of quenched bond-rand...

  17. An Analysis of Phase Transition in NK Landscapes

    OpenAIRE

    Culberson, J.; Gao, Y.

    2011-01-01

    In this paper, we analyze the decision version of the NK landscape model from the perspective of threshold phenomena and phase transitions under two random distributions, the uniform probability model and the fixed ratio model. For the uniform probability model, we prove that the phase transition is easy in the sense that there is a polynomial algorithm that can solve a random instance of the problem with the probability asymptotic to 1 as the problem size tends to infinity. For the fixed rat...

  18. Effect of point defects and disorder on structural phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Toulouse, J.

    1997-06-01

    Since the beginning in 1986, the object of this project has been Structural Phase Transitions (SPT) in real as opposed to ideal materials. The first stage of the study has been centered around the role of Point Defects in SPT`s. Our intent was to use the previous knowledge we had acquired in the study of point defects in non-transforming insulators and apply it to the study of point defects in insulators undergoing phase transitions. In non-transforming insulators, point defects, in low concentrations, marginally affect the bulk properties of the host. It is nevertheless possible by resonance or relaxation methods to study the point defects themselves via their local motion. In transforming solids, however, close to a phase transition, atomic motions become correlated over very large distances; there, even point defects far removed from one another can undergo correlated motions which may strongly affect the transition behavior of the host. Near a structural transition, the elastic properties win be most strongly affected so as to either raise or decrease the transition temperature, prevent the transition from taking place altogether, or simply modify its nature and the microstructure or domain structure of the resulting phase. One of the well known practical examples is calcium-stabilized zirconia in which the high temperature cubic phase is stabilized at room temperature with greatly improved mechanical properties.

  19. Effective Hamiltonians for correlated narrow energy band systems and magnetic insulators: Role of spin-orbit interactions in metal-insulator transitions and magnetic phase transitions

    Science.gov (United States)

    Chakraborty, Subrata; Vijay, Amrendra

    2016-04-01

    Using a second-quantized many-electron Hamiltonian, we obtain (a) an effective Hamiltonian suitable for materials whose electronic properties are governed by a set of strongly correlated bands in a narrow energy range and (b) an effective spin-only Hamiltonian for magnetic materials. The present Hamiltonians faithfully include phonon and spin-related interactions as well as the external fields to study the electromagnetic response properties of complex materials and they, in appropriate limits, reduce to the model Hamiltonians due to Hubbard and Heisenberg. With the Hamiltonian for narrow-band strongly correlated materials, we show that the spin-orbit interaction provides a mechanism for metal-insulator transition, which is distinct from the Mott-Hubbard (driven by the electron correlation) and the Anderson mechanism (driven by the disorder). Next, with the spin-only Hamiltonian, we demonstrate the spin-orbit interaction to be a reason for the existence of antiferromagnetic phase in materials which are characterized by a positive isotropic spin-exchange energy. This is distinct from the Néel-VanVleck-Anderson paradigm which posits a negative spin-exchange for the existence of antiferromagnetism. We also find that the Néel temperature increases as the absolute value of the spin-orbit coupling increases.

  20. Quantum phase transitions and string orders in the spin-1/2 Heisenberg–Ising alternating chain with Dzyaloshinskii–Moriya interaction

    International Nuclear Information System (INIS)

    Quantum phase transitions (QPTs) and the ground-state phase diagram of the spin-1/2 Heisenberg–Ising alternating chain (HIAC) with uniform Dzyaloshinskii–Moriya (DM) interaction are investigated by a matrix-product-state (MPS) method. By calculating the odd- and even-string order parameters, we recognize two kinds of Haldane phases, i.e. the odd- and even-Haldane phases. Furthermore, doubly degenerate entanglement spectra on odd and even bonds are observed in odd- and even-Haldane phases, respectively. A rich phase diagram including four different phases, i.e. an antiferromagnetic (AF), AF stripe, odd- and even-Haldane phases, is obtained. These phases are found to be separated by continuous QPTs: the topological QPT between the odd- and even-Haldane phases is verified to be continuous and corresponds to conformal field theory with central charge c = 1; while the rest of the phase transitions in the phase diagram are found to be c = 1/2. We also revisit, with our MPS method, the exactly solvable case of HIAC model with DM interactions only on odd bonds and find that the even-Haldane phase disappears, but the other three phases, i.e. the AF, AF stripe and odd-Haldane phases, still remain in the phase diagram. We exhibit the evolution of the even-Haldane phase by tuning the DM interactions on the even bonds gradually. (paper)

  1. Quantum phase transitions and string orders in the spin-1/2 Heisenberg-Ising alternating chain with Dzyaloshinskii-Moriya interaction.

    Science.gov (United States)

    Liu, Guang-Hua; You, Wen-Long; Li, Wei; Su, Gang

    2015-04-29

    Quantum phase transitions (QPTs) and the ground-state phase diagram of the spin-1/2 Heisenberg-Ising alternating chain (HIAC) with uniform Dzyaloshinskii-Moriya (DM) interaction are investigated by a matrix-product-state (MPS) method. By calculating the odd- and even-string order parameters, we recognize two kinds of Haldane phases, i.e. the odd- and even-Haldane phases. Furthermore, doubly degenerate entanglement spectra on odd and even bonds are observed in odd- and even-Haldane phases, respectively. A rich phase diagram including four different phases, i.e. an antiferromagnetic (AF), AF stripe, odd- and even-Haldane phases, is obtained. These phases are found to be separated by continuous QPTs: the topological QPT between the odd- and even-Haldane phases is verified to be continuous and corresponds to conformal field theory with central charge c = 1; while the rest of the phase transitions in the phase diagram are found to be c = 1/2. We also revisit, with our MPS method, the exactly solvable case of HIAC model with DM interactions only on odd bonds and find that the even-Haldane phase disappears, but the other three phases, i.e. the AF, AF stripe and odd-Haldane phases, still remain in the phase diagram. We exhibit the evolution of the even-Haldane phase by tuning the DM interactions on the even bonds gradually.

  2. Quantum phase transitions and string orders in the spin-1/2 Heisenberg-Ising alternating chain with Dzyaloshinskii-Moriya interaction

    Science.gov (United States)

    Liu, Guang-Hua; You, Wen-Long; Li, Wei; Su, Gang

    2015-04-01

    Quantum phase transitions (QPTs) and the ground-state phase diagram of the spin-1/2 Heisenberg-Ising alternating chain (HIAC) with uniform Dzyaloshinskii-Moriya (DM) interaction are investigated by a matrix-product-state (MPS) method. By calculating the odd- and even-string order parameters, we recognize two kinds of Haldane phases, i.e. the odd- and even-Haldane phases. Furthermore, doubly degenerate entanglement spectra on odd and even bonds are observed in odd- and even-Haldane phases, respectively. A rich phase diagram including four different phases, i.e. an antiferromagnetic (AF), AF stripe, odd- and even-Haldane phases, is obtained. These phases are found to be separated by continuous QPTs: the topological QPT between the odd- and even-Haldane phases is verified to be continuous and corresponds to conformal field theory with central charge c = 1 while the rest of the phase transitions in the phase diagram are found to be c = 1/2. We also revisit, with our MPS method, the exactly solvable case of HIAC model with DM interactions only on odd bonds and find that the even-Haldane phase disappears, but the other three phases, i.e. the AF, AF stripe and odd-Haldane phases, still remain in the phase diagram. We exhibit the evolution of the even-Haldane phase by tuning the DM interactions on the even bonds gradually.

  3. Quantum Phase Transitions and Dimerized Phases in Frustrated Spin Ladder

    Institute of Scientific and Technical Information of China (English)

    WEN Rui; LIU Guang-Hua; TIAN Guang-Shan

    2011-01-01

    In this paper, we study the phase diagram of a frustrated spin ladder model by applying the bosonization technique and the density-matrix renormalization-group (DMRG) algorithm. Effect of the intra-chain next-nearestneighbor (NNN) super-exchange interaction is investigated in detail and the order parameters are calculated to detect the emergence of the dimerized phases. We find that the intra-chain NNN interaction plays a key role in inducing dimerized phases.

  4. Quark-Hadron Phase Transitions in Viscous Early Universe

    CERN Document Server

    Tawfik, A

    2011-01-01

    Based on hot big bang theory, the cosmological matter is conjectured to undergo QCD phase transition(s) to hadrons, when the universe was about $1-10 \\mu$s old. In the present work, we study the quark-hadron phase transition, by taking into account the effect of the bulk viscosity. We analyze the evolution of the quantities relevant for the physical description of the early universe, namely, the energy density $\\rho$, temperature $T$, Hubble parameter $H$ and scale factor $a$ before, during and after the phase transition. To study the cosmological dynamics and the time evolution we use both analytical and numerical methods. By assuming that the phase transition may be described by an effective nucleation theory (prompt {\\it first-order} phase transition), we also consider the case where the universe evolved through a mixed phase with a small initial supercooling and monotonically growing hadronic bubbles. The numerical estimation of the cosmological parameters, $a$ and $H$ for instance, makes it clear that th...

  5. Phase transitions of a polymer threading a membrane coupled to coil-globule transitions

    OpenAIRE

    Matsuyama, Akihiko

    2004-01-01

    We theoretically study phase transitions of a polymer threading through a pore imbedded in a membrane. We focus on the coupling between a partition of the polymer segments through the membrane and a coil-globule transition of the single polymer chain. Based on the Flory model for collapse transitions of a polymer chain, we calculate the fraction of polymer segments and the expansion factor of a polymer coil on each side of the membrane. We predict a first-order phase transition of a polymer t...

  6. Phase Transition in Unrestricted Random SAT

    CERN Document Server

    Schuh, Bernd R

    2012-01-01

    For random CNF formulae with m clauses, n variables and an unrestricted number of literals per clause the transition from high to low satisfiability can be determined exactly for large n. The critical density m/n turns out to be strongly n-dependent, ccr = ln(2)/(1-p)^^n, where pn is the mean number of positive literals per clause.This is in contrast to restricted random SAT problems (random K-SAT), where the critical ratio m/n is a constant. All transition lines are calculated by the second moment method applied to the number of solutions N of a formula. In contrast to random K-SAT, the method does not fail for the unrestricted model, because long range interactions between solutions are not cut off by disorder.

  7. Phase transition in extended thermodynamic phase space and charged Horava-Lifshitz black holes

    CERN Document Server

    Poshteh, Mohammad Bagher Jahani

    2016-01-01

    For charged black holes in Horava-Lifshitz gravity, it is shown that a second order phase transition takes place in extended phase space. We study the behavior of specific heat and free energy at the point of transition in canonical and grand canonical ensembles and show that the black hole falls into a state which is locally and globally stable. We relate the second order nature of phase transition to the fact that the phase transition occurs at a sharp temperature and not over a temperature interval. By taking cosmological constant as thermodynamic pressure for charged black holes, we extend Ehrenfest's equations. We obtain nine equations and show that, all of them are satisfied at the point in which the specific heat diverges. We also apply geometrothermodynamics to extended phase space and show that the scalar curvature of Quevedo metric diverges at the point at which the second order phase transition takes place.

  8. Thermodynamic properties of frustrated arbitrary spin-S J1-J2 quantum Heisenberg antiferromagnet on the body-centered-cubic lattice in random phase approximation

    Science.gov (United States)

    Mi, Bin-Zhou

    2016-07-01

    The thermodynamic properties of the frustrated arbitrary spin-S J1-J2 Heisenberg antiferromagnet on the body-centered-cubic lattice for Néel phase are systematically calculated by use of the double-time Green's function method within the random phase approximation (RPA). The role of spin quantum number and frustration strength on sublattice magnetization, Néel temperature, internal energy, and free energy are carefully analyzed. The curve of zero-temperature sublattice magnetization / S versus frustration strength J2/J1 values are almost flat at the larger spin quantum number S=10. With the increase of normalized temperature T/TN, the larger the spin quantum number S, the faster the / S drops, and the smaller influence of J2/J1 on the / S versus T/TN curve. Under the RPA approach, the Néel temperature TN /Sp and the internal energy E/Sp at the Néel point are independent of spin quantum number S. The numerical results show that the internal energy E/Sp at the Néel point seems independent of the frustration strength J2/J1. This indicates that thermodynamic quantities have universal characteristics for large spin quantum number.

  9. A Quantum Phase Transition in the Cosmic Ray Energy Distribution

    CERN Document Server

    Widom, A; Srivastava, Y

    2015-01-01

    We here argue that the "knee" of the cosmic ray energy distribution at $E_c \\sim 1$ PeV represents a second order phase transition of cosmic proportions. The discontinuity of the heat capacity per cosmic ray particle is given by $\\Delta c=0.450196\\ k_B$. However the idea of a deeper critical point singularity cannot be ruled out by present accuracy in neither theory nor experiment. The quantum phase transition consists of cosmic rays dominated by bosons for the low temperature phase E E_c$. The low temperature phase arises from those nuclei described by the usual and conventional collective boson models of nuclear physics. The high temperature phase is dominated by protons. The transition energy $E_c$ may be estimated in terms of the photo-disintegration of nuclei.

  10. Phase Transitions in Antibody Solutions: from Pharmaceuticals to Human Disease

    Science.gov (United States)

    Wang, Ying; Lomakin, Aleksey; Benedek, George; Dana Farber Cancer Institute Collaboration; Amgen Inc. Collaboration

    2014-03-01

    Antibodies are very important proteins. Natural antibodies play essential role in the immune system of human body. Pharmaceutical antibodies are used as drugs. Antibodies are also indispensable tools in biomedical research and diagnostics. Recently, a number of observations of phase transitions of pharmaceutical antibodies have been reported. These phase transitions are undesirable from the perspective of colloid stability of drug solutions in processing and storage, but can be used for protein purification, X-ray crystallography, and improving pharmokinetics of drugs. Phase transitions of antibodies can also take place in human body, particularly in multiple myeloma patients who overproduce monoclonal antibodies. These antibodies, in some cases, crystallize at body temperature and cause severe complications called cryoglobulinemia. I will present the results of our current studies on phase transitions of both pharmaceutical antibodies and cryoglobulinemia-associated antibodies. These studies have shown that different antibodies have different propensity to undergo phase transitions, but their phase behavior has universal features which are remarkably different from those of spherical proteins. I will discuss how studies of phase behavior can be useful in assessing colloid stability of pharmaceutical antibodies and in early diagnostics of cryoglobulinemia, as well as general implications of the fact that some antibodies can precipitate at physiological conditions.

  11. Density Functional Theory for Phase-Ordering Transitions

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Jianzhong [Univ. of California, Riverside, CA (United States)

    2016-03-30

    Colloids display astonishing structural and dynamic properties that can be dramatically altered by modest changes in the solution condition or an external field. This complex behavior stems from a subtle balance of colloidal forces and intriguing mesoscopic and macroscopic phase transitions that are sensitive to the processing conditions and the dispersing environment. Whereas the knowledge on the microscopic structure and phase behavior of colloidal systems at equilibrium is now well-advanced, quantitative predictions of the dynamic properties and the kinetics of phase-ordering transitions in colloids are not always realized. Many important mesoscopic and off-equilibrium colloidal states remain poorly understood. The proposed research aims to develop a new, unifying approach to describe colloidal dynamics and the kinetics of phase-ordering transitions based on accomplishments from previous work for the equilibrium properties of both uniform and inhomogeneous systems and on novel concepts from the state-of-the-art dynamic density functional theory. In addition to theoretical developments, computational research is designed to address a number of fundamental questions on phase-ordering transitions in colloids, in particular those pertinent to a competition of the dynamic pathways leading to various mesoscopic structures, off-equilibrium states, and crystalline phases. By providing a generic theoretical framework to describe equilibrium, metastable as well as non-ergodic phase transitions concurrent with the colloidal self-assembly processes, accomplishments from this work will have major impacts on both fundamental research and technological applications.

  12. Effects of phase transition induced density fluctuations on pulsar dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Bagchi, Partha, E-mail: partha@iopb.res.in [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Das, Arpan, E-mail: arpan@iopb.res.in [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Layek, Biswanath, E-mail: layek@pilani.bits-pilani.ac.in [Department of Physics, Birla Institute of Technology and Science, Pilani - 333031 (India); Srivastava, Ajit M., E-mail: ajit@iopb.res.in [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India)

    2015-07-30

    We show that density fluctuations during phase transitions in pulsar cores may have non-trivial effects on pulsar timings, and may also possibly account for glitches and anti-glitches. These density fluctuations invariably lead to non-zero off-diagonal components of the moment of inertia, leading to transient wobbling of star. Thus, accurate measurements of pulsar timing and intensity modulations (from wobbling) may be used to identify the specific pattern of density fluctuations, hence the particular phase transition, occurring inside the pulsar core. Changes in quadrupole moment from rapidly evolving density fluctuations during the transition, with very short time scales, may provide a new source for gravitational waves.

  13. Classicality of the order parameter during a phase transition

    CERN Document Server

    Lombardo, F C; Monteoliva, D; Lombardo, Fernando C.; Mazzitelli, Francisco D.; Monteoliva, Diana

    2000-01-01

    We analize the quantum to classical transition of the order parameter insecond order phase transitions. We consider several toy models in nonrelativistic quantum mechanics. We study the dynamical evolution of a wavepacket initially peaked around a local maximum of the potential usingvariational approximations and also exact numerical results. The influence ofthe environment on the evolution of the density matrix and the Wigner functionis analized in great detail. We also discuss the relevance of our results tothe analysis of phase transitions in field theory. In particular, we argue thatprevious results about classicality of the order parameter in O(N) models maybe consequences of the large $N$ approximation.

  14. Gravitational waves from cosmological first order phase transitions

    CERN Document Server

    Hindmarsh, Mark; Rummukainen, Kari; Weir, David

    2015-01-01

    First order phase transitions in the early Universe generate gravitational waves, which may be observable in future space-based gravitational wave observatiories, e.g. the European eLISA satellite constellation. The gravitational waves provide an unprecedented direct view of the Universe at the time of their creation. We study the generation of the gravitational waves during a first order phase transition using large-scale simulations of a model consisting of relativistic fluid and an order parameter field. We observe that the dominant source of gravitational waves is the sound generated by the transition, resulting in considerably stronger radiation than earlier calculations have indicated.

  15. Exotic phase transitions of k-cores in clustered networks

    CERN Document Server

    Bhat, Uttam; Hébert-Dufresne, Laurent

    2016-01-01

    The giant $k$-core --- maximal connected subgraph of a network where each node has at least $k$ neighbors --- is important in the study of phase transitions and in applications of network theory. Unlike Erd\\H{o}s-R\\'enyi graphs and other random networks where $k$-cores emerge discontinuously for $k\\ge 3$, we show that transitive linking (or triadic closure) leads to 3-cores emerging through single or double phase transitions of both discontinuous and continuous nature. We also develop a $k$-core calculation that includes clustering and provides insights into how high-level connectivity emerges.

  16. Transition to Phase Synchronization Through Generalized Synchronization

    Institute of Scientific and Technical Information of China (English)

    高建; 郑志刚; 何岱海; 张廷宪

    2003-01-01

    Synchronization in drive-response chaotic systems is studied. For a small mismatch of the natural frequency of the drive and response oscillators, phase synchronization comes before generalized synchronization. For moderate and even large parameter misfits, generalized synchronization can be achieved before phase synchronization. The mechanism of these two different bifurcations is interpreted in terms of the local-minimal-fluctuation method.It is found that the qualitative changes of local-minimal-fluctuations of the response system well manifests the appearance of generalized synchronization.

  17. Pairing Phase Transitions of Matter under Rotation

    CERN Document Server

    Jiang, Yin

    2016-01-01

    The phases and properties of matter under global rotation have attracted much interest recently. In this paper we investigate the pairing phenomena in a system of fermions under the presence of rotation. We find that there is a generic suppression effect on pairing states with zero angular momentum. We demonstrate this effect with the chiral condensation and the color superconductivity in hot dense QCD matter as explicit examples. In the case of chiral condensation, a new phase diagram in the temperature-rotation parameter space is found, with a nontrivial critical point.

  18. Solid-solid phase transitions via melting in metals

    Science.gov (United States)

    Pogatscher, S.; Leutenegger, D.; Schawe, J. E. K.; Uggowitzer, P. J.; Löffler, J. F.

    2016-04-01

    Observing solid-solid phase transitions in-situ with sufficient temporal and spatial resolution is a great challenge, and is often only possible via computer simulations or in model systems. Recently, a study of polymeric colloidal particles, where the particles mimic atoms, revealed an intermediate liquid state in the transition from one solid to another. While not yet observed there, this finding suggests that such phenomena may also occur in metals and alloys. Here we present experimental evidence for a solid-solid transition via the formation of a metastable liquid in a `real' atomic system. We observe this transition in a bulk glass-forming metallic system in-situ using fast differential scanning calorimetry. We investigate the corresponding transformation kinetics and discuss the underlying thermodynamics. The mechanism is likely to be a feature of many metallic glasses and metals in general, and may provide further insight into phase transition theory.

  19. Exploring percolative landscapes: Infinite cascades of geometric phase transitions

    Science.gov (United States)

    Timonin, P. N.; Chitov, Gennady Y.

    2016-01-01

    The evolution of many kinetic processes in 1+1 (space-time) dimensions results in 2 D directed percolative landscapes. The active phases of these models possess numerous hidden geometric orders characterized by various types of large-scale and/or coarse-grained percolative backbones that we define. For the patterns originated in the classical directed percolation (DP) and contact process we show from the Monte Carlo simulation data that these percolative backbones emerge at specific critical points as a result of continuous phase transitions. These geometric transitions belong to the DP universality class and their nonlocal order parameters are the capacities of corresponding backbones. The multitude of conceivable percolative backbones implies the existence of infinite cascades of such geometric transitions in the kinetic processes considered. We present simple arguments to support the conjecture that such cascades of transitions are a generic feature of percolation as well as of many other transitions with nonlocal order parameters.

  20. Dynamically slow solid-to-solid phase transition induced by thermal treatment of DimimFeCl4 magnetic ionic liquid.

    Science.gov (United States)

    de Pedro, Imanol; Fabelo, Oscar; García-Saiz, Abel; Vallcorba, Oriol; Junquera, Javier; Blanco, Jesús Angel; Waerenborgh, João Carlos; Andreica, D; Wildes, Andrew; Fernández-Díaz, María Teresa; Fernández, Jesús Rodríguez

    2016-08-01

    The results reported here represent the first direct experimental observations supporting the existence of a solid-to-solid phase transition induced by thermal treatment in magnetic ionic liquids (MILs). The phase transitions of the solid phases of 1,3-dimethylimidazolium tetrachloroferrate, DimimFeCl4, are closely related to its thermal history. Two series of solid-to-solid phase transitions can be described in this MIL: (i) from room temperature (RT) phase II [space group (s.g.) = P21] to phase I-a [s.g. = P212121] via thermal quenching or via fast cooling at T > 2 K min(-1); (ii) from phase I-a to phase I-b [s.g. = P21/c] when the temperature was kept above 180 K for several minutes. The latter involves a slow translational and reorientational dynamical process of both the imidazolium cation and the tetrachloroferrate anion and has been characterized using synchrotron and neutron powder diffraction and DFT (density functional theory) studies. The transition is also related to the modification of the super-exchange pathways of low-temperature phases which show a overall antiferromagnetic behavior. A combination of several experimental methods such as magnetometry, Mössbauer and muon spectroscopy together with polarized and non-polarized neutron powder diffraction has been used in order to characterize the different features observed in these phases. PMID:27439896

  1. Structural phase transitions and topological defects in ion Coulomb crystals

    International Nuclear Information System (INIS)

    We use laser-cooled ion Coulomb crystals in the well-controlled environment of a harmonic radiofrequency ion trap to investigate phase transitions and defect formation. Topological defects in ion Coulomb crystals (kinks) have been recently proposed for studies of nonlinear physics with solitons and as carriers of quantum information. Defects form when a symmetry breaking phase transition is crossed nonadiabatically. For a second order phase transition, the Kibble–Zurek mechanism predicts that the formation of these defects follows a power law scaling in the rate of the transition. We demonstrate a scaling of defect density and describe kink dynamics and stability. We further discuss the implementation of mass defects and electric fields as first steps toward controlled kink preparation and manipulation

  2. Structural phase transitions and topological defects in ion Coulomb crystals

    Energy Technology Data Exchange (ETDEWEB)

    Partner, Heather L. [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Nigmatullin, Ramil [Institute of Quantum Physics, Ulm Univ., Ulm (Germany); Burgermeister, Tobias [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Keller, Jonas [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Pyka, Karsten [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Plenio, Martin B. [Center for Integrated Quantum Science and Technology, Ulm Univ., Ulm, (Germany):Institute for Theoretical Physics, Ulm Univ.,Ulm, (Germany); Retzker, Alex [Racah Institute of Physics, The Hebrew University of Jerusalem, Givat Ram (Israel); Zurek, Wojciech Hubert [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); del Campo, Adolfo [Univ. of Massachusetts, Amherst, MA (United States). Dept. of Physics; Mehlstaubler, Tanja E. [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany)

    2014-11-19

    We use laser-cooled ion Coulomb crystals in the well-controlled environment of a harmonic radiofrequency ion trap to investigate phase transitions and defect formation. Topological defects in ion Coulomb crystals (kinks) have been recently proposed for studies of nonlinear physics with solitons and as carriers of quantum information. Defects form when a symmetry breaking phase transition is crossed non-adiabatically. For a second order phase transition, the Kibble-Zurek mechanism predicts that the formation of these defects follows a power law scaling in the rate of the transition. We demonstrate a scaling of defect density and describe kink dynamics and stability. We further discuss the implementation of mass defects and electric fields as first steps toward controlled kink preparation and manipulation.

  3. The Physics of Phase Transitions Concepts and Applications

    CERN Document Server

    Papon, Pierre; Meijer, Paul H.E

    2006-01-01

    The physics of phase transitions is an important area at the crossroads of several fields that play central roles in materials sciences. In this second edition, new developments had been included which came up in the states of matter physics, in particular in the domain of nanomaterials and atomic Bose-Einstein condensates where progress is accelerating. The presentation of several chapters had been improved by bringing better information on some phase transition mechanisms and by illustrating them with new application examples. This work deals with all classes of phase transitions in fluids and solids. It contains chapters on evaporation, melting, solidification, magnetic transitions, critical phenomena, superconductivity, etc., and is intended for graduate students in physics and engineering; for scientists it will serve both as an introduction and an overview. End-of-chapter problems and complete answers are included.

  4. Structural phase transitions and topological defects in ion Coulomb crystals

    Energy Technology Data Exchange (ETDEWEB)

    Partner, Heather L. [Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany); Nigmatullin, Ramil [Institute of Quantum Physics, Albert-Einstein Allee-11, Ulm University, 89069 Ulm (Germany); Burgermeister, Tobias; Keller, Jonas; Pyka, Karsten [Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany); Plenio, Martin B. [Center for Integrated Quantum Science and Technology, Albert-Einstein-Allee 11, Ulm University, 89069 Ulm (Germany); Institute for Theoretical Physics, Albert-Einstein-Allee 11, Ulm University, 89069 Ulm (Germany); Retzker, Alex [Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Givat Ram (Israel); Zurek, Wojciech H. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87544 (United States); Campo, Adolfo del [Department of Physics, University of Massachusetts Boston, Boston, MA 02125 (United States); Mehlstäubler, Tanja E., E-mail: tanja.mehlstaeubler@ptb.de [Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany)

    2015-03-01

    We use laser-cooled ion Coulomb crystals in the well-controlled environment of a harmonic radiofrequency ion trap to investigate phase transitions and defect formation. Topological defects in ion Coulomb crystals (kinks) have been recently proposed for studies of nonlinear physics with solitons and as carriers of quantum information. Defects form when a symmetry breaking phase transition is crossed nonadiabatically. For a second order phase transition, the Kibble–Zurek mechanism predicts that the formation of these defects follows a power law scaling in the rate of the transition. We demonstrate a scaling of defect density and describe kink dynamics and stability. We further discuss the implementation of mass defects and electric fields as first steps toward controlled kink preparation and manipulation.

  5. Domain-wall formation in late-time phase transitions

    International Nuclear Information System (INIS)

    We investigate domain-wall formation in late-time phase transitions. We find that, as in the invisible-axion--domain-wall phenomenon, thermal effects alone are insufficient to drive different regions of the Universe to different parts of the disconnected vacuum manifold. This suggests that domain walls do not form unless either there is some supplemental (but perhaps not unreasonable) dynamics to localize the scalar field responsible for the phase transition to the low-temperature maximum (to an extraordinary precision) before the onset of the phase transition, or there is some nonthermal mechanism to produce large fluctuations in the scalar field. The fact that domain-wall production is not a robust prediction of late-time transitions may suggest future directions in model building

  6. Horava-Lifshitz early universe phase transition beyond detailed balance

    Energy Technology Data Exchange (ETDEWEB)

    Kheyri, F.; Khodadi, M.; Sepangi, H.R. [Shahid Beheshti University, Department of Physics, Tehran (Iran, Islamic Republic of)

    2013-01-15

    The early universe is believed to have undergone a QCD phase transition to hadrons at about 10 {mu}s after the big bang. We study such a transition in the context of the non-detailed balance Horava-Lifshitz theory by investigating the effects of the dynamical coupling constant {lambda} in a flat universe. The evolution of the relevant physical quantities, namely the energy density {rho}, temperature T, scale factor a and the Hubble parameter H is investigated before, during and after the phase transition, assumed to be of first order. Also, in view of the recent lattice QCD simulations data, we study a cross-over phase transition of the early universe whose results are based on two different sets of lattice data. (orig.)

  7. Chiral and Deconfining Phase Transitions from Holographic QCD Study

    CERN Document Server

    Fang, Zhen; Li, Danning

    2015-01-01

    A first attempt to accommodate the chiral and deconfining phase transitions of QCD in the bottom-up holographic framework is given. We constrain the relation between dilaton field $\\phi$ and metric warp factor $A_e$ and get several reasonable models in the Einstein-Dilaton system. Using the potential reconstruction approach, we solve the corresponding gravity background. Then we fit the background-related parameters by comparing the equation of state with the two-flavor lattice QCD results. After that we study the temperature dependent behavior of Polyakov loop and chiral condensate under those background solutions. We find that the results are in good agreement with the two-flavor lattice results. All the studies about the equation of state, the Polyakov loop and the chiral condensate signal crossover behavior of the phase transitions, which is consistent with the current understanding on the QCD phase transitions with physical quark mass. Furthermore, the extracted transition temperatures are comparable wit...

  8. Dissipation-driven quantum phase transitions in collective spin systems

    Energy Technology Data Exchange (ETDEWEB)

    Morrison, S [Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck (Austria); Parkins, A S [Department of Physics, University of Auckland, Private Bag 92019, Auckland (New Zealand)], E-mail: smor161@aucklanduni.ac.nz

    2008-10-14

    We consider two different collective spin systems subjected to strong dissipation-on the same scale as interaction strengths and external fields-and show that either continuous or discontinuous dissipative quantum phase transitions can occur as the dissipation strength is varied. First, we consider a well-known model of cooperative resonance fluorescence that can exhibit a second-order quantum phase transition, and analyse the entanglement properties near the critical point. Next, we examine a dissipative version of the Lipkin-Meshkov-Glick interacting collective spin model, where we find that either first- or second-order quantum phase transitions can occur, depending only on the ratio of the interaction and external field parameters. We give detailed results and interpretation for the steady-state entanglement in the vicinity of the critical point, where it reaches a maximum. For the first-order transition we find that the semiclassical steady states exhibit a region of bistability. (fast track communication)

  9. Neutron diffraction evidence for kinetic arrest of first order magneto-structural phase transitions in some functional magnetic materials.

    Science.gov (United States)

    Siruguri, V; Babu, P D; Kaushik, S D; Biswas, Aniruddha; Sarkar, S K; Krishnan, Madangopal; Chaddah, P

    2013-12-11

    Neutron diffraction measurements, performed in the presence of an external magnetic field, have been used to show structural evidence for the kinetic arrest of the first order phase transition from (i) the high temperature austenite phase to the low temperature martensite phase in the magnetic shape memory alloy Ni37Co11Mn42.5Sn9.5, (ii) the higher temperature ferromagnetic phase to the lower temperature antiferromagnetic phase in the half-doped charge ordered compound La0.5Ca0.5MnO3 and (iii) the formation of glass-like arrested states in both compounds. The cooling and heating under unequal fields protocol has been used to establish phase coexistence of metastable and equilibrium states, and also to demonstrate the devitrification of the arrested metastable states in the neutron diffraction patterns. We also explore the field–temperature dependent kinetic arrest line TK(H), through the transformation of the arrested phase to the equilibrium phase. This transformation has been observed isothermally in reducing H, as also on warming in constant H. TK is seen to increase as H increases in both cases, consistent with the low-T equilibrium phase having lower magnetization.

  10. Dynamics and phase transitions in A 1C 60 compounds

    Science.gov (United States)

    Schober, H.; Renker, B.; Heid, R.; Tölle, A.

    1997-02-01

    We present an overview of extensive inelastic neutron scattering experiments carried out on powders of A 1C 60. The various phases leave strong fingerprints in the microscopic dynamics confirming the solid-state chemical reactions. The strong kinetic phase transitions can be followed in real time and turn out to be highly complex.

  11. Instabilities near the QCD phase transition in the holographic models

    NARCIS (Netherlands)

    Gürsoy, U.; Lin, S.; Shuryak, E.

    2013-01-01

    This paper discusses phenomena close to the critical QCD temperature, using the holographic model. One issue studied is the overcooled high-T phase, in which we calculate quasinormal sound modes. We do not find instabilities associated with other first-order phase transitions, but nevertheless obser

  12. Kinetics of silica-phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Duffy, C.J.

    1993-07-01

    In addition to the stable silica polymorph quartz, several metastable silica phases are present in Yucca Mountain. The conversion of these phases to quartz is accompanied by volume reduction and a decrease in the aqueous silica activity, which may destabilize clinoptilolite and mordenite. The primary reaction sequence for the silica phases is from opal or glass to disordered opal-CT, followed by ordering of the opal-CT and finally by the crystallization of quartz. The ordering of opal-CT takes place in the solid state, whereas the conversion of opal-CT takes place through dissolution-reprecipitation involving the aqueous phase. It is proposed that the rate of conversion of opal-CT to quartz is controlled by diffusion of defects out of a disordered surface layer formed on the crystallizing quartz. The reaction rates are observed to be dependent on temperature, pressure, degree of supersaturation, and pH. Rate equations selected from the literature appear to be consistent with observations at Yucca Mountain.

  13. High-field spin dynamics of antiferromagnetic quantum spin chains

    DEFF Research Database (Denmark)

    Enderle, M.; Regnault, L.P.; Broholm, C.;

    2000-01-01

    The characteristic internal order of macroscopic quantum ground states in one-dimensional spin systems is usually not directly accessible, but reflected in the spin dynamics and the field dependence of the magnetic excitations. In high magnetic fields quantum phase transitions are expected. We...... present recent work on the high-field spin dynamics of the S = I antiferromagnetic Heisenberg chains NENP (Haldane ground state) and CsNiCl3 (quasi-1D HAF close to the quantum critical point), the uniform S = 1/2 chain CTS, and the spin-Peierls system CuGeO3. (C) 2000 Elsevier Science B,V. All rights...

  14. A transverse Ising bilayer film with an antiferromagnetic spin configuration

    Science.gov (United States)

    Kaneyoshi, T.

    2015-10-01

    The phase diagrams and temperature dependences of magnetizations in a transverse Ising bilayer film with an antiferromagnetic spin configuration are studied by the uses of the effective-field theory (EFT) with correlations, in order to clarify whether the appearance of a compensation point is possible below the transition temperature in the system. From these investigations, we have found a lot of characteristic phenomena in these properties, when the value of an interlayer coupling takes a large value, such as the reentrant phenomenon free from the disorder-induced frustration and the novel types of magnetization curve with a compensation point.

  15. Phase transitions of pyrolite mantle composition in the lower mantle

    Science.gov (United States)

    Ono, S.

    2006-12-01

    Knowledge of the phase relations of lower mantle materials is essential for evaluating seismic observations and their geodynamic implications. Several interesting phase transitions in pure compositions have been reported by previous studies. It is also important to investigate the phase transitions in natural compositions. Here, using an in situ X-ray measurement combined with a laser-heated diamond anvil cell, a phase relationship in pyrolite composition sample was investigated in order to determine the stability of phases in the lower mantle. The phase change from an orthorhombic Mg-perovskite to a CaIrO3-type postperovskite bearing assemblage in the pyrolitic mantle composition was also observed at 125 GPa, which corresponds to the same mantle depth as the seismic discontinuity. The phase boundary between the orthorhombic Mg-perovskite and CaIrO3-type bearing assemblage was determined to be P (GPa) = 124 + 0.008 x (T - 2500) (K) [1]. The bulk modulus of CaIrO3-type postperovskite in pure MgSiO3 was also measured using gold [2] and NaCl [3] as pressure calibrant. There is a possibility that the CaIrO3-type postperovskite phase contributes to the high electrical conductivity at the base of the lower mantle [4]. The phase transition of Ca-perovskite from tetragonal (or orthorhombic [5]) to cubic was confirmed in the pyrolite mantle composition [6,7]. The distortion of Ca-perovskite increases as pressure increases at 300 K. The temperature from tetragonal to cubic structure transition, therefore, appears to increase with increasing pressure. However, cubic structure is likely to be stable at high temperatures corresponding to the mantle geotherm [6]. Recently, the high-spin to low-spin transition in (Mg,Fe)O was observed [8]. We investigated the phase transition of pure FeO. Although the rhombohedral phase remains stable up to 140 GPa corresponding to the CMB, a discontinuous volume change without any structural changes was observed at 90 GPa. Our observation in

  16. Quantum phase transition in Bose-Fermi mixtures

    CERN Document Server

    Ludwig, D; Moroz, S; Wetterich, C

    2011-01-01

    We study a quantum Bose-Fermi mixture near a broad Feshbach resonance at zero temperature. Within a quantum field theoretical model, a two-step Gaussian approximation allows us to capture the main features of the quantum phase diagram. We show that a repulsive boson-boson interaction is necessary for thermodynamic stability. The quantum phase diagram is mapped in chemical-potential and density space, and both first- and second-order quantum phase transitions are found. We discuss typical characteristics of the first-order transition, such as hysteresis or a droplet formation of the condensate, which may be searched for experimentally.

  17. Quantum phase transition in Bose-Fermi mixtures

    Energy Technology Data Exchange (ETDEWEB)

    Ludwig, D.; Moroz, S.; Wetterich, C. [Institut fuer Theoretische Physik, Universitaet Heidelberg, Philosophenweg 16, D-69120 Heidelberg (Germany); Floerchinger, S. [Institut fuer Theoretische Physik, Universitaet Heidelberg, Philosophenweg 16, D-69120 Heidelberg (Germany); Physics Department, Theory Unit, CERN, CH-1211 Geneve 23 (Switzerland)

    2011-09-15

    We study a quantum Bose-Fermi mixture near a broad Feshbach resonance at zero temperature. Within a quantum field theoretical model, a two-step Gaussian approximation allows us to capture the main features of the quantum phase diagram. We show that a repulsive boson-boson interaction is necessary for thermodynamic stability. The quantum phase diagram is mapped in chemical-potential and density space, and both first- and second-order quantum phase transitions are found. We discuss typical characteristics of the first-order transition, such as hysteresis or a droplet formation of the condensate, which may be searched for experimentally.

  18. Non-equilibrium quantum phase transition via entanglement decoherence dynamics

    Science.gov (United States)

    Lin, Yu-Chen; Yang, Pei-Yun; Zhang, Wei-Min

    2016-01-01

    We investigate the decoherence dynamics of continuous variable entanglement as the system-environment coupling strength varies from the weak-coupling to the strong-coupling regimes. Due to the existence of localized modes in the strong-coupling regime, the system cannot approach equilibrium with its environment, which induces a nonequilibrium quantum phase transition. We analytically solve the entanglement decoherence dynamics for an arbitrary spectral density. The nonequilibrium quantum phase transition is demonstrated as the system-environment coupling strength varies for all the Ohmic-type spectral densities. The 3-D entanglement quantum phase diagram is obtained. PMID:27713556

  19. Ferrofluid nucleus phase transitions in an external uniform magnetic field

    Institute of Scientific and Technical Information of China (English)

    B. M. Tanygin; S. I. Shulyma; V. F. Kovalenko; M. V. Petrychuk

    2015-01-01

    The phase transition between a massive dense phase and a diluted superparamagnetic phase has been studied by means of a direct molecular dynamics simulation. The equilibrium structures of the ferrofluid aggregate nucleus are obtained for different values of a temperature and an external magnetic field magnitude. An approximate match of experiment and simulation has been shown for the ferrofluid phase diagram coordinates “field–temperature”. The provided phase coexistence curve has an opposite trend comparing to some of known theoretical results. This contradiction has been discussed. For given experimental parameters, it has been concluded that the present results describe more precisely the transition from linear chains to a dense globes phase. The theoretical concepts which provide the opposite binodal curve dependency trend match other experimental conditions:a diluted ferrofluid, a high particle coating rate, a high temperature, and/or a less particles coupling constant value.

  20. Topological phase transition in quasi-one dimensional organic conductors.

    Science.gov (United States)

    Ye, Xiao-Shan; Liu, Yong-Jun; Zeng, Xiang-Hua; Wu, Guoqing

    2015-01-01

    We explore topological phase transition, which involves the energy spectra of field-induced spin-density-wave (FISDW) states in quasi-one dimensional (Q1D) organic conductors, using an extended Su-Schrieffer-Heeger (SSH) model. We show that, in presence of half magnetic-flux FISDW state, the system exhibits topologically nontrivial phases, which can be characterized by a nonzero Chern number. The nontrivial evolution of the bulk bands with chemical potential in a topological phase transition is discussed. We show that the system can have a similar phase diagram which is discussed in the Haldane's model. We suggest that the topological feature should be tested experimentally in this organic system. These studies enrich the theoretical research on topologically nontrivial phases in the Q1D lattice system as compared to the Haldane topological phase appearing in the two-dimensional lattices. PMID:26612317

  1. A third-order phase transition in random tilings

    CERN Document Server

    Colomo, F

    2013-01-01

    We consider the domino tilings of an Aztec diamond with a cut-off corner of macroscopic square shape and given size, and address the bulk properties of tilings as the size is varied. We observe that the free energy exhibits a third-order phase transition when the cut-off square, increasing in size, reaches the arctic ellipse---the phase separation curve of the original (unmodified) Aztec diamond. We obtain this result by studying the thermodynamic limit of certain nonlocal correlation function of the underlying six-vertex model with domain wall boundary conditions, the so-called emptiness formation probability (EFP). We consider EFP in two different representations: as a tau-function for Toda chains and as a random matrix model integral. The latter has a discrete measure and a linear potential with hard walls; the observed phase transition shares properties with both Gross-Witten-Wadia and Douglas-Kazakov phase transitions.

  2. Quantum phase transitions in the noncommutative Dirac Oscillator

    CERN Document Server

    Panella, O

    2014-01-01

    We study the (2+1) dimensional Dirac oscillator in a homogeneous magnetic field in the non-commutative plane. It is shown that the effect of non-commutativity is twofold: $i$) momentum non commuting coordinates simply shift the critical value ($B_{\\text{cr}}$) of the magnetic field at which the well known left-right chiral quantum phase transition takes place (in the commuting phase); $ii$) non-commutativity in the space coordinates induces a new critical value of the magnetic field, $B_{\\text{cr}}^*$, where there is a second quantum phase transition (right-left), --this critical point disappears in the commutative limit--. The change in chirality associated with the magnitude of the magnetic field is examined in detail for both critical points. The phase transitions are described in terms of the magnetisation of the system. Possible applications to the physics of silicene and graphene are briefly discussed.

  3. Holographic metal/superconductor phase transitions with dark matter sector

    CERN Document Server

    Peng, Yan

    2015-01-01

    In this paper, we investigate the holographic phase transitions with dark matter sector in the AdS black hole background away from the probe limit. We firstly detect the formation of the scalar hair by examining the behaviors of the superconducting solutions and the effective mass of the scalar field. Then we study the condensation of the scalar operator with respect to the Hawking temperature T. As a further step, we disclose the properties of the phase transitions from the holographic topological entanglement entropy of the system. The holographic topological entanglement entropy is proved to be very useful in characterizing the difference between various phases. At last, we also derive the qualitative properties through the analytical methods. In summary, we find that the model parameters can provide rich physics in the general holographic metal/superconductor phase transitions.

  4. Uniqueness transition in noisy phase retrieval

    International Nuclear Information System (INIS)

    Previous criteria for the feasibility of reconstructing phase information from intensity measurements, both in x-ray crystallography and more recently in coherent x-ray imaging, have been based on the Maxwell constraint counting principle. We propose a new criterion, based on Shannon's mutual information, that is better suited for noisy data or contrast that has strong priors not well modeled by continuous variables. A natural application is magnetic domain imaging, where the criterion for uniqueness in the reconstruction takes the form that the number of photons, per pixel of contrast in the image, exceeds a certain minimum. Through detailed studies of a simple model, we develop an analogy between reconstruction uniqueness and the phases of a spin glass.

  5. Diffusive phase transitions in ferroelectrics and antiferroelectrics

    OpenAIRE

    Prosandeev, S. A.; Raevski, I. P.; Waghmare, U. V.

    2003-01-01

    In this paper, we present a microscopic model for heterogeneous ferroelectric and an order parameter for relaxor phase. We write a Landau theory based on this model and its application to ferroelectric PbFe$_{1/2}$Ta$_{1/2}$O$_3$ (PFT) and antiferroelectric NaNbO$_3$:Gd. We later discuss the coupling between soft mode and domain walls, soft mode and quasi-local vibration and resulting susceptibility function.

  6. Structural phase transitions in multipole traps

    CERN Document Server

    Marciante, Mathieu; Calisti, Annette; Knoop, Martina

    2012-01-01

    A small number of laser-cooled ions trapped in a linear radiofrequency multipole trap forms a hollow tube structure. We have studied, by means of molecular dynamics simulations, the structural transition from a double ring to a single ring of ions. We show that the single-ring configuration has the advantage to inhibit the thermal transfer from the rf-excited radial components of the motion to the axial component, allowing to reach the Doppler limit temperature along the direction of the trap axis. Once cooled in this particular configuration, the ions experience an angular dependency of the confinement if the local adiabaticity parameter exceeds the empirical limit. Bunching of the ion structures can then be observed and an analytic expression is proposed to take into account for this behaviour.

  7. The Origins of Phase Transitions in Small Systems

    OpenAIRE

    Muelken, Oliver; Stamerjohanns, Heinrich; Borrmann, Peter

    2001-01-01

    The identification and classification of phases in small systems, e.g. nuclei, social and financial networks, clusters, and biological systems, where the traditional definitions of phase transitions are not applicable, is important to obtain a deeper understanding of the phenomena observed in such systems. Within a simple statistical model we investigate the validity and applicability of different classification schemes for phase transtions in small systems. We show that the whole complex tem...

  8. High-Pressure Phase Transition in Cyclo-octane

    Institute of Scientific and Technical Information of China (English)

    GAO Ling-Ling; ZOU Guang-Tian; JIANG Sheng; LIU Dan; HAO Jian; JIN Yun-Xia; WANG Feng; WANG Qiu-Shi; LIU Jing; CUI Qi-Liang

    2008-01-01

    Structural behaviour of cyclo-octane under high pressure is studied by using a synchrotron x-ray source in a diamond anvil cell (DAC) up to 40.2 GPa at room temperature. The cyclo-octane firstly solidifies to the triclinic phase at 0.87 GPa. With the increasing pressure, the phase of cyclo-octane changes to the tetragonal phase at about 6.0 GPa and then transforms to amorphous phase above 18.2 GPa, which is kept till to 40.2 GPa. All the phase transitions of cyclo-octane are irreversible.

  9. Phase transition properties of a cylindrical ferroelectric nanowire

    Indian Academy of Sciences (India)

    Wang Ying; Yang Xiong

    2013-11-01

    Based on the transverse Ising model (TIM) and using the mean-field theory, we investigate the phase transition properties of a cylindrical ferroelectric nanowire. Two different kinds of phase diagrams are constructed. We discuss systematically the effects of exchange interactions and the transverse field parameters on the phase diagrams. Moreover, the cross-over features of the parameters from the ferroelectric dominant phase diagram to the paraelectric dominant phase diagram are determined for the ferroelectric nanowire. In addition, the polarizations of the surface shell and the core are illustrated in detail by modifying the TIM parameters.

  10. Phase transitions in the assembly of multivalent signalling proteins

    Energy Technology Data Exchange (ETDEWEB)

    Li, Pilong; Banjade, Sudeep; Cheng, Hui-Chun; Kim, Soyeon; Chen, Baoyu; Guo, Liang; Llaguno, Marc; Hollingsworth, Javoris V.; King, David S.; Banani, Salman F.; Russo, Paul S.; Jiang, Qiu-Xing; Nixon, B. Tracy; Rosen, Michael K. (IIT); (UCB); (LSU); (UTSMC); (Penn)

    2013-04-08

    Cells are organized on length scales ranging from angstrom to micrometers. However, the mechanisms by which angstrom-scale molecular properties are translated to micrometer-scale macroscopic properties are not well understood. Here we show that interactions between diverse synthetic, multivalent macromolecules (including multi-domain proteins and RNA) produce sharp liquid-liquid-demixing phase separations, generating micrometer-sized liquid droplets in aqueous solution. This macroscopic transition corresponds to a molecular transition between small complexes and large, dynamic supramolecular polymers. The concentrations needed for phase transition are directly related to the valency of the interacting species. In the case of the actin-regulatory protein called neural Wiskott-Aldrich syndrome protein (N-WASP) interacting with its established biological partners NCK and phosphorylated nephrin1, the phase transition corresponds to a sharp increase in activity towards an actin nucleation factor, the Arp2/3 complex. The transition is governed by the degree of phosphorylation of nephrin, explaining how this property of the system can be controlled to regulatory effect by kinases. The widespread occurrence of multivalent systems suggests that phase transitions may be used to spatially organize and biochemically regulate information throughout biology.

  11. Oxygen octahedra distortion induced structural and magnetic phase transitions in Bi1-xCaxFe1-xMnxO3 ceramics

    Science.gov (United States)

    Kumar, Pawan; Shankhwar, Nisha; Srinivasan, A.; Kar, Manoranjan

    2015-05-01

    The co-doping of Ca and Mn in respective Bi and Fe-sites of BiFeO3 lattice leads to structural transition from rhombohedral (R3c space group) to orthorhombic (Pbnm space group) crystal symmetry. The tilt angle for anti-phase rotation of the oxygen octahedra of BiFeO3 at room temperature is observed to be ˜13.8°. It decreases with the increase in the co-doping percentage which suggests the composition-driven structural phase transition. The remnant magnetization for sample with 15% of co-doping becomes about 16 times that of BiFeO3. It may be attributed to the suppression of cycloid spin structure and uncompensated spins at the surface of nanocrystallites. Further increase in co-doping percentage results in the sharp reduction of remnant magnetization due to the dominant contribution from the collinear antiferromagnetic ordering in the Pbnm space group. The Arrott plot analysis clearly indicates the composition-driven crossover from the antiferromagnetic to weak ferromagnetic ordering and vice versa. Electron spin resonance results provide the evidence for the composition-driven phase transitions from an incommensurate spin cycloidal modulated state to one with nearly homogeneous spin order. The band gap (2.17 eV) of BiFeO3 measured using UV-Vis spectra was supported by the resonance Raman spectra.

  12. Annealing induced coherent evolutions of biaxial strain and antiferromagnetic-insulator phase in La0.625Ca0.375MnO3 films

    Science.gov (United States)

    Han, Yunxin; Wu, Wenbin; Jiang, Guoshun; Zhu, Changfei

    2012-09-01

    La0.625Ca0.375MnO3 (LCMO) films with thicknesses between 7 and 54 nm were epitaxially grown on (LaAlO3)0.3(Sr2AlTaO6)0.35 (001) [LSAT (001)] substrates by using pulsed laser deposition. For this epitaxial system, antiferromagnetic-insulator (AFI) state can be controlled by changing the film thickness and annealing time with various epitaxial strain states, although this phenomenon is absent in the relatively thick films or bulk samples. The consistency between magnetization and resistivity data suggests all these interesting transport behaviors are attributed to the fluctuation of AFI volume fractions and their instability. Especially, there are huge low-field magnetoresistance over -54% (32 nm) at 0.1 T and enhanced magnetoresistance over a broad temperature range. Based on these above results, annealing induced coherent evolutions of biaxial strain and AFI phase in LCMO epitaxial films is a consequence of the strain-driven orbital ordered state, and this may make an approach for a possible application of strongly correlated electron devices.

  13. Pressure-induced phase transitions of indium selenide

    Science.gov (United States)

    Rasmussen, Anya Marie

    In2Se3 has potential as a phase-change material for memory applications. Understanding its phase diagram is important to achieve controlled switching between phases. Pressure-dependent phase transitions of In2Se3 bulk powders and nanowire samples were studied at room temperature and at elevated temperatures using synchrotron x-ray diffraction and diamond-anvil cells (DACs). alpha-In2Se3 transforms into the beta phase at 0.7 GPa, an order of magnitude lower than phase-transition critical pressures in typical semiconductors. The bulk moduli are reported and the c/a ratio for the beta phase is shown to have a highly nonlinear dependence on pressure. gamma-In2Se3, metastable under ambient conditions, transforms into to the high-pressure beta phase between 2.8 GPa and 3.2 GPa in bulk powder samples and at slightly higher pressures, between 3.2 GPa and 3.7 GPa in nanowire samples. While the gamma phase bulk modulus is similar to that of the beta phase, the decrease due to pressure in the unit cell parameter ratio, c/a, is less than half the decrease seen in the beta phase. Using high-temperature DACs, we investigated how elevated temperatures and pressures affect the crystal structure of In 2Se3. From these measurements, the high-pressure beta phase was found to be metastable. The high-pressure beta phase transitions into the high-temperature beta phase at temperatures above 380 °C.

  14. A comparison of observables for solid-solid phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Smilowitz, Laura B [Los Alamos National Laboratory; Henson, Bryan F [Los Alamos National Laboratory; Romero, Jerry J [Los Alamos National Laboratory

    2009-01-01

    The study of solid-solid phase transformations is hindered by the difficulty of finding a volumetric probe to use as a progress variable. Solids are typically optically opaque and heterogeneous. Over the past several years, second harmonic generation (SHG) has been used as a kinetic probe for a solid-solid phase transition in which the initial and final phases have different symmetries. Bulk generation of SHG is allowed by symmetry only in noncentrosymmetric crystallographic space groups. For the organic energetic nitramine octahydro-1,3 ,5,7 -tetranitro-1,3 ,5,7 -tatrazocine (HMX), the beta phase is centro symmetric (space group P2{sub 1}/c) and the delta phase iS noncentrosymmetric (space group P6{sub 1}22) making SHG an extremely sensitive, essentially zero background probe of the phase change progress. We have used SHG as a tool to follow the progress of the transformation from beta to delta phase during the solid-solid transformation. However, kinetic models of the transformation derived using different observables from several other groups have differed, showing later onset for the phase change and faster progression to completion. In this work, we have intercompared several techniques to understand these differences. The three techniques discussed are second harmonic generation, Raman spectroscopy, and differential scanning calorimetry (DSC). The progress of the beta to delta phase transition in HMX observed with each of these different probes will be discussed and advantages and disadvantages of each technique described. This paper compares several different observables for use in measuring the kinetics of solid-solid phase transitions. Relative advantages and disadvantages for each technique are described and a direct comparison of results is made for the beta to delta polymorphic phase transition of the energetic nitramine, octahydro-1,3,5,7-tetranitro-1,3,5,7-tatrazocine.

  15. First-Order Transitions and the Magnetic Phase Diagram of CeSb

    DEFF Research Database (Denmark)

    Lebech, Bente; Clausen, Kurt Nørgaard; Vogt, O.

    1980-01-01

    The high-temperature (14-17K) low-magnetic field (0-0.8 T) region of the phase diagram of the anomalous antiferromagnet CeSb has been reinvestigated by neutron diffraction in an attempt to locate a possible tricritical point. Previous neutron diffraction studies indicated that a tricritical point...

  16. THE NEXT GENERATION TRANSIT SURVEY PROTOTYPING PHASE

    Directory of Open Access Journals (Sweden)

    J. McCormac

    2014-01-01

    Full Text Available El Next Generation Transit Survey (NGTS es un nuevo sondeo d e exoplanetas transitantes de campo amplio que tiene como objetivo descubrir exoplanetas del tama ̃no d e Neptuno y super-Tierras entorno a estrellas brillantes ( V < 13 cercanas. NGTS consiste de un arreglo de 12 telescopios o perados rob ́oticamente observando en la banda de 600 − 900 nm. NGTS sondear ́a m ́as de cinco veces el n ́umero de estre llas, con V < 13, que Kepler y por lo tanto proveer ́a los objetivos m ́as brillantes para s er caracterizados con instrumentaci ́on existente y futura (VLT, E-ELT y JWST. En 2009/10 un prototipo del NGTS f ue probado en La Palma, comprobando que un sistema as ́ı puede alcanzar nuestros objetivos de fot ometr ́ıa estelar esencialmente limitada s ́olo por el ruido blanco. Los resultados son resumidos aqu ́ı. NGTS se al imenta de la experiencia del proyecto SuperWASP, que, por muchos a ̃nos, ha liderado la detecci ́on terrestre d e exoplanetas transitantes.

  17. Non-equilibrium phase transitions in a liquid crystal

    Science.gov (United States)

    Dan, K.; Roy, M.; Datta, A.

    2015-09-01

    The present manuscript describes kinetic behaviour of the glass transition and non-equilibrium features of the "Nematic-Isotropic" (N-I) phase transition of a well known liquid crystalline material N-(4-methoxybenzylidene)-4-butylaniline from the effects of heating rate and initial temperature on the transitions, through differential scanning calorimetry (DSC), Fourier transform infrared and fluorescence spectroscopy. Around the vicinity of the glass transition temperature (Tg), while only a change in the baseline of the ΔCp vs T curve is observed for heating rate (β) > 5 K min-1, consistent with a glass transition, a clear peak for β ≤ 5 K min-1 and the rapid reduction in the ΔCp value from the former to the latter rate correspond to an order-disorder transition and a transition from ergodic to non-ergodic behaviour. The ln β vs 1000/T curve for the glass transition shows convex Arrhenius behaviour that can be explained very well by a purely entropic activation barrier [Dan et al., Eur. Phys. Lett. 108, 36007 (2014)]. Fourier transform infrared spectroscopy indicates sudden freezing of the out-of-plane distortion vibrations of the benzene rings around the glass transition temperature and a considerable red shift indicating enhanced coplanarity of the benzene rings and, consequently, enhancement in the molecular ordering compared to room temperature. We further provide a direct experimental evidence of the non-equilibrium nature of the N-I transition through the dependence of this transition temperature (TNI) and associated enthalpy change (ΔH) on the initial temperature (at fixed β-values) for the DSC scans. A plausible qualitative explanation based on Mesquita's extension of Landau-deGennes theory [O. N. de Mesquita, Braz. J. Phys. 28, 257 (1998)] has been put forward. The change in the molecular ordering from nematic to isotropic phase has been investigated through fluorescence anisotropy measurements where the order parameter, quantified by the

  18. Quantum fluctuations in the competition among spin glass, antiferromagnetism and local pairing superconductivity

    Energy Technology Data Exchange (ETDEWEB)

    Magalhaes, S.G. [Laboratorio de Mecanica Estatistica e Teoria da Materia Condensada (PPGFIS-Dep. Fisica) UFSM, 97105-900 Santa Maria (Brazil)]. E-mail: ggarcia@ccne.ufsm.br; Zimmer, F.M. [Laboratorio de Mecanica Estatistica e Teoria da Materia Condensada (PPGFIS-Dep. Fisica) UFSM, 97105-900 Santa Maria (Brazil); Kipper, C.J. [Laboratorio de Mecanica Estatistica e Teoria da Materia Condensada (PPGFIS-Dep. Fisica) UFSM, 97105-900 Santa Maria (Brazil); Calegari, E.J. [Laboratorio de Mecanica Estatistica e Teoria da Materia Condensada (PPGFIS-Dep. Fisica) UFSM, 97105-900 Santa Maria (Brazil)

    2007-03-15

    The competition among spin glass (SG), antiferromagnetism (AF) and local pairing superconductivity (PAIR) is studied in a two-sublattice fermionic Ising SG model with a local BCS pairing interaction in the presence of a transverse magnetic field {gamma}. The spins in different sublattices interact with Gaussian random couplings with an antiferromagnetic mean. The problem is formulated in a Grassmann path integral formalism. The static ansatz and the replica symmetry are used to obtain the half-filling thermodynamic potential. The results are shown in phase diagrams that exhibit a complex transition line separating the PAIR phase from the others. This line is second order at high temperature which ends in a tricritical point. The presence of {gamma} affects deeply the transition lines.

  19. d-wave superconductivity, antiferromagnetism and spin liquid in quasi-two-dimensional organic superconductors

    Directory of Open Access Journals (Sweden)

    P. Sahebsara

    2006-09-01

    Full Text Available   The self-energy-functional approach is a powerful many-body tool to investigate different broken symmetry phases of strongly correlated electron systems. We use the variational cluster perturbation theory (also called the variational cluster approximation to investigate the interplay between the antiferromagnetism and d-wave superconductivity of κ-(ET2 X conductors. These compounds are described by the so-called dimer Hubbard model, with various values of the on-site repulsion U and diagonal hopping amplitude t. At strong coupling, our zero-temperature calculations show a transition from Néel antiferromagnetism to a spin-liquid phase with no long range order, at around t ~ 0.9. At lower values of U, we find d-wave superconductivity. Taking into account the point group symmetries of the lattice, we find a transition between dx2-y2 and dxy pairing symmetries, the latter happening for smaller values of U.

  20. Magnetic field induced phase branches of the superconducting transition in two-dimensional square Π-loop arrays

    Institute of Scientific and Technical Information of China (English)

    Liu Dang-Ting; Tian Ye; Chen Geng-Hua; Yang Qian-Sheng

    2008-01-01

    Based on the results of explicit forms of free energy density for each possible arrangement of magnetization fluxes in large-scale two-dimensional (2D) square Π-loop arrays given by Li et al [2007 Chin.Phys.16 1450],the field-cooled superconducting phase transition is further investigated by analysing the free energy of the arrays with a simplified symmetrical model.Our analytical result is exactly the same as that obtained in Li's paper by means of numerical calculations.It is shown that the phase transition splits into two branches with either ferromagnetic or anti-ferromagnetic flux ordering,which depends periodically on the strength of external magnetic flux φe through each loop and monotonically on the screen parameter β of the loops in the arrays.In principle,the diagram of the phase branches is similar to that of its one-dimensional counterpart.The influence of thermal fluctuation on the flux ordering during the transition from normal to superconducting states of the Π-loop arrays is also discussed.

  1. Error-correcting codes and phase transitions

    CERN Document Server

    Manin, Yuri I

    2009-01-01

    The theory of error-correcting codes is concerned with constructing codes that optimize simultaneously transmission rate and relative minimum distance. These conflicting requirements determine an asymptotic bound, which is a continuous curve in the space of parameters. The main goal of this paper is to relate the asymptotic bound to phase diagrams of quantum statistical mechanical systems. We first identify the code parameters with Hausdorff and von Neumann dimensions, by considering fractals consisting of infinite sequences of code words. We then construct operator algebras associated to individual codes. These are Toeplitz algebras with a time evolution for which the KMS state at critical temperature gives the Hausdorff measure on the corresponding fractal. We extend this construction to algebras associated to limit points of codes, with non-uniform multi-fractal measures, and to tensor products over varying parameters.

  2. Localized charged states and phase separation near second order phase transition

    OpenAIRE

    Kabanov, V. V.; Mamin, R. F.; Shaposhnikova, T. S.

    2008-01-01

    Localized charged states and phase segregation are described in the framework of the phenomenological Ginzburg-Landau theory of phase transitions. The Coulomb interactions determines the charge distribution and the characteristic length of the phase separated states. The phase separation with charge segregation becomes possible because of the large dielectric constant and the small density of extra charge in the range of charge localization. The phase diagram is calculated and the energy gain...

  3. Postperovskite phase transition of ZnGeO3: comparative crystal chemistry of postperovskite phase transition from germanate perovskites.

    Science.gov (United States)

    Yusa, Hitoshi; Tsuchiya, Taku; Akaogi, Masaki; Kojitani, Hiroshi; Yamazaki, Daisuke; Hirao, Naohisa; Ohishi, Yasuo; Kikegawa, Takumi

    2014-11-01

    The postperovskite phase of ZnGeO3 was confirmed by laser heating experiments of the perovskite phase under 110-130 GPa at high temperature. Ab initio calculations indicated that the phase transition occurs at 133 GPa at 0 K. This postperovskite transition pressure is significantly higher than those reported for other germanates, such as MnGeO3 and MgGeO3. The comparative crystal chemistry of the perovskite-to-postperovskite transition suggests that a relatively elongated b-axis in the low-pressure range resulted in the delay in the transition to the postperovskite phase. Similar to most GdFeO3-type perovskites that transform to the CaIrO3-type postperovskite phase, ZnGeO3 perovskite eventually transformed to the CaIrO3-type postperovskite phase at a critical rotational angle of the GeO6 octahedron. The formation of the postperovskite structure at a very low critical rotational angle for MnGeO3 suggests that relatively large divalent cations likely break down the corner-sharing GeO6 frameworks without a large rotation of GeO6 to form the postperovskite phase. PMID:25310272

  4. High pressure phase transition in Pr-monopnictides

    Energy Technology Data Exchange (ETDEWEB)

    Raypuria, Gajendra Singh, E-mail: sosfizix@gmail.com, E-mail: gsraypuria@gmail.com; Gupta, Dinesh Chandra [Condensed Matter Theory Group, School of Studies in Physics, Jiwaji University, Gwalior - 474011 (India); Department of Physics, Govt. K.R.G. P.G. Autonomous College, Gwalior - 474001 (India)

    2015-06-24

    The Praseodymium-monopnictides compounds have been found to undergo transition from their initial NaCl-type structure to high pressure body centered tetragonal (BCT) structure (distorted CsCl-type P4/mmm) using CTIP model. The calculated values of cohesive energy, lattice constant, phase transition pressure, relative volume collapse agree well with the available measured data and better than those computed by earlier workers.

  5. Collective Motion and Phase Transitions of Symmetric Camphor Boats

    Science.gov (United States)

    Heisler, Eric; Suematsu, Nobuhiko J.; Awazu, Akinori; Nishimori, Hiraku

    2012-07-01

    The motion of several self-propelled boats in a narrow channel displays spontaneous pattern formation and kinetic phase transitions. In contrast with previous studies on self-propelled particles, this model does not require stochastic fluctuations and it is experimentally accessible. By varying the viscosity in the system, it is possible to form either a stationary state, correlated or uncorrelated oscillations, or unidirectional flow. Here, we describe and analyze these self organized patterns and their transitions.

  6. Phase transitions of black holes in massive gravity

    CERN Document Server

    Fernando, Sharmanthie

    2016-01-01

    In this paper we have studied thermodynamics of a black hole in massive gravity in the canonical ensemble. The massive gravity theory in consideration here has a massive graviton due to Lorentz symmetry breaking. The black hole studied here has a scalar charge due to the massive graviton and is asymptotically anti-de Sitter. We have computed various thermodynamical quantities such as temperature, specific heat and free energy. Both the local and global stability of the black hole are studied by observing the behavior of the specific heat and the free energy. We have observed that there is a first order phase transition between small and large black hole for a certain range of the scalar charge. This phase transition is similar to the liquid/gas phase transition at constant temperature for a Van der Waals fluid. The coexistence curves for the small and large black hole branches are also discussed in detail.

  7. Thermodynamics and Phase Transition in Rotational Kiselev Black Hole

    CERN Document Server

    Xu, Zhaoyi

    2016-01-01

    We calculate the thermodynamical features of rotational Kiselev black holes, specifically we use one order approximate of horizon to calculate thermodynamical features for all $\\omega$. The thermodynamics features include areas, entropies, horizon radii, surface gravities, surface temperatures, Komar energies and irreducible masses at the Cauchy horizon and Event horizon. At the same time the products of these features have been discussed. We find that the products are independent with mass of black hole and determined by $\\omega$ and $\\alpha$. The features in the situations of $\\omega=-2/3,1/3$ and $0$ (quintessence matter, radiation and dust) have been discussed in detail. We also generalize the Smarr mass formula and Christodoulou-Ruffini mass formula to these black holes. Finally we study the phase transition for black holes with different $\\omega$ and obtain the state equation. We analyze the phase transition for $\\omega=1/3$, and find that $\\alpha$ shifts the critical point of phase transition.

  8. Canonical Entropy and Phase Transition of Rotating Black Hole

    Institute of Scientific and Technical Information of China (English)

    ZHAO Ren; WU Yue-Qin; ZHANG Li-Chun

    2008-01-01

    Recently, the Hawking radiation of a black hole has been studied using the tunnel effect method. The radiation spectrum of a black hole is derived. By discussing the correction to spectrum of the rotating black hole, we obtain the canonical entropy. The derived canonical entropy is equal to the sum of Bekenstein-Hawking entropy and correction term. The correction term near the critical point is different from the one near others. This difference plays an important role in studying the phase transition of the black hole. The black hole thermal capacity diverges at the critical point. However, the canonical entropy is not a complex number at this point. Thus we think that the phase transition created by this critical point is the second order phase transition. The discussed black hole is a five-dimensional Kerr-AdS black hole. We provide a basis for discussing thermodynamic properties of a higher-dimensional rotating black hole.

  9. Perceptions of healthy eating in transitional phases of life

    DEFF Research Database (Denmark)

    Bech-Larsen, Tino; Kazbare, Laura

    2014-01-01

    Purpose - Although adolescents and older adults are often targets for nutritional change interventions, little has been done to explore how people in these transitional life phases perceive the matter themselves. The purpose of the study reported in this article is to explore and compare adolesce......Purpose - Although adolescents and older adults are often targets for nutritional change interventions, little has been done to explore how people in these transitional life phases perceive the matter themselves. The purpose of the study reported in this article is to explore and compare......). Originality/value - The study and findings reported in this article contribute by providing the first steps towards a better understanding of how social cognition and self-efficacy perceptions related to healthy eating develop in the transitional phases of adolescence and older adulthood. In order...

  10. Lifshitz scaling effects on holographic paramagnetism/ferromagneism phase transition

    CERN Document Server

    Zhang, Cheng-Yuan; Jin, Yong-Yi; Chai, Yun-Tian; Hu, Mu-Hong; Zhang, Zhuo

    2016-01-01

    In the probe limit, we investigate holographic paramagnetism-ferromagnetism phase transition in the four-dimensional (4D) and five-dimensional(5D) Lifshitz black holes by means of numerical and semi-analytical methods, which is realized by introducing a massive 2-form field coupled to the Maxwell field. We find that the Lifshitz dynamical exponent $z$ contributes evidently to magnetic moment and hysteresis loop of single magnetic domain quantitatively not qualitatively. Concretely, in the case without external magnetic field, the spontaneous magnetization and ferromagnetic phase transition happen when the temperature gets low enough, and the critical exponent for the magnetic moment is always $1/2$, which is in agreement with the result from mean field theory. And the increasing $z$ enhances the phase transition and increases the DC resistivity which behaves as the colossal magnetic resistance effect in some materials. Furthermore, in the presence of the external magnetic field, the magnetic susceptibility sa...

  11. Gravitational radiation generated by cosmological phase transition magnetic fields

    International Nuclear Information System (INIS)

    We study gravitational waves generated by the cosmological magnetic fields induced via bubble collisions during the electroweak (EW) and QCD phase transitions. The magnetic field generation mechanisms considered here are based on the use of the fundamental EW minimal supersymmetric and QCD Lagrangians. The gravitational waves spectrum is computed using a magnetohydrodynamic turbulence model. We find that the gravitational wave spectrum amplitude generated by the EW phase transition peaks at a frequency of approximately 1-2 mHz, and is of the order of 10-20-10-21; thus this signal is possibly detectable by the Laser Interferometer Space Antenna (LISA). The gravitational waves generated during the QCD phase transition, however, are outside the LISA sensitivity bands.

  12. Photonic quantum-corral ring laser A fermionic phase transition

    CERN Document Server

    Kwon, O D; Kim, J Y; Bae, J; Kim, M J; Ahn, J C; Kwon, O H

    2002-01-01

    Extensive Bose-Einstein condensation research activities have recently led to studies of fermionic atoms and optical confinements. Here we present a case of micro-optical fermionic electron phase transition. Optically confined ordering and phase transitions of a fermionic cloud in dynamic steady state are associated with Rayleigh emissions from photonic quantum ring manifold which are generated by nature without any ring lithography. The whispering gallery modes, produced in a semiconductor Rayleigh-Fabry-Perot toroidal cavity at room temperature, exhibit novel properties of ultralow thresholds open to nano-ampere regime, thermal stabilities from square-root-T-dependent spectral shift, and angularly varying intermode spacings. The photonic quantum ring phenomena are associated with a photonic field-driven phase transition of quantum-well-to-quantum-wire and hence the photonic (non-de Broglie) quantum corral effect on the Rayleigh cavity-confined carriers in dynamic steady state. Based upon the intra-cavity fe...

  13. Analytic approach to the motion of cosmological phase transition fronts

    International Nuclear Information System (INIS)

    We consider the motion of planar phase-transition fronts in first-order phase transitions of the Universe. We find the steady state wall velocity as a function of a friction coefficient and thermodynamical parameters, taking into account the different hydrodynamic modes of propagation. We obtain analytical approximations for the velocity by using the thin wall approximation and the bag equation of state. We compare our results to those of numerical calculations and discuss the range of validity of the approximations. We analyze the structure of the stationary solutions. Multiple solutions may exist for a given set of parameters, even after discarding non-physical ones. We discuss which of these will be realized in the phase transition as the stationary wall velocity. Finally, we discuss on the saturation of the friction at ultra-relativistic velocities and the existence of runaway solutions.

  14. Non-equilibrium physics at a holographic chiral phase transition

    International Nuclear Information System (INIS)

    The D3/D7 system holographically describes an N=2 gauge theory which spontaneously breaks a chiral symmetry by the formation of a quark condensate in the presence of a magnetic field. At finite temperature it displays a first order phase transition. We study out of equilibrium dynamics associated with this transition by placing probe D7 branes in a geometry describing a boost-invariant expanding or contracting plasma. We use an adiabatic approximation to track the evolution of the quark condensate in a heated system and reproduce the phase structure expected from equilibrium dynamics. We then study solutions of the full partial differential equation that describes the evolution of out of equilibrium configurations to provide a complete description of the phase transition including describing aspects of bubble formation. (orig.)

  15. Phase transitions of black holes in massive gravity

    Science.gov (United States)

    Fernando, Sharmanthie

    2016-05-01

    In this paper, we have studied thermodynamics of a black hole in massive gravity in the canonical ensemble. The massive gravity theory in consideration here has a massive graviton due to Lorentz symmetry breaking. The black hole studied here has a scalar charge due to the massive graviton and is asymptotically anti-de Sitter (AdS). We have computed various thermodynamical quantities such as temperature, specific heat and free energy. Both the local and global stability of the black hole are studied by observing the behavior of the specific heat and the free energy. We have observed that there is a first-order phase transition between small (SBH) and large black hole (LBH) for a certain range of the scalar charge. This phase transition is similar to the liquid/gas phase transition at constant temperature for a van der Waals fluid. The coexistence curves for the SBH and LBH branches are also discussed in detail.

  16. Fluctuation of Voids in Hadronization at Phase Transition

    CERN Document Server

    Hwa, R C; Hwa, Rudolph C.; Zhang, Qing-hui

    2000-01-01

    Starting from the recognition that hadrons are not produced smoothly at phase transition, the fluctuation of spatial patterns is investigated by finding a measure of the voids that exhibits scaling behavior. The Ising model is used to simulate a cross-over in quark-hadron phase transition. A threshold in hadron density is used to define a void. The dependence of the scaling exponents on that threshold is found to provide useful information on some properties of the hadronization process. The complication in heavy-ion collision introduces the possibility of configuration mixing, which can also be studied in this approach. Numerical criteria on the scaling exponents have been found that can be used to discriminate phase-transition processes from other hadronization processes having nothing to do with critical phenomena.

  17. Gravitational Radiation from First-Order Phase Transitions

    CERN Document Server

    Child, Hillary L

    2012-01-01

    It is believed that first order phase transitions at or around the GUT scale will produce high-frequency gravitational radiation. This radiation is a consequence of the collisions and coalescence of multiple bubbles during the transition. We employ high-resolution lattice simulations to numerically evolve a system of bubbles, track the anisotropic stress during the process and evolve the metric perturbations associated with gravitational radiation. Although the radiation produced during the bubble collisions has previously been estimated, we find that the coalescence phase that greatly enhances this radiation even in the absence of turbulence. We comment on how these simulations scale and propose that the same enhancement should be found at the Electroweak scale; this modification should make direct detection of a first-order electroweak phase transition easier.

  18. Benford's law detects quantum phase transitions similarly as earthquakes

    Science.gov (United States)

    Sen(De, Aditi; Sen, Ujjwal

    2011-09-01

    A century ago, it was predicted that the first significant digit appearing in a data would be nonuniformly distributed, with the number one appearing with the highest frequency. This law goes by the name of Benford's law. It holds for data ranging from infectious-disease cases to national greenhouse gas emissions. Quantum phase transitions are cooperative phenomena where qualitative changes occur in many-body systems at zero temperature. We show that the century-old Benford's law can detect quantum phase transitions, much like it detects earthquakes. Therefore, being certainly of very different physical origins, seismic activity and quantum cooperative phenomena may be detected by similar methods. The result has immediate implications in precise measurements in experiments in general, and for realizable quantum computers in particular. It shows that estimation of the first significant digit of measured physical observables is enough to detect the presence of quantum phase transitions in macroscopic systems.

  19. Combined Piezoelectrooptic Effect in Rochelle Salt at the Phase Transition

    CERN Document Server

    Vlokh, R; Kostyrko, M

    2004-01-01

    The results of study of piezoelectrooptic (PEO) effect in the course of ferroelectric-ferroelastic phase transition in Rochelle salt crystals are presented. The coefficient of the combined effect is obtained from measurements of the changes in the electrooptic coefficients under the action of mechanical stress and the changes in the piezooptic coefficients under the action of electric field (or spontaneous polarization). It is shown experimentally that the values of both coefficients are the same, as predicted by the theory. The temperature dependence of the coefficient of combined PEO effect is obtained. Its anomalous behaviour at the phase transition appears due to the dielectric permitivity anomaly. It is also demonstrated that the change in the piezooptic coefficients at the phase transition in Rochelle salt crystals may be satisfactorily explained as a result of linear and quadratic PEO effect induced by spontaneous polarization.

  20. Luminescence detection of phase transitions in crystals and nanoparticle inclusions

    Energy Technology Data Exchange (ETDEWEB)

    Townsend, P. D. [Science and Technology, University of Sussex, Brighton, BN1 9QH (United Kingdom); Yang, B. [Physics Department, Beijing Normal University, Beijing 100875 (China); Wang, Y. [School of Materials Science and Technology, China University of Geosciences, Beijing 100083 (China)]. e-mail: p.d.townsend@sussex.ac.uk

    2008-11-15

    Luminescence measurements are extremely sensitive to variations in structural environment and thus have the potential to probe distortions of fluorescence sites. Changes can be monitored via luminescence efficiency, emission spectra or excited state lifetimes and these factors are influenced by the local neighbourhood around the emission site, and therefore by structure, composition, pressure and temperature. A rarely exploited approach for condensed matter has been to use the changes in luminescence responses during heating or cooling of a material to provide a rapid survey to detect the presence of phase transitions. One can often differentiate between bulk and surface effects by contrasting results from radioluminescence for bulk responses, and cathodoluminescence or photoluminescence for surface effects. One expects that discontinuous changes in optical parameters occur during temperature changes through phase transitions of insulating materials. In practice, optical signals also exist from surface states of fullerenes and high temperature superconductors etc which identify the presence of structural or superconducting transitions. Numerous examples are cited which match standard documented transitions. Interestingly many examples show the host signals are strongly sensitive to impurity phase transitions from inclusions such as nanoparticles of water, N{sub 2}, O{sub 2} or CO{sub 2}. Recent luminescence data reveal many examples of new transitions, hysteresis and irreversible changes. The signals equally respond to relaxations of a structure and surprisingly indicate that in some materials, such as SrTiO{sub 3} or ZnO, ion implantation of the surface triggers relaxations and phase changes throughout the bulk of the material. Luminescence routes to detect phase transitions are powerful tools but have a tiny literature and so the subject is ideal for rapid exploitation and development. (Author)

  1. Phase transition in aluminous silica in the lowermost mantle

    Science.gov (United States)

    Tronnes, R. G.; Andrault, D.; Konopkova, Z.; Morgenroth, W.; Liermann, H.

    2012-12-01

    Lower mantle basaltic lithologies contain 35-40% Mg-perovskite, 20-30% Ca-perovskite, 15-25% Al-rich phases (NAL and Ca-ferrite phases) and 15-20% silica-dominated phases. The Fe-rich Mg-perovskite makes basaltic material denser than peridotite throughout the lower mantle below 720 km depth, with important implications for mantle dynamics. Partial separation of subducted basaltic crust from depleted lithosphere might occur within the strongly heterogeneous D" zone. Further details on phase transitions and equation of states for the various minerals, however, are needed for more complete insights. The silica-dominated phases have considerable solubility of alumina [1]. We investigated silica with 4 and 6 wt% alumina to 120 GPa, using LH-DAC at the Extreme Conditions Beamline (P02.2) at PETRA-III, DESY. Powdered glass mixed with 10-15 wt% Pt-powder was compressed and heated in NaCl pressure media in Re-gaskets. The transition from the CaCl2-structured phase to seifertite (alpha-PbO2-structure) occurs at about 116 GPa at 2500 K. This is intermediate between the transition pressures of about 122 GPa and 100-113 GPa reported for similar temperatures for pure SiO2 [2] and a basalt composition [1], respectively. The CaCl2-structured silica phase crystallized along with seifertite, consistent with a binary phase loop trending towards lower pressure with increasing Al-content. The presence of an Al-rich Ca-ferrite phase (near the MgAl2O4-NaAlSiO4-join) in basaltic material indicates that the Al-solubility limits for the silica-dominated phases in basaltic compositions may be similar to those in the binary system SiO2-AlO1.5. Based on the X-ray pattern refinement, our samples show no significant volume change across the transition. Even so, the transition could be associated with a significant density change if the Al substitution mechanisms are different in CaCl2-structured phase and seifertite. The most likely situation is that Al-substitution occurs via O-vacancies in the

  2. Photon-induced phase transitions of individual electronic phase separated domains in manganites strips

    Science.gov (United States)

    Lin, Hanxuan; Zhang, Kai; Liu, Hao; Miao, Tian; Yu, Yang; Yin, Lifeng; Shen, Jian

    Effective photosensors should be built on materials whose properties depend sensitively on light. Manganites are one of the candidates, where light can trigger resistivity change by several orders of magnitude. Such dramatic change is often associated with photoinduced phase transitions of electronic phase separated (EPS) domains in manganites. Previous studies of the light effect all use macroscopic manganite samples, which consist of large numbers of EPS domains smearing out the photon-induced phase transitions. Here, we observe the signature of individual domains' photoinduced phase transition by macroscopic transport measurement of spatially confined manganites strips. Pronounced photon-induced resistivity jumps emerge in the warming process, which reveals the dynamics of the phase transitions of individual EPS domains upon interaction with light. Magnetic force microscope (MFM) has been used to investigate the mechanism of those resistivity jumps. Supervisor.

  3. A Solvable Model for Nuclear Shape Phase Transitions

    International Nuclear Information System (INIS)

    There has been considerable interest recently in phase transitions that occur between some well-defined nuclear shapes, e.g. the spherical vibrator, the axially deformed rotor and the γ-unstable rotor, which are assigned to the U(5), SU(3) and 0(6) symmetries. These shape phase transitions occur through critical points of the IBM phase diagram and correspond to rapid structural changes. The first transition of this type describes transition form the spherical to the γ-unstable phase and has been associated with an E(5) symmetry. Later further critical point symmetries e.g. X(5) and Y(5) have also been proposed for transitions between other nuclear shape phases. In another application the chain of even Ru isotopes was considered from A 98 to 112 [2]. The parameters were extracted from a fit to the low-lying energy spectrum of each nucleus and were used to plot the corresponding potential. It was found that up to A =102 the potential is essentially an harmonic oscillator, while at A =104 a rather flat potential was seen, in accordance with the expected phase transition and E(5) symmetry there. With increasing A then the minimum got increasingly deeper and moved away from β = 0. We discuss the possibility of generalizing the formalism in two ways: first by including dependence on the 7 variable allowing for the approximate description of nuclei close to the X(5) symmetry, and second, including higher-lying energy levels in the quasi-exactly solvable formalism

  4. Chern-Simons diffusion rate across different phase transitions

    CERN Document Server

    Rougemont, Romulo

    2016-01-01

    We investigate how the dimensionless ratio given by the Chern-Simons diffusion rate $\\Gamma_{\\textrm{CS}}$ divided by the product of the entropy density $s$ and temperature $T$ behaves across different kinds of phase transitions in the class of bottom-up non-conformal Einstein-dilaton holographic models originally proposed by Gubser and Nellore. By tuning the dilaton potential, one is able to holographically mimic a first order, a second order, or a crossover transition. In a first order phase transition, $\\Gamma_{\\textrm{CS}}/sT$ jumps at the critical temperature (as previously found in the holographic literature), while in a second order phase transition it develops an infinite slope. On the other hand, in a crossover, $\\Gamma_{\\textrm{CS}}/sT$ behaves smoothly, although displaying a fast variation around the pseudo-critical temperature. Furthermore, we also find that $\\Gamma_{\\textrm{CS}}/sT$ increases by orders of magnitude below the critical temperature in a second order phase transition and in a crossov...

  5. Cosmological phase transitions and their properties in the NMSSM

    Science.gov (United States)

    Kozaczuk, Jonathan; Profumo, Stefano; Haskins, Laurel Stephenson; Wainwright, Carroll L.

    2015-01-01

    We study cosmological phase transitions in the Next-to-Minimal Supersymmetric Standard Model (NMSSM) in light of the Higgs discovery. We use an effective field theory approach to calculate the finite temperature effective potential, focusing on regions with significant tree-level contributions to the Higgs mass, a viable neutralino dark matter candidate, 1-2 TeV stops, and with the remaining particle spectrum compatible with current LHC searches and results. The phase transition structure in viable regions of parameter space exhibits a rich phenomenology, potentially giving rise to one- or two-step first-order phase transitions in the singlet and/or SU(2) directions. We compute several parameters pertaining to the bubble wall profile, including the bubble wall width and Δ β (the variation of the ratio in Higgs vacuum expectation values across the wall). These quantities can vary significantly across small regions of parameter space and can be promising for successful electroweak baryogenesis. We estimate the wall velocity microphysically, taking into account the various sources of friction acting on the expanding bubble wall. Ultra-relativistic solutions to the bubble wall equations of motion typically exist when the electroweak phase transition features substantial supercooling. For somewhat weaker transitions, the bubble wall instead tends to be sub-luminal and, in fact, likely sub-sonic, suggesting that successful electroweak baryogenesis may indeed occur in regions of the NMSSM compatible with the Higgs discovery.

  6. The quark-hadron phase transition and primordial nucleosynthesis

    Science.gov (United States)

    Hogan, Craig J.

    1987-01-01

    After presenting the current view of the processes taking place during the cosmological transition from 'quark soup' to normal hadron matter, attention is given to what happens to cosmological nucleosynthesis in the presence of small-scale baryon inhomogeneities. The QCD phase transition is among the plausible sources of this inhomogeneity. It is concluded that the formation of primordial 'quark nuggets' and other cold exotica requires very low entropy regions at the outset, and that even the more modest nonlinearities perturbing nucleosynthesis probably require some ingredient in addition to a quiescent, mildly supercooled transition.

  7. Stress Induced Phase Transition of Iron-Rhodium Alloys

    OpenAIRE

    Takahashi, M; Oshima, R.

    1995-01-01

    Stress-induced phase transitions(B2-L10, B2-fcc) on an FeRh alloy were investigated with X-ray diffraction (XRD) and transmission electron microscopy(TEM). An Fe-50.5at%Rh alloy was rolled to 80µm thickness, and annealed at 1370K for 173ks. Annealed sample sheets were cold rolled at various rolling rates, and changes of the sample alloy on the phase state were investigated with XRD. The L10 phase appeared in the early stage of cold work. With heavy work appearance of the fcc phase and consequ...

  8. Histogram Monte Carlo study of multicritical behavior in the hexagonal easy-axis Heisenberg antiferromagnet

    OpenAIRE

    Mailhot, A.; Plumer, M. L.; Caillé, A.

    1993-01-01

    The results of a detailed histogram Monte-Carlo study of critical-fluctuation effects on the magnetic-field temperature phase diagram associated with the hexagonal Heisenberg antiferromagnet with weak axial anisotropy are reported. The multiphase point where three lines of continuous transitions merge at the spin-flop boundary exhibits a structure consistent with scaling theory but without the usual umbilicus as found in the case of a bicritical point.

  9. Beyond nuclear "pasta" : Phase transitions and neutrino opacity of new "pasta" phases

    Science.gov (United States)

    Alcain, P. N.; Giménez Molinelli, P. A.; Dorso, C. O.

    2014-12-01

    In this work, we focus on different length scales within the dynamics of nucleons in conditions according to the neutron star crust, with a semiclassical molecular dynamics model, studying isospin symmetric matter at subsaturation densities. While varying the temperature, we find that a solid-liquid phase transition exists, which can be also characterized with a morphology transition. For higher temperatures, above this phase transition, we study the neutrino opacity, and find that in the liquid phase, the scattering of low momenta neutrinos remain high, even though the morphology of the structures differ significatively from those of the traditional nuclear pasta.

  10. Spin Texture and Spin Dynamics in Superconducting Cuprates Near the Phase Transition Revealed by the Electron Paramagnetic Resonance

    Science.gov (United States)

    Kochelaev, B. I.

    2016-04-01

    A short review of experimental results and theoretical models of the spin texture and spin dynamics in superconducting cuprates near the phase transition developed on the basis of the EPR measurements is given. Distortions of the long-range antiferromagnetic order in the YBa_2 Cu_3 O_{6+y} were investigated for y=0.1-0.4 using Yb^{3+} ions as the EPR probe. In weakly doped samples with y=0.1 , a strong anisotropy of the EPR linewidth is revealed which was related to the indirect spin-spin interaction between the ytterbium ions via antiferromagnetic spin-waves. In the case of the doping level y=0.2-0.3 , the EPR signal consists of narrow and broad lines, which were attributed to formation of charged domain walls. A theoretical analysis is well consistent with experimental results for the case of coplanar elliptical domain walls. A discussion of possible reasons for the observed unusual planar oxygen isotope effect on a critical temperature T_c related to charge heterogeneity in underdoped cuprates is given.

  11. Electronic nematic phase transition in the presence of anisotropy

    OpenAIRE

    Yamase, Hiroyuki

    2014-01-01

    We study the phase diagram of electronic nematic instability in the presence of xy anisotropy. While a second order transition cannot occur in this case, mean-field theory predicts that a first order transition occurs near van Hove filling and its phase boundary forms a wing structure, which we term a Griffiths wing, referring to his original work of He3-He4 mixtures. When crossing the wing, the anisotropy of the electronic system exhibits a discontinuous change, leading to a meta-nematic tra...

  12. Phase transition from hadronic matter to quark matter

    OpenAIRE

    Wang, P.; Thomas, A W; Williams, A. G.

    2006-01-01

    We study the phase transition from nuclear matter to quark matter within the SU(3) quark mean field model and NJL model. The SU(3) quark mean field model is used to give the equation of state for nuclear matter, while the equation of state for color superconducting quark matter is calculated within the NJL model. It is found that at low temperature, the phase transition from nuclear to color superconducting quark matter will take place when the density is of order 2.5$\\rho_0$ - 5$\\rho_0$. At ...

  13. Distribution of current in nonequilibrium diffusive systems and phase transitions.

    Science.gov (United States)

    Bodineau, T; Derrida, B

    2005-12-01

    We consider diffusive lattice gases on a ring and analyze the stability of their density profiles conditionally to a current deviation. Depending on the current, one observes a phase transition between a regime where the density remains constant and another regime where the density becomes time dependent. Numerical data confirm this phase transition. This time dependent profile persists in the large drift limit and allows one to understand on physical grounds the results obtained earlier for the totally asymmetric exclusion process on a ring. PMID:16486013

  14. Detection of phase transition via convolutional neural network

    CERN Document Server

    Tanaka, Akinori

    2016-01-01

    We design a Convolutional Neural Network (CNN) which studies correlation between discretized inverse temperature and spin configuration of 2D Ising model and show that it can find a feature of the phase transition without teaching any a priori information for it. We also define a new order parameter via the CNN and show that it provides well approximated critical inverse temperature. In addition, we compare the activation functions for convolution layer and find that the Rectified Linear Unit (ReLU) is important to detect the phase transition of 2D Ising model.

  15. An Investigation of the Structural Phase Transition of Ammonia Borane

    Energy Technology Data Exchange (ETDEWEB)

    Paolone, Annalisa; Palumbo, Oriele; Rispoli, Pasquale; Cantelli, Rosario; Autrey, Thomas

    2010-09-25

    A detailed anelastic spectroscopy study of the structural phase transition of ammonia borane was conducted for the first time. The transformation from the tetragonal high temperature phase into the orthorhombic low temperature one is detected on cooling around 220K by a huge drop of the elastic modulus and a spike of the elastic energy dissipation.We find clear indications of a hysteresis, which led us to conclude that the transition is of first-order. The kinetics of the transitionwas investigated in detail. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  16. Pressure Induced Phase Transition in TiB

    Institute of Scientific and Technical Information of China (English)

    李凤英; 陈良辰; 王莉君; 顾惠成; 王汝菊; 车荣钲; 沈中毅

    2001-01-01

    In situ high pressure x-ray diffraction and electrical resistance experiments on TiB have been carried out by using a diamond anvil cell device. The results revealed that the sample undergoes a first-order phase transition at pressures of 3.5 - 5.0 Gpa and 4.0 - 5.5 Gpa for the x-ray diffraction and electrical resistance experiments, respectively. The parameters of the state equation are calculated before and after the phase transition and compared with the values calculated by Mohn et al. [J. Phys. C: Solid State Phys. 21(1988)2829] using the augmented spherical wave method.

  17. Cold dark matter and the cosmic phase transition

    Science.gov (United States)

    Sinha, Bikash

    2016-01-01

    It is entirely plausible that during the primordial quark- hadron phase transition in the universe, microseconds after the Big Bang, supercooling takes place, accompanied by miniinflation. With µ/T ∼ 1 (µ is chemical potential), leading to a first order phase transition from quarks to hadrons; there will be relics in the form of quark nuggets, and, that they consist of Strange Quark Matter. The possibility that these SQM nuggets may well be the candidates of cold dark matter is critically examined. A cursory comparison with the neutron star is presented at the end.

  18. Meson loop effect on high density chiral phase transition

    CERN Document Server

    Sakaguchi, T; Kouno, H; Yahiro, M; Sakaguchi, Tomohiko; Matsuzaki, Masayuki; Kouno, Hiroaki; Yahiro, Masanobu

    2006-01-01

    We test the stability of the mean-field solution in the Nambu--Jona-Lasinio model. For stable solutions with respect to both the \\sigma and \\pi directions, we investigate effects of the mesonic loop corrections of 1/N_c, which correspond to the next-to-leading order in the 1/N_c expansion, on the high density chiral phase transition. The corrections weaken the first order phase transition and shift the critical chemical potential to a lower value. At N_c=3, however, instability of the mean field effective potential prevents us from determining the minimum of the corrected one.

  19. Plasticity and beyond microstructures, crystal-plasticity and phase transitions

    CERN Document Server

    Hackl, Klaus

    2014-01-01

    The book presents the latest findings in experimental plasticity, crystal plasticity, phase transitions, advanced mathematical modeling of finite plasticity and multi-scale modeling. The associated algorithmic treatment is mainly based on finite element formulations for standard (local approach) as well as for non-standard (non-local approach) continua and for pure macroscopic as well as for directly coupled two-scale boundary value problems. Applications in the area of material design/processing are covered, ranging from grain boundary effects in polycrystals and phase transitions to deep-drawing of multiphase steels by directly taking into account random microstructures.

  20. Gravitational waves from first-order cosmological phase transitions

    Science.gov (United States)

    Kosowsky, Arthur; Turner, Michael S.; Watkins, Richard

    1992-01-01

    A first-order cosmological phase transition that proceeds through the nucleation and collision of true-vacuum bubbles is a potent source of gravitational radiation. Possibilities for such include first-order inflation, grand-unified-theory-symmetry breaking, and electroweak-symmetry breaking. We have calculated gravity-wave production from the collision of two scalar-field vacuum bubbles, and, using an approximation based upon these results, from the collision of 20 to 30 vacuum bubbles. We present estimates of the relic background of gravitational waves produced by a first-order phase transition.