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Sample records for metal-insulator phase transition

  1. Metal-insulator phase transition in hydrogenated thin films of V2O3

    Science.gov (United States)

    Andreev, V. N.; Klimov, V. A.; Kompan, M. E.

    2017-12-01

    Temperature dependences of the electrical conductivity of thin vanadium sesquioxide V2O3 films obtained by using the laser sputtering technique have been studied. A significant decrease (by four-five orders of magnitude) in the electrical conductivity has been observed below 150 K as a result of a metal-insulator phase transition. It is shown that hydrogenation of films lowers the temperature of this phase transition.

  2. Phase coexistence in the metal-insulator transition of a VO2 thin film

    International Nuclear Information System (INIS)

    Chang, Y.J.; Koo, C.H.; Yang, J.S.; Kim, Y.S.; Kim, D.H.; Lee, J.S.; Noh, T.W.; Kim, Hyun-Tak; Chae, B.G.

    2005-01-01

    Vanadium dioxide (VO 2 ) shows a metal-insulator transition (MIT) near room temperature, accompanied by an abrupt resistivity change. Since the MIT of VO 2 is known to be a first order phase transition, it is valuable to check metallic and insulating phase segregation during the MIT process. We deposited (100)-oriented epitaxial VO 2 thin films on R-cut sapphire substrates. From the scanning tunneling spectroscopy (STS) spectra, we could distinguish metallic and insulating regions by probing the band gap. Optical spectroscopic analysis also supported the view that the MIT in VO 2 occurs through metal and insulator phase coexistence

  3. Metal-Insulator Transition Driven by Vacancy Ordering in GeSbTe Phase Change Materials.

    Science.gov (United States)

    Bragaglia, Valeria; Arciprete, Fabrizio; Zhang, Wei; Mio, Antonio Massimiliano; Zallo, Eugenio; Perumal, Karthick; Giussani, Alessandro; Cecchi, Stefano; Boschker, Jos Emiel; Riechert, Henning; Privitera, Stefania; Rimini, Emanuele; Mazzarello, Riccardo; Calarco, Raffaella

    2016-04-01

    Phase Change Materials (PCMs) are unique compounds employed in non-volatile random access memory thanks to the rapid and reversible transformation between the amorphous and crystalline state that display large differences in electrical and optical properties. In addition to the amorphous-to-crystalline transition, experimental results on polycrystalline GeSbTe alloys (GST) films evidenced a Metal-Insulator Transition (MIT) attributed to disorder in the crystalline phase. Here we report on a fundamental advance in the fabrication of GST with out-of-plane stacking of ordered vacancy layers by means of three distinct methods: Molecular Beam Epitaxy, thermal annealing and application of femtosecond laser pulses. We assess the degree of vacancy ordering and explicitly correlate it with the MIT. We further tune the ordering in a controlled fashion attaining a large range of resistivity. Employing ordered GST might allow the realization of cells with larger programming windows.

  4. Metal - Insulator Transition Driven by Vacancy Ordering in GeSbTe Phase Change Materials

    Science.gov (United States)

    Bragaglia, Valeria; Arciprete, Fabrizio; Zhang, Wei; Mio, Antonio Massimiliano; Zallo, Eugenio; Perumal, Karthick; Giussani, Alessandro; Cecchi, Stefano; Boschker, Jos Emiel; Riechert, Henning; Privitera, Stefania; Rimini, Emanuele; Mazzarello, Riccardo; Calarco, Raffaella

    2016-04-01

    Phase Change Materials (PCMs) are unique compounds employed in non-volatile random access memory thanks to the rapid and reversible transformation between the amorphous and crystalline state that display large differences in electrical and optical properties. In addition to the amorphous-to-crystalline transition, experimental results on polycrystalline GeSbTe alloys (GST) films evidenced a Metal-Insulator Transition (MIT) attributed to disorder in the crystalline phase. Here we report on a fundamental advance in the fabrication of GST with out-of-plane stacking of ordered vacancy layers by means of three distinct methods: Molecular Beam Epitaxy, thermal annealing and application of femtosecond laser pulses. We assess the degree of vacancy ordering and explicitly correlate it with the MIT. We further tune the ordering in a controlled fashion attaining a large range of resistivity. Employing ordered GST might allow the realization of cells with larger programming windows.

  5. Axially engineered metal-insulator phase transition by graded doping VO2 nanowires.

    Science.gov (United States)

    Lee, Sangwook; Cheng, Chun; Guo, Hua; Hippalgaonkar, Kedar; Wang, Kevin; Suh, Joonki; Liu, Kai; Wu, Junqiao

    2013-03-27

    The abrupt first-order metal-insulator phase transition in single-crystal vanadium dioxide nanowires (NWs) is engineered to be a gradual transition by axially grading the doping level of tungsten. We also demonstrate the potential of these NWs for thermal sensing and actuation applications. At room temperature, the graded-doped NWs show metal phase on the tips and insulator phase near the center of the NW, and the metal phase grows progressively toward the center when the temperature rises. As such, each individual NW acts as a microthermometer that can be simply read out with an optical microscope. The NW resistance decreases gradually with the temperature rise, eventually reaching 2 orders of magnitude drop, in stark contrast to the abrupt resistance change in undoped VO2 wires. This novel phase transition yields an extremely high temperature coefficient of resistivity ~10%/K, simultaneously with a very low resistivity down to 0.001 Ω·cm, making these NWs promising infrared sensing materials for uncooled microbolometers. Lastly, they form bimorph thermal actuators that bend with an unusually high curvature, ~900 m(-1)·K(-1) over a wide temperature range (35-80 °C), significantly broadening the response temperature range of previous VO2 bimorph actuators. Given that the phase transition responds to a diverse range of stimuli-heat, electric current, strain, focused light, and electric field-the graded-doped NWs may find wide applications in thermo-opto-electro-mechanical sensing and energy conversion.

  6. Excitonic metal-insulator phase transition of the Mott type in compressed calcium

    Science.gov (United States)

    Voronkova, T. O.; Sarry, A. M.; Sarry, M. F.; Skidan, S. G.

    2017-05-01

    It has been experimentally found that, under the static compression of a calcium crystal at room temperature, it undergoes a series of structural phase transitions: face-centered cubic lattice → body-centered cubic lattice → simple cubic lattice. It has been decided to investigate precisely the simple cubic lattice (because it is an alternative lattice) with the aim of elucidating the possibility of the existence of other (nonstructural) phase transitions in it by using for this purpose the Hubbard model for electrons with half-filled ns-bands and preliminarily transforming the initial electronic system into an electron-hole system by means of the known Shiba operators (applicable only to alternative lattices). This transformation leads to the fact that, in the new system of fermions, instead of the former repulsion, there is an attraction between electrons and holes. Elementary excitations of this new system are bound boson pairs—excitons. This system of fermions has been quantitatively analyzed by jointly using the equation-of-motion method and the direct algebraic method. The numerical integration of the analytically exact transcendental equations derived from the first principles for alternative (one-, two-, and three-dimensional) lattices has demonstrated that, in systems of two-species (electrons + hole) fermions, temperature-induced metal-insulator phase transitions of the Mott type are actually possible. Moreover, all these crystals are in fact excitonic insulators. This conclusion is in complete agreement with the analytically exact calculations of the ground state of a one-dimensional crystal (with half-filled bands), which were performed by Lieb and Wu with the aim to find out the Mott insulator-metal transition of another type.

  7. Metal-Insulator Phase Transition in Quasi-One-Dimensional VO2 Structures

    Directory of Open Access Journals (Sweden)

    Woong-Ki Hong

    2015-01-01

    Full Text Available The metal-insulator transition (MIT in strongly correlated oxides has attracted considerable attention from both theoretical and experimental researchers. Among the strongly correlated oxides, vanadium dioxide (VO2 has been extensively studied in the last decade because of a sharp, reversible change in its optical, electrical, and magnetic properties at approximately 341 K, which would be possible and promising to develop functional devices with advanced technology by utilizing MITs. However, taking the step towards successful commercialization requires the comprehensive understanding of MIT mechanisms, enabling us to manipulate the nature of transitions. In this regard, recently, quasi-one-dimensional (quasi-1D VO2 structures have been intensively investigated due to their attractive geometry and unique physical properties to observe new aspects of transitions compared with their bulk counterparts. Thus, in this review, we will address recent research progress in the development of various approaches for the modification of MITs in quasi-1D VO2 structures. Furthermore, we will review recent studies on realizing novel functional devices based on quasi-1D VO2 structures for a wide range of applications, such as a gas sensor, a flexible strain sensor, an electrical switch, a thermal memory, and a nonvolatile electrical memory with multiple resistance.

  8. Metal Insulator transition in Vanadium Dioxide

    Science.gov (United States)

    Jovaini, Azita; Fujita, Shigeji; Suzuki, Akira; Godoy, Salvador

    2012-02-01

    MAR12-2011-000262 Abstract Submitted for the MAR12 Meeting of The American Physical Society Sorting Category: 03.9 (T) On the metal-insulator-transition in vanadium dioxide AZITA JOVAINI, SHIGEJI FUJITA, University at Buffalo, SALVADOR GODOY, UNAM, AKIRA SUZUKI, Tokyo University of Science --- Vanadium dioxide (VO2) undergoes a metal-insulator transition (MIT) at 340 K with the structural change from tetragonal to monoclinic crystal. The conductivity _/ drops at MIT by four orders of magnitude. The low temperature monoclinic phase is known to have a lower ground-state energy. The existence of the k-vector k is prerequisite for the conduction since the k appears in the semiclassical equation of motion for the conduction electron (wave packet). The tetragonal (VO2)3 unit is periodic along the crystal's x-, y-, and z-axes, and hence there is a three-dimensional k-vector. There is a one-dimensional k for a monoclinic crystal. We believe this difference in the dimensionality of the k-vector is the cause of the conductivity drop. Prefer Oral Session X Prefer .

  9. Interplay between Ferroelastic and Metal-Insulator Phase Transitions in Strained Quasi-Two-Dimensional VO2 Nanoplatelets

    Energy Technology Data Exchange (ETDEWEB)

    Tselev, Alexander [ORNL; Strelcov, Evgheni [Southern Illinois University; Luk' yanchuk, Prof. Igor A. [University of Picardie Jules Verne, Amiens, France; Ivanov, Ilia N [ORNL; Budai, John D [ORNL; Tischler, Jonathan Zachary [ORNL; Jones, Keith M [ORNL; Proksch, Roger [Asylum Research, Santa Barbara, CA; Kalinin, Sergei V [ORNL; Kolmakov, Andrei [ORNL

    2010-01-01

    Formation of ferroelastic twin domains in VO_2 nanosystems can strongly affect local strain distributions, and hence couple to the strain-controlled metal-insulator transition. Here we report polarized-light optical and scanning microwave microscopy studies of interrelated ferroelastic and metal-insulator transitions in single-crystalline vanadium dioxide (VO_2) quasi-two-dimensional (quasi-2D) nanoplatelets (NPls). In contrast to quasi-1D single-crystalline nanobeams, the geometric frustration results in emergence of several possible families of ferroelastic domains in NPls, thus allowing systematic studies of strain-controlled transitions in the presence of geometrical frustration. We demonstrate possibility of controlling the ferroelastic domain population by the strength of the NPl-substrate interaction, mechanical stress, and by the NPl lateral size. Ferroelastic domain species and domain walls are identified based on standard group-theoretical considerations. Using variable temperature microscopy, we imaged the development of domains of metallic and semiconducting phases during the metal-insulator phase transition and non-trivial strain-driven reentrant domain formation. A long-range reconstruction of ferroelastic structures accommodating metal-insulator domain formation has been observed. These studies illustrate that complete picture of the phase transitions in single-crystalline and disordered VO_2 structures can be drawn only if both ferroelastic and metal-insulator strain effects are taken into consideration and understood.

  10. Metal-insulator transition in vanadium dioxide

    International Nuclear Information System (INIS)

    Zylbersztejn, A.; Mott, N.F.

    1975-01-01

    The basic physical parameters which govern the metal-insulator transition in vanadium dioxide are determined through a review of the properties of this material. The major importance of the Hubbard intra-atomic correlation energy in determining the insulating phase, which was already evidence by studies of the magnetic properties of V 1 -/subx/Cr/subx/O 2 alloys, is further demonstrated from an analysis of their electrical properties. An analysis of the magnetic susceptibility of niobium-doped VO 2 yields a picture for the current carrier in the low-temperature phase in which it is accompanied by a spin cloud (owing to Hund's-rule coupling), and has therefore an enhanced mass (m approx. = 60m 0 ). Semiconducting vanadium dioxide turns out to be a borderline case for a classical band-transport description; in the alloys at high doping levels, Anderson localization with hopping transport can take place. Whereas it is shown that the insulating phase cannot be described correctly without taking into account the Hubbard correlation energy, we find that the properties of the metallic phase are mainly determined by the band structure. Metallic VO 2 is, in our view, similar to transition metals like Pt or Pd: electrons in a comparatively wide band screening out the interaction between the electrons in a narrow overlapping band. The magnetic susceptibility is described as exchange enhanced. The large density of states at the Fermi level yields a substantial contribution of the entropy of the metallic electrons to the latent heat. The crystalline distortion removes the band degeneracy so that the correlation energy becomes comparable with the band width and a metal-insulator transition takes place

  11. Metal-Insulator Phase Transition in thin VO2 films: A Look from the Far Infrared Side

    DEFF Research Database (Denmark)

    Jepsen, Peter Uhd; Fischer, B. M.; Thoman, A.

    Vanadium dioxide (VO2) displays a well-known metal-insulator (MI) transition at atemperature of 68oC. The MI transition in VO2 has been studied extensively by a widerange of optical, electrical, structural, and magnetic measurements. In spite of this there isstill some controversy about the nature...

  12. Dynamic phase coexistence and non-Gaussian resistance fluctuations in VO2 near the metal-insulator transition

    Science.gov (United States)

    Samanta, Sudeshna; Raychaudhuri, A. K.; Zhong, Xing; Gupta, A.

    2015-11-01

    We have carried out an extensive investigation on the resistance fluctuations (noise) in an epitaxial thin film of VO2 encompassing the metal-insulator transition (MIT) region to investigate the dynamic phase coexistence of metal and insulating phases. Both flicker noise as well as the Nyquist noise (thermal noise) were measured. The experiments showed that flicker noise, which has a 1 /f spectral power dependence, evolves with temperature in the transition region following the evolution of the phase fractions and is governed by activated kinetics. Importantly, closer to the insulating end of the transition, when the metallic phase fraction is low, the magnitude of the noise shows an anomaly and a strong non-Gaussian component of noise develops. In this region, the local electron temperature (as measured through the Nyquist noise thermometry) shows a deviation from the equilibrium bath temperature. It is proposed that this behavior arises due to current crowding where a substantial amount of the current is carried through well separated small metallic islands leading to a dynamic correlated current path redistribution and an enhanced effective local current density. This leads to a non-Gaussian component to the resistance fluctuation and an associated local deviation of the electron temperature from the bath. Our experiment establishes that phase coexistence leads to a strong inhomogeneity in the region of MIT that makes the current transport strongly inhomogeneous and correlated.

  13. Reentrant Metal-Insulator Transitions in Silicon -

    Science.gov (United States)

    Campbell, John William M.

    This thesis describes a study of reentrant metal -insulator transitions observed in the inversion layer of extremely high mobility Si-MOSFETs. Magneto-transport measurements were carried out in the temperature range 20mK-4.2 K in a ^3He/^4 He dilution refrigerator which was surrounded by a 15 Tesla superconducting magnet. Below a melting temperature (T_{M}~500 mK) and a critical electron density (n_{s }~9times10^{10} cm^{-2}), the Shubnikov -de Haas oscillations in the diagonal resistivity enormous maximum values at the half filled Landau levels while maintaining deep minima corresponding to the quantum Hall effect at filled Landau levels. At even lower electron densities the insulating regions began to spread and eventually a metal-insulator transition could be induced at zero magnetic field. The measurement of extremely large resistances in the milliKelvin temperature range required the use of very low currents (typically in the 10^ {-12} A range) and in certain measurements minimizing the noise was also a consideration. The improvements achieved in these areas through the use of shielding, optical decouplers and battery operated instruments are described. The transport signatures of the insulating state are considered in terms of two basic mechanisms: single particle localization with transport by variable range hopping and the formation of a collective state such as a pinned Wigner crystal or electron solid with transport through the motion of bound dislocation pairs. The experimental data is best described by the latter model. Thus the two dimensional electron system in these high mobility Si-MOSFETs provides the first and only experimental demonstration to date of the formation of an electron solid at zero and low magnetic fields in the quantum limit where the Coulomb interaction energy dominates over the zero point oscillation energy. The role of disorder in favouring either single particle localization or the formation of a Wigner crystal is explored by

  14. Harnessing the metal-insulator transition for tunable metamaterials

    Science.gov (United States)

    Charipar, Nicholas A.; Charipar, Kristin M.; Kim, Heungsoo; Bingham, Nicholas S.; Suess, Ryan J.; Mathews, Scott A.; Auyeung, Raymond C. Y.; Piqué, Alberto

    2017-08-01

    The control of light-matter interaction through the use of subwavelength structures known as metamaterials has facilitated the ability to control electromagnetic radiation in ways not previously achievable. A plethora of passive metamaterials as well as examples of active or tunable metamaterials have been realized in recent years. However, the development of tunable metamaterials is still met with challenges due to lack of materials choices. To this end, materials that exhibit a metal-insulator transition are being explored as the active element for future metamaterials because of their characteristic abrupt change in electrical conductivity across their phase transition. The fast switching times (▵t properties associated with thin film metal-insulator transition materials are strongly dependent on the growth conditions. For this work, we have studied how growth conditions (such as gas partial pressure) influence the metalinsulator transition in VO2 thin films made by pulsed laser deposition. In addition, strain engineering during the growth process has been investigated as a method to tune the metal-insulator transition temperature. Examples of both the optical and electrical transient dynamics facilitating the metal-insulator transition will be presented together with specific examples of thin film metamaterial devices.

  15. Synchronization of pairwise-coupled, identical, relaxation oscillators based on metal-insulator phase transition devices: A model study

    Science.gov (United States)

    Parihar, Abhinav; Shukla, Nikhil; Datta, Suman; Raychowdhury, Arijit

    2015-02-01

    Computing with networks of synchronous oscillators has attracted wide-spread attention as novel materials and device topologies have enabled realization of compact, scalable and low-power coupled oscillatory systems. Of particular interest are compact and low-power relaxation oscillators that have been recently demonstrated using MIT (metal-insulator-transition) devices using properties of correlated oxides. Further the computational capability of pairwise coupled relaxation oscillators has also been shown to outperform traditional Boolean digital logic circuits. This paper presents an analysis of the dynamics and synchronization of a system of two such identical coupled relaxation oscillators implemented with MIT devices. We focus on two implementations of the oscillator: (a) a D-D configuration where complementary MIT devices (D) are connected in series to provide oscillations and (b) a D-R configuration where it is composed of a resistor (R) in series with a voltage-triggered state changing MIT device (D). The MIT device acts like a hysteresis resistor with different resistances in the two different states. The synchronization dynamics of such a system has been analyzed with purely charge based coupling using a resistive (RC) and a capacitive (CC) element in parallel. It is shown that in a D-D configuration symmetric, identical and capacitively coupled relaxation oscillator system synchronizes to an anti-phase locking state, whereas when coupled resistively the system locks in phase. Further, we demonstrate that for certain range of values of RC and CC, a bistable system is possible which can have potential applications in associative computing. In D-R configuration, we demonstrate the existence of rich dynamics including non-monotonic flows and complex phase relationship governed by the ratios of the coupling impedance. Finally, the developed theoretical formulations have been shown to explain experimentally measured waveforms of such pairwise coupled

  16. Materials Characterization and Microelectronic Implementation of Metal-insulator Transition Materials and Phase Change Materials

    Science.gov (United States)

    2015-03-26

    the case with Ti2O3 (shown in Figure 23). Although it is diamagnetic (repelled by magnetic fields), some interesting magnetic properties are...which is uncommon but forms the basis for important perovskite ternary structures, (b) rutile (body-centered tetragonal) which is common in dioxides...Transition MM Metamaterial MO Molecular Orbital MRAM Magnetic Random Access Memory MTFET Mott Transition Field-effect Transistor NA Numerical

  17. Unusual metal-insulator transition in disordered ferromagnetic films

    International Nuclear Information System (INIS)

    Muttalib, K.A.; Wölfle, P.; Misra, R.; Hebard, A.F.

    2012-01-01

    We present a theoretical interpretation of recent data on the conductance near and farther away from the metal-insulator transition in thin ferromagnetic Gd films of thickness b≈2-10 nm. For increasing sheet resistances a dimensional crossover takes place from d=2 to d=3 dimensions, since the large phase relaxation rate caused by scattering of quasiparticles off spin wave excitations renders the dephasing length L φ ≲b at strong disorder. The conductivity data in the various regimes obey fractional power-law or logarithmic temperature dependence. One observes weak localization and interaction induced corrections at weaker disorder. At strong disorder, near the metal-insulator transition, the data show scaling and collapse onto two scaling curves for the metallic and insulating regimes. We interpret this unusual behavior as proof of two distinctly different correlation length exponents on both sides of the transition.

  18. On metal-insulator transition in cubic fullerides

    Science.gov (United States)

    Iwahara, Naoya; Chibotaru, Liviu

    The interplay between degenerate orbital and electron correlation is a key to characterize the electronic phases in, for example, transition metal compounds and alkali-doped fullerides. Besides, the degenerate orbital couples to spin and lattice degrees of freedom ,giving rise to exotic phenomena. Here, we develop the self-consistent Gutzwiller approach for the simultaneous treatment of the Jahn-Teller effect and electron correlation, and apply the methodology to reveal the nature of the ground electronic state of fullerides. For small Coulomb repulsion on site U, the fulleride is quasi degenerate correlated metal. With increase of U, we found the quantum phase transition from the metallic phase to JT split phase. In the latter, the Mott transition (MT) mainly develops in the half-filled subband, whereas the empty and the completely filled subbands are almost uninvolved. Therefore, we can qualify the metal-insulator transition in fullerides as an orbital selective MT induced by JT effect.

  19. Holographic metal-insulator transition in higher derivative gravity

    Energy Technology Data Exchange (ETDEWEB)

    Ling, Yi, E-mail: lingy@ihep.ac.cn [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); Shanghai Key Laboratory of High Temperature Superconductors, Shanghai, 200444 (China); Liu, Peng, E-mail: liup51@ihep.ac.cn [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); Wu, Jian-Pin, E-mail: jianpinwu@mail.bnu.edu.cn [Institute of Gravitation and Cosmology, Department of Physics, School of Mathematics and Physics, Bohai University, Jinzhou 121013 (China); Shanghai Key Laboratory of High Temperature Superconductors, Shanghai, 200444 (China); Zhou, Zhenhua, E-mail: zhouzh@ihep.ac.cn [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China)

    2017-03-10

    We introduce a Weyl term into the Einstein–Maxwell-Axion theory in four dimensional spacetime. Up to the first order of the Weyl coupling parameter γ, we construct charged black brane solutions without translational invariance in a perturbative manner. Among all the holographic frameworks involving higher derivative gravity, we are the first to obtain metal-insulator transitions (MIT) when varying the system parameters at zero temperature. Furthermore, we study the holographic entanglement entropy (HEE) of strip geometry in this model and find that the second order derivative of HEE with respect to the axion parameter exhibits maximization behavior near quantum critical points (QCPs) of MIT. It testifies the conjecture in that HEE itself or its derivatives can be used to diagnose quantum phase transition (QPT).

  20. Metal-insulator transition in epitaxial vanadium sesquioxide thin films

    Science.gov (United States)

    Allimi, Bamidele S.

    Of all the transition metal oxides which exhibit metal-insulator transitions (MIT), one of the most extensively studied in recent years is the vanadium sesquioxide (V2O3), both from experimental and theoretical point of view. At a transition temperature of about 160 K at an ambient pressure of 1 atm, pure V2O3 transforms from a rhombohedral paramagnetic metallic (PM) to a monoclinic antiferromagnetic insulating (AFI) phase upon cooling, with a jump in the resistivity of about seven orders of magnitude. Experimental studies have focused more on bulk V2O3 and recently there have been significant interest in thin film fabrication of this material due to potential applications as thermal sensors, current limiters, Positive Temperature Coefficient (PTC) thermistors, and optical switches. This study addresses the deposition, characterization, and properties of high-quality epitaxial V2O3 thin films grown on a-, c-Al2O3 and c-LiTaO 3 substrates by a straightforward method of pulsed laser deposition (PLD). Various characterization techniques including X-ray diffraction, atomic force microscopy, scanning electron microscopy, and X-ray photoemission spectroscopy were used to examine the structural, crystallographic, and surface properties, while four point probe resistivity measurements were used to examine the electrical properties of the films. V2O3 thin films of different thicknesses ranging from 10-450 nm were deposited on c-Al 2O3 and c-LiTaO3 substrates by PLD to understand also the role of epitaxial strains. Resistivity measurements showed that depending on the thicknesses of films, different electrical transitions were exhibited by the samples. While some of the samples displayed the expected metal-insulator transition typical of bulk V2O3, some showed insulating behavior only and others exhibited metallic characteristics only over the whole temperature range. For example, for films on c-LiTaO3 with increasing film thickness, first an insulator-insulator, then a

  1. On holographic disorder-driven metal-insulator transitions

    International Nuclear Information System (INIS)

    Baggioli, Matteo; Pujolàs, Oriol

    2017-01-01

    We give a minimal holographic model of a disorder-driven metal-insulator transition. It consists in a CFT with a charge sector and a translation-breaking sector that interact in the most generic way allowed by the symmetries and by dynamical consistency. In the gravity dual, it reduces to a Massive Gravity-Maxwell model with a new direct coupling between the gauge field and the metric that is allowed when gravity is massive. We show that the effect of this coupling is to decrease the DC electrical conductivity generically. This gives a nontrivial check that holographic massive gravity can be consistently interpreted as disorder from the CFT perspective. The suppression of the conductivity happens to such an extent that it does not obey any lower bound and it can be very small in the insulating phase. In some cases, the large disorder limit produces gradient instabilities that hint at the formation of modulated phases.

  2. Electrically Induced Multiple Metal-Insulator Transitions in Oxide Nanodevices

    Science.gov (United States)

    del Valle, Javier; Kalcheim, Yoav; Trastoy, Juan; Charnukha, Aliaksei; Basov, Dimitri N.; Schuller, Ivan K.

    2017-11-01

    We show that electrical resistive switching can trigger the appearance of multiple metal-insulator transitions (MITs) in VO2 and V2O3 planar nanodevices. We have fabricated planar devices to electrically induce oxygen vacancy drift and filament formation. We show that oxygen migration can create ordered vanadium-oxide phases of varying stoichiometry with an intrinsic MIT, resulting in well-defined hysteresis loops in the R vs T characteristics of the device. We also show that oxygen migration induces oxide phases displaying correlated behaviors. Our results open up the possibility to electrically control the MIT, enabling alternative functionalities in memristive devices and allowing for alternative paradigms in neuromorphic computing or memory applications.

  3. A Review on Disorder-Driven Metal-Insulator Transition in Crystalline Vacancy-Rich GeSbTe Phase-Change Materials.

    Science.gov (United States)

    Wang, Jiang-Jing; Xu, Ya-Zhi; Mazzarello, Riccardo; Wuttig, Matthias; Zhang, Wei

    2017-07-27

    Metal-insulator transition (MIT) is one of the most essential topics in condensed matter physics and materials science. The accompanied drastic change in electrical resistance can be exploited in electronic devices, such as data storage and memory technology. It is generally accepted that the underlying mechanism of most MITs is an interplay of electron correlation effects (Mott type) and disorder effects (Anderson type), and to disentangle the two effects is difficult. Recent progress on the crystalline Ge₁Sb₂Te₄ (GST) compound provides compelling evidence for a disorder-driven MIT. In this work, we discuss the presence of strong disorder in GST, and elucidate its effects on electron localization and transport properties. We also show how the degree of disorder in GST can be reduced via thermal annealing, triggering a disorder-driven metal-insulator transition. The resistance switching by disorder tuning in crystalline GST may enable novel multilevel data storage devices.

  4. Disorder-Driven Metal-Insulator Transitions in Deformable Lattices.

    Science.gov (United States)

    Di Sante, Domenico; Fratini, Simone; Dobrosavljević, Vladimir; Ciuchi, Sergio

    2017-01-20

    We show that, in the presence of a deformable lattice potential, the nature of the disorder-driven metal-insulator transition is fundamentally changed with respect to the noninteracting (Anderson) scenario. For strong disorder, even a modest electron-phonon interaction is found to dramatically renormalize the random potential, opening a mobility gap at the Fermi energy. This process, which reflects disorder-enhanced polaron formation, is here given a microscopic basis by treating the lattice deformations and Anderson localization effects on the same footing. We identify an intermediate "bad insulator" transport regime which displays resistivity values exceeding the Mott-Ioffe-Regel limit and with a negative temperature coefficient, as often observed in strongly disordered metals. Our calculations reveal that this behavior originates from significant temperature-induced rearrangements of electronic states due to enhanced interaction effects close to the disorder-driven metal-insulator transition.

  5. Characterization of Metal-Insulator-Transition (MIT) Phase Change Materials (PCM) for Reconfigurable Components, Circuits, and Systems

    Science.gov (United States)

    2013-03-01

    65  Figure 40: Nano Indenter used to measure the Young’s modulus of thin films. ............... 67  Figure 41: SEM...heater. ...... 63  Table 2: Young’s modulus of amorphous GeTe films measured using the nano indenter at varying frequencies...micromachining techniques [3]. These cells are comprised of a bottom electrode (BEC), a Tungsten (W) pillar, a phase change layer, and a top electrode ( TEC

  6. Structurally triggered metal-insulator transition in rare-earth nickelates.

    Science.gov (United States)

    Mercy, Alain; Bieder, Jordan; Íñiguez, Jorge; Ghosez, Philippe

    2017-11-22

    Rare-earth nickelates form an intriguing series of correlated perovskite oxides. Apart from LaNiO 3 , they exhibit on cooling a sharp metal-insulator electronic phase transition, a concurrent structural phase transition, and a magnetic phase transition toward an unusual antiferromagnetic spin order. Appealing for various applications, full exploitation of these compounds is still hampered by the lack of global understanding of the interplay between their electronic, structural, and magnetic properties. Here we show from first-principles calculations that the metal-insulator transition of nickelates arises from the softening of an oxygen-breathing distortion, structurally triggered by oxygen-octahedra rotation motions. The origin of such a rare triggered mechanism is traced back in their electronic and magnetic properties, providing a united picture. We further develop a Landau model accounting for the metal-insulator transition evolution in terms of the rare-earth cations and rationalizing how to tune this transition by acting on oxygen rotation motions.

  7. Metal-insulator transition: the Mott criterion and coherence length

    CERN Document Server

    Pergament, A

    2003-01-01

    On the basis of the Mott criterion for metal-insulator transition (MIT), an expression for the correlation length, identical to that for the coherence length in the theory of superconductivity, is obtained. This correlation length characterizes the size of an electron-hole pair (in an excitonic insulator) or the effective Bohr radius (as, e.g., in doped semiconductors). The relation obtained is used for calculation of the coherence length in vanadium dioxide. The presence of two characteristic coherence lengths (xi sub 1 approx 20 A and xi sub 2 approx 2 A) is found. This is associated with the specific features of the transition mechanism in VO sub 2 : this mechanism represents a combination of the purely electronic Mott-Hubbard contribution and the structural (Peierls-like) one. It is shown, however, that the driving force of the MIT in VO sub 2 is the electron-correlation Mott-Hubbard transition.

  8. Tuning the metal-insulator transition in manganite films through surface exchange coupling with magnetic nanodots.

    Science.gov (United States)

    Ward, T Z; Gai, Z; Xu, X Y; Guo, H W; Yin, L F; Shen, J

    2011-04-15

    In strongly correlated electronic systems, the global transport behavior depends sensitively on spin ordering. We show that spin ordering in manganites can be controlled by depositing isolated ferromagnetic nanodots at the surface. The exchange field at the interface is tunable with nanodot density and makes it possible to overcome dimensionality and strain effects in frustrated systems to greatly increasing the metal-insulator transition and magnetoresistance. These findings indicate that electronic phase separation can be controlled by the presence of magnetic nanodots.

  9. On the Problem of Metal-Insulator Transitions in Vanadium Oxides

    OpenAIRE

    A. A. Velichko; N. A. Kuldin; G. B. Stefanovich; A. L. Pergament

    2013-01-01

    The problem of metal-insulator transition is considered. It is shown that the Mott criterion aB(nc)1/3≈0.25 is applicable not only to heavily doped semiconductors but also to many other materials, including some transition-metal compounds, such as vanadium oxides (particularly, VO2 and V2O3). The low-temperature transition (“paramagnetic metal—antiferromagnetic insulator”) in vanadium sesquioxide is described on the basis of this concept in terms of an intervening phase, between metal and ins...

  10. Metal-insulator transitions and superconductivity in ditetramethyltetraselenafulvalenium flourosulfonate [(TMTSF)2FSO3

    International Nuclear Information System (INIS)

    Lacoe, R.C.; Wolf, S.A.; Chaikin, P.M.; Wudl, F.; Aharon-Shalom, E.

    1983-01-01

    We have investigated the phase diagram of the organic charge-transfer salt ditetramethyltetraselenafulvalenium flourosulfonate [(TMTSF) 2 FSO 3 ] which contains an asymmetric dipolar anion. At low pressures there is a metal-insulator transition related to anion ordering. Between 5 and 6 kbar, there is a dipolar glass phase with increased resistivity. However, thermopower and superconducting measurements indicate that the Fermi surface remains ungapped. Above 5 kbar there is a superconducting transition with T/sub c/>2 K. This is the highest T/sub c/ for this family of compounds and suggests that the anions can enhance T/sub c/

  11. New Light on the Metal-Insulator Transition in VO2: A Terahertz Perspective

    DEFF Research Database (Denmark)

    Jepsen, Peter Uhd; Fischer, Bernd M.; Thoman, Andreas

    2005-01-01

    We investigate the metal-insulator (MI) transition in vanadium dioxide (VO2), thin films with Terahertz Time-Domains Spectroscopy (THz-TDS). The capability of detecting both amplitude and phase of the transmission characteristics as the phase of the transmitted THz signal switches at a markedly...

  12. Study of the metal-insulator transition and superconducting correlations of a generalized Hubbard model

    Science.gov (United States)

    Arrachea, Liliana; Aligia, A. A.; Gagliano, E.

    1996-02-01

    We study the metal-insulator transition of a generalized Hubbard model in which the magnitude of the nearest-neighbor hopping depends on the occupations of the sites involved. Numerical results for finite chains at half-filling show that when 0 0 for which the system is metallic. This is consistent with a Hartree-Fock calculation. The metallic phase collapses to one point, U = 0, in the Hubbard limit. In the metallic phase we obtain that the superconducting correlations are the dominant ones, at least for doped systems.

  13. Quantum chemical studies of the physics around the metal-insulator transition in (EDO-TTF)2PF6

    NARCIS (Netherlands)

    Linker, Gerrit-Jan

    2016-01-01

    In this thesis, the physics of molecular charge transfer crystals is studied by using quantum chemical methods. We looked in detail at the metal insulator phase transition in the (EDO TTF)2PF6 molecular crystal and also into related geometrical reorganisations and charge ordering phenomena. Unlike

  14. Electric field-triggered metal-insulator transition resistive switching of bilayered multiphasic VOx

    Science.gov (United States)

    Won, Seokjae; Lee, Sang Yeon; Hwang, Jungyeon; Park, Jucheol; Seo, Hyungtak

    2018-01-01

    Electric field-triggered Mott transition of VO2 for next-generation memory devices with sharp and fast resistance-switching response is considered to be ideal but the formation of single-phase VO2 by common deposition techniques is very challenging. Here, VOx films with a VO2-dominant phase for a Mott transition-based metal-insulator transition (MIT) switching device were successfully fabricated by the combined process of RF magnetron sputtering of V metal and subsequent O2 annealing to form. By performing various material characterizations, including scanning transmission electron microscopy-electron energy loss spectroscopy, the film is determined to have a bilayer structure consisting of a VO2-rich bottom layer acting as the Mott transition switching layer and a V2O5/V2O3 mixed top layer acting as a control layer that suppresses any stray leakage current and improves cyclic performance. This bilayer structure enables excellent electric field-triggered Mott transition-based resistive switching of Pt-VOx-Pt metal-insulator-metal devices with a set/reset current ratio reaching 200, set/reset voltage of less than 2.5 V, and very stable DC cyclic switching upto 120 cycles with a great set/reset current and voltage distribution less than 5% of standard deviation at room temperature, which are specifications applicable for neuromorphic or memory device applications. [Figure not available: see fulltext.

  15. Metal-insulator transition in one-dimensional lattices with chaotic energy sequences

    International Nuclear Information System (INIS)

    Pinto, R.A.; Rodriguez, M.; Gonzalez, J.A.; Medina, E.

    2005-01-01

    We study electronic transport through a one-dimensional array of sites by using a tight binding Hamiltonian, whose site-energies are drawn from a chaotic sequence. The correlation degree between these energies is controlled by a parameter regulating the dynamic Lyapunov exponent measuring the degree of chaos. We observe the effect of chaotic sequences on the localization length, conductance, conductance distribution and wave function, finding evidence of a metal-insulator transition (MIT) at a critical degree of chaos. The one-dimensional metallic phase is characterized by a Gaussian conductance distribution and exhibits a peculiar non-selfaveraging

  16. Metal-insulator transition in disordered systems from the one-body density matrix

    DEFF Research Database (Denmark)

    Olsen, Thomas; Resta, Raffaele; Souza, Ivo

    2017-01-01

    systems. In particular, for noninteracting systems the geometrical marker can be obtained from the configurational average of the norm-squared one-body density matrix, which can be calculated within open as well as periodic boundary conditions. This is in sharp contrast to a classification based......The insulating state of matter can be probed by means of a ground state geometrical marker, which is closely related to the modern theory of polarization (based on a Berry phase). In the present work we show that this marker can be applied to determine the metal-insulator transition in disordered...

  17. Multilevel radiative thermal memory realized by the hysteretic metal-insulator transition of vanadium dioxide

    International Nuclear Information System (INIS)

    Ito, Kota; Nishikawa, Kazutaka; Iizuka, Hideo

    2016-01-01

    Thermal information processing is attracting much interest as an analog of electronic computing. We experimentally demonstrated a radiative thermal memory utilizing a phase change material. The hysteretic metal-insulator transition of vanadium dioxide (VO 2 ) allows us to obtain a multilevel memory. We developed a Preisach model to explain the hysteretic radiative heat transfer between a VO 2 film and a fused quartz substrate. The transient response of our memory predicted by the Preisach model agrees well with the measured response. Our multilevel thermal memory paves the way for thermal information processing as well as contactless thermal management

  18. Mesoscopic Metal-Insulator Transition at Ferroelastic Domain Walls in VO2

    Energy Technology Data Exchange (ETDEWEB)

    Jones, Keith M [ORNL; Kalinin, Sergei V [ORNL; Kolmakov, Andrei [ORNL; Luk' yanchuk, Prof. Igor A. [University of Picardie Jules Verne, Amiens, France; Meunier, Vincent [ORNL; Proksch, Roger [Asylum Research, Santa Barbara, CA; Shelton Jr, William Allison [ORNL; Strelcov, Evgheni [Southern Illinois University; Tselev, Alexander [ORNL

    2010-01-01

    The novel phenomena induced by symmetry breaking at homointerfaces between ferroic variants in ferroelectric and ferroelastic materials have attracted recently much attention. Using variable temperature scanning microwave microscopy, we demonstrate the mesoscopic strain-induced metal-insulator phase transitions in the vicinity of ferroelastic domain walls in the semiconductive VO2 that nucleated at temperatures as much as 10-12 C below bulk transition, resulting in the formation of conductive channels in the material. Density functional theory is used to rationalize the process low activation energy. This behavior, linked to the strain inhomogeneity inherent in ferroelastic materials, can strongly affect interpretation of phase-transition studies in VO2 and similar materials with symmetry-lowering transitions, and can also be used to enable new generations of electronic devices though strain engineering of conductive and semiconductive regions.

  19. Theoretical study of metal-insulator transition in rhombohedral vanadium sesquioxide

    Science.gov (United States)

    Liu, Guang-Hua; Deng, Xiao-Yan; Wang, Chun-Hai

    2011-09-01

    The electronic structure and the metal-insulator transition (MIT) of V2O3 are investigated in the framework of density functional theory and GGA+U. It is found that, both the insulating and metallic phases can be realized in rhombohedral structure by varying the on-site Coulomb interaction, and the MIT in V2O3 can take place without any structure phase transition. Our calculated energy gap (0.63 eV) agrees with experimental result very well. The metallic phase exhibits high spin (S=1) character, but it becomes S=1/2 in insulating phase. According to our analysis, the Mott-Hubbard and the charge-transfer induce the MIT together, and it supports the mechanism postulated by Tanaka (2002) [11].

  20. Distinct Length Scales in the VO2 Metal-Insulator Transition Revealed by Bi-chromatic Optical Probing

    International Nuclear Information System (INIS)

    Wang, Lei; Novikova, Irina B.; Klopf, John M.; Madaras, Scott E.; Williams, Gwyn P.; Madaras, Eric; Lu, Liwei; Wolf, Stuart A.; Lukaszew, Rosa A.

    2014-01-01

    Upon a heating-induced metal-insulator transition (MIT) in VO 2 , microscopic metallic VO 2 puddles nucleate and coarsen within the insulating matrix. This coexistence of the two phases across the transition spans distinct length scales as their relative domain sizes change. Far-field optical probing is applied to follow the dynamic evolution of the highly correlated metallic domains as the MIT progresses

  1. Hyperfine spectroscopic study of the metal-insulator transition in V2O3

    Science.gov (United States)

    Forker, M.; Saitovitch, H.; de Jesus Silva, P. R.

    1983-12-01

    The metal-insulator (M-I) transition in vanadium sesquioxide V2O3 has been investigated by time differential perturbed angular correlation measurements of the electric fieldgradient (EFG) and the magnetic hyperfine field at dilute111Cd impurities. The EFG undergoes a first-order change at the M-I transition at Tt=160 K, but does not reflect the high temperature resistivity anomaly. The increase of the EFG with temperature in the metallic phase can be attributed to thermal variations of the oxygen sublattice. The temperature dependence of the magnetic hyperfine field in the insulating phase follows a Brioullin function with a saturation value of Hhf(O)=15 KOe and an extrapolated Neel temperature, which, depending on the impurity concentration, varies between 188 and 230 K.

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

    KAUST Repository

    Cossu, Fabrizio

    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.

  3. Electronic Structure Evolution across the Peierls Metal-Insulator Transition in a Correlated Ferromagnet

    Directory of Open Access Journals (Sweden)

    P. A. Bhobe

    2015-10-01

    Full Text Available Transition metal compounds often undergo spin-charge-orbital ordering due to strong electron-electron correlations. In contrast, low-dimensional materials can exhibit a Peierls transition arising from low-energy electron-phonon-coupling-induced structural instabilities. We study the electronic structure of the tunnel framework compound K_{2}Cr_{8}O_{16}, which exhibits a temperature-dependent (T-dependent paramagnetic-to-ferromagnetic-metal transition at T_{C}=180  K and transforms into a ferromagnetic insulator below T_{MI}=95  K. We observe clear T-dependent dynamic valence (charge fluctuations from above T_{C} to T_{MI}, which effectively get pinned to an average nominal valence of Cr^{+3.75} (Cr^{4+}∶Cr^{3+} states in a 3∶1 ratio in the ferromagnetic-insulating phase. High-resolution laser photoemission shows a T-dependent BCS-type energy gap, with 2G(0∼3.5(k_{B}T_{MI}∼35  meV. First-principles band-structure calculations, using the experimentally estimated on-site Coulomb energy of U∼4  eV, establish the necessity of strong correlations and finite structural distortions for driving the metal-insulator transition. In spite of the strong correlations, the nonintegral occupancy (2.25 d-electrons/Cr and the half-metallic ferromagnetism in the t_{2g} up-spin band favor a low-energy Peierls metal-insulator transition.

  4. Pressure-driven metal-insulator transition in hematite from dynamical mean-field theory

    Czech Academy of Sciences Publication Activity Database

    Kuneš, Jan; Korotin, D. M.; Korotin, M. A.; Anisimov, V.I.; Werner, P.

    2009-01-01

    Roč. 102, č. 14 (2009), 146402/1-146402/4 ISSN 0031-9007 Institutional research plan: CEZ:AV0Z10100521 Keywords : metal-insulator transitions and other electronic transitions * strongly correlated electron systems * heavy fermions Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 7.328, year: 2009

  5. Control of metal-insulator transition in (EDO-TTF)2SbF6

    Science.gov (United States)

    Maesato, Mitsuhiko; Nakano, Yoshiaki; Shao, Xiangfeng; Yoshida, Yukihiro; Yamochi, Hideki; Saito, Gunzi; Moreac, Alain; Ameline, Jean-Claude; Collet, Eric; Uruichi, Mikio; Yakushi, Kyuya

    2009-02-01

    We have examined the temperature dependence of optical reflectance spectra of (EDO-TTF)2SbF6 salt, and succeeded to detect the thermal hysteresis by the reflectance spectra. In order to investigate high pressure effects on the metal-insulator transition of SbF6 salt, we have performed Raman experiments under pressures up to 6 kbar. Drastic changes in the frequencies of charge sensitive C=C stretching modes suggested the pressure-induced reentrant metal-insulator-metal transition at room temperature.

  6. The electronic structure and metal-insulator transitions in vanadium oxides

    International Nuclear Information System (INIS)

    Mossanek, Rodrigo Jose Ochekoski

    2010-01-01

    The electronic structure and metal-insulator transitions in vanadium oxides (SrVO 3 , CaVO 3 , LaVO 3 and YVO 3 ) are studied here. The purpose is to show a new interpretation to the spectra which is coherent with the changes across the metal-insulator transition. The main experimental techniques are the X-ray photoemission (PES) and X-ray absorption (XAS) spectroscopies. The spectra are interpreted with cluster model, band structure and atomic multiplet calculations. The presence of charge-transfer satellites in the core-level PES spectra showed that these vanadium oxides cannot be classified in the Mott-Hubbard regime. Further, the valence band and core-level spectra presented a similar behavior across the metal insulator transition. In fact, the structures in the spectra and their changes are determined by the different screening channels present in the metallic or insulating phases. The calculated spectral weight showed that the coherent fluctuations dominate the spectra at the Fermi level and give the metallic character to the SrVO 3 and CaVO 3 compounds. The vanishing of this charge fluctuation and the replacement by the Mott-Hubbard screening in the LaVO 3 and YVO 3 systems is ultimately responsible for the opening of a band gap and the insulating character. Further, the correlation effects are, indeed, important to the occupied electronic structure (coherent and incoherent peaks). On the other hand, the unoccupied electronic structure is dominated by exchange and crystal field effects (t2g and eg sub-bands of majority and minority spins). The optical conductivity spectrum was obtained by convoluting the removal and addition states. It showed that the oxygen states, as well as the crystal field and exchange effects are necessary to correctly compare and interpret the experimental results. Further, a correlation at the charge-transfer region of the core-level and valence band optical spectra was observed, which could be extended to other transition metal

  7. Various scenarios of metal-insulator transition in strongly correlated materials

    Czech Academy of Sciences Publication Activity Database

    Kuneš, Jan; Anisimov, V.I.

    2011-01-01

    Roč. 523, 8-9 (2011), 682-688 ISSN 0003-3804 R&D Projects: GA ČR GAP204/10/0284 Institutional research plan: CEZ:AV0Z10100521 Keywords : electronic correlations * metal-insulator transition * dynamical mean-field theory Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.841, year: 2011

  8. Metal-insulator transition and Frohlich conductivity in the Su-Schrieffer-Heeger model

    NARCIS (Netherlands)

    Michielsen, K.F L; de Raedt, H.A.

    1996-01-01

    A quantum molecular dynamics technique is used to study the single-particle density of states, Drude weight, optical conductivity and flux quantization in the Su-Schrieffer-Heeger (SSH) model. Our simulation data show that the SSH model has a metal-insulator transition away from half-filling. In the

  9. Experimental Observation of a Metal-insulator Transition in 2D at Zero Magnetic Field

    Science.gov (United States)

    Kravchenko, S. V.

    1996-03-01

    The scaling theory of Abrahams et al. ^1 has had considerable success in describing many features of metal-insulator transitions. Within this theory, which was developed for non-interacting electrons, no such transition is possible in two-dimensional electron systems (2DES) in the absence of a magnetic field. However, we show experimentally that an ultra-high-mobility 2DES on the surface of silicon does exhibit the signature of a true metal-insulator phase transition at zero magnetic field at a critical electron density n_c ~10^11 cm-2. The energy of electron-electron interactions, ignored in the scaling theory,^1 is the dominant parameter in this 2DES. The resistivity, ρ, is empirically found to scale near the critical point both with temperature T and electric field E so that it can be represented by the form ρ(T,n_s)=ρ(T/T_0(n_s)) as Earrow0 or ρ(E,n_s)=ρ(E/E_0(n_s)) as Tarrow0. At the transition, the resistivity is close to 3h/e^2. Both scaling parameters, T0 and E_0, show power law behavior at the critical point. This is characteristic of a true phase transition and strongly resembles, in particular, the superconductor-insulator transition in disordered thin films,^2 as well as the transition between quantum Hall liquid and insulator.^3 Many high-mobility samples from two different sources (Institute for Metrological Service, Russia, and Siemens AG, Germany) with different oxide thicknesses and gate materials have been studied and similar results were found. Work done in collaboration with J. E. Furneaux, Whitney Mason, V. M. Pudalov, and M. D'Iorio, supported by NSF. ^1 E. Abrahams, P. W. Anderson, D. C. Licciardello, and T. V. Ramakrishnan, Phys. Rev. Lett. 42, 673 (1979). ^2 Y. Liu, K. A. McGreer, B. Nease, D. B. Haviland, G. Martinez, J. W. Halley, and A. M. Goldman, Phys. Rev. Lett. 67, 2068 (1991). ^3 T. Wang, K. P. Clark, G. F. Spencer, A. M. Mack, and W. P. Kirk, Phys. Rev. Lett. 72, 709 (1994).

  10. Metal-Insulator transition at very high magnetic fields in an organic conductor

    Science.gov (United States)

    Graf, D.; Choi, E. S.; Brooks, J. S.; Mielke, C.; Harrison, N.; Murata, K.; Konoike, T.; Papavassiliou, G. C.

    2003-03-01

    Tau-phase organic conductors based on the P-(S,S)-DMEDT-TTF donor molecule exhibit a first order phase transition in high magnetic fields. Low temperature magnetoresistance measurements of τ-(P-(S,S)-DMEDT-TTF)_2(AuBr_2)_1_+y show an abrupt upturn when fields are swept beyond 35 tesla. Observations of sample current indicate that conduction ceases completely in the insulating state. Skin depth, magnetocaloric, and magnetization measurements in pulsed magnetic fields were also used to characterize the high field phase diagram of this metal-insulator transition. Measurements of the angular dependence reveal this to be an isotropic bulk effect rather than an orbital effect in stark contrast to conventional low dimensional metals. In contrast, τ-(EDO-(S,S)-DMEDT-TTF)_2(AuBr_2)_1_+y exhibits pronounced SdH oscillations against a less pronounced, but isotropic rise in magnetoresistance. Models for this new type of transition in an organic conductor will be considered.

  11. Metal-insulator transition of alloyed radical cation salts, (MexEDO-TTF)2PF6

    Science.gov (United States)

    Murata, Tsuyoshi; Shao, Xiangfeng; Nakano, Yoshiaki; Yamochi, Hideki; Saito, Gunzi; Uruichi, Mikio; Yakushi, Kyuya; Tanaka, Koichiro

    2010-06-01

    Ternary radical cation salts containing ethylenedioxytetrathiafulvalene, its mono-methyl substituted derivative, and hexafluorophosphate, [(EDO-TTF)1-x(MeEDO-TTF)x]2PF6 (x=mole fraction of MeEDO-TTF, x=0.01-0.13) were prepared by electrooxidation. Mole fractions of EDO-TTF and MeEDO-TTF in EDO-TTF rich alloys were consistent with the donor mixing ratios in preparation. Crystal structures of these alloys at room temperature were isostructural to that of (EDO-TTF)2PF6, where the donor molecules formed a nearly uniform stacking column to give a quasi-one-dimensional Fermi surface. The alloys exhibited a metal-insulator transition with tetramerization within the donor stack and anion-ordering. Temperature-variable structural analysis and Raman spectra revealed that the charge-ordering took place in the low temperature phase of x=0.05 alloy, however, this feature vanished in the x=0.13 alloy. The phase transition temperature decreased with increasing x value from 279 K of pristine (EDO-TTF)2PF6 to 188 K of x=0.13 alloy.

  12. Metal-insulator transition and superconductivity in heavily boron-doped diamond and related materials

    Energy Technology Data Exchange (ETDEWEB)

    Achatz, Philipp

    2009-05-15

    During this PhD project, the metal-insulator transition and superconductivity of highly boron-doped single crystal diamond and related materials have been investigated. The critical boron concentration n{sub c} for the metal-insulator transition was found to be the same as for the normal-superconductor transition. All metallic samples have been found to be superconducting and we were able to link the occurence of superconductivity to the proximity to the metal-insulator transition. For this purpose, a scaling law approach based on low temperature transport was proposed. Furthermore, we tried to study the nature of the superconductivity in highly boron doped single crystal diamond. Raman spectroscopy measurements on the isotopically substituted series suggest that the feature occuring at low wavenumbers ({approx} 500 cm{sup -1}) is the A1g vibrational mode associated with boron dimers. Usual Hall effect measurements yielded a puzzling situation in metallic boron-doped diamond samples, leading to carrier concentrations up to a factor 10 higher than the boron concentration determined by secondary ion mass spectroscopy (SIMS). The low temperature transport follows the one expected for a granular metal or insulator, depending on the interplay of intergranular and intragranular (tunneling) conductance. The metal-insulator transition takes place at a critical conductance g{sub c}. The granularity also influences significantly the superconducting properties by introducing the superconducting gap {delta} in the grain and Josephson coupling J between superconducting grains. A peak in magnetoresistance is observed which can be explained by superconducting fluctuations and the granularity of the system. Additionally we studied the low temperature transport of boron-doped Si samples grown by gas immersion laser doping, some of which yielded a superconducting transition at very low temperatures. Furthermore, preliminary results on the LO-phonon-plasmon coupling are shown for the

  13. Discrepancy of structural and electronic transitions in the vicinity of the Metal-Insulator-transition in V2 O 3

    Science.gov (United States)

    Kim, Hyun-Tak; Shin, Jun-Hwan; Choi, Jung-Young; Kim, Bong-Jun

    2011-03-01

    Vanadium sesquioxide (V2 O3) , representative of strongly correlated electronic system, has been known as undergoing the MIT (Metal-Insulator-Transition) which is between rhombohedral paramagnetic metallic phase and monoclinic antiferromagnetic insulating phase near the transition temperature, (Tc) ~ }150 K. In order to reveal a relation between electronic and structural atomic transition, we has measured the temperature dependence of DC conductivity and structural crystallographic characterization with various temperatures from 90 K to 300 K by using low-temperature X-Ray diffraction (LTXRD). The obtained results show a discrepancy of structural and electronic transitions. This discrepancy can be explained by forming of the metallic puddles whose the size and number increased by nucleation and percolation[1,2] during the electronic transition progress from 120 K to 180 K. The puddles have an insulating monoclinic structure before the structural phase transition at ~ 185 K. These metallic puddles are induced by the MIT not related to the SPT (structure phase transition). (1. M. M. Qazilbash et al., Science 318, 1750 (2007); 2. B. J. Kim et al., Phys. Rev. B 77, 235401(2008))

  14. Metal-insulator transition in SrIrO3 with strong spin-orbit interaction.

    Science.gov (United States)

    Wu, Fei-Xiang; Zhou, Jian; Zhang, L Y; Chen, Y B; Zhang, Shan-Tao; Gu, Zheng-Bin; Yao, Shu-Hua; Chen, Yan-Feng

    2013-03-27

    The thickness-dependent metal-insulator transition is observed in meta-stable orthorhombic SrIrO3 thin films synthesized by pulsed laser deposition. SrIrO3 films with thicknesses less than 3 nm demonstrate insulating behaviour, whereas those thicker than 4 nm exhibit metallic conductivity at high temperature, and insulating-like behaviour at low temperature. Weak/Anderson localization is mainly responsible for the observed thickness-dependent metal-insulator transition in SrIrO3 films. Temperature-dependent resistance fitting shows that electrical-conductivity carriers are mainly scattered by the electron-boson interaction rather than the electron-electron interaction. Analysis of the magneto-conductance proves that the spin-orbit interaction plays a crucial role in the magneto-conductance property of SrIrO3.

  15. Practical Improvements to the Lee-More Conductivity Near the Metal-Insulator Transition

    International Nuclear Information System (INIS)

    Desjarlais, Michael P.

    2000-01-01

    The wide-range conductivity model of Lee and More is modified to allow better agreement with recent experimental data and theories for dense plasmas in the metal-insulator transition regime. Modifications primarily include a new ionization equilibrium model, consisting of a smooth blend between single ionization Saha (with a pressure ionization correction) and the generic Thomas-Fermi ionization equilibrium, a more accurate treatment of electron-neutral collisions using a polarization potential, and an empirical modification to the minimum allowed collision time. These simple modifications to the Lee-More algorithm permit a more accurate modeling of the physics near the metal-insulator transition, while preserving the generic Lee-More results elsewhere

  16. Practical improvements to the Lee-More conductivity near the metal-insulator transition

    International Nuclear Information System (INIS)

    Desjarlais, M.P.

    2001-01-01

    The wide-range conductivity model of Lee and More is modified to allow better agreement with recent experimental data and theories for dense plasmas in the metal-insulator transition regime. Modifications primarily include a new ionization equilibrium model, consisting of a smooth blend between single ionization Saha (with a pressure ionization correction) and the generic Thomas-Fermi ionization equilibrium, a more accurate treatment of electron-neutral collisions using a polarization potential, and an empirical modification to the minimum allowed collision time. These simple modifications to the Lee-More algorithm permit a more accurate modeling of the physics near the metal-insulator transition, while preserving the generic Lee-More results elsewhere. (orig.)

  17. Metal-Insulator Transition in nanoparticle solids: a kinetic Monte Carlo study

    Science.gov (United States)

    Zimanyi, Gergely; Qu, Luman; Voros, Marton

    Nanoparticle (NP) solids recently emerged as a promising platform for high performance electronic/optoelectronic devices, including third generation solar cells, light emitting diodes and field effect transistors. A challenge of NP films is that their charge transport is in the unfavorable hopping/insulating regime. Recent experiments showed that it is possible to tune the NP solids through a Metal-Insulator Transition (MIT) via ligand engineering and ALD matrix infilling. However, the microscopic understanding of this transition is not yet clear. To address this challenge, we developed a Kinetic Monte Carlo transport modeling framework that builds on determining NP parameters from ab initio-based calculations of the energy level structures, charging energies and overlaps, and then uses these to compute the hopping mobility across a disordered NP array by the Marcus and Miller-Abrahams mechanisms. We reproduced and explained the observed non-monotonous dependence of the mobility on the NP diameter. Centrally, we extended our platform to be able to capture the MIT. We determined the MIT phase boundary on the (NP-NP overlap - Electron density) plane. We demonstrated that all mobilities fall on a universal scaling curve, allowing us to determine the critical behavior across the MIT. Supported by: UC Davis Office of Research RISE ANSWER Grant.

  18. Structural distortion on metal-insulator transition in ordered double perovskite Ca sub 2 FeReO sub 6

    CERN Document Server

    Oikawa, K; Kato, H; Tokura, Y

    2003-01-01

    The crystal and magnetic structures of an ordered double perovskite, Ca sub 2 FeReO sub 6 , were studied by high-resolution neutron powder diffraction as a function of the temperature from 7 K to 550 K. All of the diffraction data were precisely refined by the Rietveld method, and we confirmed a structural phase transition at around 140 K where the metal-insulator transition occurs from ferrimagnetic metal (FM) to ferrimagnetic insulator (FI) phases. At this temperature, there exists a change in the distortion direction of [ReO sub 6] octahedra together with a spin reorientation, which strongly supports the occurrence of orbital ordering of the t sub 2 sub g electrons. FM and FI phases coexist in a narrow temperature range at around 140 K, which is typically seen in the first-order phase transition. A phase separation was not detected in our well-characterized sample. (author)

  19. Kondo Lattices and the Mott Metal-Insulator Transition

    Science.gov (United States)

    Nozières, Ph.

    2005-01-01

    In Kondo lattices with one magnetic impurity at every lattice site, few electrons must quench many spins. This old “exhaustion” issue has been pending for years: it now appears it does not arise: the coherence temperature at which a singlet ground state emerges is the Kondo temperature itself. We survey the evolution of that problem. We then argue that such a lattice Kondo effect governs the Mott transition from a paramagnetic metal to an incoherent spin disordered insulator. It explains the appearance of a narrow resonance in the middle of a large preformed gap. Our naive arguments can be extended to an orbitally degenerate situation: they provide a qualitative understanding of the effect discovered numerically by Capone et al. [Science 296 (2002) 2364], namely the appearance of s-wave superconductivity near the Mott transition when the atomic ground state is a singlet with no residual degeneracy.

  20. Oxygen Vacancy Induced Room-Temperature Metal-Insulator Transition in Nickelate Films and Its Potential Application in Photovoltaics.

    Science.gov (United States)

    Wang, Le; Dash, Sibashisa; Chang, Lei; You, Lu; Feng, Yaqing; He, Xu; Jin, Kui-juan; Zhou, Yang; Ong, Hock Guan; Ren, Peng; Wang, Shiwei; Chen, Lang; Wang, Junling

    2016-04-20

    Oxygen vacancy is intrinsically coupled with magnetic, electronic, and transport properties of transition-metal oxide materials and directly determines their multifunctionality. Here, we demonstrate reversible control of oxygen content by postannealing at temperature lower than 300 °C and realize the reversible metal-insulator transition in epitaxial NdNiO₃ films. Importantly, over 6 orders of magnitude in the resistance modulation and a large change in optical bandgap are demonstrated at room temperature without destroying the parent framework and changing the p-type conductive mechanism. Further study revealed that oxygen vacancies stabilized the insulating phase at room temperature is universal for perovskite nickelate films. Acting as electron donors, oxygen vacancies not only stabilize the insulating phase at room temperature, but also induce a large magnetization of ∼50 emu/cm³ due to the formation of strongly correlated Ni²⁺ t(2g)⁶e(g)² states. The bandgap opening is an order of magnitude larger than that of the thermally driven metal-insulator transition and continuously tunable. Potential application of the newly found insulating phase in photovoltaics has been demonstrated in the nickelate-based heterojunctions. Our discovery opens up new possibilities for strongly correlated perovskite nickelates.

  1. Can a Metal-Insulator Transition Induce s-Wave Superconductivity?

    Science.gov (United States)

    Nozières, Ph.

    2004-04-01

    A recent paper of Capone et al. has studied an extended Hubbard model, in which local orbital degrees of freedom allow an even integer occupation at each site. A strong local repulsion U triggers a metal-insulator transition. Within a DMFT numerical analysis they show that when the ground state is a singlet a pocket of s-wave superconductivity appears in the vicinity of the Mott transition, with a strongly enhanced superconducting gap. A qualitative understanding of their result is proposed, and suggestions are made of possible systems in which this beautiful effect might be searched.

  2. First-order metal-insulator transitions in the extended Hubbard model due to self-consistent screening of the effective interaction

    Science.gov (United States)

    Schüler, M.; van Loon, E. G. C. P.; Katsnelson, M. I.; Wehling, T. O.

    2018-04-01

    While the Hubbard model is the standard model to study Mott metal-insulator transitions, it is still unclear to what extent it can describe metal-insulator transitions in real solids, where nonlocal Coulomb interactions are always present. By using a variational principle, we clarify this issue for short- and long-range nonlocal Coulomb interactions for half-filled systems on bipartite lattices. We find that repulsive nonlocal interactions generally stabilize the Fermi-liquid regime. The metal-insulator phase boundary is shifted to larger interaction strengths to leading order linearly with nonlocal interactions. Importantly, nonlocal interactions can raise the order of the metal-insulator transition. We present a detailed analysis of how the dimension and geometry of the lattice as well as the temperature determine the critical nonlocal interaction leading to a first-order transition: for systems in more than two dimensions with nonzero density of states at the Fermi energy the critical nonlocal interaction is arbitrarily small; otherwise, it is finite.

  3. Single-particle spectral function of a generalized Hubbard model: Metal-insulator transition

    Science.gov (United States)

    Gagliano, E. R.; Aligia, A. A.; Arrachea, Liliana; Avignon, Michel

    1995-05-01

    A generalized Hubbard model with correlated hoppings is studied at half filling using exact diagonalization methods. For certain values of the hopping parameters our results for several static properties, the Drude weight and the single-particle spectra function, suggest the occurrence of a metal-insulator transition (MIT) at a finite value of the local Coulomb interaction Uc. We identify the regions of the hopping parameters where the MIT is of the Mott type. In these regions, for large U

  4. Hyperfine spectroscopic study of the metal-insulator transition in V/sub 2/O/sub 3/

    Energy Technology Data Exchange (ETDEWEB)

    Forker, M.; Saitovitch, H.; de Jesus Silva, P.R. (Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro)

    1983-12-01

    The metal-insulator (M-I) transition in vanadium sesquioxide V/sub 2/O/sub 3/ has been investigated by time differential perturbed angular correlation measurements of the electric field gradient (EFG) and the magnetic hyperfine field at dilute /sup 111/Cd impurities. The EFG undergoes a first-order change at the M-I transition at 160 K, but does not reflect the high temperature resistivity anomaly. The increase of the EFG with temperature in the metallic phase can be attributed to thermal variations of the oxygen sublattice. The temperature dependence of the magnetic hyperfine field in the insulating phase follows a Brioullin function with a saturation value of 15 KOe and an extrapolated Neel temperature, which, depending on the impurity concentration, varies between 188 and 230 K.

  5. Metal-Insulator Transition Revisited for Cold Atoms in Non-Abelian Gauge Potentials

    International Nuclear Information System (INIS)

    Satija, Indubala I.; Dakin, Daniel C.; Clark, Charles W.

    2006-01-01

    We discuss the possibility of realizing metal-insulator transitions with ultracold atoms in two-dimensional optical lattices in the presence of artificial gauge potentials. For Abelian gauges, such transitions occur when the magnetic flux penetrating the lattice plaquette is an irrational multiple of the magnetic flux quantum. Here we present the first study of these transitions for non-Abelian U(2) gauge fields. In contrast to the Abelian case, the spectrum and localization transition in the non-Abelian case is strongly influenced by atomic momenta. In addition to determining the localization boundary, the momentum fragments the spectrum. Other key characteristics of the non-Abelian case include the absence of localization for certain states and satellite fringes around the Bragg peaks in the momentum distribution and an interesting possibility that the transition can be tuned by the atomic momenta

  6. Dynamically tracking the joule heating effect on the voltage induced metal-insulator transition in VO2 crystal film

    Directory of Open Access Journals (Sweden)

    G. M. Liao

    2016-04-01

    Full Text Available Insulator to metal phase transitions driven by external electric field are one of the hottest topics in correlated oxide study. While this electric triggered phenomena always mixes the electric field switching effect and joule thermal effect together, which are difficult to clarify the intrinsic mechanism. In this paper, we investigate the dynamical process of voltage-triggered metal-insulator transition (MIT in a VO2 crystal film and observe the temperature dependence of the threshold voltages and switching delay times, which can be explained quite well based on a straightforward joule thermal model. By conducting the voltage controlled infrared transmittance measurement, the delayed infrared transmission change is also observed, further confirming the homogeneous switching process for a large-size film. All of these results show strong evidences that joule thermal effect plays a dominated role in electric-field-induced switching of VO2 crystal.

  7. Current-induced metal-insulator transition in VO x thin film prepared by rapid-thermal-annealing

    International Nuclear Information System (INIS)

    Cho, Choong-Rae; Cho, SungIl; Vadim, Sidorkin; Jung, Ranju; Yoo, Inkyeong

    2006-01-01

    The phenomenon of metal-insulator transition (MIT) in polycrystalline VO x thin films and their preparations have been studied. The films were prepared by sputtering of vanadium thin films succeeded by Rapid Thermal Annealing (RTA) in oxygen ambient at 500 deg. C. Crystalline, compositional, and morphological characterizations reveal a continuous change of phase from vanadium metal to the highest oxide phase, V 2 O 5 , with the time of annealing. Electrical MIT switching has been observed in these films. Sweeping mode, electrode area, and temperature dependent MIT has been studied in Pt/VO x /Pt vertical structure. The important parameters for MIT in VO x have been found to be the current density and the electric field, which depend on carrier density in the films

  8. First-principles study of pressure-induced metal-insulator transition in BiNiO3

    Science.gov (United States)

    Cai, M. Q.; Yang, G. W.; Tan, X.; Cao, Y. L.; Wang, L. L.; Hu, W. Y.; Wang, Y. G.

    2007-09-01

    First-principles calculation is used to study the pressure-induced metal-insulator transition in BiNiO3. It is found that the G-antiferromagnetic insulator triclinic phase in BiNiO3 transforms to the ferromagnetic half-metallic orthorhombic phase with a volume collapse of 6.2% when the applied pressure is 3.46GPa. The interaction between neighbor Ni atoms creates the energy band gap of 1.96eV in the majority density of states. The pressure suppresses the charge disproportion of Bi. The strong hybridizations of Ni-O and Bi-O lead to the decrease of the spin magnetic moment with 1.74μB compared with the Ni3+ with d7 configuration 3μB.

  9. Substitution effect on metal-insulator transition of K2V8O16

    International Nuclear Information System (INIS)

    Isobe, Masahiko; Koishi, Shigenori; Yamazaki, Satoshi; Yamaura, Jun-ichi; Gotou, Hirotada; Yagi, Takehiko; Ueda, Yutaka

    2009-01-01

    The effect of the substitution of various ions on the metal-insulator (MI) transition at 170 K in K 2 V 8 O 16 has been investigated. Both Rb and Ti form complete solid solution systems: K 2-x Rb x V 8 O 16 and K 2 V 8-y Ti y O 16 , respectively. The substitution of Rb for K or of Ti for V splits the transition into two transitions: the high-temperature transition is a first-order MI transition from a tetragonal structure to a tetragonal structure, and the low-temperature transition is a second-order transition to a monoclinic structure. In K 2-x Rb x V 8 O 16 , the former terminates to an MI transition at around 220 K in Rb 2 V 8 O 16 , while the latter disappears at x > 0.6. In K 2 V 8-y Ti y O 16 , both transitions disappear at y > 0.5. The substitution of Cr for V also results in a similar splitting of the transition and the rapid disappearance of both transitions. The substitution of Na or Ba for K suppresses the MI transition without any splitting of the transition, although the solubility of both ions is limited. These substitution effects reveal that the MI transition of K 2 V 8 O 16 consists of two parts: a first-order MI transition and a parasitic second-order structural transition; the substitution of some ions causes a clear splitting of these transitions, probably due to the difference between the chemical pressure effects on the two transitions. The first-order MI transition is very sensitive to charge randomness, suggesting the charge ordering nature of the MI transition, while the second-order structural transition is very sensitive to both charge and structural randomnesses. (author)

  10. Metal-insulator transition and nonlinear optical responseof sputter-deposited V3O5 thin films

    Science.gov (United States)

    Rúa, Armando; Díaz, Ramón D.; Kumar, Nardeep; Lysenko, Sergiy; Fernández, Félix E.

    2017-06-01

    The compound V3O5, a member of the vanadium oxide Magnéli series, exhibits a metal-insulator transition near 430 K, the highest known temperature value among all vanadium oxides. It has been studied before mainly in single-crystal form, and for the very few cases in which thin films have been fabricated before, the procedure has required extensive post-deposition annealing of other oxides or vanadium metal at high temperatures in tightly controlled atmospheres. For the present work, V3O5 films were deposited directly on SiO2 glass substrates, without subsequent annealing, by DC magnetron sputtering. X-ray diffraction study of the samples evidenced oxygen deficiency, accommodated by oxygen vacancies. Resistivity measurements from 300 to 500 K revealed the metal-insulator transition by Tc ˜ 430 K, with an associated resistivity change by a factor of 20, and no detectable hysteresis in heating-cooling cycles, in agreement with most single-crystal studies. Resistivity values obtained were, however, lower than published results for bulk crystal values, particularly at temperatures below Tc. This was attributed to conduction electrons generated by the oxygen vacancies. Gradual resistivity increase in a very thin sample, through heating in air at temperatures up to 500 K, lends support to this argument. Using a pump-probe scattering technique, the V3O5 films were also probed for ultrafast nonlinear optical response. A reduction in the transient relative scattered light signal was recorded, which reached -10% within ˜800 fs. This observed response, likely related to the photoinduced insulator-to-metal phase transition, should stimulate additional interest in this material.

  11. Electronic Structure of the Pyrochlore-Type Ru Oxides through the Metal--Insulator Transition

    International Nuclear Information System (INIS)

    Okamoto, J.; Fujimori, S.I.; Okane, T.; Fujimori, A.; Abbate, M.; Yoshii, S.; Sato, M.

    2003-01-01

    The electronic structures of the pyrochlore-type Ru oxides Sm 2-x Ca x Ru 2 O 7 and Sm 2-x Bi x Ru 2 O 7 , which show metal-insulator transition with increasing Ca or Bi concentration, have been studied by ultraviolet photoemission spectroscopy. Spectral changes near the Fermi level are different but reflect the tendency of their transport properties in both systems. The Sm 2-x Ca x Ru 2 O 7 system shows an energy shift, which is expected from the increase of hole in the Ru 4d t 2g band and the Sm 2 - x Bi x Ru 2 O 7 system shows spectral weight transfer within the Ru 4d t 2g band, which is expected to be observed in bandwidth-control Mott-Hubbard system. (author)

  12. Critical metal-insulator transition and divergence in a two-particle irreducible vertex in disordered and interacting electron systems

    Czech Academy of Sciences Publication Activity Database

    Janiš, Václav; Pokorný, Vladislav

    2014-01-01

    Roč. 90, č. 4 (2014), "045143-1"-"045143-11" ISSN 1098-0121 Institutional support: RVO:68378271 Keywords : metal-insulator transition * disordered and interacting electron systems * dynamical mean-field theory * critical behavior Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.736, year: 2014

  13. Metal-insulator transition in NiS.sub.2-x./sub.Se.sub.x./sub

    Czech Academy of Sciences Publication Activity Database

    Kuneš, Jan; Baldassarre, L.; Schachner, B.; Rabia, K.; Kuntscher, C.A.; Korotin, D. M.; Anisimov, V.I.; McLeod, J.A.; Kurmaev, E.Z.; Moewes, A.

    2010-01-01

    Roč. 81, č. 3 (2010), 035112/1-035112/6 ISSN 1098-0121 Institutional research plan: CEZ:AV0Z10100521 Keywords : metal-insulator transition * dynamical mean-field theory Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.772, year: 2010 http://prb.aps.org/abstract/PRB/v81/i3/e035122

  14. Resistance noise spectroscopy across the thermally and electrically driven metal-insulator transitions in VO2 nanobeams

    Science.gov (United States)

    Alsaqqa, Ali; Kilcoyne, Colin; Singh, Sujay; Horrocks, Gregory; Marley, Peter; Banerjee, Sarbajit; Sambandamurthy, G.

    Vanadium dioxide (VO2) is a strongly correlated material that exhibits a sharp thermally driven metal-insulator transition at Tc ~ 340 K. The transition can also be triggered by a DC voltage in the insulating phase with a threshold (Vth) behavior. The mechanisms behind these transitions are hotly discussed and resistance noise spectroscopy is a suitable tool to delineate different transport mechanisms in correlated systems. We present results from a systematic study of the low frequency (1 mHz noise behavior in VO2 nanobeams across the thermally and electrically driven transitions. In the thermal transition, the power spectral density (PSD) of the resistance noise is unchanged as we approach Tc from 300 K and an abrupt drop in the magnitude is seen above Tc and it remains unchanged till 400 K. However, the noise behavior in the electrically driven case is distinctly different: as the voltage is ramped from zero, the PSD gradually increases by an order of magnitude before reaching Vth and an abrupt increase is seen at Vth. The noise magnitude decreases above Vth, approaching the V = 0 value. The individual roles of percolation, Joule heating and signatures of correlated behavior will be discussed. This work is supported by NSF DMR 0847324.

  15. Influence of oxygen flow rate on metal-insulator transition of vanadium oxide thin films grown by RF magnetron sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Xu; Liu, Xinkun; Li, Haizhu; Huang, Mingju [Henan University, Key Lab of Informational Opto-Electronical Materials and Apparatus, School of Physics and Electronics, Kaifeng (China); Zhang, Angran [South China Normal University, Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, Guangzhou (China)

    2017-03-15

    High-quality vanadium oxide (VO{sub 2}) films have been fabricated on Si (111) substrates by radio frequency (RF) magnetron sputtering deposition method. The sheet resistance of VO{sub 2} has a significant change (close to 5 orders of magnitude) in the process of the metal-insulator phase transition (MIT). The field emission-scanning electron microscope (FE-SEM) results show the grain size of VO{sub 2} thin films is larger with the increase of oxygen flow. The X-ray diffraction (XRD) results indicate the thin films fabricated at different oxygen flow rates grow along the (011) crystalline orientation. As the oxygen flow rate increases from 3 sccm to 6 sccm, the phase transition temperature of the films reduces from 341 to 320 K, the width of the thermal hysteresis loop decreases from 32 to 9 K. The thin films fabricated in the condition of 5 sccm have a high temperature coefficient of resistance (TCR) -3.455%/K with a small resistivity of 2.795 ρ/Ω cm. (orig.)

  16. Heteroepitaxial VO{sub 2} thin films on GaN: Structure and metal-insulator transition characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Zhou You; Ramanathan, Shriram [Harvard School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States)

    2012-10-01

    Monolithic integration of correlated oxide and nitride semiconductors may open up new opportunities in solid-state electronics and opto-electronics that combine desirable functional properties of both classes of materials. Here, we report on epitaxial growth and phase transition-related electrical properties of vanadium dioxide (VO{sub 2}) thin films on GaN epitaxial layers on c-sapphire. The epitaxial relation is determined to be (010){sub vo{sub 2}} parallel (0001){sub GaN} parallel (0001){sub A1{sub 2O{sub 3}}} and [100]{sub vo{sub 2}} parallel [1210]{sub GaN} parallel [0110]{sub A1{sub 2O{sub 3}}} from x-ray diffraction. VO{sub 2} heteroepitaxial growth and lattice mismatch are analyzed by comparing the GaN basal plane (0001) with the almost close packed corrugated oxygen plane in vanadium dioxide and an experimental stereographic projection describing the orientation relationship is established. X-ray photoelectron spectroscopy suggests a slightly oxygen rich composition at the surface, while Raman scattering measurements suggests that the quality of GaN layer is not significantly degraded by the high-temperature deposition of VO{sub 2}. Electrical characterization of VO{sub 2} films on GaN indicates that the resistance changes by about four orders of magnitude upon heating, similar to epitaxial VO{sub 2} films grown directly on c-sapphire. It is shown that the metal-insulator transition could also be voltage-triggered at room temperature and the transition threshold voltage scaling variation with temperature is analyzed in the framework of a current-driven Joule heating model. The ability to synthesize high quality correlated oxide films on GaN with sharp phase transition could enable new directions in semiconductor-photonic integrated devices.

  17. Surface conditions for the observation of metal-insulator transitions on Cr-doped V 2O 3

    Science.gov (United States)

    Toledano, David S.; Metcalf, Patricia; Henrich, Victor E.

    2000-03-01

    Chromium-doped vanadium sesquioxide, (V 1- xCr x) 2O 3, displays two metal-insulator transitions with temperature for 0.005< x<0.0179. The high-temperature (˜300 K) transition occurs in a temperature range that is of interest for catalysis; the physics of the transition is also of fundamental interest. However, so far that transition has been observed only on cleaved samples. Due to the difficulty in obtaining doped single crystals for cleaving, alternate preparation methods are required. (V 0.985Cr 0.015) 2O 3 (0001) was prepared both by scraping with a diamond file and by ion bombardment followed by annealing in oxygen; the resulting surfaces were examined by ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) for evidence of the high-temperature metal-insulator transition. Although resistance measurements across the transition temperature showed that a transition had taken place in the bulk, no changes were observed in photoemission spectra of scraped samples; they appeared insulating both above and below the transition. Annealed samples, on the other hand, displayed a clear increase in the density of states at EF, as well as changes in core-level XPS consistent with a metallic surface, as the temperature was lowered through the transition. Sharp (1×1) low energy electron diffraction (LEED) patterns were obtained from annealed surfaces, and Auger spectra showed no evidence of chromium segregation following annealing.

  18. Absence of Mass Renormalization upon the Metal-Insulator Transition in La_1-xSr_xMnO_3

    Science.gov (United States)

    Okuda, T.; Asamitsu, A.; Tokura, Y.

    1998-03-01

    The low-temperature specific heat as well as the resistivity of La_1-xSr_xMnO3 crystals has been measured under magnetic fields to investigate the critical behavior of the metal-insulator (MI) transition, which is induced by carrier doping around a critical composition of x_c=0.17. We observed the reduction of specific heat by application of magnetic fields, which is due to the suppression of the contribution of spin wave. Thus, the magnetic contribution to the specific heat was carefully removed to extract the electronic contribution. The effective mass, derived from obtained electronic specific heat coefficient γ, is a few times as large as a bare mass in the ferromagnetic metallic state, e.g. γ = 3.5 (mJ/K^2 mole) at x=0.3, and does not critically increase around the critical point while showing the maximum value γ = 5.1 (mJ/K^2 mole) at x=0.18. This is in contrast with the conspicuous mass renormalization effect as observed for other transition metal oxide, eg. V_2O3 and LaTiO_3. The γ value rather decreases with the decrease of x from 0.18 to 0.15, namely in the immediate vicinity of the MI boundary. This suggests that the Fermi surface gradually shrinks towards the insulating phase and finally disappears at the MI phase boundary. This work was supported by New Energy and Industrial Technology Development Organization (NEDO) of Japan.

  19. Structural and metal-insulator transitions in rhenium-based double perovskites via orbital ordering

    Science.gov (United States)

    Lee, Alex Taekyung; Marianetti, Chris A.

    2018-01-01

    Re-based double perovskites (DPs) have garnered substantial attention due to their high Curie temperatures (TC) and display of complex interplay of structural and metal-insulator transitions (MIT). Here we systematically study the ground-state electronic and structural properties for a family of Re-based DPs A2B ReO6 (A =Sr, Ca and B =Cr, Fe), which are related by a common low-energy Hamiltonian, using density functional theory +U calculations. We show that the on-site interaction U of Re induces orbital ordering (denoted C-OO), with each Re site having an occupied dx y orbital and a C-type alternation among dx z/dy z , resulting in an insulating state consistent with experimentally determined insulators Sr2CrReO6 , Ca2CrReO6 , and Ca2FeReO6 . The threshold value of UR e for orbital ordering is reduced by inducing Eg octahedral distortions of the same C-type wavelength (denoted C-OD), which serves as a structural signature of the orbital ordering; octahedral tilting also reduces the threshold. The C-OO and the concomitant C-OD are a spontaneously broken symmetry for the Sr-based materials (i.e., a0a0c- tilt pattern), while not for the Ca-based systems (i.e., a-a-b+ tilt pattern). Spin-orbit coupling does not qualitatively change the physics of the C-OO/C-OD, but can induce relevant quantitative changes. We prove that a single set of UC r,UF e,UR e capture the experimentally observed metallic state in Sr2FeReO6 and insulating states in other three systems. We predict that the C-OO is the origin of the insulating state in Sr2CrReO6 , and that the concomitant C-OD may be experimentally observed at sufficiently low temperatures (i.e., space group P 42/m ) in pure samples. Additionally, given our prescribed values of U , we show that the C-OO induced insulating state in Ca2CrReO6 will survive even if the C-OD amplitude is suppressed (e.g., due to thermal fluctuations). The role of the C-OO/C-OD in the discontinuous, temperature driven MIT in Ca2FeReO6 is discussed.

  20. Influence of the disorder in doped germanium changed by compensation on the critical indices of the metal-insulator transition

    International Nuclear Information System (INIS)

    Rentzsch, R.; Reich, Ch.; Ionov, A.N.; Ginodman, V.; Slimak, I.; Fozooni, P.; Lea, M.J.

    1999-01-01

    We present a critical review of the present status of the critical exponent puzzle of the metal-insulator transition of doped semiconductors with the emphasis on the role of meso- and macroscopy inhomogeneity caused by the disorder of acceptors and donors in the crystals. By using the isotopic and engineering and the neutron transmutation doping of germanium we found for low compensations (at K = 1.4 and 12%) that the critical exponents of the localization length and the dielectric constant are nearly ν = 1/2 and ξ = 1, which double for medium compensations (at K = 39 and 54%) to ν 1 and ξ = 2, respectively

  1. Electric controlling of surface metal-insulator transition in the doped BaTiO3 film

    Directory of Open Access Journals (Sweden)

    Wei Xun

    2017-07-01

    Full Text Available Based on first-principles calculations, the BaTiO3(BTO film with local La-doping is studied. For a selected concentration and position of doping, the surface metal-insulator transition occurs under the applied electric field, and the domain appears near the surface for both bipolar states. Furthermore, for the insulated surface state, i.e., the downward polarization state in the doped film, the gradient bandgap structure is achieved, which favors the absorption of solar energy. Our investigation can provide an alternative avenue in modification of surface property and surface screening effect in polar materials.

  2. Electric controlling of surface metal-insulator transition in the doped BaTiO3 film

    Science.gov (United States)

    Xun, Wei; Hao, Xiang; Pan, Tao; Zhong, Jia-Lin; Ma, Chun-Lan; Hou, Fang; Wu, Yin-Zhong

    2017-07-01

    Based on first-principles calculations, the BaTiO3(BTO) film with local La-doping is studied. For a selected concentration and position of doping, the surface metal-insulator transition occurs under the applied electric field, and the domain appears near the surface for both bipolar states. Furthermore, for the insulated surface state, i.e., the downward polarization state in the doped film, the gradient bandgap structure is achieved, which favors the absorption of solar energy. Our investigation can provide an alternative avenue in modification of surface property and surface screening effect in polar materials.

  3. Electric controlling of surface metal-insulator transition in the doped BaTiO3 film

    OpenAIRE

    Wei Xun; Xiang Hao; Tao Pan; Jia-Lin Zhong; Chun-Lan Ma; Fang Hou; Yin-Zhong Wu

    2017-01-01

    Based on first-principles calculations, the BaTiO3(BTO) film with local La-doping is studied. For a selected concentration and position of doping, the surface metal-insulator transition occurs under the applied electric field, and the domain appears near the surface for both bipolar states. Furthermore, for the insulated surface state, i.e., the downward polarization state in the doped film, the gradient bandgap structure is achieved, which favors the absorption of solar energy. Our investiga...

  4. Covalency, Excitons, Double Counting and the Metal-Insulator Transition in Transition Metal Oxides

    Science.gov (United States)

    Wang, Xin

    2012-02-01

    We present single-site dynamical mean-field studies of realistic models of transition metal oxides, including the cuprate superconductors and rare earth nickelates (in bulk and superlattice form). We include orbital multiplet effects and hybridization to ligands. We explicitly calculate the d-d exciton spectra for cuprates, finding sharp exciton lines in both metallic and insulating phases, which should be visible in experiments. We also find that the additional d3z^2-r^2 orbital does not contribute to an additional Fermi surface at any reasonable doping, in contradiction to previous slave-boson studies. The hybridization to ligands is shown to have crucial effects, for example suppressing the ferro-orbital order previously found in Hubbard model studies of nickelates. Hybridization to ligands is shown to be most naturally parametrized by the d-orbital occupancy. For cuprates and nickelates, insulating behavior is found to be present only for a very narrow range of d-occupancy, irrespective of the Coulomb repulsion. The d-occupancy predicted by standard band calculations is found to be very far from the values required to obtain an insulating phase, calling into question the interpretation of these materials as charge transfer insulators. [4pt] This work is done in collaboration with A.J. Millis, M.J. Han, C.A. Marianetti, L. de' Medici, and H.T. Dang, and is supported by NSF-DMR-1006282, the Army Office of Scientific Research, and the Condensed Matter Theory Center and CNAM at University of Maryland. [4pt] [1] X. Wang, H. T. Dang, and A. J. Millis, Phys. Rev. B 84, 014530 (2011).[0pt] [2] X. Wang, M. J. Han, L. de' Medici, C. A. Marianetti, and A. J. Millis, arXiv:1110.2782.[0pt] [3] M. J. Han, X. Wang, C. A. Marianetti, and A. J. Millis, Phys. Rev. Lett. 107, 206804 (2011).

  5. On the Mott transition and the new metal-insulator transitions in doped covalent and polar crystals

    International Nuclear Information System (INIS)

    Dzhumanov, S.; Begimkulov, U.; Kurbanov, U.T.; Yavidov, B.Y.

    2001-10-01

    The Mott transition and new metal-insulator transitions (MIT's) and their distinctive features in doped covalent semiconductors and polar compounds are studied within the continuum model of extrinsic carrier self-trapping, the Hubbard impurity band model (with on-site Coulomb repulsion and screening effects) and the extrinsic (bi)polaronic band model (with short- and long-range carrier-impurity, impurity-phonon and carrier-phonon interactions and intercarrier correlation) using the appropriate tight-binding approximations and variational methods. We have shown the formation possibility of large-radius localized one- and two-carrier impurity (or defect) states and narrow impurity bands in the band gap and charge transfer gap of these carrier-doped systems. The extrinsic Mott-Hubbard and (bi)polaronic insulating gaps are calculated exactly. The proper criterions for Mott transition, extrinsic excitonic and (bi)polaronic MIT's are obtained. We have demonstrated that the Mott transition occurs in doped covalent semiconductors (i.e. Si and Ge) and some insulators with weak carrier-phonon coupling near the large-radius dopants. While, in doped polar compounds (e.g. oxide high-T c superconductors (HTSC) and related materials) the MIT's are new extrinsic (or intrinsic) (bi)polaronic MIT's. We have found that the anisotropy of the dielectric (or (bi)polaronic) properties of doped cuprate HTSC is responsible for smooth (or continuous) MIT's, stripe formation and suppression of high-T c superconductivity. Various experimental results on in-gap states, bands and MIT's in doped covalent semiconductors, oxide HTSC and related materials are in good agreement with the developed theory of Mott transition and new (bi)polaronic MIT's. (author)

  6. Topotactic Metal-Insulator Transition in Epitaxial SrFeOx Thin Films.

    Science.gov (United States)

    Khare, Amit; Shin, Dongwon; Yoo, Tae Sup; Kim, Minu; Kang, Tae Dong; Lee, Jaekwang; Roh, Seulki; Jung, In-Ho; Hwang, Jungseek; Kim, Sung Wng; Noh, Tae Won; Ohta, Hiromichi; Choi, Woo Seok

    2017-10-01

    Topotactic phase transformation enables structural transition without losing the crystalline symmetry of the parental phase and provides an effective platform for elucidating the redox reaction and oxygen diffusion within transition metal oxides. In addition, it enables tuning of the emergent physical properties of complex oxides, through strong interaction between the lattice and electronic degrees of freedom. In this communication, the electronic structure evolution of SrFeO x epitaxial thin films is identified in real-time, during the progress of reversible topotactic phase transformation. Using real-time optical spectroscopy, the phase transition between the two structurally distinct phases (i.e., brownmillerite and perovskite) is quantitatively monitored, and a pressure-temperature phase diagram of the topotactic transformation is constructed for the first time. The transformation at relatively low temperatures is attributed to a markedly small difference in Gibbs free energy compared to the known similar class of materials to date. This study highlights the phase stability and reversibility of SrFeO x thin films, which is highly relevant for energy and environmental applications exploiting the redox reactions. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Ca-site substitution induced a metal-insulator transition in manganite CaMnO3

    International Nuclear Information System (INIS)

    Sousa, D.; Nunes, M.R.; Silveira, C.; Matos, I.; Lopes, A.B.; Melo Jorge, M.E.

    2008-01-01

    A systematic study of the A-site doping in Mn(IV)-rich perovskite manganites Ca 1-x Ho x MnO 3 , over a large homogeneity range (0.1 ≤ x ≤ 0.4), has been performed. A significant increase in the lattice parameters indicated the presence of mixed valence state of Mn: Mn 3+ and Mn 4+ . The substitution of calcium by holmium also induces strong changes in the electrical properties. We found that small Ho concentration produces an important decrease in the electrical resistivity and induces an electrical transition, the temperature corresponding to the metal-insulator transition (T MI ) shifts with the holmium content. This electrical behavior is attributed to the Mn 3+ ions content and a charge order effect

  8. Superconductor-Metal-Insulator transition in two dimensional Ta thin Films

    Science.gov (United States)

    Park, Sun-Gyu; Kim, Eunseong

    2013-03-01

    Superconductor-insulator transition has been induced by tuning film thickness or magnetic field. Recent electrical transport measurements of MoGe, Bi, Ta thin films revealed an interesting intermediate metallic phase which intervened superconducting and insulating phases at certain range of magnetic field. Especially, Ta thin films show the characteristic IV behavior at each phase and the disorder tuned intermediate metallic phase [Y. Li, C. L. Vicente, and J. Yoon, Physical Review B 81, 020505 (2010)]. This unexpected metallic phase can be interpreted as a consequence of vortex motion or contribution of fermionic quasiparticles. In this presentation, we report the scaling behavior during the transitions in Ta thin film as well as the transport measurements in various phases. Critical exponents v and z are obtained in samples with wide ranges of disorder. These results reveal new universality class appears when disorder exceeds a critical value. Dynamical exponent z of Superconducting sample is found to be 1, which is consistent with theoretical prediction of unity. z in a metallic sample is suddenly increased to be approximately 2.5. This critical exponent is much larger than the value found in other system and theoretical prediction. We gratefully acknowledge the financial support by the National Research Foundation of Korea through the Creative Research Initiatives.

  9. The metal-insulator transition of RNiO3 perovskites. What can we learn from neutron diffraction?

    International Nuclear Information System (INIS)

    Medarde, M.L.

    1996-01-01

    RNiO 3 perovskites (R = rare earth) provide a remarkable opportunity to study the relationship between structural and physical properties since by moving along the 4f rare earth series, the evolution of several transport and magnetic properties can be nicely correlated to the steric effects associated with the lanthanide contraction. The most appealing example is probably the metal-insulator transition discovered for the compounds with R≠La, whose critical temperature T M-I increases with decreasing size of the rare earth ion. In this lecture, a summary of the most relevant neutron diffraction results on this system is presented. Moreover, the nickelates are used as an example to illustrate the performance of the diffractometers HRPT and DMCG to be installed at the SINQ. (author) 12 figs., 2 tabs., 17 refs

  10. The metal-insulator transition of RNiO{sub 3} perovskites. What can we learn from neutron diffraction?

    Energy Technology Data Exchange (ETDEWEB)

    Medarde, M.L. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

    1996-11-01

    RNiO{sub 3} perovskites (R = rare earth) provide a remarkable opportunity to study the relationship between structural and physical properties since by moving along the 4f rare earth series, the evolution of several transport and magnetic properties can be nicely correlated to the steric effects associated with the lanthanide contraction. The most appealing example is probably the metal-insulator transition discovered for the compounds with R{ne}La, whose critical temperature T{sub M-I} increases with decreasing size of the rare earth ion. In this lecture, a summary of the most relevant neutron diffraction results on this system is presented. Moreover, the nickelates are used as an example to illustrate the performance of the diffractometers HRPT and DMCG to be installed at the SINQ. (author) 12 figs., 2 tabs., 17 refs.

  11. Optical Response of Cu1-xZnxIr2S4 Due to Metal--Insulator Transition

    International Nuclear Information System (INIS)

    Chen, L.; Matsunami, M.; Nanba, T.; Cao, G.; Suzuki, H.; Isobe, M.; Matsumoto, T.

    2003-01-01

    The mother material CuIr 2 S 4 of the thiospinel system Cu 1-x Zn x Ir 2 S 4 undergoes a temperature-induced metal--insulator (Mi) transition. We report the temperature dependence of the optical reflection spectra of Cu 1-x Zn x Ir 2 S 4 (x ≤ 0.5) at the temperatures of 8-300 K in the energy regions of 0.005--30 eV in order to study the change in the electronic structure due to the Zn substitution for Cu. Zn substitution induced mainly the splitting of the hybridization band between the Ir-5d(t 2g ) and S-3 p states crossing the E F . Obtained optical conductivity (σ ) spectrum is discussed in relation to the change in the electronic structure close to the E F . (author)

  12. Thickness-dependent evolution of structure, electronic structure, and metal-insulator transition in ultrathin V2O3(0001) films on Ag(001)

    Science.gov (United States)

    Kundu, Asish K.; Menon, Krishnakumar S. R.

    2017-05-01

    Epitaxial hexagonal V2O3(0001) films were grown on cubic Ag(001) substrate for coverages ranging from 1-20 monolayers equivalent (MLE) and have studied their structure, electronic structure and the metal-insulator transition (MIT) using Low Energy Electron Diffraction (LEED), X-ray Photoelectron Spectroscopy (XPS) and Angle-Resolved Photoemission Spectroscopy (ARPES) techniques. Detailed LEED and XPS study reveal that, for the lower film coverages (∼1 MLE), a complex (coexisting phase of) vanadium oxide is formed while from 3 MLE coverage onwards, three-dimensional crystallites of V2O3 grows epitaxially. Our LEED results also show that the hexagonal surface of V2O3(0001) is stabilizing on top of square symmetry substrate by the formation of twin-domain structure, where each domain is rotated by 90o. Our photoemission results show that the surface of V2O3 is more insulating than its bulk, similar to the case of many strongly correlated oxide surfaces which is discussed based on the valence band electronic structure with varying probing depth. Evolution of the surface electronic structure was also studied as a function of the film thickness. Further, the effect of lattice strain, film thickness and the domain formation on the metal-insulator transition (MIT) are discussed. The change in the orbital occupancy of (a1 g, egπ) and (egπ, egπ) orbitals of V 3 d, a vanishing of quasiparticle (QP) peak and opening an energy gap at the Fermi level is observed below a critical temperature as a consequence of the MIT.

  13. Topotactic Metal-Insulator Transition in Epitaxial SrFeO x Thin Films

    International Nuclear Information System (INIS)

    Khare, Amit; Shin, Dongwon; Yoo, Tae Sup; Kim, Minu; Kang, Tae Dong

    2017-01-01

    Multivalent transition metal oxides provide fascinating and rich physics related to oxygen stoichiometry. In particular, the adoptability of various valence states of transition metals enables perovskite oxides to display mixed (oxygen) ionic and electronic conduction and catalytic activity useful in many practical applications, including solid-oxide fuel cells (SOFCs), rechargeable batteries, gas sensors, and memristive devices. For proper realization of the ionic conduction and catalytic activity, it is essential to understand the reversible oxidation and reduction process, which is governed by oxygen storage/release steps in oxides. Topotactic phase transformation facilitates the redox process in perovskites with specific oxygen vacancy ordering by largely varying the oxygen concentration of a material without losing the lattice framework. The concentration and diffusion of oxide ions (O 2– ), the valence state of the transition metal cations, and the thermodynamic structural integrity together provide fundamental understanding and ways to explicitly control the redox reaction.[6] In addition, it offers an attractive route for tuning the emergent physical properties of transition metal oxides, via strong coupling between the crystal lattice and electronic structure.

  14. Volume-based considerations for the metal-insulator transition of CMR oxides

    Energy Technology Data Exchange (ETDEWEB)

    Neumeier, J.J. [Florida Atlantic Univ., Boca Raton, FL (United States). Dept. of Physics]|[Los Alamos National Lab., NM (United States). Condensed Matter and Thermal Physics Group; Hundley, M.F.; Cornelius, A.L. [Los Alamos National Lab., NM (United States). Condensed Matter and Thermal Physics Group; Andres, K. [Walther-Meissner-Inst. fuer Tieftemperaturforschung, Garching (Germany)

    1998-03-01

    The sensitivity of {rho} [electrical resistivity] to changes in volume which occur through: (1) applied pressure, (2) variations in temperature, and (3) phase transitions, is evaluated for some selected CMR oxides. It is argued that the changes in volume associated with phase changes are large enough to produce self pressures in the range of 0.18 to 0.45 GPa. The extreme sensitivity of the electrical resistivity to pressure indicates that these self pressures are responsible for large features in the electrical resistivity and are an important component for occurrence the metallicity below {Tc}. It is suggested that this is related to a strong volume dependence of the electron phonon coupling in the CMR oxides.

  15. The magnetic response at the metal-insulator transition in La1 - xSrxTiO3 (abstract)

    Science.gov (United States)

    Osborn, R.; Aronson, M. C.; Goremychkin, E. A.; Greedan, J. E.

    1996-04-01

    We report on recent inelastic neutron scattering measurements of the magnetic response close to the metal-insulator transition in La1-xSrxTiO3. Specific heat and susceptibility data from Tokura et al. give evidence for a divergent effective mass at the critical concentration xc=0.05 in agreement with recent mean-field theories of the transition. The mass enhancement is believed to arise from the formation of a d-electron resonance at the Fermi energy close to the transition. The aim of this investigation is to look for evidence of this resonance in the dynamic magnetic susceptibility. We studied samples with x=0, 0.05, and 0.2 using incident energies between 25 and 200 meV. After correction for the phonon scattering, we observe a broad response above a threshold of 20-30 meV extending to over 100 meV. In addition, the Mott insulating antiferromagnet (x=0) has a peak at 40 meV, consistent with the estimated activation energy derived from resistivity measurements. This feature becomes washed out with temperature and doping. Possible origins for this peak are discussed.

  16. Correlation-driven metal-insulator transition in proximity to an iron-based superconductor

    Science.gov (United States)

    Charnukha, A.; Yin, Z. P.; Song, Y.; Cao, C. D.; Dai, Pengcheng; Haule, K.; Kotliar, G.; Basov, D. N.

    2017-11-01

    We report the direct spectroscopic observation of a metal to correlated-insulator transition in the family of iron-based superconducting materials. By means of optical spectroscopy we demonstrate that the excitation spectrum of NaFe1 -xCuxAs develops a large gap with increasing copper substitution. Dynamical mean-field theory calculations show a good agreement with the experimental data and suggest that the formation of the charge gap requires an intimate interplay of strong on-site electronic correlations and spin-exchange coupling, revealing the correlated Slater-insulator nature of the antiferromagnetic ground state. Our calculations further predict the high-temperature paramagnetic state of the same compound to be a highly incoherent correlated metal. We verify this prediction experimentally by showing that the doping-induced weakening of antiferromagnetic correlations enables a thermal crossover from an insulating to an incoherent metallic state. Redistribution of the optical spectral weight in this crossover uncovers the characteristic energy of Hund's-coupling and Mott-Hubbard electronic correlations essential for the electronic localization. Our results demonstrate that NaFe1 -xCuxAs continuously transitions from the typical itinerant phases of iron pnictides to a highly incoherent metal and ultimately a correlated insulator. Such an electronic state is expected to favor high-temperature superconductivity.

  17. Field-induced quantum metal-insulator transition in the pyrochlore iridate Nd2Ir2O7

    Science.gov (United States)

    Tian, Zhaoming; Kohama, Yoshimitsu; Tomita, Takahiro; Ishizuka, Hiroaki; Hsieh, Timothy H.; Ishikawa, Jun J.; Kindo, Koichi; Balents, Leon; Nakatsuji, Satoru

    2016-02-01

    The metal-insulator transition (MIT) is a hallmark of strong correlation in solids. Quantum MITs at zero temperature have been observed in various systems tuned by either carrier doping or bandwidth. However, such transitions have rarely been induced by application of magnetic field, as normally the field scale is too small in comparison with the charge gap, whose size is a fraction of the Coulomb repulsion energy (~1 eV). Here we report the discovery of a quantum MIT tuned by a field of ~10 T, whose magnetoresistance exceeds 60,000%. In particular, our anisotropic magnetotransport measurements on the cubic insulator Nd2Ir2O7 (ref. ) reveal that the insulating state can be suppressed by such a field to a zero-temperature quantum MIT, but only for fields near the [001] axis. The strong sensitivity to the field direction is remarkable for a cubic crystal, as is the fact that the MIT can be driven by such a small magnetic field, given the 45 meV gap energy, which is of order of 50 times the Zeeman energy for an Ir4+ spin. The systematic change in the MIT from continuous near zero field to first order under fields indicates the existence of a tricritical point proximate to the quantum MIT. We argue that these phenomena imply both strong correlation effects on the Ir electrons and an active role for the Nd spins.

  18. Hartree-Fock study of the Anderson metal-insulator transition in the presence of Coulomb interaction: Two types of mobility edges and their multifractal scaling exponents

    Science.gov (United States)

    Lee, Hyun-Jung; Kim, Ki-Seok

    2018-04-01

    We investigate the role of Coulomb interaction in the multifractality of Anderson metal-insulator transition, where the Coulomb interaction is treated within the Hartree-Fock approximation, but disorder effects are taken into account exactly. An innovative technical aspect in our simulation is to utilize the Ewald-sum technique, which allows us to introduce the long-range nature of the Coulomb interaction into Hartree-Fock self-consistent equations of order parameters more accurately. This numerical simulation reproduces the Altshuler-Aronov correction in a metallic state and the Efros-Shklovskii pseudogap in an insulating phase, where the density of states ρ (ω ) is evaluated in three dimensions. Approaching the quantum critical point of a metal-insulator transition from either the metallic or insulting phase, we find that the density of states is given by ρ (ω ) ˜|ω| 1 /2 , which determines one critical exponent of the McMillan-Shklovskii scaling theory. Our main result is to evaluate the eigenfunction multifractal scaling exponent αq, given by the Legendre transformation of the fractal dimension τq, which characterizes the scaling behavior of the inverse participation ratio with respect to the system size L . Our multifractal analysis leads us to identify two kinds of mobility edges, one of which occurs near the Fermi energy and the other of which appears at a high energy, where the density of states at the Fermi energy shows the Coulomb-gap feature. We observe that the multifractal exponent at the high-energy mobility edge remains to be almost identical to that of the Anderson localization transition in the absence of Coulomb interactions. On the other hand, we find that the multifractal exponent near the Fermi energy is more enhanced than that at the high-energy mobility edge, suspected to result from interaction effects. However, both the multifractal exponents do not change even if the strength of the Coulomb interaction varies. We also show that the

  19. Metal Insulator Transition of Cr doped V2O3 calculated by hybrid density functional

    OpenAIRE

    Guo, Yuzheng; Clark, Stewart J.; Robertson, John

    2013-01-01

    The electronic structure of vanadium sesquioxide in its different phases has been calculated using the screened exchange (sX) hybrid functional. The hybrid functional reproduces the electronic properties of all three phases, the paramagnetic metal (PM) phase, the anti-ferromagnetic insulating phase, and the Cr-doped paramagnetic insulating (PI) phase. A fully relaxed supercell model of Cr-doped V2O3 has a polaronic distortion around the substitutional Cr atoms and this local strain drives the...

  20. Orbital electronic occupation effect on metal-insulator transition in Ti x V1-x O2

    Science.gov (United States)

    Huang, Kang; Meng, Yifan; Xu, XiaoFeng; Chen, Pingping; Lu, Aijiang; Li, Hui; Wu, Binhe; Wang, Chunrui; Chen, Xiaoshuang

    2017-09-01

    A series of Ti x V1-x O2 (0%  ⩽  x  ⩽  4.48%) thin films on c-plane sapphire substrates have been fabricated by co-sputtering oxidation solutions, and the metal-insulator transition temperature (T MIT) of Ti x V1-x O2 films rises monotonically at the rate of 1.64 K/at.% Ti. The x-ray diffraction measurement results show that, after Ti4+ ion doping, the rutile structure expands along the c r axis while shrinking along the a r and b r axis simultaneously. It makes the V-O bond length shorter, which is believed to upshift the π * orbitals. The rising of π * orbitals in Ti-doped VO2 has been illustrated by ultraviolet-infrared spectroscopy and first-principles calculation. With the Ti4+ ion doping concentration increasing, the energy levels of π * orbitals are elevated and the electronic occupation of π * orbitals decreases, which weakens the shielding for the strong electron-electron correlations in the d|| orbital and result in the T MIT rising. The research reveals that the T MIT of VO2 can be effected by the electronic occupancy of π * orbitals in a rutile state, which is helpful for developing VO2-based thermal devices.

  1. Metal-insulator transition in Pt-C nanowires grown by focused-ion-beam-induced deposition

    International Nuclear Information System (INIS)

    Fernandez-Pacheco, A.; Ibarra, M. R.; De Teresa, J. M.; Cordoba, R.

    2009-01-01

    We present a study of the transport properties of Pt-C nanowires created by focused-ion-beam (FIB)-induced deposition. By means of the measurement of the resistance while the deposit is being performed, we observe a progressive decrease in the nanowire resistivity with thickness, changing from 10 8 μΩ cm for thickness ∼20 nm to a lowest saturated value of 700 μΩ cm for thickness >150 nm. Spectroscopy analysis indicates that this dependence on thickness is caused by a gradient in the metal-carbon ratio as the deposit is grown. We have fabricated nanowires in different ranges of resistivity and studied their conduction mechanism as a function of temperature. A metal-insulator transition as a function of the nanowire thickness is observed. The results will be discussed in terms of the Mott-Anderson theory for noncrystalline materials. An exponential decrease in the conductance with the electric field is found for the most resistive samples, a phenomenon understood by the theory of hopping in lightly doped semiconductors under strong electric fields. This work explains the important discrepancies found in the literature for Pt-C nanostructures grown by FIB and opens the possibility to tune the transport properties of this material by an appropriate selection of the growth parameters.

  2. Observation of a Pseudogap in the Vicinity of the Metal-Insulator Transition in the Perovskite-type Vanadium Oxides Nd1-xSrxVO3

    Science.gov (United States)

    Yamamoto, Shintaro; Ootsuki, Daiki; Shimonaka, Daiya; Shibata, Daisuke; Kodera, Kenjiro; Okawa, Mario; Saitoh, Tomohiko; Horio, Masafumi; Fujimori, Atsushi; Kumigashira, Hiroshi; Ono, Kanta; Ikenaga, Eiji; Miyasaka, Shigeki; Tajima, Setsuko; Yoshida, Teppei

    2018-02-01

    We have performed a photoemission study of the Mott-Hubbard system Nd1-xSrxVO3 (x = 0.20 and 0.30) to investigate the electronic structure in the vicinity of the metal-insulator transition. By using bulk sensitive hard X-ray photoemission spectroscopy, we have observed a large coherent spectral weight near the Fermi level compared to those observed with surface-sensitive low photons. In particular, a pseudogap with an energy of ˜0.2 eV has been observed near the Fermi level, which is consistent with a prediction with a dynamical cluster approximation calculation. In order to understand the characteristic features in the Mott-Hubbard-type metal-insulator transition, particularly the pseudogap opening at x = 0.2 and 0.3, a phenomenological model of the self-energy has been proposed.

  3. Metal-insulator-superconductor transition of spin-3/2 atoms on optical lattices

    Science.gov (United States)

    De Silva, Theja N.

    2018-01-01

    We use a slave-rotor approach within a mean-field theory to study the competition of metallic, Mott-insulating, and superconducting phases of spin-3/2 fermions subjected to a periodic optical lattice potential. In addition to the metallic, the Mott-insulating, and the superconducting phases that are associated with the gauge symmetry breaking of the spinon field, we identify an emerging superconducting phase that breaks both roton and spinon field gauge symmetries. This superconducting phase emerges as a result of the competition between spin-0 singlet and spin-2 quintet interaction channels naturally available for spin-3/2 systems. The two superconducting phases can be distinguished from each other by quasiparticle weight. We further discuss the properties of these phases for both two-dimensional square and three-dimensional cubic lattices at zero and finite temperatures.

  4. Sharpness and intensity modulation of the metal-insulator transition in ultrathin VO2 films by interfacial structure manipulation

    Science.gov (United States)

    McGee, Ryan; Goswami, Ankur; Pal, Soupitak; Schofield, Kalvin; Bukhari, Syed Asad Manzoor; Thundat, Thomas

    2018-03-01

    Vanadium dioxide (VO2) undergoes a structural transformation from monoclinic (insulator) to tetragonal (metallic) upon heating above 340 K, accompanied by abrupt changes to its electronic, optical, and mechanical properties. Not only is this transition scientifically intriguing, but there are also numerous applications in sensing, memory, and optoelectronics. Here we investigate the effect different substrates and the processing conditions have on the characteristics metal-insulator transition (MIT), and how the properties can be tuned for specific applications. VO2 thin films were grown on c -plane sapphire (0001) and p-type silicon by pulsed laser deposition. High-resolution x-ray diffraction along with transmission electron microscopy reveals textured epitaxial growth on sapphire by domain-matching epitaxy, while the presence of a native oxide layer on silicon prevented any preferential growth resulting in a polycrystalline film. An orientation relationship of (010)VO2|| (0001)Al 2O3 was established for VO2 grown on sapphire, while no such relationship was found for VO2 grown on silicon. Surface-energy minimization is the driving force behind grain growth, as the lowest energy VO2 plane grew on silicon, while on sapphire the desire for epitaxial growth was dominant. Polycrystallinity of films grown on silicon caused a weaker and less prominent MIT than observed on sapphire, whose MIT was higher in magnitude and steeper in slope. The position of the MIT was shown to depend on the competing effects of misfit strain and grain growth. Higher deposition temperatures caused an increase in the MIT, while compressive strain resulted in a decreased MIT.

  5. Conductance fluctuations and distribution at metal-insulator transition induced by electric field in disordered chain

    International Nuclear Information System (INIS)

    Senouci, Khaled

    2000-08-01

    A simple Kronig-Penney model for 1D mesoscopic systems with δ peak potentials is used to study numerically the influence of a constant electric field on the conductance fluctuations and distribution at the transition. We found that the conductance probability distribution has a system-size independent form with large fluctuations in good agreement with the previous works in 2D and 3D systems. (author)

  6. Temperature-dependent photoemission and x-ray absorption studies of the metal-insulator transition in Bi1-xLaxNiO3

    Science.gov (United States)

    Wadati, Hiroki; Tanaka, Kiyohisa; Fujimori, Atsushi; Mizokawa, Takashi; Kumigashira, Hiroshi; Oshima, Masaharu; Ishiwata, Shintaro; Azuma, Masaki; Takano, Mikio

    2007-11-01

    Perovskite-type BiNiO3 is an insulating antiferromagnet in which a charge disproportionation occurs at the Bi site. La substitution for Bi suppresses the charge disproportionation and makes the system metallic, and for 0.05≤x≤0.1 a broad metal-insulator transition (MIT) occurs as a function of temperature. We have measured the temperature dependence of the photoemission and x-ray absorption (XAS) spectra of Bi1-xLaxNiO3 to investigate how the electronic structure changes across the MIT. From the Ni2p XAS spectra of x=0.05 , we found almost no change in the valence of Ni across the MIT. In the valence-band photoemission spectra, the Fermi cutoff disappeared for x=0.05 at a low temperature, whereas for x=0.1 and 0.2, it remained at all temperatures but the intensity at the Fermi level decreased gradually with decreasing temperature. Our experimental results suggest that the MIT is caused by the localization of holes in the O2p band and that the “insulating” phase below the MIT is indeed a mixture of insulating and metallic regions.

  7. Tuning the metal-insulator transition in NdNiO3 thin films

    Science.gov (United States)

    Shiyani, T.; Shekhada, K. G.; Savaliya, C. R.; Markna, J. H.

    2017-05-01

    The RNiO3 (R is rare earth) perovskites are famous for their metal to insulator transition (MIT). The temperature can be transformed and depends on the nature of the rare earth. The MIT in thin films and heterostructures of RNiO3 propose the chance to control the MIT as a function of thickness via strain using different substrates. We have reported the electrical transport properties of NdNiO3/NdGaO3, and NNO/NGO/STO structures. These structures were fabricated by pulsed laser deposition (PLD) method. The temperature of the MIT changes from 155K to 195 K. The electrical resistivity of the heterostructures undergoes MIT, depending on the thickness and deposition conditions. Thickness and deposition temperature were found to have a great impact on the electrical transport properties. The shift in TMI changes with thickness and it larger for thinner NdNiO3. The MIT of NNO thin films is responsive to strain and its partial relaxation creates an inhomogeneous strain field that broadens the MIT. This study may be potentially applicable to Mott transistor devices.

  8. Probing the Metal-Insulator Transition in BaTiO3 by Electrostatic Doping

    Science.gov (United States)

    Raghavan, Santosh; Zhang, Jack Y.; Shoron, Omor F.; Stemmer, Susanne

    2016-07-01

    The metal-to-insulator transition in BaTiO3 is investigated using electrostatic doping, which avoids effects from disorder and strain that would accompany chemical doping. SmTiO3/BaTiO3/SrTiO3 heterostructures are doped with a constant sheet carrier density of 3 ×1014 cm-2 that is introduced via the polar SmTiO3/BaTiO3 interface. Below a critical BaTiO3 thickness, the structures exhibit metallic behavior with high carrier mobilities at low temperatures, similar to SmTiO3/SrTiO3 interfaces. Above this thickness, data indicate that the BaTiO3 layer becomes ferroelectric. The BaTiO3 lattice parameters increase to a value consistent with a strained, tetragonal unit cell, the structures are insulating below ˜125 K , and the mobility drops by more than an order of magnitude, indicating self-trapping of carriers. The results shed light on the interplay between charge carriers and ferroelectricity.

  9. Metal-insulator transition in vanadium dioxide and titanium oxide using the three-dimensional periodic shell model and DV-X

    Science.gov (United States)

    Nakatsugawa, Hiroshi

    The purpose of this study is to calculate electronic structures of the metallic and insulating phases of vanadium dioxide and titanium sesquioxide by using a combination of the three-dimensional periodic shell model and the discrete-variational (DV)-X alpha cluster method. When temperature decreases, vanadium dioxide undergoes a crystallographic phase transition and a metal-insulator (MI) transition at 340K. Unlike the clear cut MI transition in vanadium dioxide, titanium sesquioxide exhibits a broad crossover between a metallic and an insulating state around 450K, which is also an MI transition. Since the DV-X alpha cluster method can calculate the energies of electron states, the combination of the periodic shell model and the cluster method must contain the possibility to clarify the origin of the MI transition in vanadium dioxide and titanium sesquioxide from the energetic point of view. Therefore, the calculation using this combination is of great significance in order to understand the very important phenomena of vanadium dioxide and titanium sesquioxide, particularly the MI transition. Besides the effects of intersite repulsive nearest neighbor electron-electron (d-d) Coulombic interaction and the spin-spin interaction by means of a generalized Hubbard Hamiltonian, the Hamiltonian in the insulating phase includes Anderson's attractive potential due to the electron-phonon interaction which stabilize the three-dimensional periodic distribution of cation pairs. The shell model estimates the electron-phonon coupling constants and provides direct theoretical evidence that the three- dimensional periodic distribution of cation pairs are stabilized in the insulating phase. In addition, the DV-X alpha cluster method calculates the electron energy in clusters, the values for the intersite repulsive nearest- neighbor d-d interaction, and the spin- spin interaction. In vanadium dioxide, the electron-phonon interaction effect and the correlation effect for 3d electrons

  10. Internally shunted Josephson junctions with barriers tuned near the metal-insulator transition for RSFQ logic applications

    Energy Technology Data Exchange (ETDEWEB)

    Yu Lei [Department of Electrical Engineering, Arizona State University, Tempe, AZ 85287-6006 (United States); Gandikota, Raghuram [Chemical and Materials Engineering, Arizona State University, Tempe, AZ 85287-6006 (United States); Singh, Rakesh K [Chemical and Materials Engineering, Arizona State University, Tempe, AZ 85287-6006 (United States); Gu Lin [Center for Solid State Science, Arizona State University, Tempe, AZ 85287 (United States); Smith, David J [Center for Solid State Science, Arizona State University, Tempe, AZ 85287 (United States); Meng Xiaofan [Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, CA 94720 (United States); Zeng Xianghui [Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, CA 94720 (United States); Duzer, Theodore van [Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, CA 94720 (United States); Rowell, John M [Chemical and Materials Engineering, Arizona State University, Tempe, AZ 85287-6006 (United States); Newman, N [Department of Electrical Engineering, Arizona State University, Tempe, AZ 85287-6006 (United States)

    2006-08-15

    The fabrication of self-shunted SNS (superconductor/normal conductor/superconductor) Josephson junctions for rapid single flux quantum (RSFQ) logic could potentially facilitate increased circuit density, as well as reduced parasitic capacitance and inductance over the currently used externally shunted SIS (superconductor/insulator/superconductor) trilayer junction process. We report the deposition, fabrication, and device characterization of Josephson junctions prepared with Nb{sub 1-y}Ti{sub y}N electrodes and Ta{sub x}N barriers tuned near the metal-insulator transition, deposited on practical large-area oxide-buffered silicon wafers. When scaled to practical device dimensions, this type of junction is found to have an I{sub c}R{sub n} product of over 0.5 mV and a critical current (I{sub c}) and normal resistance (R{sub n}) of magnitudes suitable for single flux quantum digital circuits. A longer than expected normal-metal coherence length ({xi}{sub n}) of 5.8 nm is inferred from the thickness dependence of J{sub c} at 4.2 K for junctions fabricated using a barrier resistivity of 13 m{omega} cm. Although not well understood and not quantitatively predicted by conventional theories, this results in a sufficiently high I{sub c} and I{sub c}R{sub n} to make the junctions suitable for practical applications. Similar observations of unexpectedly large Josephson coupling currents in SNS junctions have been documented in other systems, particularly in cases when the barrier is near the M-I transition, and have become known as the giant proximity effect. The temperature dependence of {xi}{sub n}, I{sub c}R{sub n}, and J{sub c} are also reported. For this technology to be used in practical applications, significant improvements in our fabrication process are needed as we observe large variations in I{sub c} and R{sub n} values across a 100 mm wafer, presumably as a result of variations in the Ta:N stoichiometry and the resulting changes in the Ta{sub x}N barrier

  11. Strain-induced metal-insulator phase coexistence in perovskite manganites.

    Science.gov (United States)

    Ahn, K H; Lookman, T; Bishop, A R

    2004-03-25

    The coexistence of distinct metallic and insulating electronic phases within the same sample of a perovskite manganite, such as La(1-x-y)Pr(y)Ca(x)MnO3, presents researchers with a tool for tuning the electronic properties in materials. In particular, colossal magnetoresistance in these materials--the dramatic reduction of resistivity in a magnetic field--is closely related to the observed texture owing to nanometre- and micrometre-scale inhomogeneities. Despite accumulated data from various high-resolution probes, a theoretical understanding for the existence of such inhomogeneities has been lacking. Mechanisms invoked so far, usually based on electronic mechanisms and chemical disorder, have been inadequate to describe the multiscale, multiphase coexistence within a unified picture. Moreover, lattice distortions and long-range strains are known to be important in the manganites. Here we show that the texturing can be due to the intrinsic complexity of a system with strong coupling between the electronic and elastic degrees of freedom. This leads to local energetically favourable configurations and provides a natural mechanism for the self-organized inhomogeneities over both nanometre and micrometre scales. The framework provides a physical understanding of various experimental results and a basis for engineering nanoscale patterns of metallic and insulating phases.

  12. Detailed Mapping of the Local Ir4+ Dimers through the Metal-Insulator Transitions of CuIr2S4 Thiospinel by X-Ray Atomic Pair Distribution Function Measurements

    Science.gov (United States)

    Božin, E. S.; Masadeh, A. S.; Hor, Y. S.; Mitchell, J. F.; Billinge, S. J. L.

    2011-01-01

    The evolution of the short-range structural signature of the Ir4+ dimer state in CuIr2S4 thiospinel has been studied across the metal-insulator phase transitions as the metallic state is induced by temperature, Cr doping, and x-ray fluence. An atomic pair distribution function (PDF) approach reveals that there are no local dimers that survive into the metallic phase when this is invoked by temperature and doping. The PDF shows Ir4+ dimers when they exist, regardless of whether or not they are long-range ordered. At 100 K, exposure to a 98 keV x-ray beam melts the long-range dimer order within a few seconds, though the local dimers remain intact. This shows that the metallic state accessed on warming and doping is qualitatively different from the state obtained under x-ray irradiation.

  13. Detailed mapping of the local Ir{sup 4+} dimers through the metal-insulator transitions of CuIr{sub 2}S{sub 4} thiospinel by x-ray atomic pair distribution function measurements.

    Energy Technology Data Exchange (ETDEWEB)

    Bozin, E. S.; Masadeh, A. S.; Hor, Y. S.; Mitchell, J. F.; Billinge, S. J. L.; Materials Science Division; BNL; Michigan State Univ.; Univ. of Jordan; Columbia Univ.

    2011-01-24

    The evolution of the short-range structural signature of the Ir{sup 4+} dimer state in CuIr{sub 2}S{sub 4} thiospinel has been studied across the metal-insulator phase transitions as the metallic state is induced by temperature, Cr doping, and x-ray fluence. An atomic pair distribution function (PDF) approach reveals that there are no local dimers that survive into the metallic phase when this is invoked by temperature and doping. The PDF shows Ir{sup 4+} dimers when they exist, regardless of whether or not they are long-range ordered. At 100 K, exposure to a 98 keV x-ray beam melts the long-range dimer order within a few seconds, though the local dimers remain intact. This shows that the metallic state accessed on warming and doping is qualitatively different from the state obtained under x-ray irradiation.

  14. Numerical simulations of quantum many-body systems with applications to superfluid-insulator and metal-insulator transitions

    International Nuclear Information System (INIS)

    Niyaz, P.

    1993-01-01

    Quantum Monte Carlo techniques were used to study two quantum many-body systems, the one-dimensional extended boson-Hubbard Hamiltonian, a model of superfluid-insulator quantum phase transitions, and the two-dimensional Holstein Model, a model for electron-phonon interactions. For the extended boson-Hubbard model, the authors studied the ground state properties at commensurate filling (density = 1) and half-integer filling (density = 1/2). At commensurate filling, the system has two possible insulating phases for strong coupling. If the on-site repulsion dominates, the system freezes into an insulating phase where each site is singly occupied. If the intersite repulsion dominates, doubly occupied and empty sites alternate. At weak coupling, the system becomes a superfluid. The authors investigated the order of phase transitions between these different phases. At half-integer filling, the authors found one strong coupling insulating phase, where singly occupied and empty sites alternate, and a weak coupling superfluid phase. The authors also investigated the possibility of a supersolid phase and found no clear evidence of such a new phase. For the electron-phonon (Holstein) model, the authors focused on the finite temperature phase transition from a metallic state to an insulating charge density wave (CDW) state as the temperature is lowered. The authors present the first calculation of the spectral density from Monte Carlo data for this system. The authors also investigated the formation of a CDW state as a function of various parameters characterizing the electron-phonon interactions. Using these numerical results as benchmarks, the authors then investigated different levels of Migdal approximations. The authors found the solutions of a set of gapped Migdal-Eliashberg equations agreed qualitatively with the Monte Carlo results

  15. Density of states and spatially inhomogeneous conductance near the metal-insulator transition in Pr{sub 0.68}Pb{sub 0.32}MnO{sub 3} single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Wirth, S; Roessler, Sahana; Ernst, S; Steglich, F [Max Planck Institute for Chemical Physics of Solids, Noethnitzer Strasse 40, 01187 Dresden (Germany); Padmanabhan, B; Bhat, H L; Elizabeth, Suja [Department of Physics, Indian Institute of Science, Bangalore 560012 (India)

    2008-10-29

    Single crystals of Pr{sub 0.68}Pb{sub 0.32}MnO{sub 3} have been investigated by scanning tunneling microscopy over a broad temperature range. In this material, a distinct separation of the ferromagnetic and the metal-insulator transition temperature, T{sub C}{approx}210 K and T{sub MI}{approx}255 K, respectively, was observed. Spectroscopic tunneling studies revealed that even on a local scale the system switches from predominantly metallic to insulating within a narrow temperature range around T{sub MI}. Inhomogeneities of the zero-bias conductance with small patches of metallic clusters on a length scale of 2-3 nm, however, were only observed within the temperature range T{sub C}phase separation in the paramagnetic metallic state, but homogeneous ferromagnetic and insulating states.

  16. Isotope effect on metal-insulator transition of (EDO-TTF) 2XF 6 (X = P, As) with multi-instability of metallic state

    Science.gov (United States)

    Nakano, Yoshiaki; Balodis, Karlis; Yamochi, Hideki; Saito, Gunzi; Uruichi, Mikio; Yakushi, Kyuya

    2008-12-01

    The partially deuterated 4,5-ethylenedioxy-tetrathiafulvalene- d2 (EDO-TTF- d2) was synthesized from the undeuterated EDO-TTF- d0. The single crystals of (EDO-TTF- d2) 2XF 6 (X = P, As) were prepared by the conventional electrocrystallization technique. The deuterium contents of EDO-TTF- d2 itself and the radical cation salts were 99% D by mass spectral analysis. The magnetic susceptibility measurement revealed that (EDO-TTF- d2) 2XF 6 undergoes a metal-insulator transition at 2-3 K higher temperature than the undeuterated salts. In infrared and Raman spectra, significant isotope shifts were observed not only on C-H vibrational modes but also on TTF-skeletal modes. The assignment of experimental bands was performed on the basis of normal-mode analysis at B3LYP/6-31G(d,p) level of theory.

  17. The one-particle scenario for the metal-insulator transition in two-dimensional systems at T = 0

    CERN Document Server

    Tarasov, Y V

    2003-01-01

    The conductance of bounded disordered electron systems is calculated by reducing the original dynamic problem of arbitrary dimensionality to a set of strictly one-dimensional problems for one-particle mode propagators. The metallic ground state of a two-dimensional conductor, which is considered as a limiting case of three-dimensional quantum waveguide, is shown to result from its multi-modeness. As the waveguide thickness is reduced, e.g., by applying a 'pressing' potential, the electron system undergoes a set of continuous phase transitions related to discrete variations of the number of extended modes. The closing of the last current carrying mode is regarded as a phase transition of the electron system from metallic to dielectric state. The obtained results agree qualitatively with the observed 'anomalies' of resistivity of different two-dimensional electron and hole systems.

  18. Temperature and electric field induced metal-insulator transition in atomic layer deposited VO2 thin films

    Science.gov (United States)

    Tadjer, Marko J.; Wheeler, Virginia D.; Downey, Brian P.; Robinson, Zachary R.; Meyer, David J.; Eddy, Charles R.; Kub, Fritz J.

    2017-10-01

    Amorphous vanadium oxide (VO2) films deposited by atomic layer deposition (ALD) were crystallized with an ex situ anneal at 660-670 °C for 1-2 h under a low oxygen pressure (10-4 to 10-5 Torr). Under these conditions the crystalline VO2 phase was maintained, while formation of the V2O5 phase was suppressed. Electrical transition from the insulator to the metallic phase was observed in the 37-60 °C range, with an ROFF/RON ratio of up to about 750 and ΔTC ≅ 7-10 °C. Lateral electric field applied across two-terminal device structures induced a reversible phase change, with a room temperature transition field of about 25 kV/cm in the VO2 sample processed with the 2 h long O2 anneal. Both the width and slope of the field induced MIT I-V hysteresis were dependent upon the VO2 crystalline quality.

  19. Charge driven metal-insulator transitions in LaMnO3|SrTiO3 (111) superlattices

    KAUST Repository

    Cossu, Fabrizio

    2017-08-01

    Interfaces of perovskite oxides, due to the strong interplay between the lattice, charge and spin degrees of freedom, can host various phase transitions, which is particularly interesting if these transitions can be tuned by external fields. Recently, ferromagnetism was found together with a seemingly insulating state in superlattices of manganites and titanates. We therefore study the (111) oriented $(\\\\text{LaMnO}_3)_{6-x}\\\\vert(\\\\text{SrTiO}_3)_{6+x}~(x = -0.5, 0, 0.5)$ superlattices by means of ab initio calculations, predicting a ferromagnetic ground state due to double exchange in all cases. We shed light on the ferromagnetic coupling in the LaMnO3 region and at the interfaces. The insulating states of specific superlattices can be understood on the basis of Jahn-Teller modes and electron/hole doping.

  20. Local structural aspects of the metal-insulator transition in CuIr2S4 from total scattering x-ray study

    Science.gov (United States)

    Bozin, E.; Masadeh, A. S.; Kim, H. J.; Juhas, P.; Billinge, S. J. L.; Mitchell, J. F.

    2008-03-01

    A thiospinel CuIr2S4 exhibits a metal-insulator (MI) transition at T=230 K, with simultaneous spin-dimerization and charge-ordering [1]. The transition can also be driven by extended exposure to the x-rays at low T [2, 3]. Total x-ray scattering study of CuIr2S4 was carried out using 100 KeV synchrotron beam and rapid acquisition pair distribution function (RAPDF) approach. The RAPDF results indicate consistency of the local and average structure at high T. At 100 K long x-ray exposure melts the long-range order (LRO) of the dimerization pattern, without affecting the local structure, in agreement with diffuse scattering result [3]. The dependence of the LRO related superlattice peak intensity on the exposure time reveals that the melting occurs within approximately 15 seconds of exposure under experimental conditions used. At 100 K the LRO is recovered without temperature increase quickly after the cessation of the beamtime exposure. Results on Cr doped samples will be addressed as well. [1] P.G. Radaelli et al., Nature 416, 155 (2002). [2] V. Kiryukhin et al., Phys. Rev. Lett. 97, 225503 (2006). [3] H. Ishibashi et al., Phys. Rev. B 66, 144424 (2002). This work is supported by the NSF under grant DMR-0304391. ANL is supported under DOE contract No. DE-AC02-06CH11357.

  1. Enhanced Metal-Insulator Transition Performance in Scalable Vanadium Dioxide Thin Films Prepared Using a Moisture-Assisted Chemical Solution Approach.

    Science.gov (United States)

    Liang, Weizheng; Gao, Min; Lu, Chang; Zhang, Zhi; Chan, Cheuk Ho; Zhuge, Lanjian; Dai, Jiyan; Yang, Hao; Chen, Chonglin; Park, Bae Ho; Jia, Quanxi; Lin, Yuan

    2018-03-07

    Vanadium dioxide (VO 2 ) is a strong-correlated metal-oxide with a sharp metal-insulator transition (MIT) for a range of applications. However, synthesizing epitaxial VO 2 films with desired properties has been a challenge because of the difficulty in controlling the oxygen stoichiometry of VO x , where x can be in the range of 1 < x < 2.5 and V has multiple valence states. Herein, a unique moisture-assisted chemical solution approach has been developed to successfully manipulate the oxygen stoichiometry, to significantly broaden the growth window, and to significantly enhance the MIT performance of VO 2 films. The obvious broadening of the growth window of stoichiometric VO 2 thin films, from 4 to 36 °C, is ascribed to a self-adjusted process for oxygen partial pressure at different temperatures by introducing moisture. A resistance change as large as 4 orders of magnitude has been achieved in VO 2 thin films with a sharp transition width of less than 1 °C. The much enhanced MIT properties can be attributed to the higher and more uniform oxygen stoichiometry. This technique is not only scientifically interesting but also technologically important for fabricating wafer-scaled VO 2 films with uniform properties for practical device applications.

  2. Reflectance study on the metal-insulator transition driven by crystallinity change in poly(3,4-ethylenedioxy thiophene)/poly(styrenesulfonate) films

    International Nuclear Information System (INIS)

    Cho, Shinuk; Park, Sungheum; Lee, Kwanghee

    2005-01-01

    We report optical reflectance, R(ω), studies on free-standing films of poly(3,4-ethylene dioxy thiophene)/poly(style ne sulfonate) (PEDOT-PSS) measured over a range from 0.02 - 5.0 eV. When the PEDOT-PSS films were prepared at an elevated temperature of 60 .deg. C, the films exhibit an increased dc-conductivity (σ dc ∼ 104 S/cm) and an optical conductivity, σ(ω), in the intraband transitions below 1.0 eV as compared with the films prepared at room temperature (σ dc ∼ 47 S/cm). Detailed analysis of σ(ω) in terms of the 'localization-modified Drude (LMD) model' demonstrated that the heat-treated PEDOT-PSS was a disordered metal near the metal-insulator transition (MIT) while the as-grown films could be better described as a Fermi glass on the insulating side of MIT. The heat-annealing process increased the degree of crystallinity of the films, thereby inducing a MIT near the critical limit.

  3. Unexpected metal-insulator transition in thick Ca1-xSrxVO3 film on SrTiO3 (100) single crystal

    Science.gov (United States)

    Takayanagi, Makoto; Tsuchiya, Takashi; Namiki, Wataru; Ueda, Shigenori; Minohara, Makoto; Horiba, Koji; Kumigashira, Hiroshi; Terabe, Kazuya; Higuchi, Tohru

    2018-03-01

    Epitaxial Ca1-xSrxVO3 (0 ≦ x ≦ 1) thin films were grown on (100)-oriented SrTiO3 substrates by using the pulsed laser deposition technique. In contrast to the previous report that metal-insulator transition (MIT) in Ca1-xSrxVO3 (CSVO) was achieved only for extremely thin films (several nm thick), MIT was observed at 39, 72, and 113 K for films with a thickness of 50 nm. The electronic structure was investigated by hard and soft X-ray photoemission spectroscopy (HX-PES and SX-PES). The difference between these PES results was significant due to the variation in an escape depth of photoelectrons of PES. While HX-PES showed that the V 2p3/2 spectra consisted of four peaks (V5+, V4+, V3+, and V2+/1+), SX-PES showed only three peaks (V5+, V4+, and V3+). This difference can be caused by a strain from the substrate, which leads to the chemical disorder (V5+, V4+, V3+, and V2+/1+). The thin film near the substrate is affected by the strain. The positive magnetoresistance is attributed to the effect of electron-electron interactions in the disorder system. Therefore, the emergence of MIT can be explained by the electron-electron interactions from the chemical disorder due to the strain.

  4. Metal-insulator-semiconductor photodetectors.

    Science.gov (United States)

    Lin, Chu-Hsuan; Liu, Chee Wee

    2010-01-01

    The major radiation of the sun can be roughly divided into three regions: ultraviolet, visible, and infrared light. Detection in these three regions is important to human beings. The metal-insulator-semiconductor photodetector, with a simpler process than the pn-junction photodetector and a lower dark current than the MSM photodetector, has been developed for light detection in these three regions. Ideal UV photodetectors with high UV-to-visible rejection ratio could be demonstrated with III-V metal-insulator-semiconductor UV photodetectors. The visible-light detection and near-infrared optical communications have been implemented with Si and Ge metal-insulator-semiconductor photodetectors. For mid- and long-wavelength infrared detection, metal-insulator-semiconductor SiGe/Si quantum dot infrared photodetectors have been developed, and the detection spectrum covers atmospheric transmission windows.

  5. Metal-Insulator-Semiconductor Photodetectors

    Directory of Open Access Journals (Sweden)

    Chu-Hsuan Lin

    2010-09-01

    Full Text Available The major radiation of the Sun can be roughly divided into three regions: ultraviolet, visible, and infrared light. Detection in these three regions is important to human beings. The metal-insulator-semiconductor photodetector, with a simpler process than the pn-junction photodetector and a lower dark current than the MSM photodetector, has been developed for light detection in these three regions. Ideal UV photodetectors with high UV-to-visible rejection ratio could be demonstrated with III-V metal-insulator-semiconductor UV photodetectors. The visible-light detection and near-infrared optical communications have been implemented with Si and Ge metal-insulator-semiconductor photodetectors. For mid- and long-wavelength infrared detection, metal-insulator-semiconductor SiGe/Si quantum dot infrared photodetectors have been developed, and the detection spectrum covers atmospheric transmission windows.

  6. Disorder induced metal-insulator transition in crystalline Ge{sub 1}Sb{sub 2}Te{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Volker, Hanno; Jost, Peter; Woda, Michael; Merkelbach, Philipp; Schlockermann, Carl; Wuttig, Matthias [1. Institute of Physics, RWTH Aachen (Germany); Siegrist, Theo [1. Institute of Physics, RWTH Aachen (Germany); Department of Chemical and Biochemical Engineering, FSU, Tallahassee, FL (United States)

    2011-07-01

    Localization of charge carriers in crystalline solids has been the subject of numerous investigations over more than half a century. Materials showing a metal to insulator transition (MIT) without a structural change are therefore of great interest. Concepts based on electron correlation (Mott) or disorder (Anderson) are often invoked to explain such an MIT, but a clear distinction between the two mechanisms is difficult. In this study we report the observation of an MIT in crystalline Ge{sub 1}Sb{sub 2}Te{sub 4} which is caused by disorder-induced localization in the 3-dimensional solid. A combination of X-ray diffraction experiments as well as optical (FT-IR) and electrical measurements reveals that the observed MIT is an intra-grain effect. The Hall carrier density barely changes during the MIT and is much higher than predicted by the Mott criterion. Therefore, the MIT is not of the Mott type, but driven by disorder.

  7. Recovery of the metal-insulator transition in electron-doped La{sub 0.7}Ce{sub 0.3}MnO{sub 3-{delta}} films by photoexcitation

    Energy Technology Data Exchange (ETDEWEB)

    Thiessen, Andreas; Beyreuther, Elke; Grafstroem, Stefan; Eng, Lukas M. [Institut fuer Angewandte Photophysik, TechnischeUniversitaet Dresden (Germany); Doerr, Kathrin [Institut fuer Metallische Werkstoffe, IFW Dresden (Germany)

    2008-07-01

    The question whether electron-doped mixed-valence manganites, such as La{sub 0.7}Ce{sub 0.3}MnO{sub 3}, can be synthesized as single-phase compounds has been under debate for a decade. Meanwhile it has become clear that electron doping can indeed be achieved in epitaxial thin films. However, as-prepared films often suffer from overoxygenation and concomitant hole doping, which can be overcome by deoxygenation through a post-deposition annealing procedure. Disappointingly, those reduced samples do not exhibit the typical metal-insulator transition (MIT) any longer. In the present work, we show that the MIT of La{sub 0.7}Ce{sub 0.3}MnO{sub 3-{delta}} films can be recovered by exposition to visible light. Our films turn out to be highly photoconductive: Laser illumination at 514 nm with a power of 400 mW gave rise to a dramatic resistance drop of around seven orders of magnitude at 100 K as compared to the dark state, while illumination had no impact on the conductivity of an as-prepared reference film.

  8. Superconductivity and crystal structural origins of the metal-insulator transition in Ba6 -xSrxNb10O30 tetragonal tungsten bronzes

    Science.gov (United States)

    Kolodiaznyi, Taras; Sakurai, Hiroya; Isobe, Masaaki; Matsushita, Yoshitaka; Forbes, Scott; Mozharivskyj, Yurij; Munsie, Timothy J. S.; Luke, Graeme M.; Gurak, Mary; Clarke, David R.

    2015-12-01

    Ba6 -xSrxNb10O30 solid solution with 0 ≤ x ≤6 forms the filled tetragonal tungsten bronze (TTB) structure. The Ba-end member crystallizes in the highest symmetry P 4 /m b m space group (a =b =12.5842 (18 )Å and c =3.9995 (8 )Å ) and so do all the compositions with 0 ≤ x ≤5 . The Sr-end member of the solid solution crystallizes in the tentatively assigned A m a m space group (a *=17.506 (4 )Å , b *=34.932 (7 )Å , and c *=7.7777 (2 )Å ). The latter space group is related to the parent P 4 /m b m TTB structure as a * ≈ √{2 }a ,b * ≈2 √{2 }a ,c *=2 c . Low-temperature specific heat measurements indicate that the Ba-rich compositions with x ≤2 are conventional BCS superconductors with TC ≤1.6 K and superconducting energy gaps of ≤0.38 meV. The values of the TC in the cation-filled Nb-based TTBs reported here are comparable with those of the unfilled KxWO3 and NaxWO3 TTBs having large alkali ion deficiency. As the unit cell volume decreases with increasing x , an unexpected metal-insulator transition (MIT) in Ba6 -xSrxNb10O30 occurs at x ≥3 . We discuss the possible origins of the MIT in terms of the carrier concentration, symmetry break, and Anderson localization.

  9. A Theoretical Exploration of the Metal Insulator Transition in Vanadium Dioxide with an Eye Towards Applications: A First Principles Approach

    Science.gov (United States)

    2009-06-10

    in the rutile phase. It requires a value of U = 2.2 eV, which is more screened than the values considered in the literature so far [19]. (2) Orbitally...measured in angle integrated photoemission and XAS. Our theoretical results compared very well with existing experiments in the literature . (3) Effects...Phys. Rev. B 48, 4359 (1993). [3] P. Kierkegaard , and J. Longo, Acta Chem. Scand. 24, 420 (1970). [4] G. Andresson, Acta Chem. Scand. 10, 623-628 (1956

  10. Thouless energy as a unifying concept for Josephson junctions tuned through the Mott metal-insulator transition

    Science.gov (United States)

    Tahvildar-Zadeh, A. N.; Freericks, J. K.; Nikolić, B. K.

    2006-05-01

    The Thouless energy was introduced in the 1970s as a semiclassical energy for electrons diffusing through a finite-sized conductor. It turns out to be an important quantum-mechanical energy scale for many systems ranging from disordered metals to quantum chaos to quantum chromodynamics. In particular, it has been quite successful in describing the properties of Josephson junctions when the barrier is a diffusive normal-state metal. The Thouless energy concept can be generalized to insulating barriers by extracting an energy scale from the two-probe Kubo conductance of a strongly correlated electron system (metallic or insulating) via a generalized definition of the quantum-mechanical level spacing to many-body systems. This energy scale is known to determine the crossover from tunneling to Ohmic (thermally activated) transport in normal tunnel junctions. Here we use it to illustrate how the quasiclassical picture of transport in Josephson junctions is modified as the strongly correlated barrier passes through the Mott transition. Surprisingly, we find the quasiclassical form holds well beyond its putative realm of validity.

  11. k-dependent spectrum and optical conductivity near metal-insulator transition in multi-orbital hubbard bands

    International Nuclear Information System (INIS)

    Miura, Oki; Fujiwara, Takeo

    2006-01-01

    We apply the dynamical mean field theory (DMFT) combined with the iterative perturbation theory (IPT) to the doubly degenerate e g and the triply degenerate f 2g bands on a simple cubic lattice and a body-centered cubic lattice and calculate the spectrum and optical conductivity in arbitrary electron occupation. The spectrum simultaneously shows the effects of multiplet structure together with the electron ionization and affinity levels of different electron occupations, coherent peaks at the Fermi energy in the metallic phase and an energy gap at an integer filling of electrons for sufficiently large Coulomb U. We also discuss the critical value of the Coulomb U for degenerate orbitals on a simple cubic lattice and a body-centered cubic lattice. (author)

  12. The evolution of Griffiths-phase-like features and colossal magnetoresistance in La(1-x)Ca(x)MnO(3) (0.18 ≤ x ≤ 0.27) across the compositional metal-insulator boundary.

    Science.gov (United States)

    Jiang, Wanjun; Zhou, Xuezhi; Williams, Gwyn; Mukovskii, Y; Privezentsev, R

    2009-10-14

    Detailed measurements of the magnetic and transport properties of single crystals of La(1-x)Ca(x)MnO(3) (0.18 ≤ x ≤ 0.27) are summarized, and lead to the following conclusions. While temperature-dependent (magneto-) resistance measurements narrow the compositionally modulated metal-insulator (M-I) transition to lie between 0.19 ≤ x(c) ≤ 0.20 in the series studied, comparisons between the latter magnetic data provide the first unequivocal demonstration that (i) the presence of Griffiths-phase-like (GP) features do not guarantee colossal magnetoresistance (CMR), while confirming (ii) that neither are the appearance of such features a prerequisite for CMR. These data also reveal that (iii) whereas continuous magnetic transitions occur for 0.18 ≤ x ≤ 0.25, the universality class of these transitions belongs to that of a nearest-neighbour 3D Heisenberg model only for x≤0.20, beyond which complications due to GP-like behaviour occur. The implications of the variation (or lack thereof) in critical exponents and particularly critical amplitudes and temperatures across the compositionally mediated M-I transition support the assertion that the dominant mechanism underlying ferromagnetism across the M-I transition changes from ferromagnetic super-exchange (SE) stabilized by orbital ordering in the insulating phase to double-exchange (DE) in the orbitally disordered metallic regime. The variations in the acoustic spin-wave stiffness, D, and the coercive field, H(C), support this conclusion. These SE and DE interaction mechanisms are demonstrated to not only belong to the same universality class but are also characterized by comparable coupling strengths. Nevertheless, their percolation thresholds are manifestly different in this system.

  13. Phase transitions

    CERN Document Server

    Sole, Ricard V; Solé, Ricard V; Solé, Ricard V; Sol, Ricard V; 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 of diverse ecosystems, the book illustrates the power of simple models to reveal how phase transitions occur. Introductory chapters provide the critical concepts and the simplest mathematical techniques required to study phase transitions. In a series of example-driven chapters, Ricard Solé shows how such concepts and techniques can be applied to the analysis and prediction of complex system behavior, including the origins of ...

  14. Quantum phase transitions of a disordered antiferromagnetic topological insulator

    Science.gov (United States)

    Baireuther, P.; Edge, J. M.; Fulga, I. C.; Beenakker, C. W. J.; Tworzydło, J.

    2014-01-01

    We study the effect of electrostatic disorder on the conductivity of a three-dimensional antiferromagnetic insulator (a stack of quantum anomalous Hall layers with staggered magnetization). The phase diagram contains regions where the increase of disorder first causes the appearance of surface conduction (via a topological phase transition), followed by the appearance of bulk conduction (via a metal-insulator transition). The conducting surface states are stabilized by an effective time-reversal symmetry that is broken locally by the disorder but restored on long length scales. A simple self-consistent Born approximation reliably locates the boundaries of this so-called "statistical" topological phase.

  15. Dimensional effects in a disordered system near metal-insulator transitions and superconductor-insulator transitions; Effets dimensionnels dans un systeme desordonne au voisinage des transitions metal-isolant et supraconducteur-isolant

    Energy Technology Data Exchange (ETDEWEB)

    Akiko Marrache-Kikuchi, C

    2006-02-15

    Low temperature transport in disordered conducting materials implies quantum interference, Coulomb repulsion, and superconducting fluctuations. Since 2-D is the lower critical dimension for the existence of metallic and superconducting states, we have studied two quantum phase transitions - the Superconductor-to-Insulator Transition (SIT) and the Metal-to-Insulator Transition (MIT) - when the thickness of a disordered system - here a-NbSi - is lowered. The underlying problem is the transition between the different states and the conditions for a 2-D metal to exist. We have studied the field and disorder-induced SIT. The principal characteristics we have observed (renormalization, role of the field orientation) are well explained by M.P.A. Fisher's theory. However, we do not find the critical exponents values and a universal resistance at the transition as predicted by this theory. Concerning the MIT, we have decreased the thickness of a metallic system to reach the dimension 2 and an insulating state. In both transitions, the passage to the insulating state clearly shows the existence of dissipative states at zero temperature that are not predicted by conventional theories. We propose an interpretation of all our results that implies the existence of a novel phase in 2-D, a Bose Metal, between the superconducting and the metallic states. This new state has been predicted by recent theories. We trace the corresponding phase diagram for the model system NbSi with respect to concentration and film thickness. In the second appendix it is shown how superconducting thin films of Nb{sub x}Si{sub 1-x} are used to make transition edge sensors used in the particle detection field. (author)

  16. A Brillouin scattering study of La0.77Ca0.23MnO3 across the metal-insulator transition

    International Nuclear Information System (INIS)

    Seikh, Md Motin; Narayana, Chandrabhas; Sudheendra, L; Sood, A K; Rao, C N R

    2004-01-01

    Temperature-dependent Brillouin scattering studies have been carried out on La 0.77 Ca 0.23 MnO 3 across the paramagnetic insulator-ferromagnetic metal (I-M) transition (T C ∼ 230 K). The spectra show modes corresponding to a surface Rayleigh wave (SRW) and a high velocity pseudo-surface wave (HVPSAW) along with bulk acoustic waves (B1 and B2). The Brillouin shifts associated with the SRW and HVPSAW increase, whereas the B1 and B2 frequencies decrease, below T C . The temperature dependence of the SRW and HVPSAW modes is related to the increase in the elastic constant C 11 across the I-M transition. The decrease in frequency across the I-M transition of the bulk modes is understood to be due to enhanced self-energy corrections as a result of increased magnon-phonon interaction across the I-M transition. Correspondingly, these modes show a large increase in the full width at half maximum (FWHM) as the temperature decreases. We also observe a central peak whose width is maximum at T C

  17. Quantum phase transitions of strongly correlated electron systems

    International Nuclear Information System (INIS)

    Imada, Masatoshi

    1998-01-01

    Interacting electrons in solids undergo various quantum phase transitions driven by quantum fluctuations. The quantum transitions take place at zero temperature by changing a parameter to control quantum fluctuations rather than thermal fluctuations. In contrast to classical phase transitions driven by thermal fluctuations, the quantum transitions have many different features where quantum dynamics introduces a source of intrinsic fluctuations tightly connected with spatial correlations and they have been a subject of recent intensive studies as we see below. Interacting electron systems cannot be fully understood without deep analyses of the quantum phase transitions themselves, because they are widely seen and play essential roles in many phenomena. Typical and important examples of the quantum phase transitions include metal-insulator transitions, (2, 3, 4, 5, 6, 7, 8, 9) metal-superconductor transitions, superconductor-insulator transitions, magnetic transitions to antiferromagnetic or ferromagnetic phases in metals as well as in Mott insulators, and charge ordering transitions. Here, we focus on three different types of transitions

  18. Addendum to "Switching effect and the metal-insulator transition in electric field" by A.L. Pergament et al. [J. Phys. Chem. Solids 71 (2010) 874

    Science.gov (United States)

    Pergament, A. L.; Velichko, A. A.; Stefanovich, G. B.

    2015-02-01

    In the paper mentioned above we reported on the switching mechanism in vanadium dioxide which was shown to be based on the electronically-induced Mott insulator-to-metal transition occurring in conditions of the non-equilibrium carrier density excess in the applied electric field, and the proposed model involved the dependence of the carrier density n on electric field (the Poole-Frenkel effect), as well as the dependence of the critical electric field on n. The data on the n(T) dependence were obtained on the assumption of a temperature-independent carrier mobility μ, and the problem of n reduction at lower temperatures was not fully understood. In this Letter we revisit this problem in the light of some recent data on the μ(T) dependence for VO2. It is shown that the adjusted values of n, taking into account this μ(T), correspond to the Mott critical density within an order of magnitude.

  19. Quantum phase transitions

    International Nuclear Information System (INIS)

    Sachdev, S.

    1999-01-01

    Phase transitions are normally associated with changes of temperature but a new type of transition - caused by quantum fluctuations near absolute zero - is possible, and can tell us more about the properties of a wide range of systems in condensed-matter physics. Nature abounds with phase transitions. The boiling and freezing of water are everyday examples of phase transitions, as are more exotic processes such as superconductivity and superfluidity. The universe itself is thought to have passed through several phase transitions as the high-temperature plasma formed by the big bang cooled to form the world as we know it today. Phase transitions are traditionally classified as first or second order. In first-order transitions the two phases co-exist at the transition temperature - e.g. ice and water at 0 deg., or water and steam at 100 deg. In second-order transitions the two phases do not co-exist. In the last decade, attention has focused on phase transitions that are qualitatively different from the examples noted above: these are quantum phase transitions and they occur only at the absolute zero of temperature. The transition takes place at the ''quantum critical'' value of some other parameter such as pressure, composition or magnetic field strength. A quantum phase transition takes place when co-operative ordering of the system disappears, but this loss of order is driven solely by the quantum fluctuations demanded by Heisenberg's uncertainty principle. The physical properties of these quantum fluctuations are quite distinct from those of the thermal fluctuations responsible for traditional, finite-temperature phase transitions. In particular, the quantum system is described by a complex-valued wavefunction, and the dynamics of its phase near the quantum critical point requires novel theories that have no analogue in the traditional framework of phase transitions. In this article the author describes the history of quantum phase transitions. (UK)

  20. 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.

  1. Cosmological phase transitions

    International Nuclear Information System (INIS)

    Kolb, E.W.

    1987-01-01

    If the universe stated from conditions of high temperature and density, there should have been a series of phase transitions associated with spontaneous symmetry breaking. The cosmological phase transitions could have observable consequences in the present Universe. Some of the consequences including the formation of topological defects and cosmological inflation are reviewed here. One of the most important tools in building particle physics models is the use of spontaneous symmetry breaking (SSB). The proposal that there are underlying symmetries of nature that are not manifest in the vacuum is a crucial link in the unification of forces. Of particular interest for cosmology is the expectation that are the high temperatures of the big bang symmetries broken today will be restored, and that there are phase transitions to the broken state. The possibility that topological defects will be produced in the transition is the subject of this section. The possibility that the Universe will undergo inflation in a phase transition will be the subject of the next section. Before discussing the creation of topological defects in the phase transition, some general aspects of high-temperature restoration of symmetry and the development of the phase transition will be reviewed. 29 references, 1 figure, 1 table

  2. Strain engineering and one-dimensional organization of metal-insulator domains in single-crystal vanadium dioxide beams.

    Science.gov (United States)

    Cao, J; Ertekin, E; Srinivasan, V; Fan, W; Huang, S; Zheng, H; Yim, J W L; Khanal, D R; Ogletree, D F; Grossman, J C; Wu, J

    2009-11-01

    Correlated electron materials can undergo a variety of phase transitions, including superconductivity, the metal-insulator transition and colossal magnetoresistance. Moreover, multiple physical phases or domains with dimensions of nanometres to micrometres can coexist in these materials at temperatures where a pure phase is expected. Making use of the properties of correlated electron materials in device applications will require the ability to control domain structures and phase transitions in these materials. Lattice strain has been shown to cause the coexistence of metallic and insulating phases in the Mott insulator VO(2). Here, we show that we can nucleate and manipulate ordered arrays of metallic and insulating domains along single-crystal beams of VO(2) by continuously tuning the strain over a wide range of values. The Mott transition between a low-temperature insulating phase and a high-temperature metallic phase usually occurs at 341 K in VO(2), but the active control of strain allows us to reduce this transition temperature to room temperature. In addition to device applications, the ability to control the phase structure of VO(2) with strain could lead to a deeper understanding of the correlated electron materials in general.

  3. Metallic insulation transport and strainer clogging tests

    International Nuclear Information System (INIS)

    Hyvaerinen, J.; Hongisto, O.

    1994-06-01

    Experiments to probe the transport and clogging properties of metallic (metal reflective) insulation have been carried out in order to provide data for evaluation of their influence on the emergency core cooling and containment spray systems of the Finnish boiling water reactors in the event of a design basis accident. The specific metallic insulation tested was DARMET, provided by Darchem Engineering Ltd. The inner foils of Darmet are dimped. Available literature on the metallic insulation performance under design basis accident conditions has been reviewed. On the basis of the review a parametric approach has been chosen for the transport and clogging experiments. This approach involves testing a wide size range of various shapes of foil pieces. Five sets of experiments have been carried out. The first three sets investigate transport properties of the foil pieces, starting from sedimentation in stagnant waste pool and proceeding to transport in horizontal and vertically circulating flows. The clogging experiments have been addressed the differential pressures obtained due to accumulation of both pure and metallic and a mixture of metallic and fibrous (mineral wool) depris. (4 refs., 24 figs., 2 tabs.)

  4. 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.

  5. paraelectric phase transition

    Indian Academy of Sciences (India)

    at% of La, x = 3, 5, 6, 10 and 12] have been measured in the frequency range 1 Hz–1 MHz using the vector impedance ... The ferroelectric phase transition is diffuse in nature and broadening of the peak increases with La content. Keywords. PLZT ..... formation from rhombohedral–tetragonal–cubic phase with increase in ...

  6. Phase diagram of the anisotropic Anderson transition with the atomic kicked rotor: theory and experiment

    Science.gov (United States)

    Lopez, Matthias; Clément, Jean-François; Lemarié, Gabriel; Delande, Dominique; Szriftgiser, Pascal; Garreau, Jean Claude

    2013-06-01

    We realize experimentally a cold-atom system, the quasiperiodic kicked rotor, equivalent to the three-dimensional Anderson model of disordered solids where the anisotropy between the x direction and the y-z plane can be controlled by adjusting an experimentally accessible parameter. This allows us to study experimentally the disorder versus anisotropy phase diagram of the Anderson metal-insulator transition. Numerical and experimental data compare very well with each other and a theoretical analysis based on the self-consistent theory of localization correctly describes the observed behavior, illustrating the flexibility of cold-atom experiments for the study of transport phenomena in complex quantum systems.

  7. Phase transitions in nuclear physics

    Energy Technology Data Exchange (ETDEWEB)

    Moretto, L.G.; Phair, L.; Wozniak, G.J.

    1997-08-01

    A critical overview of the low energy phase transitions in nuclei is presented with particular attention to the 2nd (1st) order pairing phase transitions, and to the 1st order liquid-vapor phase transition. The role of fluctuations in washing out these transitions is discussed and illustrated with examples. A robust indicator of phase coexistence in multifragmentation is presented.

  8. Electronic phase transitions

    CERN Document Server

    Kopaev, YuV

    1992-01-01

    Electronic Phase Transitions deals with topics, which are presently at the forefront of scientific research in modern solid-state theory. Anderson localization, which has fundamental implications in many areas of solid-state physics as well as spin glasses, with its influence on quite different research activities such as neural networks, are two examples that are reviewed in this book. The ab initio statistical mechanics of structural phase transitions is another prime example, where the interplay and connection of two unrelated disciplines of solid-state theory - first principle ele

  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. 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

  11. Near-Field Nanoscopy of Metal-Insulator Phase Transitions Towards Synthesis of Novel Correlated Transition Metal Oxides and Their Interaction with Plasmon Resonances

    Science.gov (United States)

    2016-01-05

    infrared antennas, Physical Chem Chem Physics (08 2013) Yohannes Abate, Sampath Gamage, Li Zhen, Stephen B. Cronin, Han Wang, Viktoriia Babicheva ...Nanowires, Journal of the American Chemical Society 135, 4850-4855 (2013). 8. Y. Abate, L. Zhen, S. B. Cronin, H. Wang, V. Babicheva , M. H. Javani, M. I...V. Babicheva , M. H. Javani, and M. I. Stockman, Nanoscopy Reveals Metallic Black Phosphorus, arXiv:1506.05431, 1-9 (2015). 27. J. Kim, S. S. Baik

  12. Magnetic and transport properties of Ni2MnGa-BaTiO3 metal-insulator particulate composite with percolation threshold

    International Nuclear Information System (INIS)

    Won, C.J.; Kambale, R.C.; Hur, N.

    2011-01-01

    Highlights: → The Ni 2 MnGa-BaTiO 3 type composites were first time prepared by solid state reaction. → Temperature dependent magnetic properties reveal two kinds of transitions in these composite. → The present materials show negative magnetoresistance effect. → The present studies on magnetic and electrical transport of metal/insulator (NMG/BTO) composites shows the resistivity change associated to filamentary conducting path at percolation threshold. - Abstract: Here we report the magnetic and transport properties of the metal/insulator (f NMG )Ni 2 MnGa/(1 - f NMG )BaTiO 3 composites. The X-ray diffraction study confirms the formation of both the phases in composite. The microstructure reveals that the conducting Ni 2 MnGa particles are well dispersed in an insulating BaTiO 3 matrix. Temperature dependent magnetization shows two transitions one above 300 K and other below 150 K. The temperature dependence resistivity near the percolation threshold f NMG = 0.4 had drastic changes which is higher than the f NMG = 0.5. Also the negative magnetoresistance effect was observed for the studied materials. We suggest that magnetic and transport properties at the percolation threshold can be adjusted by the strain from the surrounding insulator particle.

  13. Continuous quantum phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Sondhi, S.L. [Department of Physics, Princeton University, Princeton, New Jersey 08544 (United States); Girvin, S.M.; Carini, J.P. [Department of Physics, Indiana University, Bloomington, Indiana 47405 (United States); Shahar, D. [Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544 (United States)

    1997-01-01

    A quantum system can undergo a continuous phase transition at the absolute zero of temperature as some parameter entering its Hamiltonian is varied. These transitions are particularly interesting for, in contrast to their classical finite-temperature counterparts, their dynamic and static critical behaviors are intimately intertwined. Considerable insight is gained by considering the path-integral description of the quantum statistical mechanics of such systems, which takes the form of the {ital classical} statistical mechanics of a system in which time appears as an extra dimension. In particular, this allows the deduction of scaling forms for the finite-temperature behavior, which turns out to be described by the theory of finite-size scaling. It also leads naturally to the notion of a temperature-dependent dephasing length that governs the crossover between quantum and classical fluctuations. Using these ideas, a scaling analysis of experiments on Josephson-junction arrays and quantum-Hall-effect systems is presented. {copyright} {ital 1997} {ital The American Physical Society}

  14. Phase transition in finite systems

    International Nuclear Information System (INIS)

    Chomaz, Ph.; Duflot, V.; Duflot, V.; Gulminelli, F.

    2000-01-01

    In this paper we present a review of selected aspects of Phase transitions in finite systems applied in particular to the liquid-gas phase transition in nuclei. We show that the problem of the non existence of boundary conditions can be solved by introducing a statistical ensemble with an averaged constrained volume. In such an ensemble the microcanonical heat capacity becomes negative in the transition region. We show that the caloric curve explicitly depends on the considered transformation of the volume with the excitation energy and so does not bear direct informations on the characteristics of the phase transition. Conversely, partial energy fluctuations are demonstrated to be a direct measure of the equation of state. Since the heat capacity has a negative branch in the phase transition region, the presence of abnormally large kinetic energy fluctuations is a signal of the liquid gas phase transition. (author)

  15. Generalized definitions of phase transitions

    International Nuclear Information System (INIS)

    Chomaz, Ph.; Gulminelli, F.

    2001-09-01

    We define a first order phase transition as a bimodality of the event distribution in the space of observations and we show that this is equivalent to a curvature anomaly of the thermodynamical potential and that it implies the Yang Lee behavior of the zeros of the partition sum. Moreover, it allows to study phase transitions out of equilibrium. (authors)

  16. Nanostructured Anodic Multilayer Dielectric Stacked Metal-Insulator-Metal Capacitors.

    Science.gov (United States)

    Karthik, R; Kannadassan, D; Baghini, Maryam Shojaei; Mallick, P S

    2015-12-01

    This paper presents the fabrication of Al2O3/TiO2/Al2O3 metal-insulator-metal (MIM) capacitor using anodization technique. High capacitance density of > 3.5 fF/μm2, low quadratic voltage coefficient of capacitance of capacitor.

  17. Charging damage in floating metal-insulator-metal capacitors

    NARCIS (Netherlands)

    Ackaert, Jan; Wang, Zhichun; De Backer, E.; Coppens, P.

    2002-01-01

    In this paper, charging induced damage (CID) to metal-insulator-metal capacitors (MIMC) is reported. The damage is caused by the build up of a voltage potential difference between the two plates of the capacitor. A simple logarithmic relation is discovered between the damage by this voltage

  18. Plasma damage in floating metal-insulator-metal capacitors

    NARCIS (Netherlands)

    Ackaert, Jan; Wang, Zhichun; De Backer, E.; Coppens, P.

    2002-01-01

    In this paper, charging induced damage (CID) to metal-insulator-metal capacitors (MIMCs), is reported. CID does not necessarily lead to direct yield loss, but may also induce latent damage leading to reliability losses. The damage is caused by the build up of a voltage potential difference between

  19. 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

  20. Non-equilibrium phase transitions

    CERN Document Server

    Henkel, Malte; Lübeck, Sven

    2009-01-01

    This book describes two main classes of non-equilibrium phase-transitions: (a) static and dynamics of transitions into an absorbing state, and (b) dynamical scaling in far-from-equilibrium relaxation behaviour and ageing. The first volume begins with an introductory chapter which recalls the main concepts of phase-transitions, set for the convenience of the reader in an equilibrium context. The extension to non-equilibrium systems is made by using directed percolation as the main paradigm of absorbing phase transitions and in view of the richness of the known results an entire chapter is devoted to it, including a discussion of recent experimental results. Scaling theories and a large set of both numerical and analytical methods for the study of non-equilibrium phase transitions are thoroughly discussed. The techniques used for directed percolation are then extended to other universality classes and many important results on model parameters are provided for easy reference.

  1. Atomic Origins of Monoclinic-Tetragonal (Rutile) Phase Transition in Doped VO2 Nanowires.

    Science.gov (United States)

    Asayesh-Ardakani, Hasti; Nie, Anmin; Marley, Peter M; Zhu, Yihan; Phillips, Patrick J; Singh, Sujay; Mashayek, Farzad; Sambandamurthy, Ganapathy; Low, Ke-Bin; Klie, Robert F; Banerjee, Sarbajit; Odegard, Gregory M; Shahbazian-Yassar, Reza

    2015-11-11

    There has been long-standing interest in tuning the metal-insulator phase transition in vanadium dioxide (VO2) via the addition of chemical dopants. However, the underlying mechanisms by which doping elements regulate the phase transition in VO2 are poorly understood. Taking advantage of aberration-corrected scanning transmission electron microscopy, we reveal the atomistic origins by which tungsten (W) dopants influence the phase transition in single crystalline WxV1-xO2 nanowires. Our atomically resolved strain maps clearly show the localized strain normal to the (122̅) lattice planes of the low W-doped monoclinic structure (insulator). These strain maps demonstrate how anisotropic localized stress created by dopants in the monoclinic structure accelerates the phase transition and lead to relaxation of structure in tetragonal form. In contrast, the strain distribution in the high W-doped VO2 structure is relatively uniform as a result of transition to tetragonal (metallic) phase. The directional strain gradients are furthermore corroborated by density functional theory calculations that show the energetic consequences of distortions to the local structure. These findings pave the roadmap for lattice-stress engineering of the MIT behavior in strongly correlated materials for specific applications such as ultrafast electronic switches and electro-optical sensors.

  2. Atomic Origins of Monoclinic-Tetragonal (Rutile) Phase Transition in Doped VO 2 Nanowires

    KAUST Repository

    Asayesh-Ardakani, Hasti

    2015-10-12

    There has been long-standing interest in tuning the metal-insulator phase transition in vanadium dioxide (VO) via the addition of chemical dopants. However, the underlying mechanisms by which doping elements regulate the phase transition in VO are poorly understood. Taking advantage of aberration-corrected scanning transmission electron microscopy, we reveal the atomistic origins by which tungsten (W) dopants influence the phase transition in single crystalline WVO nanowires. Our atomically resolved strain maps clearly show the localized strain normal to the (122¯) lattice planes of the low W-doped monoclinic structure (insulator). These strain maps demonstrate how anisotropic localized stress created by dopants in the monoclinic structure accelerates the phase transition and lead to relaxation of structure in tetragonal form. In contrast, the strain distribution in the high W-doped VO structure is relatively uniform as a result of transition to tetragonal (metallic) phase. The directional strain gradients are furthermore corroborated by density functional theory calculations that show the energetic consequences of distortions to the local structure. These findings pave the roadmap for lattice-stress engineering of the MIT behavior in strongly correlated materials for specific applications such as ultrafast electronic switches and electro-optical sensors.

  3. Correlation-Driven Lifshitz Transition at the Emergence of the Pseudogap Phase in the Two-Dimensional Hubbard Model

    Science.gov (United States)

    Bragança, Helena; Sakai, Shiro; Aguiar, M. C. O.; Civelli, Marcello

    2018-02-01

    We study the relationship between the pseudogap and Fermi-surface topology in the two-dimensional Hubbard model by means of the cellular dynamical mean-field theory. We find two possible mean-field metallic solutions on a broad range of interactions, doping, and frustration: a conventional renormalized metal and an unconventional pseudogap metal. At half filling, the conventional metal is more stable and displays an interaction-driven Mott metal-insulator transition. However, for large interactions and small doping, a region that is relevant for cuprates, the pseudogap phase becomes the ground state. By increasing doping, we show that a first-order transition from the pseudogap to the conventional metal is tied to a change of the Fermi surface from hole- to electronlike, unveiling a correlation-driven mechanism for a Lifshitz transition. This explains the puzzling link between the pseudogap phase and Fermi surface topology that has been pointed out in recent experiments.

  4. Phase transitions in surfactant monolayers

    International Nuclear Information System (INIS)

    Casson, B.D.

    1998-01-01

    Two-dimensional phase transitions have been studied in surfactant monolayers at the air/water interface by sum-frequency spectroscopy and ellipsometry. In equilibrium monolayers of medium-chain alcohols C n H 2n+1 OH (n = 9-14) a transition from a two-dimensional crystalline phase to a liquid was observed at temperatures above the bulk melting point. The small population of gauche defects in the solid phase increased only slightly at the phase transition. A model of the hydrocarbon chains as freely rotating rigid rods allowed the area per molecule and chain tilt in the liquid phase to be determined. The area per molecule, chain tilt and density of the liquid phase all increased with increasing chain length, but for each chain length the density was higher than in a bulk liquid hydrocarbon. In a monolayer of decanol adsorbed at the air/water interface a transition from a two-dimensional liquid to a gas was observed. A clear discontinuity in the coefficient of ellipticity as a function of temperature showed that the transition is first-order. This result suggests that liquid-gas phase transitions in surfactant monolayers may be more widespread than once thought. A solid-liquid phase transition has also been studied in mixed monolayers of dodecanol with an anionic surfactant (sodium dodecyl sulphate) and with a homologous series of cationic surfactants (alkyltrimethylammonium bromides: C n TABs, n = 12, 14, 16). The composition and structure of the mixed monolayers was studied above and below the phase transition. At low temperatures the mixed monolayers were as densely packed as a monolayer of pure dodecanol in its solid phase. At a fixed temperature the monolayers under-went a first-order phase transition to form a phase that was less dense and more conformationally disordered. The proportion of ionic surfactant in the mixed monolayer was greatest in the high temperature phase. As the chain length of the C n TAB increased the number of conformational defects

  5. Phase transitions and quantum entropy

    International Nuclear Information System (INIS)

    Arrachea, L.; Canosa, N.; Plastino, A.; Portesi, M.; Rossignoli, R.

    1990-01-01

    An examination is made of the possibility to predict phase transitions of the fundamental state of finite quantum system, knowing the quantum entropy of these states, defined on the basis of the information theory. (Author). 7 refs., 3 figs

  6. Phase transition in finite systems

    International Nuclear Information System (INIS)

    Chomaz, Ph.; Duflot, V.; Duflot, V.; Gulminelli, F.

    2000-01-01

    The general problem of the definition of a phase transition without employing the thermodynamical limit is addressed. Different necessary conditions are considered and illustrated with examples from different nuclear and general physics phenomenologies. (authors)

  7. Phase transition in finite systems

    Energy Technology Data Exchange (ETDEWEB)

    Chomaz, Ph.; Duflot, V. [Grand Accelerateur National d' Ions Lourds (GANIL), 14 - Caen (France); Duflot, V.; Gulminelli, F. [Laboratoire de Physique Corpusculaire, LPC-ISMRa, CNRS-IN2P3, 14 - Caen (France)

    2000-07-01

    The general problem of the definition of a phase transition without employing the thermodynamical limit is addressed. Different necessary conditions are considered and illustrated with examples from different nuclear and general physics phenomenologies. (authors)

  8. Magnetism variations and susceptibility hysteresis at the metal-insulator phase transition temperature of VO2 in a composite film containing vanadium and tungsten oxides

    CSIR Research Space (South Africa)

    Akande, AA

    2015-02-01

    Full Text Available properties of V1−xCrxO2 compounds under high pressure, Phy Rev. B 77, 235111-9, 2008 [25] B. W. Mwakikunga, E. Sideras-Haddad, M. Maaza, First synthesis of vanadium dioxide by ultrasonic nebula-spray pyrolysis, Optical Materials 29 (2007) 481–487 [26] S...

  9. Learning phase transitions by confusion

    Science.gov (United States)

    van Nieuwenburg, Evert P. L.; Liu, Ye-Hua; Huber, Sebastian D.

    2017-02-01

    Classifying phases of matter is key to our understanding of many problems in physics. For quantum-mechanical systems in particular, the task can be daunting due to the exponentially large Hilbert space. With modern computing power and access to ever-larger data sets, classification problems are now routinely solved using machine-learning techniques. Here, we propose a neural-network approach to finding phase transitions, based on the performance of a neural network after it is trained with data that are deliberately labelled incorrectly. 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 the development of a generic tool for identifying unexplored phase transitions.

  10. Ground-state tuning of metal-insulator transition by compositional variations in BaI r1 -xR uxO3(0 ≤x ≤1 )

    Science.gov (United States)

    Yuan, S. J.; Butrouna, K.; Terzic, J.; Zheng, H.; Aswartham, S.; DeLong, L. E.; Ye, Feng; Schlottmann, P.; Cao, G.

    2016-04-01

    Hexagonal BaIr O3 is a magnetic insulator driven by the spin-orbit interaction (SOI), whereas BaRu O3 is an enhanced paramagnetic metal. Our investigation of structural, magnetic, transport, and thermal properties reveals that substitution of R u4 + (4 d4 ) ions for I r4 + (5 d5 ) ions in BaIr O3 reduces the magnitudes of the SOI and a monoclinic structural distortion and rebalances the competition between the SOI and the lattice degrees of freedom to render an evolution from a magnetic insulting state to a robust metallic state. The central findings of this paper are as follows: (1) light Ru doping (0 transition-metal oxides.

  11. Phase transition study in strongly correlated VO{sub 2} based sensing systems

    Energy Technology Data Exchange (ETDEWEB)

    Simo, A., E-mail: alinesimo.aline@gmail.com [UNESCO-UNISA Africa Chair in Nanoscience’s/Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk ridge, P.O. Box 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure road, Somerset West 7129, P.O. Box 722, Somerset West, Western Cape Province (South Africa); Kaviyarasu, K. [UNESCO-UNISA Africa Chair in Nanoscience’s/Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk ridge, P.O. Box 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure road, Somerset West 7129, P.O. Box 722, Somerset West, Western Cape Province (South Africa); Mwakikunga, B. [Council for Scientific and Industrial Research, P.O. Box 395, Pretoria 0001 (South Africa); Madjoe, R. [Physics Department, University of Western Cape, 7535 Belville Cape Town (South Africa); Gibaud, A. [Laboratoire de Physique de l’Etat Condensé, Université du Maine Faculte des sciences, UPRESA 6087, 72085, Le Mans Cedex 9 (France); Maaza, M. [UNESCO-UNISA Africa Chair in Nanoscience’s/Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk ridge, P.O. Box 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure road, Somerset West 7129, P.O. Box 722, Somerset West, Western Cape Province (South Africa)

    2017-04-15

    Highlights: • At 230 °C for about 48 h to prepare successfully VO{sub 2} nanobelts. • 1D shows good sensing performance due to the large active surface of the material. • The good selectivity of methanol compared to acetone and isopropanol. • VOC compounds was observed at room temperature. - Abstract: Intermediate phase monoclinic M2 was observed by inducing in situ X-ray thermo diffraction on VO{sub 2} (M) nanoplatelets. The solid-solid phase transition occurs at around 65 °C assisted with the percolative transition metal-insulator. The existence of an intermediate crystalline phase with room temperature insulator phase and high temperature metallic phase across MIT in VO{sub 2} could be of relevance to understand structural contributions to the phase transition dynamics. In addition, pellet of VO{sub 2} nanostructures have shown to present good sensing properties to various alcohols vapors at room temperature and good selectivity of methanol with 5.54% sensitivity and limit detection below 5 ppm, compared to isopropanol 3.2% and acetone 2.4% respectively.

  12. Phase transitions in field theory

    International Nuclear Information System (INIS)

    Carvalho, C.A.A. de; Bollini, C.G.; Giambiagi, J.J.

    1984-01-01

    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) [pt

  13. A Difference in Using Atomic Layer Deposition or Physical Vapour Deposition TiN as Electrode Material in Metal-Insulator-Metal and Metal-Insulator-Silicon Capacitors

    NARCIS (Netherlands)

    Groenland, A.W.; Wolters, Robertus A.M.; Kovalgin, Alexeij Y.; Schmitz, Jurriaan

    2011-01-01

    In this work, metal-insulator-metal (MIM) and metal-insulator-silicon (MIS) capacitors are studied using titanium nitride (TiN) as the electrode material. The effect of structural defects on the electrical properties on MIS and MIM capacitors is studied for various electrode configurations. In the

  14. Phase transitions and neutron scattering

    International Nuclear Information System (INIS)

    Shirane, G.

    1993-01-01

    A review is given of recent advances in neutron scattering studies of solid state physics. I have selected the study of a structural phase transition as the best example to demonstrate the power of neutron scattering techniques. Since energy analysis is relatively easy, the dynamical aspects of a transition can be elucidated by the neutron probe. I shall discuss in some detail current experiments on the 100 K transition in SrTiO 3 , the crystal which has been the paradigm of neutron studies of phase transitions for many years. This new experiment attempts to clarify the relation between the neutron central peak, observed in energy scans, and the two length scales observed in recent x-ray diffraction studies where only scans in momentum space are possible. (author)

  15. Phase transitions and neutron scattering

    International Nuclear Information System (INIS)

    Shirane, G.

    1993-01-01

    A review is given of recent advances in neutron scattering studies of solid state physics. The author has selected the study of a structural phase transition as the best example to demonstrate the power of neutron scattering techniques. Since energy analysis is relatively easy, the dynamical aspects of a transition can be elucidated by the neutron probe. He will discuss in some detail current experiments on the 100K transition in SrTiO 3 , the crystal which has been the paradigm of neutron studies of phase transitions for many years. This new experiment attempts to clarify the relation between the neutron central peak, observed in energy scans, and the two length scales observed in recent x-ray diffraction studies where only scans in momentum space are possible

  16. 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.

  17. Phase transitions in operational risk.

    Science.gov (United States)

    Anand, Kartik; Kühn, Reimer

    2007-01-01

    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. Consequences of the analytical theory developed are analyzed using phase diagrams. We find coexistence of operational and nonoperational phases, much as in liquid-gas systems. Such systems are susceptible to discontinuous phase transitions from the operational to nonoperational phase via catastrophic breakdown. We find this feature to be robust against variation of the microscopic modeling assumptions.

  18. Infrared-transmittance tunable metal-insulator conversion device with thin-film-transistor-type structure on a glass substrate

    Directory of Open Access Journals (Sweden)

    Takayoshi Katase

    2017-05-01

    Full Text Available Infrared (IR transmittance tunable metal-insulator conversion was demonstrated on a glass substrate by using thermochromic vanadium dioxide (VO2 as the active layer in a three-terminal thin-film-transistor-type device with water-infiltrated glass as the gate insulator. Alternative positive/negative gate-voltage applications induce the reversible protonation/deprotonation of a VO2 channel, and two-orders of magnitude modulation of sheet-resistance and 49% modulation of IR-transmittance were simultaneously demonstrated at room temperature by the metal-insulator phase conversion of VO2 in a non-volatile manner. The present device is operable by the room-temperature protonation in an all-solid-state structure, and thus it will provide a new gateway to future energy-saving technology as an advanced smart window.

  19. Plasmon filters and resonators in metal-insulator-metal waveguides.

    Science.gov (United States)

    Neutens, P; Lagae, L; Borghs, G; Van Dorpe, P

    2012-02-13

    We present the numerical and experimental demonstration of plasmonic Bragg filters and resonators inside metal-insulator-metal (MIM) waveguides. The presented filters and resonators are fabricated using standard top down lithography methods. The optical bandgap of the integrated Bragg filters is experimentally observed and its optical properties are investigated as a function of the grating pitch and the number of grating periods. Transmission filters based on a nanocavity resonance were measured, obtaining Q-factors above 30. Tuning of the cavity wavelength was experimentally achieved by varying the cavity length.

  20. Heavy ion seeks phase transition

    International Nuclear Information System (INIS)

    Ducomet, B.

    1987-11-01

    The emergence of the phase transition language in the context of heavy ion collisions at the so called ''GANIL energies'' (typically 10 - 100 MeV/u) has led us to make more precise some current definitions adopted in statistical mechanics, and used in a much less clear way in the nuclear physics context [fr

  1. Disorder-induced localization in crystalline phase-change materials.

    Science.gov (United States)

    Siegrist, T; Jost, P; Volker, H; Woda, M; Merkelbach, P; Schlockermann, C; Wuttig, M

    2011-03-01

    Localization of charge carriers in crystalline solids has been the subject of numerous investigations over more than half a century. Materials that show a metal-insulator transition without a structural change are therefore of interest. Mechanisms leading to metal-insulator transition include electron correlation (Mott transition) or disorder (Anderson localization), but a clear distinction is difficult. Here we report on a metal-insulator transition on increasing annealing temperature for a group of crystalline phase-change materials, where the metal-insulator transition is due to strong disorder usually associated only with amorphous solids. With pronounced disorder but weak electron correlation, these phase-change materials form an unparalleled quantum state of matter. Their universal electronic behaviour seems to be at the origin of the remarkable reproducibility of the resistance switching that is crucial to their applications in non-volatile-memory devices. Controlling the degree of disorder in crystalline phase-change materials might enable multilevel resistance states in upcoming storage devices.

  2. The vanadium Magneli phases VnO(2n-1)

    OpenAIRE

    Schwingenschloegl, Udo; Eyert, Volker

    2004-01-01

    To compare the metal-insulator transitions (MITs) of VO2 and V2O3 we analyze the relations between the structural and electronic properties of the vanadium Magneli phases. These materials set up the homologous series VnO(2n-1) (3

  3. 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

  4. Phase transitions in dense matter

    Science.gov (United States)

    Dexheimer, Veronica; Hempel, Matthias; Iosilevskiy, Igor; Schramm, Stefan

    2017-11-01

    As the density of matter increases, atomic nuclei disintegrate into nucleons and, eventually, the nucleons themselves disintegrate into quarks. The phase transitions (PT's) between these phases can vary from steep first order to smooth crossovers, depending on certain conditions. First-order PT's with more than one globally conserved charge, so-called non-congruent PT's, have characteristic differences compared to congruent PT's. In this conference proceeding we discuss the non-congruence of the quark deconfinement PT at high densities and/or temperatures relevant for heavy-ion collisions, neutron stars, proto-neutron stars, supernova explosions, and compact-star mergers.

  5. Phase Transitions and Free Boundaries

    Science.gov (United States)

    1991-10-31

    V PHASE TRANSITIONS AND FREE BOUNDARIES FINAL REPORT AD -A243 412 DECO 3 1991 WILLARD MILLER, JR. U October 31, 1991 OFFICE OF NAVAL RESEARCH N0014-91...Einstein- University of Michigan Yang/Mills equations Abstract: The only static solution to the vacuum Einstein equations is the celebrated Schwarzschild ...equations to Maxwell’s equations, the only static solution is the Reissner- Nordstr6m metric which is again singular at the origin. Finally, for any gauge

  6. Gate-tunable phase transitions in thin flakes of 1T-TaS2

    Science.gov (United States)

    Yu, Yijun; Yang, Fangyuan; Lu, Xiu Fang; Yan, Ya Jun; Cho, Yong-Heum; Ma, Liguo; Niu, Xiaohai; Kim, Sejoong; Son, Young-Woo; Feng, Donglai; Li, Shiyan; Cheong, Sang-Wook; Chen, Xian Hui; Zhang, Yuanbo

    2015-03-01

    The ability to tune material properties using gating by electric fields is at the heart of modern electronic technology. It is also a driving force behind recent advances in two-dimensional systems, such as the observation of gate electric-field-induced superconductivity and metal-insulator transitions. Here, we describe an ionic field-effect transistor (termed an iFET), in which gate-controlled Li ion intercalation modulates the material properties of layered crystals of 1T-TaS2. The strong charge doping induced by the tunable ion intercalation alters the energetics of various charge-ordered states in 1T-TaS2 and produces a series of phase transitions in thin-flake samples with reduced dimensionality. We find that the charge-density wave states in 1T-TaS2 collapse in the two-dimensional limit at critical thicknesses. Meanwhile, at low temperatures, the ionic gating induces multiple phase transitions from Mott-insulator to metal in 1T-TaS2 thin flakes, with five orders of magnitude modulation in resistance, and superconductivity emerges in a textured charge-density wave state induced by ionic gating. Our method of gate-controlled intercalation opens up possibilities in searching for novel states of matter in the extreme charge-carrier-concentration limit.

  7. Metal-Insulator-Semiconductor Nanowire Network Solar Cells.

    Science.gov (United States)

    Oener, Sebastian Z; van de Groep, Jorik; Macco, Bart; Bronsveld, Paula C P; Kessels, W M M; Polman, Albert; Garnett, Erik C

    2016-06-08

    Metal-insulator-semiconductor (MIS) junctions provide the charge separating properties of Schottky junctions while circumventing the direct and detrimental contact of the metal with the semiconductor. A passivating and tunnel dielectric is used as a separation layer to reduce carrier recombination and remove Fermi level pinning. When applied to solar cells, these junctions result in two main advantages over traditional p-n-junction solar cells: a highly simplified fabrication process and excellent passivation properties and hence high open-circuit voltages. However, one major drawback of metal-insulator-semiconductor solar cells is that a continuous metal layer is needed to form a junction at the surface of the silicon, which decreases the optical transmittance and hence short-circuit current density. The decrease of transmittance with increasing metal coverage, however, can be overcome by nanoscale structures. Nanowire networks exhibit precisely the properties that are required for MIS solar cells: closely spaced and conductive metal wires to induce an inversion layer for homogeneous charge carrier extraction and simultaneously a high optical transparency. We experimentally demonstrate the nanowire MIS concept by using it to make silicon solar cells with a measured energy conversion efficiency of 7% (∼11% after correction), an effective open-circuit voltage (Voc) of 560 mV and estimated short-circuit current density (Jsc) of 33 mA/cm(2). Furthermore, we show that the metal nanowire network can serve additionally as an etch mask to pattern inverted nanopyramids, decreasing the reflectivity substantially from 36% to ∼4%. Our extensive analysis points out a path toward nanowire based MIS solar cells that exhibit both high Voc and Jsc values.

  8. Gibbs measures and phase transitions

    CERN Document Server

    Georgii, Hans-Otto

    2011-01-01

    From a review of the first edition: ""This book […] covers in depth a broad range of topics in the mathematical theory of phase transition in statistical mechanics. […] It is in fact one of the author's stated aims that this comprehensive monograph should serve both as an introductory text and as a reference for the expert."" (F. Papangelou, Zentralblatt MATH) The second edition has been extended by a new section on large deviations and some comments on the more recent developments in the area.

  9. 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

  10. 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.

  11. Phase transition in tensor models

    Energy Technology Data Exchange (ETDEWEB)

    Delepouve, Thibault [Laboratoire de Physique Théorique, CNRS UMR 8627, Université Paris Sud,91405 Orsay Cedex (France); Centre de Physique Théorique, CNRS UMR 7644, École Polytechnique,91128 Palaiseau Cedex (France); Gurau, Razvan [Centre de Physique Théorique, CNRS UMR 7644, École Polytechnique,91128 Palaiseau Cedex (France); Perimeter Institute for Theoretical Physics,31 Caroline St. N, N2L 2Y5, Waterloo, ON (Canada)

    2015-06-25

    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.

  12. Imaging metal-like monoclinic phase stabilized by surface coordination effect in vanadium dioxide nanobeam

    Science.gov (United States)

    Li, Zejun; Wu, Jiajing; Hu, Zhenpeng; Lin, Yue; Chen, Qi; Guo, Yuqiao; Liu, Yuhua; Zhao, Yingcheng; Peng, Jing; Chu, Wangsheng; Wu, Changzheng; Xie, Yi

    2017-06-01

    In correlated systems, intermediate states usually appear transiently across phase transitions even at the femtosecond scale. It therefore remains an open question how to determine these intermediate states--a critical issue for understanding the origin of their correlated behaviour. Here we report a surface coordination route to successfully stabilize and directly image an intermediate state in the metal-insulator transition of vanadium dioxide. As a prototype metal-insulator transition material, we capture an unusual metal-like monoclinic phase at room temperature that has long been predicted. Coordinate bonding of L-ascorbic acid molecules with vanadium dioxide nanobeams induces charge-carrier density reorganization and stabilizes metallic monoclinic vanadium dioxide, unravelling orbital-selective Mott correlation for gap opening of the vanadium dioxide metal-insulator transition. Our study contributes to completing phase-evolution pathways in the metal-insulator transition process, and we anticipate that coordination chemistry may be a powerful tool for engineering properties of low-dimensional correlated solids.

  13. Dynamical constraints on phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Morawetz, K. [Grand Accelerateur National d' Ions Lourds (GANIL), 14 - Caen (France); Laboratoire de Physique Corpusculaire, IN2P3-CNRS, ISMRA et Universite, 14 - Caen (France)

    2000-07-01

    The numerical solutions of nonlocal and local Boltzmann kinetic equations for the simulation of central heavy ion reactions are parameterized in terms of time dependent thermodynamical variables in the Fermi liquid sense. This allows to discuss dynamical trajectories in phase space. The nonequilibrium state is characterized by non-isobaric, non-isochoric etc conditions, called iso-nothing conditions. Therefore a combination of thermodynamical observables is constructed which allows to locate instabilities and points of possible phase transition in a dynamical sense. We find two different mechanisms of instability, a short time surface - dominated instability and later a spinodal - dominated volume instability. The latter one occurs only if the incident energies are not exceeding much the Fermi energy and might be attributed to spinodal decomposition. Oppositely the fast surface explosion occurs far outside the spinodal and pertains also in the cases where the system develops too fast for suffering the spinodal decomposition and where the system approaches equilibrium outside the spinodal. (author)

  14. Dynamical constraints on phase transitions

    International Nuclear Information System (INIS)

    Morawetz, K.

    2000-01-01

    The numerical solutions of nonlocal and local Boltzmann kinetic equations for the simulation of central heavy ion reactions are parameterized in terms of time dependent thermodynamical variables in the Fermi liquid sense. This allows to discuss dynamical trajectories in phase space. The nonequilibrium state is characterized by non-isobaric, non-isochoric etc conditions, called iso-nothing conditions. Therefore a combination of thermodynamical observables is constructed which allows to locate instabilities and points of possible phase transition in a dynamical sense. We find two different mechanisms of instability, a short time surface - dominated instability and later a spinodal - dominated volume instability. The latter one occurs only if the incident energies are not exceeding much the Fermi energy and might be attributed to spinodal decomposition. Oppositely the fast surface explosion occurs far outside the spinodal and pertains also in the cases where the system develops too fast for suffering the spinodal decomposition and where the system approaches equilibrium outside the spinodal. (author)

  15. Symmetry and Phase Transitions in Nuclei

    International Nuclear Information System (INIS)

    Iachello, F.

    2009-01-01

    Phase transitions in nuclei have received considerable attention in recent years, especially after the discovery that, contrary to expectations, systems at the critical point of a phase transition display a simple structure. In this talk, quantum phase transitions (QPT), i.e. phase transitions that occur as a function of a coupling constant that appears in the quantum Hamiltonian, H, describing the system, will be reviewed and experimental evidence for their occurrence in nuclei will be presented. The phase transitions discussed in the talk will be shape phase transitions. Different shapes have different symmetries, classified by the dynamic symmetries of the Interacting Boson Model, U(5), SU(3) and SO(6). Very recently, the concept of Quantum Phase Transitions has been extended to Excited State Quantum Phase Transitions (ESQPT). This extension will be discussed and some evidence for incipient ESQPT in nuclei will be presented. Systems at the critical point of a phase transition are called 'critical systems'. Approximate analytic formulas for energy spectra and other properties of 'critical nuclei', in particular for nuclei at the critical point of the second order U(5)-SO(6) transition, called E(5), and along the line of first order U(5)-SU(3) transitions, called X(5), will be presented. Experimental evidence for 'critical nuclei' will be also shown. Finally, the microscopic derivation of shape phase transitions in nuclei within the framework of density functional methods will be briefly discussed.(author)

  16. 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.

  17. Li-ion batteries: Phase transition

    International Nuclear Information System (INIS)

    Hou Peiyu; Zhang Yantao; Zhang Lianqi; Chu Geng; Gao Jian

    2016-01-01

    Progress in the research on phase transitions during Li + extraction/insertion processes in typical battery materials is summarized as examples to illustrate the significance of understanding phase transition phenomena in Li-ion batteries. Physical phenomena such as phase transitions (and resultant phase diagrams) are often observed in Li-ion battery research and already play an important role in promoting Li-ion battery technology. For example, the phase transitions during Li + insertion/extraction are highly relevant to the thermodynamics and kinetics of Li-ion batteries, and even physical characteristics such as specific energy, power density, volume variation, and safety-related properties. (topical review)

  18. Sound speed during the QCD phase transition

    International Nuclear Information System (INIS)

    Nagasawa, Michiyasu; Yokoyama, Jun'ichi

    1998-01-01

    The Jeans scale is estimated during the coexistence epoch of quark-gluon and hadron phases in the first-order QCD phase transition. It is shown that, contrary to previous claims, reduction of the sound speed is so little that the phase transition does not affect evolution of cosmological density fluctuations appreciably. (author)

  19. Transport and screen blockage characteristics of reflective metallic insulation materials

    International Nuclear Information System (INIS)

    Brocard, D.N.

    1984-01-01

    In the event of a LOCA within a nuclear power plant, it is possible for insulation debris to be generated by the break jet. Such debris has the potential for PWR sump screen (or BWR RHR suction inlet) blockage and thus can affect the long-term recirculation capability. In addition to the variables of break jet location and orientation, the types and quantities of debris which could be generated are dependent on the insulation materials employed. This experimental investigation was limited to reflective metallic insulation and components thereof. The study was aimed at determining the flow velocities needed to transport the insulation debris to the sump screens and the resulting modes of screen blockage. The tests revealed that thin metallic foils (0.0025 in. and 0.004 in.) could transport at low flow velocities, 0.2 to 0.5 ft/sec. Thicker foils (0.008 in.) transported at higher velocities, 0.4 to 0.8 ft/sec, and as fabricated half cylinder insulation units required velocities in excess of 1.0 ft/sec for transport. The tests also provided information on screen blockage patterns that showed blockage could occur at the lower portion of the screen as foils readily flipped on the screen when reaching it

  20. High-pressure electron-resonance studies of electronic, magnetic, and structural phase transitions. Progress report

    International Nuclear Information System (INIS)

    Pifer, J.H.; Croft, M.C.

    1983-01-01

    Research is described in development of a high-pressure electron-resonance probe capable of operating down to 1.5 0 K temperatures. The apparatus has been used to measure the EPR of a sample of DPPH at room temperature and zero pressure. EPR has been used to measure valence field instabilities in alloy systems. Studies have been done on metal-insulator transitions at high pressure, and are briefly described

  1. A metal/insulator tunnel transistor with 16 nm channel length

    OpenAIRE

    Sasajima, Ryouta; Fujimaru, Kouji; Matsumura, Hideki

    1999-01-01

    A nanometer transistor, metal/insulator tunnel transistor (MITT), which consists of only metal and insulator is experimentally studied. In the MITT, the Fowler-Nordheim tunneling currents through an insulator in lateral metal/insulator/metal structure are controlled by changing a voltage at a gate electrode upon the middle insulator, due to variation of tunnel-barrier thickness at the insulator. It is demonstrated that the MITT with 16 nm channel length fabricated by conventional photolithogr...

  2. Structural phase transition at the percolation threshold in epitaxial (La0.7Ca0.3MnO3)1-x:(MgO)x nanocomposite films.

    Science.gov (United States)

    Moshnyaga, V; Damaschke, B; Shapoval, O; Belenchuk, A; Faupel, J; Lebedev, O I; Verbeeck, J; van Tendeloo, G; Mücksch, M; Tsurkan, V; Tidecks, R; Samwer, K

    2003-04-01

    'Colossal magnetoresistance' in perovskite manganites such as La0.7Ca0.3MnO3 (LCMO), is caused by the interplay of ferro-paramagnetic, metal-insulator and structural phase transitions. Moreover, different electronic phases can coexist on a very fine scale resulting in percolative electron transport. Here we report on (LCMO)1-x:(MgO)x (0 strain. The largest colossal magnetoresistance of 10(5)% was observed at the percolation threshold in the conductivity at xc 0.3, which is coupled to a structural phase transition from orthorhombic (0 < x < or 0.1) to rhombohedral R3c structure (0.33 < or = x < or = 0.8). An increase of the Curie temperature for the Rc phase was observed. These results may provide a general method for controlling the magnetotransport properties of manganite-based composite films by appropriate choice of the second phase.

  3. 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...

  4. Locating phase transitions in computationally hard problems

    Indian Academy of Sciences (India)

    automatic planning and models of associative memory among others, all indicate the widespread prevalence of phase transitions in a computational context. It has also been .... depicted by the colour; number of nodes N = 250. Note the sharp inflection corresponding to a phase transition. is an evolution of the system to ...

  5. Late time phase transition as dark energy

    Indian Academy of Sciences (India)

    Abstract. We show that the dark energy field can naturally be described by the scalar condensates of a non-abelian gauge group. This gauge group is unified with the standard model gauge groups and it has a late time phase transition. The small phase transition explains why the positive acceleration of the universe is ...

  6. Scaling Concepts in Describing Continuous Phase Transitions

    Indian Academy of Sciences (India)

    Advanced Scientific. Research, Bengaluru. His research addresses the behaviour of liquids and disordered soft matter, including glassy dynamics and the glass transition, glasses, jamming, and phase transformations in liquids. Phase transitions, like the boiling of water upon increasing temperature, are a part of everyday ...

  7. Phases and phase transitions of S=1 bosons

    Indian Academy of Sciences (India)

    smukerjee

    Quantum phases and phase transitions of bosons. Subroto Mukerjee. Dept. of Physics & Centre for Quantum. Information and Quantum Computing (CQIQC). Indian Institute of Science, Bangalore. 77th annual meeting of the IAS, Nov. 20 2011, PRL Ahmedabad ...

  8. Phase transitions in solids under high pressure

    CERN Document Server

    Blank, Vladimir Davydovich

    2013-01-01

    Phase equilibria and kinetics of phase transformations under high pressureEquipment and methods for the study of phase transformations in solids at high pressuresPhase transformations of carbon and boron nitride at high pressure and deformation under pressurePhase transitions in Si and Ge at high pressure and deformation under pressurePolymorphic α-ω transformation in titanium, zirconium and zirconium-titanium alloys Phase transformations in iron and its alloys at high pressure Phase transformations in gallium and ceriumOn the possible polymorphic transformations in transition metals under pressurePressure-induced polymorphic transformations in АIBVII compoundsPhase transformations in AIIBVI and AIIIBV semiconductor compoundsEffect of pressure on the kinetics of phase transformations in iron alloysTransformations during deformation at high pressure Effects due to phase transformations at high pressureKinetics and hysteresis in high-temperature polymorphic transformations under pressureHysteresis and kineti...

  9. Quantum phase transition with dissipative frustration

    Science.gov (United States)

    Maile, D.; Andergassen, S.; Belzig, W.; Rastelli, G.

    2018-04-01

    We study the quantum phase transition of the one-dimensional phase model in the presence of dissipative frustration, provided by an interaction of the system with the environment through two noncommuting operators. Such a model can be realized in Josephson junction chains with shunt resistances and resistances between the chain and the ground. Using a self-consistent harmonic approximation, we determine the phase diagram at zero temperature which exhibits a quantum phase transition between an ordered phase, corresponding to the superconducting state, and a disordered phase, corresponding to the insulating state with localized superconducting charge. Interestingly, we find that the critical line separating the two phases has a nonmonotonic behavior as a function of the dissipative coupling strength. This result is a consequence of the frustration between (i) one dissipative coupling that quenches the quantum phase fluctuations favoring the ordered phase and (ii) one that quenches the quantum momentum (charge) fluctuations leading to a vanishing phase coherence. Moreover, within the self-consistent harmonic approximation, we analyze the dissipation induced crossover between a first and second order phase transition, showing that quantum frustration increases the range in which the phase transition is second order. The nonmonotonic behavior is reflected also in the purity of the system that quantifies the degree of correlation between the system and the environment, and in the logarithmic negativity as an entanglement measure that encodes the internal quantum correlations in the chain.

  10. The quantum phase-transitions of water

    Science.gov (United States)

    Fillaux, François

    2017-08-01

    It is shown that hexagonal ices and steam are macroscopically quantum condensates, with continuous spacetime-translation symmetry, whereas liquid water is a quantum fluid with broken time-translation symmetry. Fusion and vaporization are quantum phase-transitions. The heat capacities, the latent heats, the phase-transition temperatures, the critical temperature, the molar volume expansion of ice relative to water, as well as neutron scattering data and dielectric measurements are explained. The phase-transition mechanisms along with the key role of quantum interferences and that of Hartley-Shannon's entropy are enlightened. The notions of chemical bond and force-field are questioned.

  11. For progress in natural science: Materials international investigations of structural phase transformation and THz properties across metal–insulator transition in VO2/Al2O3 epitaxial films

    Directory of Open Access Journals (Sweden)

    Mengmeng Yang

    2015-10-01

    Full Text Available Vanadium dioxide (VO2 epitaxial thin films on (0001-oriented Al2O3 substrates were prepared using radio frequency (RF magnetron sputtering techniques. To study the metal-insulator-transition (MIT mechanism and extend the applications of VO2 epitaxial films at terahertz (THz band, temperature-dependent X-ray diffraction (XRD and THz time domain spectroscopy of the VO2 epitaxial films were performed. Both the lattice constants and THz transmission exhibited a similar and sharp transition that was similar to that observed for the electrical resistance. Consequently, the MIT of the VO2/Al2O3 epitaxial films should be co-triggered by the structural phase transition and electronic transition. Moreover, the very large resistance change (on the order of ~103 and THz response (with a transmission modulation ratio of ~87% in the VO2/Al2O3 epitaxial heterostructures are promising for electrical switch and electro-optical device applications.

  12. Phase transition phenomenon: A compound measure analysis

    Science.gov (United States)

    Kang, Bo Soo; Park, Chanhi; Ryu, Doojin; Song, Wonho

    2015-06-01

    This study investigates the well-documented phenomenon of phase transition in financial markets using combined information from both return and volume changes within short time intervals. We suggest a new measure for the phase transition behaviour of markets, calculated as a return distribution conditional on local variance in volume imbalance, and show that this measure successfully captures phase transition behaviour under various conditions. We analyse the intraday trade and quote dataset from the KOSPI 200 index futures, which includes detailed information on the original order size and the type of each initiating investor. We find that among these two competing factors, the submitted order size yields more explanatory power on the phenomenon of market phase transition than the investor type.

  13. Phase transition in the hadron gas model

    International Nuclear Information System (INIS)

    Gorenstein, M.I.; Petrov, V.K.; Zinov'ev, G.M.

    1981-01-01

    A class of statistical models of hadron gas allowing an analytical solution is considered. A mechanism of a possible phase transition in such a system is found and conditions for its occurence are determined [ru

  14. Phase Transitions, Diffraction Studies and Marginal Dimensionality

    DEFF Research Database (Denmark)

    Als-Nielsen, Jens Aage

    1985-01-01

    Continuous phase transitions and the associated critical phenomena have been one of the most active areas of research in condensed matter physics for several decades. This short review is only one cut through this huge subject and the author has chosen to emphasize diffraction studies as a basic...... experimental method and illustrate how diffraction experiments have revealed the role of dimensionality in the general classification of phase transitions...

  15. Phase transitions with four-spin interactions

    OpenAIRE

    Lebowitz, Joel L.; Ruelle, David

    2010-01-01

    Using an extended Lee-Yang theorem and GKS correlation inequalities, we prove, for a class of ferromagnetic multi-spin interactions, that they will have a phase transition(and spontaneous magnetization) if, and only if, the external field $h=0$ (and the temperature is low enough). We also show the absence of phase transitions for some nonferromagnetic interactions. The FKG inequalities are shown to hold for a larger class of multi-spin interactions.

  16. Phase transitions in two dimensions

    International Nuclear Information System (INIS)

    Henderson, D.

    1980-01-01

    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.) [pt

  17. Phase transitions in crystalline solids 1

    International Nuclear Information System (INIS)

    Walker, J.R.

    1993-09-01

    Many crystalline materials of interest to the Canadian Nuclear Program have the potential to undergo phase transitions in their range of application. During such phase transitions, a representation of the space group of the higher symmetry polymorph softens to induce the transition. This report is the first in a series of reports concerned with the group-theoretic properties of phase transitions in crystalline materials. The object of the research is to identify all spectroscopically-active soft modes for the 230 three-dimensional space groups. Identification of these soft modes will enable a detailed examination of phase transitions in materials of interest to the Canadian Nuclear Program and aid in the optimization of material properties. In this report, the group-theoretic properties of crystal structures and phase transitions are reviewed. It is demonstrated that the problem of extending a group reduces to that of determining its automorphisms. The automorphism groups of the crystallographic and icosahedral point groups are derived using a consistent presentation

  18. 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.

  19. 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 energies...

  20. Symmetry structure and phase transitions

    Indian Academy of Sciences (India)

    Spontaneous symmetry breaking is one of the most important concepts of all unified gauge theories. The idea that ... stable configurations of gauge and Higgs fields in the form of domain walls, cosmic strings and monopoles on the ..... pressure to balance the surface tension and the pressure of the hadron phase. The quark.

  1. Microgravity Two-Phase Flow Transition

    Science.gov (United States)

    Parang, M.; Chao, D.

    1999-01-01

    Two-phase flows under microgravity condition find a large number of important applications in fluid handling and storage, and spacecraft thermal management. Specifically, under microgravity condition heat transfer between heat exchanger surfaces and fluids depend critically on the distribution and interaction between different fluid phases which are often qualitatively different from the gravity-based systems. Heat transfer and flow analysis in two-phase flows under these conditions require a clear understanding of the flow pattern transition and development of appropriate dimensionless scales for its modeling and prediction. The physics of this flow is however very complex and remains poorly understood. This has led to various inadequacies in flow and heat transfer modeling and has made prediction of flow transition difficult in engineering design of efficient thermal and flow systems. In the present study the available published data for flow transition under microgravity condition are considered for mapping. The transition from slug to annular flow and from bubbly to slug flow are mapped using dimensionless variable combination developed in a previous study by the authors. The result indicate that the new maps describe the flow transitions reasonably well over the range of the data available. The transition maps are examined and the results are discussed in relation to the presumed balance of forces and flow dynamics. It is suggested that further evaluation of the proposed flow and transition mapping will require a wider range of microgravity data expected to be made available in future studies.

  2. Lattice-Symmetry-Driven Phase Competition in Vanadium Dioxide

    Energy Technology Data Exchange (ETDEWEB)

    Tselev, Alexander [ORNL; Luk' yanchuk, Prof. Igor A. [University of Picardie Jules Verne, Amiens, France; Ivanov, Ilia N [ORNL; Budai, John D [ORNL; Tischler, Jonathan Zachary [ORNL; Strelcov, Evgheni [Southern Illinois University; Kolmakov, Andrei [Southern Illinois University; Kalinin, Sergei V [ORNL

    2011-01-01

    We performed group-theoretical analysis of the symmetry relationships between lattice structures of R, M1, M2, and T phases of vanadium dioxide in the frameworks of the general Ginzburg-Landau phase transition theory. The analysis leads to a conclusion that the competition between the lower-symmetry phases M1, M2, and T in the metal-insulator transition is pure symmetry driven, since all the three phases correspond to different directions of the same multi-component structural order parameter. Therefore, the lower-symmetry phases can be stabilized in respect to each other by small perturbations such as doping or stress.

  3. Search for electronic phase separation at quantum phase transitions

    NARCIS (Netherlands)

    Pfleiderer, C.; Böni, P.; Franz, C.; Keller, T.; Neubauer, A.; Niklowitz, P.G.; Schmakat, P.; Schulz, M.; Huang, Y.; Mydosh, J.A.; Vojta, M.; Duncan, W.; Grosche, F.M.; Brando, M.; Deppe, M.; Geibel, C.; Steglich, F.; Krimmel, A.; Loidl, A.

    2010-01-01

    Phase separation and extreme sensitivity to disorder and defects are key features of electronic order near quantum phase transitions. Neutron depolarization imaging and neutron Larmor diffraction are new experimental techniques capable of providing detailed real-space and reciprocal-space

  4. Phase transitions in multiplicative competitive processes

    International Nuclear Information System (INIS)

    Shimazaki, Hideaki; Niebur, Ernst

    2005-01-01

    We introduce a discrete multiplicative process as a generic model of competition. Players with different abilities successively join the game and compete for finite resources. Emergence of dominant players and evolutionary development occur as a phase transition. The competitive dynamics underlying this transition is understood from a formal analogy to statistical mechanics. The theory is applicable to bacterial competition, predicting novel population dynamics near criticality

  5. Supersymmetric electroweak phase transition beyond perturbation theory

    CERN Document Server

    Cline, J M; Cline, James M; Kainulainen, Kimmo

    1996-01-01

    We compute the three-dimensional effective action for the minimal supersymmetric standard model, which describes the light modes of the theory near the finite-temperature electroweak phase transition, keeping the one-loop corrections from the third generation quarks and squarks. Using the lattice results of Kajantie et al. for the phase transition in the same class of 3-D models, we find that the strength of the phase transition is sufficient for electroweak baryogenesis, in much broader regions of parameter space than have been indicated by purely perturbative analyses. In particular we find that, while small values of \\tan\\beta are favored, positive results persist even for arbitrarily large values of \\tan\\beta if the mass of the A^0 boson is between 40 and 100 GeV, a region of parameters which has not been previously identified as being favorable for electroweak baryogenesis.

  6. Late-time cosmological phase transitions

    International Nuclear Information System (INIS)

    Schramm, D.N.

    1990-11-01

    It is shown that the potential galaxy formation and large-scale structure problems of objects existing at high redshifts (Z approx-gt 5), structures existing on scales of 100M pc as well as velocity flows on such scales, and minimal microwave anisotropies (ΔT/T) approx-lt 10 -5 can be solved if the seeds needed to generate structure form in a vacuum phase transition after decoupling. It is argued that the basic physics of such a phase transition is no more exotic than that utilized in the more traditional GUT scale phase transitions, and that, just as in the GUT case, significant random gaussian fluctuations and/or topological defects can form. Scale lengths of ∼100M pc for large-scale structure as well as ∼1 M pc for galaxy formation occur naturally. Possible support for new physics that might be associated with such a late-time transition comes from the preliminary results of the SAGE solar neutrino experiment, implying neutrino flavor mixing with values similar to those required for a late-time transition. It is also noted that a see-saw model for the neutrino masses might also imply a tau neutrino mass that is an ideal hot dark matter candidate. However, in general either hot or cold dark matter can be consistent with a late-time transition. 47 refs., 2 figs

  7. 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.

  8. 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.

  9. Dimension changing phase transitions in instanton crystals

    International Nuclear Information System (INIS)

    Kaplunovsky, Vadim; Sonnenschein, Jacob

    2014-01-01

    We investigate lattices of instantons and the dimension-changing transitions between them. Our ultimate goal is the 3D→4D transition, which is holographically dual to the phase transition between the baryonic and the quarkyonic phases of cold nuclear matter. However, in this paper (just as in http://dx.doi.org/10.1007/JHEP11(2012)047) we focus on lower dimensions — the 1D lattice of instantons in a harmonic potential V∝M 2 2 x 2 2 +M 3 2 x 2 2 +M 4 2 x 4 2 , and the zigzag-shaped lattice as a first stage of the 1D→2D transition. We prove that in the low- and moderate-density regimes, interactions between the instantons are dominated by two-body forces. This drastically simplifies finding the ground state of the instantons’ orientations, so we made a numeric scan of the whole orientation space instead of assuming any particular ansatz. We find that depending on the M 2 /M 3 /M 4 ratios, the ground state of instanton orientations can follow a wide variety of patterns. For the straight 1D lattices, we found orientations periodically running over elements of a ℤ 2 , Klein, prismatic, or dihedral subgroup of the SU(2)/ℤ 2 , as well as irrational but link-periodic patterns. For the zigzag-shaped lattices, we detected 4 distinct orientation phases — the anti-ferromagnet, another abelian phase, and two non-abelian phases. Allowing the zigzag amplitude to vary as a function of increasing compression force, we obtained the phase diagrams for the straight and zigzag-shaped lattices in the (force,M 3 /M 4 ), (chemical potential,M 3 /M 4 ), and (density,M 3 /M 4 ) planes. Some of the transitions between these phases are second-order while others are first-order. Our techniques can be applied to other types of non-abelian crystals

  10. Gate-tunable Phase Transitions in 1T-TaS$_2$

    OpenAIRE

    Yu, Yijun; Yang, Fangyuan; Lu, Xiu Fang; Yan, Ya Jun; Cho, Y. H.; Ma, Liguo; Niu, Xiaohai; Kim, Sejoong; Son, Young-Woo; Feng, Donglai; Li, Shiyan; Cheong, Sang-Wook; Chen, Xian Hui; Zhang, Yuanbo

    2014-01-01

    The ability to tune material properties using gate electric field is at the heart of modern electronic technology. It is also a driving force behind recent advances in two-dimensional systems, such as gate-electric-field induced superconductivity and metal-insulator transition. Here we describe an ionic field-effect transistor (termed "iFET"), which uses gate-controlled lithium ion intercalation to modulate the material property of layered atomic crystal 1T-TaS$_2$. The extreme charge doping ...

  11. Space Storm as a Dynamical Phase Transition

    Science.gov (United States)

    Wanliss, J. A.

    2006-12-01

    Fluctuations of the DST index were analyzed for several magnetic storms preceded by more than a week of extremely quiet conditions to establish that there is a rapid and unidirectional change in the Hurst scaling exponent at the time of storm onset. That is, the transition is accompanied by the specific signature of a rapid unidirectional change in the temporal fractal scaling of fluctuations in DST, signaling the formation of a new dynamical phase (or mode) which is considerably more organized than the background state. We compare these results to a model of multifractional Brownian motion and suggest that the relatively sudden change from a less correlated to a more correlated pattern of multiscale fluctuations at storm onset can be characterized in terms of nonequilibrium dynamical phase transitions. Initial results show that a dynamical transition in solar wind VBs is correlated with the storm onset for intense storms, suggesting that the transition observed in DST is of external solar wind origin, rather than internal magnetospheric origin. On the other hand, some results show a dynamical transition in solar wind scaling exponents not matched in DST. As well, we also present results for small storms where there is a strong dynamical transition in DST without a similar changes in the VBs scaling statistics. The results for small storms seem to reduce the importance of the solar wind fluctuations but the evidence for the intense storms seems to point to the solar wind as being responsible for providing the scale free properties in the DST fluctuations.

  12. Dynamical quantum phase transitions: a review

    Science.gov (United States)

    Heyl, Markus

    2018-05-01

    Quantum theory provides an extensive framework for the description of the equilibrium properties of quantum matter. Yet experiments in quantum simulators have now opened up a route towards the generation of quantum states beyond this equilibrium paradigm. While these states promise to show properties not constrained by equilibrium principles, such as the equal a priori probability of the microcanonical ensemble, identifying the general properties of nonequilibrium quantum dynamics remains a major challenge, especially in view of the lack of conventional concepts such as free energies. The theory of dynamical quantum phase transitions attempts to identify such general principles by lifting the concept of phase transitions to coherent quantum real-time evolution. This review provides a pedagogical introduction to this field. Starting from the general setting of nonequilibrium dynamics in closed quantum many-body systems, we give the definition of dynamical quantum phase transitions as phase transitions in time with physical quantities becoming nonanalytic at critical times. We summarize the achieved theoretical advances as well as the first experimental observations, and furthermore provide an outlook to major open questions as well as future directions of research.

  13. Scattering theory of topological phase transitions

    NARCIS (Netherlands)

    Fulga, Ion Cosma

    2013-01-01

    This thesis deals with characterizing topological phases as well as the transitions between them, focusing on transport properties and the effects of disorder. In Chapters 2 and 3 we derived scattering matrix expressions for the topological invariants of systems. This approach is oftentimes

  14. Locating phase transitions in computationally hard problems

    Indian Academy of Sciences (India)

    - ity does not seem to justify the .... Although phase transitions occur only in the thermodynamic limit, in the limit of infinitely large systems, as .... composition) for a system in the stochastic theory of adiabatic explosion [17]. In that thermodynamic ...

  15. Magnesium hydrides and their phase transitions

    Czech Academy of Sciences Publication Activity Database

    Paidar, Václav

    2016-01-01

    Roč. 41, č. 23 (2016), s. 9769-9773 ISSN 0360-3199 R&D Projects: GA MŠk(CZ) LD13069 Institutional support: RVO:68378271 Keywords : hydrogen * magnesium and transition metal hydrides * crystal structure stability * displacive phase transformations Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.582, year: 2016

  16. Vol. 3: Statistical Physics and Phase Transitions

    International Nuclear Information System (INIS)

    Sitenko, A.

    1993-01-01

    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

  17. Monte Carlo Simulation of Phase Transitions

    OpenAIRE

    村井, 信行; N., MURAI; 中京大学教養部

    1983-01-01

    In the Monte Carlo simulation of phase transition, a simple heat bath method is applied to the classical Heisenberg model in two dimensions. It reproduces the correlation length predicted by the Monte Carlo renor-malization group and also computed in the non-linear σ model

  18. Dynamical quantum phase transitions: a review.

    Science.gov (United States)

    Heyl, Markus

    2018-02-15

    Quantum theory provides an extensive framework for the description of the equilibrium properties of quantum matter. Yet experiments in quantum simulators have now opened up a route towards the generation of quantum states beyond this equilibrium paradigm. While these states promise to show properties not constrained by equilibrium principles, such as the equal a priori probability of the microcanonical ensemble, identifying the general properties of nonequilibrium quantum dynamics remains a major challenge, especially in view of the lack of conventional concepts such as free energies. The theory of dynamical quantum phase transitions attempts to identify such general principles by lifting the concept of phase transitions to coherent quantum real-time evolution. This review provides a pedagogical introduction to this field. Starting from the general setting of nonequilibrium dynamics in closed quantum many-body systems, we give the definition of dynamical quantum phase transitions as phase transitions in time with physical quantities becoming nonanalytic at critical times. We summarize the achieved theoretical advances as well as the first experimental observations, and furthermore provide an outlook to major open questions as well as future directions of research.

  19. 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.

  20. Scaling Concepts in Describing Continuous Phase Transitions

    Indian Academy of Sciences (India)

    these relations was among the main motivations that lead to scal- ing descriptions of behaviour near critical points. Phase Transitions: Preliminaries. The theoretical analyses of critical points, as well as their exposi- tion, have employed simplified models of interacting systems. We follow the same practice here, and define ...

  1. Two phase transitions in Nuclear Physics

    International Nuclear Information System (INIS)

    Bes, D.R.

    1985-01-01

    The status of the art of the problem associated with two phase transitions in the nuclear matter, viz.: the disappearance of the nuclear superfluiditiy with the raising of the rotation velocity and the appearance of an octupolar deformation in the actinide zone, is presented. (L.C.) [pt

  2. 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.

  3. The Physics of Structural Phase Transitions

    CERN Document Server

    Fujimoto, Minoru

    2005-01-01

    Phase transitions in which crystalline solids undergo structural changes present an interesting problem in the interplay between the crystal structure and the ordering process that is typically nonlinear. Intended for readers with prior knowledge of basic condensed-matter physics, this book emphasizes the physics behind spontaneous structural changes in crystals. Starting with the relevant thermodynamic principles, the text discusses the nature of order variables in collective motion in structural phase transitions, where a singularity in such a collective mode is responsible for lattice instability as revealed by soft phonons. In this book, critical anomalies at second-order structural transitions are first analyzed with the condensate model. Discussions on the nonlinear ordering mechanism are followed with the soliton theory, thereby interpreting the role of long-range order. Relevant details for nonlinear mathematics are therefore given for minimum necessity. The text also discusses experimental methods fo...

  4. Magnetocaloric materials and first order phase transitions

    DEFF Research Database (Denmark)

    Neves Bez, Henrique

    of the properties of such materials.The experimental characterization of these materials is done through various different methods, such as X-ray diffraction, magnetometry, calorimetry, direct measurements of entropy change, capacitance dilatometry, scanning electron microscopy,energy-dispersive X-ray spectrometry...... shows a paradoxical behavior; the material shows features of both a first order phase transition and of a second order one. Identities as shift of the heat capacity peak and an asymmetric growth of of the entropy change with magnetic field would describe this material transition as a first order one...... temperature and field independent is exaggerated and perhaps cannot be taken.A series of La(Fe,Mn,Si)13Hz with slightly changes in the composition is also evaluated here. This material may present a second order phase transition for large content of Mn and Si, which will become a first order one as the Mn...

  5. Computational advances in transition phase analysis

    International Nuclear Information System (INIS)

    Morita, K.; Kondo, S.; Tobita, Y.; Shirakawa, N.; Brear, D.J.; Fischer, E.A.

    1994-01-01

    In this paper, historical perspective and recent advances are reviewed on computational technologies to evaluate a transition phase of core disruptive accidents in liquid-metal fast reactors. An analysis of the transition phase requires treatment of multi-phase multi-component thermohydraulics coupled with space- and energy-dependent neutron kinetics. Such a comprehensive modeling effort was initiated when the program of SIMMER-series computer code development was initiated in the late 1970s in the USA. Successful application of the latest SIMMER-II in USA, western Europe and Japan have proved its effectiveness, but, at the same time, several areas that require further research have been identified. Based on the experience and lessons learned during the SIMMER-II application through 1980s, a new project of SIMMER-III development is underway at the Power Reactor and Nuclear Fuel Development Corporation (PNC), Japan. The models and methods of SIMMER-III are briefly described with emphasis on recent advances in multi-phase multi-component fluid dynamics technologies and their expected implication on a future reliable transition phase analysis. (author)

  6. Structural Phase Transition in Adipic Acid

    Science.gov (United States)

    Srinivasa Gopalan, R.; Kumaradhas, P.; Kulkarni, G. U.

    1999-11-01

    The structure of adipic acid undergoing phase transition at ∼136 K has been investigated using single-crystal x-ray diffraction. On lowering the temperature, the a parameter of the room temperature monoclinic cell decreases by ∼0.25 Å. Accompanying the transition, the b parameter nearly triples while a reverts back to the room temperature value. Two-thirds of the molecules in the structure loses center of symmetry. Packing diagrams of the high- and low-temperature phases on superposition reveal that there exist alternating domains perpendicular to the b direction, which contain molecules with and without symmetry. Unsymmetric molecules show displacements along the ac diagonal. Intermolecular hydrogen contacts involving carboxylic oxygens and the methylene hydrogens seem to increase interchain interactions in the low-temperature phase.

  7. Energy transition and phasing out nuclear

    International Nuclear Information System (INIS)

    Laponche, Bernard

    2013-05-01

    In the first part of this report, the author outlines and comments the need of an energy transition in the world: overview of world challenges (world energy consumption and its constraints, a necessary energy transition, new actors and new responsibilities), and describes the German example of an energy transition policy. In the second part, he presents and discusses the main reasons for phasing out nuclear: description of a nuclear plant operation (fission and chain reaction, heat production, production of radioactive elements, how to stop a nuclear reactor), safety and risk issues (protection arrangements, risk and consequence of a nuclear accident), issue of radioactive wastes, relationship between civil techniques and proliferation of nuclear weapons. In a third part, the author proposes an overview of the energy issue in France: final energy consumption, electricity production and consumption, primary energy consumption, characteristics of the French energy system (oil dependency, electricity consumption, and high share of nuclear energy in electricity production). In a last part, the author addresses the issue of energy transition in a perspective of phasing out nuclear: presentation of the Negawatt scenario, assessments made by Global Chance, main programmes of energy transition

  8. Phase transition signals of finite systems

    International Nuclear Information System (INIS)

    Duflot-Flandrois, Veronique

    2001-01-01

    Phase transitions are universal properties of interacting matter. They are well described if the considered system is infinite, by using standard thermodynamics. But in the case of small systems like atomic nuclei, this formalism cannot be applied anymore. Our aim is to propose a statistical mechanics approach in order to define the thermodynamical features of small open systems subject to non-saturating forces. We concentrate in particular on the definition and characterization for such systems of phase transitions belonging to the liquid gas universality class. Theoretical and experimental observables are defined to signal the occurrence and the order of this transition without any ambiguity. One of the most relevant and experimentally accessible observables consists in the study of kinetic energy fluctuations for a fixed value of the total deposited energy. In a first order phase transition such fluctuations become anomaly high and at the same time the size distribution appears to behave critically. All our results are obtained within numerical simulations of the lattice gas model with a nearest neighbors attractive interaction. Finally we check the influence of non-saturating forces, developing the specific example of the Coulomb interaction in the nucleus. Future improvements and perspectives at this work consist in the analysis of specific effects occurring in nuclei: isospin and quantum mechanics. (author) [fr

  9. Space storm as a phase transition

    Science.gov (United States)

    Wanliss, J. A.; Dobias, P.

    2007-04-01

    Fluctuations of the SYM-H index were analyzed for several space storms preceded by more than a week of extremely quiet conditions to establish that there was a rapid and unidirectional change in the Hurst scaling exponent at the time of storm onset. That is, the transition was accompanied by the specific signature of a rapid unidirectional change in the temporal fractal scaling of fluctuations in SYM-H, signaling the formation of a new dynamical phase (or mode) which was considerably more organized than the background state. We compare these results to a model of multifractional Brownian motion and suggest that the relatively sudden change from a less correlated to a more correlated pattern of multiscale fluctuations at storm onset can be characterized in terms of nonequilibrium dynamical phase transitions. The results show that a dynamical transition in solar wind VB is correlated with the storm onset for intense storms, suggesting that the dynamical transition observed in SYM-H is of external solar wind origin, rather than internal magnetospheric origin. However, some results showed a dynamical transition in solar wind scaling exponents not matched by similar transitions in SYM-H. In other instances, we observed some small storms where there was a strong dynamical transition in SYM-H without similar changes in the VB scaling statistics, suggesting that changes were due to internal magnetospheric processes. In summary, the results for intense storms points to the solar wind as being responsible for providing the scale free properties in the SYM-H fluctuations but the evidence for small storms clearly limit the importance of the solar wind fluctuations; their interaction is more complex than simple causality.

  10. About the dynamics of structural phase transitions

    International Nuclear Information System (INIS)

    Medeiros, J.T.N.

    1975-01-01

    The dynamics of structural phase transitions with a fourth order interaction between the soft phonon fields is studied in the 1/n approximation, using many body methods at finite temperatures. Two limits are considered: high transition temperature T sub(c) (classical limit) and T sub(c) = 0 (quantum limit). The dynamical contribution to the critical coefficient eta of the correlation function is calculated in these limits. It is found that there is no dynamical contribution to eta in the classical limit, whereas in the quantum limit eta is non-zero only for dimensions of the system d [pt

  11. 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.

  12. Interfacial engineering of metal-insulator-semiconductor junctions for efficient and stable photoelectrochemical water oxidation

    Science.gov (United States)

    Digdaya, Ibadillah A.; Adhyaksa, Gede W. P.; Trześniewski, Bartek J.; Garnett, Erik C.; Smith, Wilson A.

    2017-06-01

    Solar-assisted water splitting can potentially provide an efficient route for large-scale renewable energy conversion and storage. It is essential for such a system to provide a sufficiently high photocurrent and photovoltage to drive the water oxidation reaction. Here we demonstrate a photoanode that is capable of achieving a high photovoltage by engineering the interfacial energetics of metal-insulator-semiconductor junctions. We evaluate the importance of using two metals to decouple the functionalities for a Schottky contact and a highly efficient catalyst. We also illustrate the improvement of the photovoltage upon incidental oxidation of the metallic surface layer in KOH solution. Additionally, we analyse the role of the thin insulating layer to the pinning and depinning of Fermi level that is responsible to the resulting photovoltage. Finally, we report the advantage of using dual metal overlayers as a simple protection route for highly efficient metal-insulator-semiconductor photoanodes by showing over 200 h of operational stability.

  13. Transition phase in LMFBR hypothetical accidents

    International Nuclear Information System (INIS)

    Ostensen, R.W.; Henninger, R.J.; Jackson, J.F.

    1976-01-01

    Mechanistic analyses of transient-under-cooling accidents have led in some cases to a mild initiating phase instead of a direct hydrodynamic disassembly of the core. The fuel is then trapped in the core by the strong mechanical surroundings and blockages formed by refrozen cladding steel and/or fuel. The formation of fuel blockages has been verified experimentally. The bottled-up core will boil on fission and decay heat, with steel as the working fluid. Boil-up in a churn turbulent flow regime may prevent recriticality due to fuel recompaction. Ultimate fuel removal from the core is probably by a two-phase blow-down after permanent leakage paths are opened. However, a vigorous recriticality can not be precluded. Reactors with void coefficients larger than that in CRBR are more likely to disassemble in the initiating phase, so the transition phase may be unique to small cores

  14. Gravitational Waves from a Dark Phase Transition.

    Science.gov (United States)

    Schwaller, Pedro

    2015-10-30

    In this work, we show that a large class of models with a composite dark sector undergo a strong first order phase transition in the early Universe, which could lead to a detectable gravitational wave signal. We summarize the basic conditions for a strong first order phase transition for SU(N) dark sectors with n_{f} flavors, calculate the gravitational wave spectrum and show that, depending on the dark confinement scale, it can be detected at eLISA or in pulsar timing array experiments. The gravitational wave signal provides a unique test of the gravitational interactions of a dark sector, and we discuss the complementarity with conventional searches for new dark sectors. The discussion includes the twin Higgs and strongly interacting massive particle models as well as symmetric and asymmetric composite dark matter scenarios.

  15. Electroweak monopoles and the electroweak phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Arunasalam, Suntharan; Kobakhidze, Archil [The University of Sydney, ARC Centre of Excellence for Particle Physics at the Terascale, School of Physics, Sydney, NSW (Australia)

    2017-07-15

    We consider an isolated electroweak monopole solution within the Standard Model with a nonlinear Born-Infeld extension of the hypercharge gauge field. Monopole (and dyon) solutions in such an extension are regular and their masses are predicted to be proportional to the Born-Infeld mass parameter. We argue that cosmological production of electroweak monopoles may delay the electroweak phase transition and make it more strongly first order for monopole masses M >or similar 9.3 . 10{sup 3} TeV, while the nucleosynthesis constraints on the abundance of relic monopoles impose the bound M phase transition. (orig.)

  16. Interface properties of SiO2/n-GaN metal-insulator-semiconductor structures

    OpenAIRE

    Yoshitaka, Nakano; Takashi, Jimbo

    2002-01-01

    Electrical characterization of SiO2/n-GaN metal-insulator-semiconductor structures fabricated on sapphire substrates was performed by using high-frequency pulsed capacitance-voltage and capacitance-transient techniques. Fast and slow capacitance transients are clearly seen after applying reverse voltages, reflecting thermal emissions of carriers from the SiO2/GaN interface. The temperature dependence of the capacitance-voltage characteristics shows capacitance saturation in deep depletion (>1...

  17. All-Graphene Planar Self-Switching MISFEDs, Metal-Insulator-Semiconductor Field-Effect Diodes

    OpenAIRE

    Al-Dirini, Feras; Hossain, Faruque M.; Nirmalathas, Ampalavanapillai; Skafidas, Efstratios

    2014-01-01

    Graphene normally behaves as a semimetal because it lacks a bandgap, but when it is patterned into nanoribbons a bandgap can be introduced. By varying the width of these nanoribbons this band gap can be tuned from semiconducting to metallic. This property allows metallic and semiconducting regions within a single Graphene monolayer, which can be used in realising two-dimensional (2D) planar Metal-Insulator-Semiconductor field effect devices. Based on this concept, we present a new class of na...

  18. Phase transitions and elementary-particle physics

    International Nuclear Information System (INIS)

    Creutz, M.

    1981-01-01

    The reason physicists have recently taken an intense interest in the statistical mechanics of certain lattice models is reviewed. Phase transitions in these systems are of direct relevance to whether the gauge theory of interacting quarks and gluons can prevent the quark as appearing as a free isolated object. Monte Carlo simulation techniques have given the strongest evidence for the confinement phenomenon and are beginning to make numerical predictions in strong interaction physics

  19. Gravitation, phase transitions, and the big bang

    International Nuclear Information System (INIS)

    Krauss, L.M.

    1982-01-01

    Introduced here is a model of the early universe based on the possibility of a first-order phase transition involving gravity, and arrived at by a consideration of instabilities in the semiclassical theory. The evolution of the system is very different from the standard Friedmann-Robertson-Walker big-bang scenario, indicating the potential importance of semiclassical finite-temperature gravitational effects. Baryosynthesis and monopole production in this scenario are also outlined

  20. 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.

  1. Compact Stars with Sequential QCD Phase Transitions.

    Science.gov (United States)

    Alford, Mark; Sedrakian, Armen

    2017-10-20

    Compact stars may contain quark matter in their interiors at densities exceeding several times the nuclear saturation density. We explore models of such compact stars where there are two first-order phase transitions: the first from nuclear matter to a quark-matter phase, followed at a higher density by another first-order transition to a different quark-matter phase [e.g., from the two-flavor color-superconducting (2SC) to the color-flavor-locked (CFL) phase]. We show that this can give rise to two separate branches of hybrid stars, separated from each other and from the nuclear branch by instability regions, and, therefore, to a new family of compact stars, denser than the ordinary hybrid stars. In a range of parameters, one may obtain twin hybrid stars (hybrid stars with the same masses but different radii) and even triplets where three stars, with inner cores of nuclear matter, 2SC matter, and CFL matter, respectively, all have the same mass but different radii.

  2. Investigation of electronic phase segregation in La0.75Ca0.15Sr0.10MnO3 manganite

    International Nuclear Information System (INIS)

    Venkatesh, R; Venkateshwarlu, D; Pryds, Nini

    2014-01-01

    The effect of electronic phase segregation in a broad metal-Insulator transition (MIT) observed in La 0.75 Ca 0.25-x Sr x MnO 3 (x=0.1) composition is investigated using heat capacity, magnetization, electrical resistivity and magnetoresistance measurements. The negative magnetoresistance of 65% in an applied magnetic field of 12 T and 15% in 1 T with a broad working range of 18 K around 300 K which is beneficial for room temperature colossal magnetoresistance (CMR) applications. The broad transition in temperature dependent zero field resistivity measurement is analyzed in the light of percolation model indicates the abundance of insulating/metallic clusters in metallic/insulating region. A significant difference between the metallic fraction around the MIT and the ferromagnetic phases observed around the Curie temperature demonstrates the interplay between volume of itinerant and polaronic electronic phases.

  3. 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

  4. Thermally tunable broadband omnidirectional and polarization-independent super absorber using phase change material VO2

    Directory of Open Access Journals (Sweden)

    Zhejun Liu

    Full Text Available In this letter, we numerically demonstrate a thermally tunable super absorber by using phase change material VO2 as absorbing layer in metal-insulator-metal structure. An omnidirectional super absorption at λ=2.56μm can be realized by heating the patterned grating VO2 film due to magnetic resonance mechanism. Furthermore, a broadband super absorption higher than 0.8 in the entire 1.6μm–4μm region is achieved when VO2 film is patterned chessboard structure and transformed to metal phase beyond transition temperature. This broadband super absorption can be fulfilled in a wide range of incident angle (0°–70° and under all polarization conditions. Keywords: Phase change material, Metal-insulator-metal, Super absorption, Magnetic resonance

  5. Phase transitions in shocked porous quartz

    Science.gov (United States)

    Akin, M. C.; Crum, R. S.; Lind, J.; Pagan, D. C.; Homel, M. A.; Hurley, R. C.; Herbold, E. B.

    2017-06-01

    The presence of porosity in granular media provides the means to probe regions of the phase diagram that do not coincide with the principal Hugoniot. In particular, the potential for increased heating is likely to lead to observable changes in phase boundaries. 55% dense quartz and forsterite were prepared by tap filling. These samples were shock compressed using the two stage light gas gun at DCS-APS to examine the impact of the increased porosity on the phase boundary. Here we discuss the observed changes to phase in quartz and forsterite compared to the fully dense materials, the effects of porosity upon compaction and phase transitions, and the implications for constructing the phase diagram. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Work was supported by LLNL's LDRD program under Grant 16-ERD-010. The Dynamic Compression Sector (35) is supported by Department of Energy / National Nuclear Security Administration under Award Number DE-NA0002442. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

  6. The transition to chaotic phase synchronization

    Science.gov (United States)

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

    2012-08-01

    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 Rössler 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 descibe how the formation of multi-layered resonance cycles in the synchronization domain is related to the torus doubling bifurcations that take place outside this domain. By examining a physiology-based model of the blood flow regulation to the individual functional unit (nephron) of the kidney we demonstrate how a similar bifurcation structure may arise in this system as a response to a periodically 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.

  7. Casimir amplitudes in topological quantum phase transitions.

    Science.gov (United States)

    Griffith, M A; Continentino, M A

    2018-01-01

    Topological phase transitions constitute a new class of quantum critical phenomena. They cannot be described within the usual framework of the Landau theory since, in general, the different phases cannot be distinguished by an order parameter, neither can they be related to different symmetries. In most cases, however, one can identify a diverging length at these topological transitions. This allows us to describe them using a scaling approach and to introduce a set of critical exponents that characterize their universality class. Here we consider some relevant models of quantum topological transitions associated with well-defined critical exponents that are related by a quantum hyperscaling relation. We extend to these models a finite-size scaling approach based on techniques for calculating the Casimir force in electromagnetism. This procedure allows us to obtain universal Casimir amplitudes at their quantum critical points. Our results verify the validity of finite-size scaling in these systems and confirm the values of the critical exponents obtained previously.

  8. Casimir amplitudes in topological quantum phase transitions

    Science.gov (United States)

    Griffith, M. A.; Continentino, M. A.

    2018-01-01

    Topological phase transitions constitute a new class of quantum critical phenomena. They cannot be described within the usual framework of the Landau theory since, in general, the different phases cannot be distinguished by an order parameter, neither can they be related to different symmetries. In most cases, however, one can identify a diverging length at these topological transitions. This allows us to describe them using a scaling approach and to introduce a set of critical exponents that characterize their universality class. Here we consider some relevant models of quantum topological transitions associated with well-defined critical exponents that are related by a quantum hyperscaling relation. We extend to these models a finite-size scaling approach based on techniques for calculating the Casimir force in electromagnetism. This procedure allows us to obtain universal Casimir amplitudes at their quantum critical points. Our results verify the validity of finite-size scaling in these systems and confirm the values of the critical exponents obtained previously.

  9. Phase stability of transition metals and alloys

    International Nuclear Information System (INIS)

    Hixson, R.S.; Schiferl, D.; Wills, J.M.; Hill, M.A.

    1997-01-01

    This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). This project was focused on resolving unexplained differences in calculated and measured phase transition pressures in transition metals. Part of the approach was to do new, higher accuracy calculations of transmission pressures for group 4B and group 6B metals. Theory indicates that the transition pressures for these baseline metals should change if alloyed with a d-electron donor metal, and calculations done using the Local Density Approximation (LDA) and the Virtual Crystal Approximation (VCA) indicate that this is true. Alloy systems were calculated for Ti, Zr and Hf based alloys with various solute concentrations. The second part of the program was to do new Diamond Anvil Cell (DAC) measurements to experimentally verify calculational results. Alloys were prepared for these systems with grain size suitable for Diamond Anvil Cell experiments. Experiments were done on pure Ti as well as Ti-V and Ti-Ta alloys. Measuring unambiguous transition pressures for these systems proved difficult, but a new technique developed yielded good results

  10. Scale invariance from phase transitions to turbulence

    CERN Document Server

    Lesne, Annick

    2012-01-01

    During a century, from the Van der Waals mean field description (1874) of gases to the introduction of renormalization group (RG techniques 1970), thermodynamics and statistical physics were just unable to account for the incredible universality which was observed in numerous critical phenomena. The great success of RG techniques is not only to solve perfectly this challenge of critical behaviour in thermal transitions but to introduce extremely useful tools in a wide field of daily situations where a system exhibits scale invariance. The introduction of scaling, scale invariance and universality concepts has been a significant turn in modern physics and more generally in natural sciences. Since then, a new "physics of scaling laws and critical exponents", rooted in scaling approaches, allows quantitative descriptions of numerous phenomena, ranging from phase transitions to earthquakes, polymer conformations, heartbeat rhythm, diffusion, interface growth and roughening, DNA sequence, dynamical systems, chaos ...

  11. Quantum phase transitions in matrix product states

    International Nuclear Information System (INIS)

    Zhu Jingmin

    2008-01-01

    We present a new general and much simpler scheme to construct various quantum phase transitions (QPTs) in spin chain systems with matrix product ground states. By use of the scheme we take into account one kind of matrix product state (MPS) QPT and provide a concrete model. We also study the properties of the concrete example and show that a kind of QPT appears, accompanied by the appearance of the discontinuity of the parity absent block physical observable, diverging correlation length only for the parity absent block operator, and other properties which are that the fixed point of the transition point is an isolated intermediate-coupling fixed point of renormalization flow and the entanglement entropy of a half-infinite chain is discontinuous. (authors)

  12. Quantum Phase Transitions in Matrix Product States

    International Nuclear Information System (INIS)

    Jing-Min, Zhu

    2008-01-01

    We present a new general and much simpler scheme to construct various quantum phase transitions (QPTs) in spin chain systems with matrix product ground states. By use of the scheme we take into account one kind of matrix product state (MPS) QPT and provide a concrete model. We also study the properties of the concrete example and show that a kind of QPT appears, accompanied by the appearance of the discontinuity of the parity absent block physical observable, diverging correlation length only for the parity absent block operator, and other properties which are that the fixed point of the transition point is an isolated intermediate-coupling fixed point of renormalization flow and the entanglement entropy of a half-infinite chain is discontinuous

  13. A difference in using atomic layer deposition or physical vapour deposition TiN as electrode material in metal-insulator-metal and metal-insulator-silicon capacitors.

    Science.gov (United States)

    Groenland, A W; Wolters, R A M; Kovalgin, A Y; Schmitz, J

    2011-09-01

    In this work, metal-insulator-metal (MIM) and metal-insulator-silicon (MIS) capacitors are studied using titanium nitride (TiN) as the electrode material. The effect of structural defects on the electrical properties on MIS and MIM capacitors is studied for various electrode configurations. In the MIM capacitors the bottom electrode is a patterned 100 nm TiN layer (called BE type 1), deposited via sputtering, while MIS capacitors have a flat bottom electrode (called BE type 2-silicon substrate). A high quality 50-100 nm thick SiO2 layer, made by inductively-coupled plasma CVD at 150 degrees C, is deposited as a dielectric on top of both types of bottom electrodes. BE type 1 (MIM) capacitors have a varying from low to high concentration of structural defects in the SiO2 layer. BE type 2 (MIS) capacitors have a low concentration of structural defects and are used as a reference. Two sets of each capacitor design are fabricated with the TiN top electrode deposited either via physical vapour deposition (PVD, i.e., sputtering) or atomic layer deposition (ALD). The MIM and MIS capacitors are electrically characterized in terms of the leakage current at an electric field of 0.1 MV/cm (I leak) and for different structural defect concentrations. It is shown that the structural defects only show up in the electrical characteristics of BE type 1 capacitors with an ALD TiN-based top electrode. This is due to the excellent step coverage of the ALD process. This work clearly demonstrates the sensitivity to process-induced structural defects, when ALD is used as a step in process integration of conductors on insulation materials.

  14. 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.

  15. Phase transitions in de Sitter space

    Directory of Open Access Journals (Sweden)

    Alexander Vilenkin

    1983-10-01

    Full Text Available An effective potential in de Sitter space is calculated for a model of two interacting scalar fields in one-loop approximation and in a self-consistent approximation which takes into account an infinite set of diagrams. Various approaches to renormalization in de Sitter space are discussed. The results are applied to analyze the phase transition in the Hawking-Moss version of the inflationary universe scenario. Requiring that inflation is sufficiently large, we derive constraints on the parameters of the model.

  16. 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.

  17. Traders' behavioral coupling and market phase transition

    Science.gov (United States)

    Ma, Rong; Zhang, Yin; Li, Honggang

    2017-11-01

    Traditional economic theory is based on the assumption that traders are completely independent and rational; however, trading behavior in the real market is often coupled by various factors. This paper discusses behavioral coupling based on the stock index in the stock market, focusing on the convergence of traders' behavior, its effect on the correlation of stock returns and market volatility. We find that the behavioral consensus in the stock market, the correlation degree of stock returns, and the market volatility all exhibit significant phase transitions with stronger coupling.

  18. Phase Transitions of Thermoelectric TAGS-85

    OpenAIRE

    Kumar, Anil; Vermeulen, Paul A.; Kooi, Bart J.; Rao, Jiancun; van Eijck, Lambert; Schwarzmueller, Stefan; Oeckler, Oliver; Blake, Graeme R.

    2017-01-01

    The alloys (GeTe)x(AgSbTe2)100–x, commonly known as TAGS-x, are among the best performing p-type thermoelectric materials for the composition range 80 ≤ x ≤ 90 and in the temperature range 200–500 °C. They adopt a rhombohedrally distorted rocksalt structure at room temperature and are reported to undergo a reversible phase transition to a cubic structure at ∼250 °C. However, we show that, for the optimal x = 85 composition (TAGS-85), both the structural and thermoelectric properties are highl...

  19. 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.

  20. Miscellaneous results on the electroweak phase transition

    International Nuclear Information System (INIS)

    Ilgenfritz, E.M.; Schiller, A.

    1994-12-01

    We present new 4-D Monte Carlo results characterizing the strength of the finite temperature phase transition for Higgs/W mass ratios 1.0 and 0.6, obtained on isotropic lattices mainly with N s = 16, N t = 2. We discuss the distribution of a gauge invariant block spin order parameter, estimating the Higgs condensate Φ c at T c . We use the Potvin/Rebbi method in order to find the interface tension α/T c 3 . We demonstrate how the multi-histogram method (giving free energy differences) can be used to avoid the limiting procedure δ K → 0. From pure-phase histograms at K c , extrapolated with the help of this method, we estimate the latent heat Δε/T c 4 . Actual time series at lower Higgs mass require blocking in order to determine the jump of the lattice observables. (orig.)

  1. Transitional Phenomena on Phase Change Materials

    Directory of Open Access Journals (Sweden)

    Wójcik Tadeusz M.

    2014-03-01

    Full Text Available One of the most significant problem with technology development is transferring of large heat fluxes, which requires constant heat transfer temperature (in the specified temperature range. This problem concern mainly the nuclear energetics, space technologies, military technologies and most of all electronics containing integrated circuits with very large scale of integrations. Intensive heat transfer and thermal energy storage are possible by the use of phase change materials (PCMs. In the paper there are presented preliminary results of research on the use of liquid-gas (L-G PCMs and solid-solid phase change materials (S-S PCMs. For L-G PCMs the boiling characteristics were determined by increasing and decreasing the heat flux, which for certain sets of structural parameters of the heating surface and the physical properties of the liquid induce a variety of forms of transitional phenomena. Thermal energy storage is much more effective when using PCMs than sensible heat.

  2. Metal-insulator transition and the Pr.sup.3+./sup./Pr.sup.4.+./sup. valence shift in (Pr.sub.1-y./sub.Y.sub.y./sub.).sub.0.7./sub.Ca.sub.0.3./sub.CoO.sub.3./sub..

    Czech Academy of Sciences Publication Activity Database

    Hejtmánek, Jiří; Šantavá, Eva; Knížek, Karel; Maryško, Miroslav; Jirák, Zdeněk; Naito, T.; Sasaki, H.; Fujishiro, H.

    2010-01-01

    Roč. 82, č. 16 (2010), 165107/1-165107/7 ISSN 1098-0121 R&D Projects: GA ČR GA202/09/0421 Institutional research plan: CEZ:AV0Z10100521 Keywords : spin-state transition * magnetic-properties * crystal-field * transport * La 1-x Sr x CoO 3 Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.772, year: 2010

  3. Influence of dimensionality on phase transition in VO2 nanocrystals

    Directory of Open Access Journals (Sweden)

    Blagojević V.A.

    2013-01-01

    Full Text Available Hydrothermally synthesized one-dimensional and two-dimensional nanocrystals of VO2 undergo phase transition around 65°C, where temperature and mechanism of phase transition are dependent on dimensionality of nanocrystals. Both nanocrystalline samples exhibit depression of phase transition temperature compared to the bulk material, the magnitude of which depends on the dimensionality of the nanocrystal. One-dimensional nanoribbons exhibit lower phase transition temperature and higher values of apparent activation energy than two-dimensional nanosheets. The phase transition exhibits as a complex process with somewhat lower value of enthalpy than the phase transition in the bulk, probably due to higher proportion of surface atoms in the nanocrystals. High values of apparent activation energy indicate that individual steps of the phase transition involve simultaneous movement of large groups of atoms, as expected for single-domain nanocrystalline materials. [Projekat Ministarstva nauke Republike Srbije, br. 142015

  4. Heat capacity characterization at phase transition temperature of Agl superionic

    International Nuclear Information System (INIS)

    Widowati, Arie

    2000-01-01

    The phase transition of Agl superionic conductor was investigated by calorometric. A single phase transition was found at (153±5) o C which corresponds to the α - β transition. Calorimetric measurement showed an anomalously high heat capacity with a large discontinues change in the Arrhenius plot, was found above the transition temperature of β - α phase. The maximum heat capacity was found to be ±19.7 cal/gmol. Key words : superionic conductor, thermal capacity

  5. Phase transitions and doping in semiconductor nanocrystals

    Science.gov (United States)

    Sahu, Ayaskanta

    impurities (or doping) allows further control over the electrical and optical properties of nanocrystals. However, while impurity doping in bulk semiconductors is now routine, doping of nanocrystals remains challenging. In particular, evidence for electronic doping, in which additional electrical carriers are introduced into the nanocrystals, has been very limited. Here, we adopt a new approach to electronic doping of nanocrystals. We utilize a partial cation exchange to introduce silver impurities into cadmium selenide (CdSe) and lead selenide (PbSe) nanocrystals. Results indicate that the silver-doped CdSe nanocrystals show a significant increase in fluorescence intensity, as compared to pure CdSe nanocrystals. We also observe a switching from n- to p-type doping in the silver-doped CdSe nanocrystals with increased silver amounts. Moreover, the silver-doping results in a change in the conductance of both PbSe and CdSe nanocrystals and the magnitude of this change depends on the amount of silver incorporated into the nanocrystals. In the bulk, silver chalcogenides (Ag2E, E=S, Se, and Te) possess a wide array of intriguing properties, including superionic conductivity. In addition, they undergo a reversible temperature-dependent phase transition which induces significant changes in their electronic and ionic properties. While most of these properties have been examined extensively in bulk, very few studies have been conducted at the nanoscale. We have recently developed a versatile synthesis that yields colloidal silver chalcogenide nanocrystals. Here, we study the size dependence of their phase-transition temperatures. We utilize differential scanning calorimetry and in-situ X-ray diffraction analyses to observe the phase transition in nanocrystal assemblies. We observe a significant deviation from the bulk alpha (low-temperature) to beta (high-temperature) phase-transition temperature when we reduce their size to a few nanometers. Hence, these nanocrystals provide great

  6. Modeling and design methodology for metal-insulator-metal plasmonic Bragg reflectors.

    Science.gov (United States)

    Hosseini, Amir; Nejati, Hamid; Massoud, Yehia

    2008-02-04

    In this paper, we present a modeling and design methodology based on characteristic impedance for plasmonic waveguides with Metal-Insulator-Metal (MIM) configuration. Finite-Difference Time-Domain (FDTD) simulations indicate that the impedance matching results in negligible reflection at discontinuities in MIM heterostructures. Leveraging the MIM impedance model, we present a general Transfer Matrix Method model for MIM Bragg reflectors and validate our model against FDTD simulations. We show that both periodically stacked dielectric layers of different thickness or different material can achieve the same performance in terms of propagation loss and minimum transmission at the central bandgap frequency in the case of a finite number of periods.

  7. All-optical logic gates in plasmonic metal-insulator-metal nanowaveguide with slot cavity resonator

    Science.gov (United States)

    Dolatabady, Alireza; Granpayeh, Nosrat

    2017-04-01

    We demonstrate the compact all-optical logic XOR and OR gates in subwavelength plasmonic metal-insulator-metal waveguides with slot cavity resonators, especially for telecommunication wavelengths, with an extinction ratio of 25 dB, which can provide nanoscale logic integrated circuits. The gates behavior is based on suppression or enhancement of resonant modes in a slot cavity resonator induced by a change in position of input ports. The performance of the gates is discussed analytically and verified by the numerical method of finite-difference time-domain (FDTD).

  8. All-optical bit magnitude comparator device using metal-insulator-metal plasmonic waveguide

    Science.gov (United States)

    Kumar, Santosh; Singh, Lokendra; Chen, Nan-Kuang

    2017-12-01

    A plasmonic metal-insulator-metal (MIM) waveguide has great success in confining the surface plasmon up to a deep subwavelength scale. The structure of a nonlinear Mach-Zehnder interferometer (MZI) using a plasmonic MIM waveguide has been analyzed. A one-bit magnitude comparator has been designed using an MZI and two linear control waveguides. The device works on the Kerr effect inside the plasmonics waveguide. The mathematical description of the device is explained. The simulation of the device is done using MATLAB® and the finite-difference time-domain (FDTD) method.

  9. A highly efficient surface plasmon polaritons excitation achieved with a metal-coupled metal-insulator-metal waveguide

    Directory of Open Access Journals (Sweden)

    Hongyan Yang

    2014-12-01

    Full Text Available We propose a novel metal-coupled metal-insulator-metal (MC-MIM waveguide which can achieve a highly efficient surface plasmon polaritons (SPPs excitation. The MC-MIM waveguide is formed by inserting a thin metal film in the insulator of an MIM. The introduction of the metal film, functioning as an SPPs coupler, provides a space for the interaction between SPPs and a confined electromagnetic field of the intermediate metal surface, which makes energy change and phase transfer in the metal-dielectric interface, due to the joint action of incomplete electrostatic shielding effect and SPPs coupling. Impacts of the metal film with different materials and various thickness on SPPs excitation are investigated. It is shown that the highest efficient SPPs excitation is obtained when the gold film thickness is 60 nm. The effect of refractive index of upper and lower symmetric dielectric layer on SPPs excitation is also discussed. The result shows that the decay value of refractive index is 0.3. Our results indicate that this proposed MC-MIM waveguide may offer great potential in designing a new SPPs source.

  10. QCD PHASE TRANSITIONS-VOLUME 15.

    Energy Technology Data Exchange (ETDEWEB)

    SCHAFER,T.

    1998-11-04

    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.

  11. Phase transitions in Ge-Sb phase change materials

    International Nuclear Information System (INIS)

    Raoux, Simone; Virwani, Kumar; Cabral, Cyril Jr.; Krusin-Elbaum, Lia; Jordan-Sweet, Jean L.; Hitzbleck, Martina; Salinga, Martin; Madan, Anita; Pinto, Teresa L.

    2009-01-01

    Thin films of the phase change material Ge-Sb with Ge concentrations between 7.3 and 81.1 at. % were deposited by cosputtering from elemental targets. Their crystallization behavior was studied using time-resolved x-ray diffraction, Auger electron spectroscopy, differential scanning calorimetry, x-ray reflectivity, profilometry, optical reflectivity, and resistivity versus temperature measurements. It was found that the crystallization temperature increases with Ge content. Calculations of the glass transition temperature (which is a lower limit for the crystallization temperature T x ) also show an increase with Ge concentration closely tracking the measured values of T x . For low Ge content samples, Sb x-ray diffraction peaks occurred during a heating ramp at lower temperature than Ge diffraction peaks. The appearance of Ge peaks is related to Ge precipitation and agglomeration. For Ge concentrations of 59.3 at. % and higher, Sb and Ge peaks occurred at the same temperature. Upon crystallization, film mass density and optical reflectivity increase as well as electrical contrast (ratio of resistivity in amorphous phase to crystalline phase) all showed a maximum for the eutectic alloy (14.5 at. % Ge). For the alloy with 59.3 at. % Ge there was very little change in any of these parameters, while the alloy with 81.1 at. % Ge behaved opposite to a typical phase change alloy and showed reduced mass density and reflectivity and increased resistivity

  12. Wilson loop's phase transition probed by non-local observable

    Directory of Open Access Journals (Sweden)

    Hui-Ling Li

    2018-04-01

    Full Text Available In order to give further insights into the holographic Van der Waals phase transition, it would be of great interest to investigate the behavior of Wilson loop across the holographic phase transition for a higher dimensional hairy black hole. We offer a possibility to proceed with a numerical calculation in order to discussion on the hairy black hole's phase transition, and show that Wilson loop can serve as a probe to detect a phase structure of the black hole. Furthermore, for a first order phase transition, we calculate numerically the Maxwell's equal area construction; and for a second order phase transition, we also study the critical exponent in order to characterize the Wilson loop's phase transition.

  13. A Steep-Slope Transistor Combining Phase-Change and Band-to-Band-Tunneling to Achieve a sub-Unity Body Factor

    OpenAIRE

    W. A. Vitale; E. A. Casu; A. Biswas; T. Rosca; C. Alper

    2017-01-01

    Steep-slope transistors allow to scale down the supply voltage and the energy per computed bit of information as compared to conventional field-effect transistors (FETs), due to their sub-60 mV/decade subthreshold swing at room temperature. Currently pursued approaches to achieve such a subthermionic subthreshold swing consist in alternative carrier injection mechanisms, like quantum mechanical band-to-band tunneling (BTBT) in Tunnel FETs or abrupt phase-change in metal-insulator transition (...

  14. Observables of non-equilibrium phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Tomasik, Boris [Univerzita Mateja Bela, FPV, Banska Bystrica (Slovakia); Ceske vysoke uceni technicke v Praze, FJFI, Prague (Czech Republic); Schulc, Martin; Kopecna, Renata [Ceske vysoke uceni technicke v Praze, FJFI, Prague (Czech Republic); Melo, Ivan [Univerzita Mateja Bela, FPV, Banska Bystrica (Slovakia); Zilinska univerzita, Elektrotechnicka fakulta, Zilina (Slovakia)

    2016-08-15

    A rapidly expanding fireball which undergoes first-order phase transition will supercool and proceed via spinodal decomposition. Hadrons are produced from the individual fragments as well as the left-over matter filling the space between them. Emission from fragments should be visible in rapidity correlations, particularly of protons. In addition to that, even within narrow centrality classes, rapidity distributions will be fluctuating from one event to another in case of fragmentation. This can be identified with the help of the Kolmogorov-Smirnov test. Finally, we present a method which allows to sort events with varying rapidity distributions, in such a way that events with similar rapidity histograms are grouped together. (orig.)

  15. Deep Neural Network Detects Quantum Phase Transition

    Science.gov (United States)

    Arai, Shunta; Ohzeki, Masayuki; Tanaka, Kazuyuki

    2018-03-01

    We detect the quantum phase transition of a quantum many-body system by mapping the observed results of the quantum state onto a neural network. In the present study, we utilized the simplest case of a quantum many-body system, namely a one-dimensional chain of Ising spins with the transverse Ising model. We prepared several spin configurations, which were obtained using repeated observations of the model for a particular strength of the transverse field, as input data for the neural network. Although the proposed method can be employed using experimental observations of quantum many-body systems, we tested our technique with spin configurations generated by a quantum Monte Carlo simulation without initial relaxation. The neural network successfully identified the strength of transverse field only from the spin configurations, leading to consistent estimations of the critical point of our model Γc = J.

  16. Thermal equilibrium during the electroweak phase transition

    International Nuclear Information System (INIS)

    Tetradis, N.

    1991-12-01

    The effective potential for the standard model develops a barrier, at temperatures around the electroweak scale, which separates the minimum at zero field and a deeper non-zero minimum. This could create out of equilibrium conditions by inducing the localization of the Higgs field in a metastable state around zero. In this picture vacuum decay would occur through bubble nucleation. I show that there is an upper bound on the Higgs mass for the above scenario to be realized. The barrier must be high enough to prevent thermal fluctuations of the Higgs expectation value from establishing thermal equilibrium between the two minima. The upper bound is estimated to be lower than the experimental lower limit. This is also imposes constraints on extensions of the standard model constructed in order to generate a strongly first order phase transition. (orig.)

  17. Kinetics of the chiral phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Hees, Hendrik van [Johann-Wolfgang-Goethe-Universitaet Frankfurt, Institut fuer Theoretische Physik, Frankfurt (Germany); Frankfurt Institute for Advanced Studies (FIAS), Frankfurt (Germany); Wesp, Christian; Meistrenko, Alex; Greiner, Carsten [Johann-Wolfgang-Goethe-Universitaet Frankfurt, Institut fuer Theoretische Physik, Frankfurt (Germany)

    2016-07-01

    We simulate the kinetics of the chiral phase transition in hot and dense strongly interacting matter within a novel kinetic-theory approach. Employing an effective linear σ model for quarks, σ mesons, and pions we treat the quarks within a test-particle ansatz for solving the Boltzmann transport equation and the mesons in terms of classical fields. The decay-recombination processes like σ <-> anti q+q are treated using a kind of wave-particle dualism using the exact conservation of energy and momentum. After demonstrating the correct thermodynamic limit for particles and fields in a ''box calculation'' we apply the simulation to the dynamics of an expanding fireball similar to the medium created in ultrarelativistic heavy-ion collisions.

  18. Magnetism and metal insulator transition in FeSi and FeGe. Ab Initio investigations of the electronic structure; Magnetismus und Metall-Isolator-Uebergang in FeSi und FeGe. Ab-initio-Untersuchungen der elektronischen Struktur

    Energy Technology Data Exchange (ETDEWEB)

    Neef, Matthias

    2007-03-19

    Aim of this thesis was to reach by a systematic study of different ab initio procedures an improved description of the electronic properties of FeSi and FeGe. Central result is the itinerant description of FeSi as a semiconductor in the neighbourhood of a ferromagnetic instability. The regardment of the nonlocal exchange in the effective one-particle approximation leads to a metastable magnetic state scarcely above the magnetic ground state. The application of the hybrid functional leads to a 1st order metal-isolator transition for large lattice parameters: FeSi transforms at increasement of the lattice parameter from an unmagnetic isolator to a magnetic metal. A similar behavior is found in the isostructural compound FeGe. The two systems FeSi and FeGe were systematically and detailedly analyzed by means of ab initio procedures. Thereby the structural, electronic, and magnetic properties were studied with DFT and HF calculations. Both calculations with spin polarization and without spin polarization were performed.

  19. Quantum phase transitions in Bose-Fermi systems

    International Nuclear Information System (INIS)

    Petrellis, D.; Leviatan, A.; Iachello, F.

    2011-01-01

    Research highlights: → We study quantum phase transitions in a system of N bosons and a single-j fermion. → Classical order parameters and correlation diagrams of quantum levels are determined. → The odd fermion strongly influences the location and nature of the phase transition. → Experimental evidence for the U(5)-SU(3) transition in odd-even nuclei is presented. - Abstract: 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.

  20. Optical control of capacitance in a metal-insulator-semiconductor diode with embedded metal nanoparticles

    Science.gov (United States)

    Mikhelashvili, V.; Ankonina, G.; Kauffmann, Y.; Atiya, G.; Kaplan, W. D.; Padmanabhan, R.; Eisenstein, G.

    2017-06-01

    This paper describes a metal-insulator-semiconductor (MIS) capacitor with flat capacitance voltage characteristics and a small quadratic voltage capacitance coefficient. The device characteristics resemble a metal-insulator-metal diode except that here the capacitance depends on illumination and exhibits a strong frequency dispersion. The device incorporates Fe nanoparticles (NPs), mixed with SrF2, which are embedded in an insulator stack of SiO2 and HfO2. Positively charged Fe ions induce dipole type traps with an electronic polarization that is enhanced by photogenerated carriers injected from the substrate and/or by inter nanoparticle exchange of carriers. The obtained characteristics are compared with those of five other MIS structures: two based on Fe NPs, one with and the other without SrF2 sublayers. Additionally, devices contain Co NPs embedded in SrF2 sublayers, and finally, two structures have no NPs, with one based on a stack of SiO2 and HfO2 and the other which also includes SrF2. Only structures containing Fe NPs, which are incorporated into SrF2, yield a voltage independent capacitance, the level of which can be changed by illumination. These properties are essential in radio frequency/analog mixed signal applications.

  1. Quantum phase transitions and local magnetism in Mott insulators: A local probe investigation using muons, neutrons, and photons

    Science.gov (United States)

    Frandsen, Benjamin A.

    destroyed at the quantum phase transition. Taken together, these findings point unambiguously to a first-order quantum phase transition in these systems. We also conducted x-ray and neutron PDF experiments, which suggest that the distinct atomic structures associated with the insulating and metallic phases similarly coexist near the quantum phase transition. These results have significant implications for our understanding of the Mott metal-insulator quantum phase transition in real materials. The second part of this thesis centers on the derivation and development of the magnetic pair distribution function (mPDF) technique and its application to the antiferromagnetic Mott insulator MnO. The atomic PDF method involves Fourier transforming the x-ray or neutron total scattering intensity from reciprocal space into real space to directly reveal the local atomic correlations in a material, which may deviate significantly from the average crystallographic structure of that material. Likewise, the mPDF method involves Fourier transforming the magnetic neutron total scattering intensity to probe the local correlations of magnetic moments in the material, which may exist on short length scales even when the material has no long-range magnetic order. After deriving the fundamental mPDF equations and providing a proof-of-principle by recovering the known magnetic structure of antiferromagnetic MnO, we used this technique to investigate the short-range magnetic correlations that persist well into the paramagnetic phase of MnO. By combining the mPDF measurements with ab initio calculations of the spin-spin correlation function in paramagnetic MnO, we were able to quantitatively account for the observed mPDF. We also used the mPDF data to evaluate competing ab initio theories, thereby resolving some longstanding questions about the magnetic exchange interactions in MnO.

  2. Magnetically ordered phase near transition to Bose-glass phase

    Science.gov (United States)

    Syromyatnikov, A. V.; Sizanov, A. V.

    2017-01-01

    We discuss a magnetically ordered ("superfluid") phase near quantum transition to the Bose-glass phase in a simple modeling system, a Heisenberg antiferromagnet with spatial dimension d >2 in an external magnetic field with disorder in exchange coupling constants. Our analytical consideration is based on hydrodynamic description of long-wavelength excitations. Results obtained are valid in the entire critical region near the quantum critical point (QCP), allowing us to describe a possible crossover from one critical behavior to another. We demonstrate that the system behaves in full agreement with predictions by M. P. Fisher et al. [Phys. Rev. B 40, 546 (1989), 10.1103/PhysRevB.40.546] in close vicinity to the QCP. We find as an extension to that analysis that the anomalous dimension η =2 -d and β =ν d /2 , where β and ν are critical exponents of the order parameter and the correlation length, respectively. The density of states per spin of low-energy localized excitations is found to be independent of d ("superuniversal"). We show that many recent experimental and numerical results obtained in various three-dimensional (3D) systems can be described by our formulas using percolation critical exponents. Then, it is a possibility that a percolation critical regime arises in the ordered phase in some 3D systems not very close to the QCP.

  3. Multiple phase transitions in palmitoleic acid under the pressure

    Energy Technology Data Exchange (ETDEWEB)

    Kos, A; Siegoczynski, R M; Rostocki, A J; Tefelski, D B; Kosciesza, R; Wieja, K [Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw (Poland)], E-mail: aldona@if.pw.edu.pl

    2008-07-15

    Long unsaturated carbon chain liquids exhibit a phase transition under a high pressure. We have investigated the phase transition in palmitoleic acid as a representative of this group not researched yet. A temperature, a relative permittivity and a dissipation factor have been measured, while the pressure was applied. We have also observed the transmitted and the scattered IR light. These parameters allowed us to find phase transitions that occurred due to the pressure. Especially the behavior of the temperature indicates several phase transitions during compression. Above certain pressure the liquid becomes opaque, it is connected with most significant phase transition that occurs around 177 MPa. We have observed asymmetry of intensity of the scattered light, which is much stronger during decompression. Observed multiple phase transitions are not present in other acids investigated by us.

  4. Decoupling the Lattice Distortion and Charge Doping Effects on the Phase Transition Behavior of VO2 by Titanium (Ti4+) Doping

    Science.gov (United States)

    Wu, Yanfei; Fan, Lele; Liu, Qinghua; Chen, Shi; Huang, Weifeng; Chen, Feihu; Liao, Guangming; Zou, Chongwen; Wu, Ziyu

    2015-01-01

    The mechanism for regulating the critical temperature (TC) of metal-insulator transition (MIT) in ions-doped VO2 systems is still a matter of debate, in particular, the unclear roles of lattice distortion and charge doping effects. To rule out the charge doping effect on the regulation of TC, we investigated Ti4+-doped VO2 (TixV1-xO2) system. It was observed that the TC of TixV1-xO2 samples first slightly decreased and then increased with increasing Ti concentration. X-ray absorption fine structure (XAFS) spectroscopy was used to explore the electronic states and local lattice structures around both Ti and V atoms in TixV1-xO2 samples. Our results revealed the local structure evolution from the initial anatase to the rutile-like structure around the Ti dopants. Furthermore, the host monoclinic VO2 lattice, specifically, the VO6 octahedra would be subtly distorted by Ti doping. The distortion of VO6 octahedra and the variation of TC showed almost the similar trend, confirming the direct effect of local structural perturbations on the phase transition behavior. By comparing other ion-doping systems, we point out that the charge doping is more effective than the lattice distortion in modulating the MIT behavior of VO2 materials. PMID:25950809

  5. Characteristics of the chiral phase transition in nonlocal quark models

    International Nuclear Information System (INIS)

    Gomez Dumm, D. Gomez; Scoccola, N.N.

    2005-01-01

    The characteristics of the chiral phase transition are analyzed within the framework of chiral quark models with nonlocal interactions in the mean-field approximation. In the chiral limit, we develop a semianalytic framework that allows us to explicitly determine the phase transition curve, the position of the critical points, some relevant critical exponents, etc. For the case of finite current quark masses, we show the behavior of various thermodynamical and chiral response functions across the phase transition

  6. Gravitational waves from global second order phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Jr, John T. Giblin [Department of Physics, Kenyon College, 201 North College Rd, Gambier, OH 43022 (United States); Price, Larry R.; Siemens, Xavier; Vlcek, Brian, E-mail: giblinj@kenyon.edu, E-mail: larryp@caltech.edu, E-mail: siemens@gravity.phys.uwm.edu, E-mail: bvlcek@uwm.edu [Center for Gravitation and Cosmology, Department of Physics, University of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, WI 53201 (United States)

    2012-11-01

    Global second-order phase transitions are expected to produce scale-invariant gravitational wave spectra. In this manuscript we explore the dynamics of a symmetry-breaking phase transition using lattice simulations. We explicitly calculate the stochastic gravitational wave background produced during the transition and subsequent self-ordering phase. We comment on this signal as it compares to the scale-invariant spectrum produced during inflation.

  7. The phase transition of RDX under hydrostatic and ramp compression

    Science.gov (United States)

    Zheng, Xianxu; Zhang, Zhaohui; Zhao, Jun; Zeng, Daipeng; Zeng, Yangyang; Zhang, Xu

    2017-06-01

    The thermodynamic state of explosive was highly dependent on the phase transition structure and phase transition of explosive crystal. However, the phase transition details of explosive have never been characterized sufficiently under different compression conditions. In this study, both the hydrostatic and ramp compression were performed to examine the phase transition of RDX crystal. Based on our experimental results, we confirmed the α- γ phase transition onset around 4 GPa under hydrostatic compression, which agree with the published literature very well. In the ramp compression experiment, a 260 ns ramp compression up to 30 GPa was generated to compress the RDX single crystal along 020 crystal axis, the PDV signal indicated that the phase transition was induced around 2.8 GPa, and the phase transition induction time was about several tens nanoseconds. Our preliminary experiments suggest that the phase transition pressure of RDX have great relation with the compression history, that probably means the phase transition mechanism were quite different between the hydrostatic and ramp compression.

  8. Phase transitions in the Haldane-Hubbard model within coherent potential approximation

    Science.gov (United States)

    Le, Duc-Anh; Tran, Minh-Tien; Tran, Thi-Thanh-Mai; Nguyen, Thi-Thao; Nguyen, Thi-Huong; Hoang, Anh-Tuan

    2018-03-01

    Within the coherent potential approximation we study the two-dimensional Haldane-Hubbard model, in which an interplay between topology and correlation effects is realized. The model essentially describes correlated electrons moving in a honeycomb lattice with zero net magnetic flux. The influence of the next-nearest-neighbor hopping and electron correlations on the metal-insulator transitions are investigated by monitoring the density of states at the Fermi level and the energy gap. The topological properties of the insulators is determined by the Chern number. With a given next-nearest-neighbor hopping, electron correlations drive the system from the topological Chern insulator to a metal, and then to the topologically trivial Mott insulator.

  9. 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.

  10. 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.

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

    Directory of Open Access Journals (Sweden)

    Xiao-Xiong Zeng

    2017-01-01

    Full Text Available Phase structure of the quintessence Reissner–Nordström–AdS black hole is probed by 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 Van der Waals-like phase transition. To reinforce this 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Zeng, Xiao-Xiong, E-mail: xxzeng@itp.ac.cn [State School of Material Science and Engineering, Chongqing Jiaotong University, Chongqing 400074 (China); Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190 (China); Li, Li-Fang, E-mail: lilf@itp.ac.cn [State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing 100190 (China)

    2017-01-10

    Phase structure of the quintessence Reissner–Nordström–AdS black hole is probed by 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 Van der Waals-like phase transition. To reinforce this 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.

  13. Phase transitions in a gas of anyons

    International Nuclear Information System (INIS)

    MacKenzie, R.; Nebia-Rahal, F.; 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 which corresponds to the total linking number between the loops. We compute the linking number using a novel approach employing certain notions from knot theory. Adding the topological term converts the particles into anyons. Interpreting the model as 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. The system continues to exhibit a phase transition as a function of the vortex mass as it becomes small. We find the following new results. The Chern-Simons term has no effect on the Wilson loop. On the other hand, it does effect the 't Hooft loop of a given configuration, adding the linking number of the 't Hooft loop with all of the dynamical vortex loops. We find the unexpected result that both the Wilson loop and the 't Hooft loop exhibit a perimeter law even though there are no massless particles in the theory, in both phases of the theory. It should be noted that our method suffers from numerical instabilities if the coefficient of the Chern-Simons term is too large; thus, we have restricted our results to small values of this parameter. Furthermore, interpreting the lattice loop gas as an effective theory describing the Abelian Higgs model is only known to be true in the infinite coupling limit; for strong but finite coupling this correspondence is only a conjecture, the validity of which is beyond the scope of this article.

  14. Unconventional phase transitions in a constrained single polymer chain

    International Nuclear Information System (INIS)

    Klushin, L I; Skvortsov, A M

    2011-01-01

    Phase transitions were recognized among the most fascinating phenomena in physics. Exactly solved models are especially important in the theory of phase transitions. A number of exactly solved models of phase transitions in a single polymer chain are discussed in this review. These are three models demonstrating the second order phase transitions with some unusual features: two-dimensional model of β-structure formation, the model of coil–globule transition and adsorption of a polymer chain grafted on the solid surface. We also discuss models with first order phase transitions in a single macromolecule which admit not only exact analytical solutions for the partition function with explicit finite-size effects but also the non-equilibrium free energy as a function of the order parameter (Landau function) in closed analytical form. One of them is a model of mechanical desorption of a macromolecule, which demonstrates an unusual first order phase transition with phase coexistence within a single chain. Features of first and second order transitions become mixed here due to phase coexistence which is not accompanied by additional interfacial free energy. Apart from that, there exist several single-chain models belonging to the same class (adsorption of a polymer chain tethered near the solid surface or liquid–liquid interface, and escape transition upon compressing a polymer between small pistons) that represent examples of a highly unconventional first order phase transition with several inter-related unusual features: no simultaneous phase coexistence, and hence no phase boundary, non-concave thermodynamic potential and non-equivalence of conjugate ensembles. An analysis of complex zeros of partition functions upon approaching the thermodynamic limit is presented for models with and without phase coexistence. (topical review)

  15. Thermodynamics of pairing phase transition in nuclei

    International Nuclear Information System (INIS)

    Karim, Afaque; Ahmad, Shakeb

    2014-01-01

    The pairing gaps, pairing energy, heat capacity and entropy are calculated within BCS (Bardeen- Cooper-Schrieffer) based quasi particle approach, including thermal fluctuations on pairing field within pairing model for all nuclei (light, medium, heavy and super heavy nuclei). Quasi particles approach in BCS theory was introduced and reformulated to study various properties. For thermodynamic behavior of nuclei at finite temperatures, the anomalous averages of creation and annihilation operators are introduced. It is solved self consistently at finite temperatures to obtain BCS Hamiltonian. After doing unitary transformation, we obtained the Hamiltonian in the diagonal form. Thus, one gets temperature dependence gap parameter and pairing energy for nuclei. Moreover, the energy at finite temperatures is the sum of the condensation energy and the thermal energy of fermionic quasi particles. With the help of BCS Hamiltonian, specific heat, entropy and free energy are calculated for different nuclei. In this paper the gap parameter occupation number and pairing energy as a function of temperature which is important for all the light, medium, heavy and super heavy nuclei is calculated. Moreover, the various thermo dynamical quantities like specific heat, entropy and free energy is also obtained for different nuclei. Thus, the thermodynamics of pairing phase transition in nuclei is studied

  16. Phase transition in L-alaninium oxalate by photoacoustics

    Indian Academy of Sciences (India)

    Unknown

    TG and DTA mea- surements were first carried out to identify any transitions. The calorimetric techniques such as DSC, TG and DTA are generally used to study the phase transition. But,. Ganguly and Rao (1981) reported from their PA study on. La2CuO4 that there would be a weak transition at 553 K but they could not see ...

  17. A grain boundary phase transition in Si–Au

    International Nuclear Information System (INIS)

    Ma, Shuailei; Meshinchi Asl, Kaveh; Tansarawiput, Chookiat; Cantwell, Patrick R.; Qi, Minghao; Harmer, Martin P.; Luo, Jian

    2012-01-01

    A grain boundary transition from a bilayer to an intrinsic (nominally clean) boundary is observed in Si–Au. An atomically abrupt transition between the two complexions (grain boundary stabilized phases) implies the occurrence of a first-order interfacial phase transition associated with a discontinuity in the interfacial excess. This observation supports a grain-boundary complexion theory with broad applications. This transition is atypical in that the monolayer complexion is absent. A model is proposed to explain the bilayer stabilization and the origin of this complexion transition.

  18. 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...... principles. We apply the developed formalism for the description of thermodynamical properties of alanine polypeptides of different length. We analyze the essential thermodynamical properties of the system such as heat capacity, phase transition temperature and latent heat of the phase transition...

  19. 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...... using Rössler systems and model maps are given. ©1999 American Institute of Physics....

  20. Local discontinuous Galerkin methods for phase transition problems

    NARCIS (Netherlands)

    Tian, Lulu

    2015-01-01

    In this thesis we develop a local discontinuous Galerkin (LDG) finite element method to solve mathematical models for phase transitions in solids and fluids. The first model we study is called a viscosity-capillarity (VC) system associated with phase transitions in elastic bars and Van der Waals

  1. Structural phase transitions and piezoelectric anomalies in ordered ...

    Indian Academy of Sciences (India)

    Home; Journals; Bulletin of Materials Science; Volume 30; Issue 4. Structural phase transitions and piezoelectric anomalies in ordered Sc0.5Ga0.5N alloys ... This alloy is found to exhibit a tremendous piezoelectric response, associated with a phase transition from nonpolar 63/(6h) space group to a polar ...

  2. Phase transitions in liquids with directed intermolecular bonding

    OpenAIRE

    Son, L.; Ryltcev, R.

    2005-01-01

    Liquids with quasi - chemical bonding between molecules are described in terms of vertex model. It is shown that this bonding results in liquid - liquid phase transition, which occurs between phases with different mean density of intermolecular bonds. The transition may be suggested to be a universal phenomena for those liquids.

  3. Supercooling across first-order phase transitions in vortex matter

    Indian Academy of Sciences (India)

    Hysteresis in cycling through first-order phase transitions in vortex matter, akin to the well-studied phenomenon of supercooling of water, has been discussed in literature. Hysteresis can be seen while varying either temperature or magnetic field (and thus the density of vortices). Our recent work on phase transitions with ...

  4. High-density QCD phase transitions inside neutron stars: Glitches ...

    Indian Academy of Sciences (India)

    2017-10-09

    Oct 9, 2017 ... ... of different high-density phases and associated phase transitions. We study effectsof density fluctuations during transitions with and without topological defect production and study the effect on pulsar timings due to changing moment of inertia of the star. We also discuss gravitational wave production due ...

  5. Electroweak phase transition and some related phenomena–a brief

    Indian Academy of Sciences (India)

    In this article, we give a bird's eye view of the research on electroweak phase transition and some related phenomena, viz., cosmological baryogenesis, electroweak bubble dynamics and generation of gravitationalwaves. Our presentation revolves around the observation that a strong first-order electroweak phase transition ...

  6. Model for pairing phase transition in atomic nuclei

    International Nuclear Information System (INIS)

    Schiller, A.; Guttormsen, M.; Hjorth-Jensen, M.; Rekstad, J.; Siem, S.

    2002-01-01

    A model is developed which allows the investigation and classification of the pairing phase transition in atomic nuclei. The regions of the parameter space are discussed for which a pairing phase transition can be observed. The model parameters include number of particles, attenuation of pairing correlations with increasing seniority, single-particle level spacing, and pairing gap parameter

  7. Nanostructured bilayer anodic TiO2/Al2O3 metal-insulator-metal capacitor.

    Science.gov (United States)

    Karthik, R; Kannadassan, D; Baghini, Maryam Shojaei; Mallick, P S

    2013-10-01

    This paper presents the fabrication of high performance bilayer TiO2/Al2O3 Metal-Insulator-Metal capacitor using anodization technique. A high capacitance density of 7 fF/microm2, low quadratic voltage coefficient of capacitance of 150 ppm/V2 and a low leakage current density of 9.1 nA/cm2 at 3 V are achieved which are suitable for Analog and Mixed signal applications. The influence of anodization voltage on structural and electrical properties of dielectric stack is studied in detail. At higher anodization voltages, we have observed the transformation of amorphous to crystalline state of TiO2/Al2O3 and improvement of electrical properties.

  8. Microrefrigeration by a pair of normal metal/insulator/superconductor junctions

    Science.gov (United States)

    Leivo, M. M.; Pekola, J. P.; Averin, D. V.

    1995-01-01

    We suggest and demonstrate experimentally that two normal metal/insulator/superconductor (NIS) tunnel junctions combined in series to form a symmetric SINIS structure can operate as an efficient Peltier refrigerator. Specifically, it is shown that the SINIS structure with normal-state junction resistences of 1.0 and 1.1 kOmega is capable of reaching a temperature of about 100 mK starting from 300 mK. We estimate the corresponding cooling power to be 1.5 pW per total junction area of 0.8 micrometers(exp 2) at T = 300 mK. This cooling power density implies that scaling of junction area up to about 1 mm(exp 2) should bring the cooling power into the microW range.

  9. Theoretical analysis of a nanoscale plasmonic filter based on a rectangular metal-insulator-metal waveguide

    International Nuclear Information System (INIS)

    Yun Binfeng; Hu Guohua; Cui Yiping

    2010-01-01

    A compact and nanometric surface plasmon polariton (SPP) band-pass filter based on a rectangular ring resonator composed of metal-insulator-metal waveguides is proposed. Using the finite difference time domain method, the effects of the structure parameters on the transmission characteristics of this SPP band-pass filter are analysed in detail. The results show that the proposed SPP filter has narrow transmission peaks and the corresponding resonance wavelengths can be linearly tuned by altering the resonator's cavity length. Moreover, the transmission ratios of the pass bands can be tuned by changing the coupling gaps between the input/output MIM waveguides and the resonator. Also the metal loss and dispersion effects on the filter responses are included. The simple band-pass SPP filter is very promising for high-density SPP waveguide integrations.

  10. Hydrogen interaction with GaN metal-insulator-semiconductor diodes

    International Nuclear Information System (INIS)

    Irokawa, Y.

    2012-01-01

    Interaction mechanism of hydrogen with GaN metal-insulator-semiconductor (MIS) diodes is investigated, focusing on the metal/semiconductor interfaces. For MIS Pt-GaN diodes with a SiO 2 dielectric, the current-voltage (I-V) characteristics reveal that hydrogen changes the conduction mechanisms from Fowler-Nordheim tunneling to Poole-Frenkel emission. In sharp contrast, Pt-Si x N y -GaN diodes exhibit Poole-Frenkel emission in nitrogen and do not show any change in the conduction mechanism upon exposure to hydrogen. The capacitance-voltage (C-V) study suggests that the work function change of the Schottky metal is not responsible mechanism for the hydrogen sensitivity.

  11. Metal-insulator crossover in superconducting cuprates in strong magnetic fields

    International Nuclear Information System (INIS)

    Marchetti, P.A.; Su Zhaobin; Yu Lu

    2001-02-01

    The metal-insulator crossover of the in-plane resistivity upon temperature decrease, recently observed in several classes of cuprate superconductors, when a strong magnetic field suppresses the superconductivity, is explained using the U(1)xSU(2) Chern-Simons gauge field theory. The origin of this crossover is the same as that for a similar phenomenon observed in heavily underdoped cuprates without magnetic field. It is due to the interplay between the diffusive motion of the charge carriers and the 'peculiar' localization effect due to short-range antiferromagnetic order. We also calculate the in-plane transverse magnetoresistance which is in a fairly good agreement with available experimental data. (author)

  12. Flexible high-κ/Metal gate metal/insulator/metal capacitors on silicon (100) fabric

    KAUST Repository

    Rojas, Jhonathan Prieto

    2013-10-01

    Implementation of memory on bendable substrates is an important step toward a complete and fully developed notion of mechanically flexible computational systems. In this paper, we have demonstrated a simple fabrication flow to build metal-insulator-metal capacitors, key components of dynamic random access memory, on a mechanically flexible silicon (100) fabric. We rely on standard microfabrication processes to release a thin sheet of bendable silicon (area: 18 {\\ m cm}2 and thickness: 25 \\\\mu{\\ m m}) in an inexpensive and reliable way. On such platform, we fabricated and characterized the devices showing mechanical robustness (minimum bending radius of 10 mm at an applied strain of 83.33% and nominal strain of 0.125%) and consistent electrical behavior regardless of the applied mechanical stress. Furthermore, and for the first time, we performed a reliability study suggesting no significant difference in performance and showing an improvement in lifetime projections. © 1963-2012 IEEE.

  13. Optical magnetism and plasmonic Fano resonances in metal-insulator-metal oligomers.

    Science.gov (United States)

    Verre, R; Yang, Z J; Shegai, T; Käll, M

    2015-03-11

    The possibility of achieving optical magnetism at visible frequencies using plasmonic nanostructures has recently been a subject of great interest. The concept is based on designing structures that support plasmon modes with electron oscillation patterns that imitate current loops, that is, magnetic dipoles. However, the magnetic resonances are typically spectrally narrow, thereby limiting their applicability in, for example, metamaterial designs. We show that a significantly broader magnetic response can be realized in plasmonic pentamers constructed from metal-insulator-metal (MIM) sandwich particles. Each MIM unit acts as a magnetic meta-atom and the optical magnetism is rendered quasi-broadband through hybridization of the in-plane modes. We demonstrate that scattering spectra of individual MIM pentamers exhibit multiple Fano resonances and a broad subradiant spectral window that signals the magnetic interaction and a hierarchy of coupling effects in these intricate three-dimensional nanoparticle oligomers.

  14. Flux pumping for non-insulated and metal-insulated HTS coils

    Science.gov (United States)

    Ma, Jun; Geng, Jianzhao; Coombs, T. A.

    2018-01-01

    High-temperature superconducting (HTS) coils wound from coated conductors without turn-to-turn insulation (non-insulated (NI) coils) have been proven with excellent electrical and thermal performances. However, the slow charging of NI coils has been a long-lasting problem. In this work, we explore using a transformer-rectifier HTS flux pump to charge an NI coil and a metal-insulated coil. The charging performance comparison is made between different coils. Comprehensive study is done to thoroughly understand the electrical-magnetic transience in charging these coils. We will show that the low-voltage high-current flux pump is especially suitable for charging NI coils with very low characteristic resistance.

  15. Spin relaxation near the metal-insulator transition: dominance of the Dresselhaus spin-orbit coupling.

    Science.gov (United States)

    Intronati, Guido A; Tamborenea, Pablo I; Weinmann, Dietmar; Jalabert, Rodolfo A

    2012-01-06

    We identify the Dresselhaus spin-orbit coupling as the source of the dominant spin-relaxation mechanism in the impurity band of a wide class of n-doped zinc blende semiconductors. The Dresselhaus hopping terms are derived and incorporated into a tight-binding model of impurity sites, and they are shown to unexpectedly dominate the spin relaxation, leading to spin-relaxation times in good agreement with experimental values. This conclusion is drawn from two complementary approaches: an analytical diffusive-evolution calculation and a numerical finite-size scaling study of the spin-relaxation time.

  16. Crossover of angular dependent magnetoresistance with the metal-insulator transition in colossal magnetoresistive manganite films

    DEFF Research Database (Denmark)

    Chen, Yunzhong; Sun, J.R.; Zhao, T.Y.

    2009-01-01

    The temperature and magnetic field dependence of angular dependent magnetoresistance (AMR) along two orthogonal directions ([100] and [01]) was investigated in a charge-orbital-ordered Sm0.5Ca0.5MnO3 (SCMO) film grown on (011)-oriented SrTiO3 substrates. A dramatic decrease of AMR magnitude in both...

  17. Electron mobility, conductivity, and superconductivity near the metal-insulator transition

    International Nuclear Information System (INIS)

    Fiory, A.T.; Hebard, A.F.

    1984-01-01

    The disorder parameter k/sub F/l for amorphous InO/sub x/ is measured by a novel application of the surface electric field effect and is varied by thermal annealing. The normal-state conductivity and superconducting T/sub c/ both vary as (k/sub F/l) -2 and critical disorder occurs at k/sub F/lroughly-equal3/sup 1/2/, as a result of Anderson localization in this low-carrier density material

  18. Phonon anomalies and the magnetic transition in pure and Cr-doped V2O3

    Science.gov (United States)

    Yethiraj, M.; Werner, S. A.; Yelon, W. B.; Honig, J. M.

    1987-12-01

    We have studied the lattice dynamics, the magnetic ordering and excitations, and the crystallographic distortions associated with the metal-insulator transitions in pure and Cr-doped vanadium sesquioxide using neutron-scattering techniques. In the paramagnetic metallic phase of pure V2O3 and in the higher-temperature paramagnetic metallic phase of 1.5-at. %-Cr-doped V2O3 we see an anomalous splitting of the transversely polarized acoustic phonon mode, propagating along the hexagonal [hh0] direction near the center of the Brillouin zone. Upon lowering the temperature, a substantial softening of a large portion of the transverse acoustic branch in the [00l] direction is observed in Cr-doped samples in the paramagnetic insulating phase as the transition to the antiferromagnetic insulating phase is approached. The loss of antiferromagnetic order with increasing temperature in 3-at. %-Cr-doped and 6-at. %-Cr-doped samples appears to be nearly continuous. The temperature dependence of the spin-wave energy gap in the 3-at. %-Cr-doped sample appears to approach zero continuously up to the Néel temperature. The monoclinic distortion of the trigonal phase at this transition is much reduced in the 6-at. %-Cr-doped sample compared to pure V2O3. These and other results are described in detail, and discussed in connection with the recent theoretical work on metal-insulator transitions.

  19. Thermodynamic phase transition of a black hole in rainbow gravity

    Directory of Open Access Journals (Sweden)

    Zhong-Wen Feng

    2017-09-01

    Full Text Available In this letter, using the rainbow functions that were proposed by Magueijo and Smolin, we investigate the thermodynamics and the phase transition of rainbow Schwarzschild black hole. First, we calculate the rainbow gravity corrected Hawking temperature. From this modification, we then derive the local temperature, free energy, and other thermodynamic quantities in an isothermal cavity. Finally, we analyze the critical behavior, thermodynamic stability, and phase transition of the rainbow Schwarzschild black hole. The results show that the rainbow gravity can stop the Hawking radiation in the final stages of black holes' evolution and lead to the remnants of black holes. Furthermore, one can observe that the rainbow Schwarzschild black hole has one first-order phase transition, two second-order phase transitions, and three Hawking–Page-type phase transitions in the framework of rainbow gravity theory.

  20. Thermodynamic phase transition of a black hole in rainbow gravity

    Science.gov (United States)

    Feng, Zhong-Wen; Yang, Shu-Zheng

    2017-09-01

    In this letter, using the rainbow functions that were proposed by Magueijo and Smolin, we investigate the thermodynamics and the phase transition of rainbow Schwarzschild black hole. First, we calculate the rainbow gravity corrected Hawking temperature. From this modification, we then derive the local temperature, free energy, and other thermodynamic quantities in an isothermal cavity. Finally, we analyze the critical behavior, thermodynamic stability, and phase transition of the rainbow Schwarzschild black hole. The results show that the rainbow gravity can stop the Hawking radiation in the final stages of black holes' evolution and lead to the remnants of black holes. Furthermore, one can observe that the rainbow Schwarzschild black hole has one first-order phase transition, two second-order phase transitions, and three Hawking-Page-type phase transitions in the framework of rainbow gravity theory.

  1. Baryon inhomogeneity from the cosmic quark-hadron phase transition

    International Nuclear Information System (INIS)

    Kurki-Suonio, H.

    1991-01-01

    We discuss the generation of inhomogeneity in the baryon-number density during the cosmic quark-hadron phase transition. We use a simple model with thin-wall phase boundaries and ideal-gas equations of state. The nucleation of the phase transition introduces a new distance scale into the universe which will be the scale of the generated inhomogeneity. We review the estimate of this scale. During the transition baryon number is likely to collect onto a layer at the phase boundary. These layers may in the end be deposited as small regions of very high baryon density. 21 refs., 1 fig

  2. CO2 Capture from Flue Gas by Phase Transitional Absorption

    Energy Technology Data Exchange (ETDEWEB)

    Liang Hu

    2009-06-30

    A novel absorption process called Phase Transitional Absorption was invented. What is the Phase Transitional Absorption? Phase Transitional Absorption is a two or multi phase absorption system, CO{sub 2} rich phase and CO{sub 2} lean phase. During Absorption, CO{sub 2} is accumulated in CO{sub 2} rich phase. After separating the two phases, CO{sub 2} rich phase is forward to regeneration. After regeneration, the regenerated CO{sub 2} rich phase combines CO{sub 2} lean phase to form absorbent again to complete the cycle. The advantage for Phase Transitional Absorption is obvious, significantly saving on regeneration energy. Because CO{sub 2} lean phase was separated before regeneration, only CO{sub 2} rich phase was forward to regeneration. The absorption system we developed has the features of high absorption rate, high loading and working capacity, low corrosion, low regeneration heat, no toxic to environment, etc. The process evaluation shows that our process is able to save 80% energy cost by comparing with MEA process.

  3. Phase Transitions In M-Theory And F-Theory

    OpenAIRE

    Witten, Edward

    1996-01-01

    Phase transitions are studied in $M$-theory and $F$-theory. In $M$-theory compactification to five dimensions on a Calabi-Yau, there are topology-changing transitions similar to those seen in conformal field theory, but the non-geometrical phases known in conformal field theory are absent. At boundaries of moduli space where such phases might have been expected, the moduli space ends, by a conventional or unconventional physical mechanism. The unconventional mechanisms, which roughly involve ...

  4. The thickness dependence of the phase transition temperature in PVDF

    Energy Technology Data Exchange (ETDEWEB)

    Mai, M. [Institute of Electrical Engineering Physics, Saarland University, D-66123 Saarbruecken (Germany); Fridkin, V. [Institute of Crystallography of Russian Academy of Sciences, 119333 Moscow (Russian Federation); Martin, B., E-mail: b.martin@mx.uni-saarland.de [Institute of Electrical Engineering Physics, Saarland University, D-66123 Saarbruecken (Germany); Leschhorn, A.; Kliem, H. [Institute of Electrical Engineering Physics, Saarland University, D-66123 Saarbruecken (Germany)

    2013-07-15

    It was found recently that in the Langmuir–Blodgett ultrathin vinylidene fluoride (PVDF) films there is ferroelectric phase transition of the first order. Earlier in the bulk PVDF this phase transition was not observed because the melting temperature of this ferroelectric polymer (∼170 °C) is lower than the point of the possible phase transition. Therefore this polymer was treated for a long time as pyroelectric. In the present work we investigate PVDF Langmuir–Blodgett films at the nanoscale and the film thickness interval, where ferroelectric phase transition disappears and transition from ferroelectric to pyroelectric state takes place. This phenomenon is explained by the finite-size effect at the nanoscale using Landau–Ginzburg–Devonshire (LGD) theory and by the Weiss mean field model.

  5. The electroweak phase transition in the Inert Doublet Model

    Energy Technology Data Exchange (ETDEWEB)

    Blinov, Nikita [Department of Physics, University of California Santa Cruz,1156 High St, Santa Cruz, CA 95064 (United States); Santa Cruz Institute for Particle Physics,1156 High St, Santa Cruz, CA 95064 (United States); Theory Department, TRIUMF,4004 Wesbrook Mall, Vancouver, BC V6T 2A3 (Canada); Department of Physics and Astronomy, University of British Columbia,Vancouver, BC V6T 1Z1 (Canada); Profumo, Stefano; Stefaniak, Tim [Department of Physics, University of California Santa Cruz,1156 High St, Santa Cruz, CA 95064 (United States); Santa Cruz Institute for Particle Physics,1156 High St, Santa Cruz, CA 95064 (United States)

    2015-07-21

    We study the strength of a first-order electroweak phase transition in the Inert Doublet Model (IDM), where particle dark matter (DM) is comprised of the lightest neutral inert Higgs boson. We improve over previous studies in the description and treatment of the finite-temperature effective potential and of the electroweak phase transition. We focus on a set of benchmark models inspired by the key mechanisms in the IDM leading to a viable dark matter particle candidate, and illustrate how to enhance the strength of the electroweak phase transition by adjusting the masses of the yet undiscovered IDM Higgs states. We argue that across a variety of DM masses, obtaining a strong enough first-order phase transition is a generic possibility in the IDM. We find that due to direct dark matter searches and collider constraints, a sufficiently strong transition and a thermal relic density matching the universal DM abundance is possible only in the Higgs funnel regime.

  6. The electroweak phase transition in the Inert Doublet Model

    Energy Technology Data Exchange (ETDEWEB)

    Blinov, Nikita; Profumo, Stefano; Stefaniak, Tim, E-mail: nblinov@triumf.ca, E-mail: profumo@ucsc.edu, E-mail: tistefan@ucsc.edu [Department of Physics, University of California Santa Cruz, 1156 High St, Santa Cruz, CA 95064 (United States)

    2015-07-01

    We study the strength of a first-order electroweak phase transition in the Inert Doublet Model (IDM), where particle dark matter (DM) is comprised of the lightest neutral inert Higgs boson. We improve over previous studies in the description and treatment of the finite-temperature effective potential and of the electroweak phase transition. We focus on a set of benchmark models inspired by the key mechanisms in the IDM leading to a viable dark matter particle candidate, and illustrate how to enhance the strength of the electroweak phase transition by adjusting the masses of the yet undiscovered IDM Higgs states. We argue that across a variety of DM masses, obtaining a strong enough first-order phase transition is a generic possibility in the IDM. We find that due to direct dark matter searches and collider constraints, a sufficiently strong transition and a thermal relic density matching the universal DM abundance is possible only in the Higgs funnel regime.

  7. Nonequilibrium topological phase transitions in two-dimensional optical lattices

    Science.gov (United States)

    Nakagawa, Masaya; Kawakami, Norio

    2014-01-01

    Recently, concepts of topological phases of matter are extended to nonequilibrium systems, especially periodically driven systems. In this paper, we construct an example which shows nonequilibrium topological phase transitions using ultracold fermions in optical lattices. We show that the Rabi oscillation has the possibility to induce nonequilibrium topological phases which are classified into time-reversal-invariant topological insulators for a two-orbital model of alkaline-earth-metal atoms. Furthermore, we study the nonequilibrium topological phases using time-dependent Schrieffer-Wolff-type perturbation theory, and we obtain an analytical expression to describe the topological phase transitions from a high-frequency limit of external driving fields.

  8. Continuous localization-delocalization transition at intermediate electron densities

    International Nuclear Information System (INIS)

    Neilson, D.; Thakur, J.S.

    1999-01-01

    We find in 2D electron layers in quantum transistors that the interplay between the electron correlations and their interactions with defects in the semiconductor substrate generates a continuous localisation-delocalisation transition for intermediate electron densities (5 ≤ r s≤ 9). We distinguish this transition from the discontinuous metal-insulator transition which is observed at lower electron densities (r s≥ 10). The approach we use is based on the behaviour of electrons at low densities. We take into account the interactions between electrons and also their interactions with disorder. We determine a zero temperature phase diagram of localised and delocalised states as a function of electron and impurity densities. The phase boundary of the continuous transition is determined by the localisation length of the electrons. Copyright (1999) CSIRO Australia

  9. Discontinuity of maximum entropy inference and quantum phase transitions

    International Nuclear Information System (INIS)

    Chen, Jianxin; Ji, Zhengfeng; Yu, Nengkun; Zeng, Bei; Li, Chi-Kwong; Poon, Yiu-Tung; Shen, Yi; Zhou, Duanlu

    2015-01-01

    In this paper, we discuss the connection between two genuinely quantum phenomena—the discontinuity of quantum maximum entropy inference and quantum phase transitions at zero temperature. It is shown that the discontinuity of the maximum entropy inference of local observable measurements signals the non-local type of transitions, where local density matrices of the ground state change smoothly at the transition point. We then propose to use the quantum conditional mutual information of the ground state as an indicator to detect the discontinuity and the non-local type of quantum phase transitions in the thermodynamic limit. (paper)

  10. Phase transition of pure zirconia under irradiation: A textbook example

    Energy Technology Data Exchange (ETDEWEB)

    Simeone, D. [CEA/Saclay, DEN/DMN/SRMA/LA2M, F-91191 Gif sur Yvette (France)]. E-mail: david.simeone@cea.fr; Baldinozzi, G. [Laboratoire de Structures, Proprietes et Modelisation des Solides, UMR CNRS 8580 Ecole Centrale Paris, F-92295 Chatenay Malabry (France); Gosset, D. [CEA/Saclay, DEN/DMN/SRMA/LA2M, F-91191 Gif sur Yvette (France); Le Caer, S. [CEA/Saclay, DSM/DRECAM/SCM/URA 331 CNRS, F-91191 Gif sur Yvette (France)

    2006-09-15

    One of the most important goals in ceramic and materials science is to be able to design materials with specific properties. Irradiation seems to be a powerful tool for the design of advanced ceramics because of its ability to modify over different scales the microstructure of solids. Nowadays, it is clearly proved that irradiation induces order-disorder phase transitions in metallic alloys and in some ceramics. In this paper, we show that a displacive phase transition can also be induced by irradiation. Based on many experimental facts, a microscopic model is proposed to explain the displacive phase transition observed in this material after irradiation. Defects, produced in the oxygen sublattice, induce important strain fields on a nanometric scale. This strain field can be handled as a secondary order parameter within the Landau theory approach, leading to a decrease of the phase transition temperature and thus quenching the high temperature tetragonal phase.

  11. Thermodynamic model of nonequilibrium phase transitions.

    Science.gov (United States)

    Martyushev, L M; Konovalov, M S

    2011-07-01

    Within the scope of a thermodynamic description using the maximum entropy production principle, transitions from one nonequilibrium (kinetic) regime to another are considered. It is shown that in the case when power-law dependencies of thermodynamic flux on force are similar for two regimes, only a transition accompanied by a positive jump of thermodynamic flux is possible between them. It is found that the difference in powers of the dependencies of thermodynamic fluxes on forces results in a number of interesting nonequilibrium transitions between kinetic regimes, including the reentrant one with a negative jump of thermodynamic flux.

  12. Do phase transitions survive binomial reducibility and thermal scaling?

    International Nuclear Information System (INIS)

    Moretto, L.G.; Phair, L.; Wozniak, G.J.

    1996-05-01

    First order phase transitions are described in terms of the microcanonical and canonical ensemble, with special attention to finite size effects. Difficulties in interpreting a 'caloric curve' are discussed. A robust parameter indicating phase coexistence (univariance) or single phase (bivariance) is extracted for charge distributions. 9 refs., 4 figs

  13. Do phase transitions survive binomial reducibility and thermal scaling?

    Energy Technology Data Exchange (ETDEWEB)

    Moretto, L.G.; Phair, L.; Wozniak, G.J.

    1996-05-01

    First order phase transitions are described in terms of the microcanonical and canonical ensemble, with special attention to finite size effects. Difficulties in interpreting a `caloric curve` are discussed. A robust parameter indicating phase coexistence (univariance) or single phase (bivariance) is extracted for charge distributions. 9 refs., 4 figs.

  14. Phase transition in a modified square Josephson-junction array

    CERN Document Server

    Han, J

    1999-01-01

    We study the phase transition in a modified square proximity-coupled Josephson-junction array with small superconducting islands at the center of each plaquette. We find that the modified square array undergoes a Kosterlitz-Thouless-Berezinskii-like phase transition, but at a lower temperature than the simple square array with the same single-junction critical current. The IV characteristics, as well as the phase transition, resemble qualitatively those of a disordered simple square array. The effects of the presence of the center islands in the modified square array are discussed.

  15. Novel phase transitions in B-site doped manganites

    International Nuclear Information System (INIS)

    Popovic, Z.V.; Cantarero, A.; Thijssen, W.H.A.; Paunovic, N.; Dohcevic-Mitrovic, Z.; Sapina, F.

    2005-01-01

    We have examined the infrared reflectivity and the electrical resistivity of La 1- x [Sr(Ba)] x Mn 1- z [Cu(Zn)] z O 3 samples in ferromagnetic metallic and insulator regime. Several phase transitions are observed, the most obvious being the transition from a ferromagnetic metallic to a ferromagnetic insulator phase that is related to the formation of short-range orbitally ordered domains. The temperature T 1 of the phase transition is dependent on doping concentration and for optimally doped samples (∼32% of Mn 4+ ions) we have found T 1 ∼0.93 T C

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

    International Nuclear Information System (INIS)

    Tran Huu Phat; Nguyen Tuan Anh; Le Viet Hoa

    2003-01-01

    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)

  17. Quantum phase transitional patterns of nuclei

    International Nuclear Information System (INIS)

    Dai Lianrong; Wang Lixing; Pan Feng; Zhong Weiwei; Liu Qi

    2013-01-01

    With the framework of Interacting Boson Model (IBM), transitional patterns from the spherical to the axially deformed limit of the IBM with a schematic Hamiltonian are studied by replacing the SU (3) quadrupole-quadrupole term with O (6) cubic interaction. But, we use the two schemes to investigate some energy ratios and B (E2) ratios for different bosons N = 8 and N = 20. The results show that with the increasing of the numbers of bosons, the transitional behaviors can be enhanced; the transitional behaviors are very similar in the two schemes. However, there are some distinctive differences for some quantities across the entire transitional region, such as energy levels and ratios, B (E2) values and ratios, and expectation values of the shape variables. Generally speaking, the transition is smoother and the nuclear shape is less well defined in the new scheme. Then we apply the two schemes to the critical point symmetry candidate, such as 152 Sm, and find the overall fitting quality of the UQ scheme is better than that of the U (5)-SU (3) scheme, especially for the inter-band E2 transitions in 152 Sm. (authors)

  18. Quantum phase transitions in random XY spin chains

    International Nuclear Information System (INIS)

    Bunder, J.E.; McKenzie, R.H.

    2000-01-01

    Full text: The XY spin chain in a transverse field is one of the simplest quantum spin models. It is a reasonable model for heavy fermion materials such as CeCu 6-x Au x . It has two quantum phase transitions: the Ising transition and the anisotropic transition. Quantum phase transitions occur at zero temperature. We are investigating what effect the introduction of randomness has on these quantum phase transitions. Disordered systems which undergo quantum phase transitions can exhibit new universality classes. The universality class of a phase transition is defined by the set of critical exponents. In a random system with quantum phase transitions we can observe Griffiths-McCoy singularities. Such singularities are observed in regions which have no long range order, so they are not classified as critical regions, yet they display phenomena normally associated with critical points, such as a diverging susceptibility. Griffiths-McCoy phases are due to rare regions with stronger than! average interactions and may be present far from the quantum critical point. We show how the random XY spin chain may be mapped onto a random Dirac equation. This allows us to calculate the density of states without making any approximations. From the density of states we can describe the conditions which should allow a Griffiths-McCoy phase. We find that for the Ising transition the dynamic critical exponent, z, is not universal. It is proportional to the disorder strength and inversely proportional to the energy gap, hence z becomes infinite at the critical point where the energy gap vanishes

  19. Highly repeatable nanoscale phase coexistence in vanadium dioxide films

    Science.gov (United States)

    Huffman, T. J.; Lahneman, D. J.; Wang, S. L.; Slusar, T.; Kim, Bong-Jun; Kim, Hyun-Tak; Qazilbash, M. M.

    2018-02-01

    It is generally believed that in first-order phase transitions in materials with imperfections, the formation of phase domains must be affected to some extent by stochastic (probabilistic) processes. The stochasticity would lead to unreliable performance in nanoscale devices that have the potential to exploit the transformation of physical properties in a phase transition. Here we show that stochasticity at nanometer length scales is completely suppressed in the thermally driven metal-insulator transition (MIT) in sputtered vanadium dioxide (V O2 ) films. The nucleation and growth of domain patterns of metallic and insulating phases occur in a strikingly reproducible way. The completely deterministic nature of domain formation and growth in films with imperfections is a fundamental and unexpected finding about the kinetics of this material. Moreover, it opens the door for realizing reliable nanoscale devices based on the MIT in V O2 and similar phase-change materials.

  20. Pressure-induced phase transition in a ternary microemulsion system

    International Nuclear Information System (INIS)

    Nagao, Michihiro; Seto, Hideki

    2002-01-01

    Static and dynamic structure of a ternary microemulsion system including AOT (Aerosol-OT; dioctyl sulfosuccinate sodium salt) were investigated in order to clarify the mechanism of the structural phase transition induced by pressure. From the static measurement by means of small-angle x-ray and neutron scattering (SAXS and SANS), it was observed that the dense water-in-oil droplet structure at ambient temperature and pressure transformed to two-phase coexistence with the lamellar phase and the bicontinuous phase with increasing pressure as the case of increasing temperature. The characteristic features of pressure-induced phase transition were quite similar to the temperature-induced one below the phase transition temperature and pressure, however, above the transition temperature and pressure, they were different. From the dynamical measurement by means of the neutron spin echo (NSE), membrane dynamics at high-pressure phase was observed completely different from the high temperature phase. The result showed that with increasing temperature the membrane became flexible and, on the other hand, it became rigid with increasing pressure. These differences suggested the different mechanism of the pressure-induced phase transition from the temperature-induced one. (author)

  1. Phonon anomalies and the magnetic transition in pure and Cr-doped V/sub 2/O/sub 3/

    Energy Technology Data Exchange (ETDEWEB)

    Yethiraj, M.; Werner, S.A.; Yelon, W.B.; Honig, J.M.

    1987-12-01

    We have studied the lattice dynamics, the magnetic ordering and excitations, and the crystallographic distortions associated with the metal-insulator transitions in pure and Cr-doped vanadium sesquioxide using neutron-scattering techniques. In the paramagnetic metallic phase of pure V/sub 2/O/sub 3/ and in the higher-temperature paramagnetic metallic phase of 1.5-at. %-Cr-doped V/sub 2/O/sub 3/ we see an anomalous splitting of the transversely polarized acoustic phonon mode, propagating along the hexagonal (hh0) direction near the center of the Brillouin zone. Upon lowering the temperature, a substantial softening of a large portion of the transverse acoustic branch in the (00l) direction is observed in Cr-doped samples in the paramagnetic insulating phase as the transition to the antiferromagnetic insulating phase is approached. The loss of antiferromagnetic order with increasing temperature in 3-at. %-Cr-doped and 6-at. %-Cr-doped samples appears to be nearly continuous. The temperature dependence of the spin-wave energy gap in the 3-at. %-Cr-doped sample appears to approach zero continuously up to the Neel temperature. The monoclinic distortion of the trigonal phase at this transition is much reduced in the 6-at. %-Cr-doped sample compared to pure V/sub 2/O/sub 3/. These and other results are described in detail, and discussed in connection with the recent theoretical work on metal-insulator transitions.

  2. QCD phase transition in Brans-Dicke cosmology

    Energy Technology Data Exchange (ETDEWEB)

    Atazadeh, K. [Shahid Beheshti University G. C., Evin, Department of Physics, Tehran (Iran, Islamic Republic of)

    2011-04-15

    In the standard picture of cosmology, when the universe was about 10 {mu}sec old it underwent a transition from quark phase to hadron one, being associated with a chiral symmetry breaking after the electro weak transition. We assume that this transition was of crossover and study the evolution of the Universe in the context of Brans-Dicke theory. The evolution of physical quantities relevant to the physical description of the early Universe, namely, the energy density, temperature and the scale factor, are studied within an effective model of lattice QCD for high temperature and also we consider in the context of hadronic resonance gas model those parameters at low temperature. We show that for different values of Brans-Dicke coupling, {omega}, a phase transition occurs and results in decreasing of the effective temperature of the quark-gluon plasma during the process of quark-hadron phase transition. (orig.)

  3. 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.

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

    International Nuclear Information System (INIS)

    Szczepanski, Petra; Wunschick, Franziska; Martin, Niklas

    2015-01-01

    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. [de

  5. Electroweak phase transition in a model with gauged lepton number

    International Nuclear Information System (INIS)

    Aranda, Alfredo; Jiménez, Enrique; Vaquera-Araujo, Carlos A.

    2015-01-01

    In this work we study the electroweak phase transition in a model with gauged lepton number. Here, a family of vector-like leptons is required in order to cancel the gauge anomalies. Furthermore, these leptons can play an important role in the transition process. We find that this framework is able to provide a strong transition, but only for a very limited number of cases.

  6. 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 formation...

  7. Phase transition in L-alaninium oxalate by photoacoustics

    Indian Academy of Sciences (India)

    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 ...

  8. Phase transitions, interfacial fluctuations and hidden symmetries for ...

    Indian Academy of Sciences (India)

    Fluids adsorbed at micro-patterned and geometrically structured substrates can exhibit novel phase transitions and interfacial fluctuation effects distinct from those characteristic of wetting at planar, homogeneous walls. We review recent theoretical progress in this area paying particular attention to filling transitions pertinent ...

  9. Quantum Shape-Phase Transitions in Finite Nuclei

    International Nuclear Information System (INIS)

    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

  10. Quantum Shape-Phase Transitions in Finite Nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Leviatan, A. [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel)

    2007-05-15

    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.

  11. The QCD phase transitions: From mechanism to observables

    Energy Technology Data Exchange (ETDEWEB)

    Shuryak, E.V.

    1997-09-22

    This paper contains viewgraphs on quantum chromodynamic phase transformations during heavy ion collisions. Some topics briefly described are: finite T transitions of I molecule pairs; finite density transitions of diquarks polymers; and the softtest point of the equation of state as a source of discontinuous behavior as a function of collision energy or centrality.

  12. Signals of a phase transition in nuclear breakup

    International Nuclear Information System (INIS)

    Campi, X.

    1987-01-01

    We show that nuclei break up like finite systems that exhibit a clean phase transition in infinite size. This is done by studying conditional moments of the fragment multiplicities, the largest fragment size produced by event and its fluctuations. The nature of this smooth phase transition cannot be determined from the available experimental data. The ''critical point'' is reached when the energy deposited in the nucleus is 90% of its binding energy

  13. Baryogenesis via leptonic CP-violating phase transition

    Science.gov (United States)

    Pascoli, Silvia; Turner, Jessica; Zhou, Ye-Ling

    2018-05-01

    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 a connection with low-energy neutrino observables.

  14. Partial dynamical symmetry at critical points of quantum phase transitions.

    Science.gov (United States)

    Leviatan, A

    2007-06-15

    We show that partial dynamical symmetries can occur at critical points of quantum phase transitions, in which case underlying competing symmetries are conserved exactly by a subset of states, and mix strongly in other states. Several types of partial dynamical symmetries are demonstrated with the example of critical-point Hamiltonians for first- and second-order transitions in the framework of the interacting boson model, whose dynamical symmetries correspond to different shape phases in nuclei.

  15. Partial Dynamical Symmetry at Critical Points of Quantum Phase Transitions

    International Nuclear Information System (INIS)

    Leviatan, A.

    2007-01-01

    We show that partial dynamical symmetries can occur at critical points of quantum phase transitions, in which case underlying competing symmetries are conserved exactly by a subset of states, and mix strongly in other states. Several types of partial dynamical symmetries are demonstrated with the example of critical-point Hamiltonians for first- and second-order transitions in the framework of the interacting boson model, whose dynamical symmetries correspond to different shape phases in nuclei

  16. Hadronization during quark-gluon plasma phase transition

    International Nuclear Information System (INIS)

    Mohanty, A.K.; Kataria, S.K.

    1996-01-01

    The hadron multiplicity distributions and factorial moments are studied in the framework of Landau theory of phase transitions. The factorial moments show a scaling law with a scaling exponent ν which characterizes the intermittency properties of the hadron phase for T c (or T t ) where T c (or T t ) is the transition temperature for second (or first) order transition. The scaling exponent ν is weakly dependent on the free energy parameters as well as on temperature. It is shown that ν remains practically constant in the hadron phase for which T c or T t whether the transition is second order or first order of second kind where the free energy expansion includes cubic term. This universality in the scaling exponent is also maintained above T c over a wide range of temperature even if the transition is strongly first order of first kind where the free energy expansion has only even order coefficients, except around the critical temperature T t where T t approx-gt T c . Therefore, the scaling exponent ν is rather more universal and only indicates the presence of a possible phase transition. It is further shown that the hadron multiplicity distribution is quite sensitive to the free energy parameters. The study of hadron multiplicity distribution at various resolution or bin size reveals more information about the dynamics of the phase transition. The calculated hadron multiplicity distributions are also compared with the negative binomial distribution, often used to explain the experimental multiplicity distributions. copyright 1996 The American Physical Society

  17. Massive Temperature-Induced Metal—Insulator Transition in Individual Nanowires of a Non-Stoichiometric Vanadium Oxide Bronze

    Energy Technology Data Exchange (ETDEWEB)

    Patridge, C.; Wu, T; Jaye, C; Ravel, B; Takeuchi, E; Fischer, D; Sambandamurthy, G; Banerjee, S

    2010-01-01

    Metal-insulator transitions in strongly correlated materials, induced by varying either temperature or dopant concentration, remain a topic of enduring interest in solid-state chemistry and physics owing to their fundamental importance in answering longstanding questions regarding correlation effects. We note here the unprecedented observation of a four-orders-of-magnitude metal-insulator transition in single nanowires of {delta}-K{sub x}V{sub 2}O{sub 5}, when temperature is varied, which thus represents a rare new addition to the pantheon of materials exhibiting pronounced metal-insulator transitions in proximity to room temperature.

  18. Liquid-liquid phase transition and glass transition in a monoatomic model system.

    Science.gov (United States)

    Xu, Limei; Buldyrev, Sergey V; Giovambattista, Nicolas; Stanley, H Eugene

    2010-01-01

    We review our recent study on the polyamorphism of the liquid and glass states in a monatomic system, a two-scale spherical-symmetric Jagla model with both attractive and repulsive interactions. This potential with a parametrization for which crystallization can be avoided and both the glass transition and the liquid-liquid phase transition are clearly separated, displays water-like anomalies as well as polyamorphism in both liquid and glassy states, providing a unique opportunity to study the interplay between the liquid-liquid phase transition and the glass transition. Our study on a simple model may be useful in understanding recent studies of polyamorphism in metallic glasses.

  19. Phase transitions and critical behaviour for charged black holes

    International Nuclear Information System (INIS)

    Carlip, S; Vaidya, S

    2003-01-01

    We investigate the thermodynamics of a four-dimensional charged black hole in a finite cavity in asymptotically flat and asymptotically de Sitter spaces. In each case, we find a Hawking-Page-like phase transition between a black hole and a thermal gas very much like the known transition in asymptotically anti-de Sitter space. For a 'supercooled' black hole - a thermodynamically unstable black hole below the critical temperature for the Hawking-Page phase transition - the phase diagram has a line of first-order phase transitions that terminates in a second-order point. For the asymptotically flat case, we calculate the critical exponents at the second-order phase transition and find that they exactly match the known results for a charged black hole in anti-de Sitter space. We find strong evidence for similar phase transitions for the de Sitter black hole as well. Thus many of the thermodynamic features of charged anti-de Sitter black holes do not really depend on asymptotically anti-de Sitter boundary conditions; the thermodynamics of charged black holes is surprisingly universal

  20. Problem-solving phase transitions during team collaboration

    DEFF Research Database (Denmark)

    Wiltshire, Travis; Butner, Jonathan E.; Fiore, Stephen M.

    2017-01-01

    ) with dynamical systems theory suggesting that when a system is undergoing a phase transition it should exhibit a peak in entropy and that entropy levels should also relate to team performance. Communications from 40 teams that collaborated on a complex problem were coded for occurrence of problem......-solving processes. We applied a sliding window entropy technique to each team's communications and specified criteria for (a) identifying data points that qualify as peaks and (b) determining which peaks were robust. We used multilevel modeling, and provide a qualitative example, to evaluate whether phases exhibit...... phases. Peaks in entropy thus corresponded to qualitative shifts in teams’ CPS communications, providing empirical evidence that teams exhibit phase transitions during CPS. Also, lower average levels of entropy at the phase transition points predicted better CPS performance. We specify future directions...

  1. Entropy and baryon number conservation in the deconfinement phase transition

    International Nuclear Information System (INIS)

    Leonidov, A.; Redlich, K.; Satz, H.; Suhonen, E.; Weber, G.

    1994-01-01

    The conservation of entropy and baryon number in the deconfinement phase transition is studied in the framework of the bag model. In the standard construction of the equilibrium phase transition from a quark-gluon plasma into a hadron gas a subsequent dilution and reheating of the system on the phase boundary is necessary to preserve the entropy and baryon number conservation. We propose modifying the bag pressure to depend explicitly on temperature and baryon chemical potential. It is shown that this modification is sufficient to construct a model in agreement with the Gibbs equilibrium criteria for a phase transition, while simultaneously assuring entropy and baryon number conservation on the phase boundary. Within this model the quark-gluon plasma hadronizes at a fixed temperature and chemical potential

  2. 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.

  3. Polymer Semiflexibility Induces Nonuniversal Phase Transitions in Diblock Copolymers

    Science.gov (United States)

    Mao, Shifan; MacPherson, Quinn; Spakowitz, Andrew J.

    2018-02-01

    The order-disorder phase transition and the associated phase diagrams of semiflexible diblock copolymers are investigated using the wormlike chain model, incorporating concentration fluctuations. The free energy up to quartic order in concentration fluctuations is developed with chain-rigidity-dependent coefficients, evaluated using our exact results for the wormlike chain model, and a one-loop renormalization treatment is used to account for fluctuation effects. The chain length N and the monomer aspect ratio α directly control the strength of immiscibility (defined by the Flory-Huggins parameter χ ) at the order-disorder transition and the resulting microstructures at different chemical compositions fA. When monomers are infinitely thin (i.e., large aspect ratio α ), the finite chain length N lowers the χ N at the phase transition. However, fluctuation effects become important when chains have a finite radius, and a decrease in the chain length N elevates the χ N at the phase transition. Phase diagrams of diblock copolymers over a wide range of N and α are calculated based on our fluctuation theory. We find that both finite N and α enhance the stability of the lamellar phase above the order-disorder transition. Our results demonstrate that polymer semiflexibility plays a dramatic role in the phase behavior, even for large chain lengths (e.g., N ≈100 ).

  4. Tunneling conductance oscillations in spin-orbit coupled metal-insulator-superconductor junctions

    Science.gov (United States)

    Kapri, Priyadarshini; Basu, Saurabh

    2018-01-01

    The tunneling conductance for a device consisting of a metal-insulator-superconductor (MIS) junction is studied in presence of Rashba spin-orbit coupling (RSOC) via an extended Blonder-Tinkham-Klapwijk formalism. We find that the tunneling conductance as a function of an effective barrier potential that defines the insulating layer and lies intermediate to the metallic and superconducting electrodes, displays an oscillatory behavior. The tunneling conductance shows high sensitivity to the RSOC for certain ranges of this potential, while it is insensitive to the RSOC for others. Additionally, when the period of oscillations is an odd multiple of a certain value of the effective potential, the conductance spectrum as a function of the biasing energy demonstrates a contrasting trend with RSOC, compared to when it is not an odd multiple. The explanations for the observation can be found in terms of a competition between the normal and Andreev reflections. Similar oscillatory behavior of the conductance spectrum is also seen for other superconducting pairing symmetries, thereby emphasizing that the insulating layer plays a decisive role in the conductance oscillations of a MIS junction. For a tunable Rashba coupling, the current flowing through the junction can be controlled with precision.

  5. Transport properties of metal-metal and metal-insulator heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Fadlallah Elabd, Mohamed Mostafa

    2010-06-09

    In this study we present results of electronic structure and transport calculations for metallic and metal-insulator interfaces, based on density functional theory and the non-equilibrium Green's function method. Starting from the electronic structure of bulk Al, Cu, Ag, and Au interfaces, we study the effects of different kinds of interface roughness on the transmission coefficient (T(E)) and the I-V characteristic. In particular, we compare prototypical interface distortions, including vacancies, metallic impurities, non-metallic impurities, interlayer, and interface alloy. We find that vacancy sites have a huge effect on transmission coefficient. The transmission coefficient of non-metallic impurity systems has the same behaviour as the transmission coefficient of vacancy system, since these systems do not contribute to the electronic states at the Fermi energy. We have also studied the transport properties of Au-MgO-Au tunnel junctions. In particular, we have investigated the influence of the thickness of the MgO interlayer, the interface termination, the interface spacing, and O vacancies. Additional interface states appear in the O-terminated configuration due to the formation of Au-O bonds. An increasing interface spacing suppresses the Au-O bonding. Enhancement of T(E) depends on the position and density of the vacancies (the number of vacancies per unit cell). (orig.)

  6. Direct Fabrication of Inkjet-Printed Dielectric Film for Metal-Insulator-Metal Capacitors

    Science.gov (United States)

    Cho, Cheng-Lin; Kao, Hsuan-ling; Wu, Yung-Hsien; Chang, Li-Chun; Cheng, Chun-Hu

    2018-01-01

    In this study, an inkjet-printed dielectric film that used a polymer-based SU-8 ink was fabricated for use in a metal-insulator-metal (MIM) capacitor. Thermal treatment of the inkjet-printed SU-8 polymer film affected its surface morphology, chemical structure, and surface wettability. A 20-min soft-bake at 60°C was applied to eliminate inkjet-printed bubbles and ripples. The ultraviolet-exposed SU-8 polymer film was crosslinked at temperatures between 120°C and 220°C and became disordered at 270°C, demonstrated using Fourier-transform infrared spectroscopy. A maximum SU-8 polymer film hard-bake temperature of 120°C was identified, and a printing process was subsequently employed because the appropriate water contact angle of the printed film was 79°. Under the appropriate inkjet printing conditions, the two-transmission-line method was used to extract the dielectric and electrical properties of the SU-8 polymer film, and the electrical behavior of the fabricated MIM capacitor was also characterized.

  7. Simulated electron affinity tuning in metal-insulator-metal (MIM) diodes

    Science.gov (United States)

    Mistry, Kissan; Yavuz, Mustafa; Musselman, Kevin P.

    2017-05-01

    Metal-insulator-metal diodes for rectification applications must exhibit high asymmetry, nonlinearity, and responsivity. Traditional methods of improving these figures of merit have consisted of increasing insulator thickness, adding multiple insulator layers, and utilizing a variety of metal contact combinations. However, these methods have come with the price of increasing the diode resistance and ultimately limiting the operating frequency to well below the terahertz regime. In this work, an Airy Function Transfer Matrix simulation method was used to observe the effect of tuning the electron affinity of the insulator as a technique to decrease the diode resistance. It was shown that a small increase in electron affinity can result in a resistance decrease in upwards of five orders of magnitude, corresponding to an increase in operating frequency on the same order. Electron affinity tuning has a minimal effect on the diode figures of merit, where asymmetry improves or remains unaffected and slight decreases in nonlinearity and responsivity are likely to be greatly outweighed by the improved operating frequency of the diode.

  8. Systematic study of metal-insulator-metal diodes with a native oxide

    KAUST Repository

    Donchev, E.

    2014-10-07

    © 2014 SPIE. In this paper, a systematic analysis of native oxides within a Metal-Insulator-Metal (MIM) diode is carried out, with the goal of determining their practicality for incorporation into a nanoscale Rectenna (Rectifying Antenna). The requirement of having a sub-10nm oxide scale is met by using the native oxide, which forms on most metals exposed to an oxygen containing environment. This, therefore, provides a simplified MIM fabrication process as the complex, controlled oxide deposition step is omitted. We shall present the results of an investigation into the current-voltage characteristics of various MIM combinations that incorporate a native oxide, in order to establish whether the native oxide is of sufficient quality for good diode operation. The thin native oxide layers are formed by room temperature oxidation of the first metal layer, deposited by magnetron sputtering. This is done in-situ, within the deposition chamber before depositing the second metal electrode. Using these structures, we study the established trend where the bigger the difference in metal workfunctions, the better the rectification properties of MIM structures, and hence the selection of the second metal is key to controlling the device\\'s rectifying properties. We show how leakage current paths through the non-optimised native oxide control the net current-voltage response of the MIM devices. Furthermore, we will present the so-called diode figures of merit (asymmetry, non-linearity and responsivity) for each of the best performing structures.

  9. Characterization of micro-resonator based on enhanced metal insulator semiconductor capacitor for glucose recognition.

    Science.gov (United States)

    Dhakal, Rajendra; Kim, E S; Jo, Yong-Hwa; Kim, Sung-Soo; Kim, Nam-Young

    2017-03-01

    We present a concept for the characterization of micro-fabricated based resonator incorporating air-bridge metal-insulator-semiconductor (MIS) capacitor to continuously monitor an individual's state of glucose levels based on frequency variation. The investigation revealed that, the micro-resonator based on MIS capacitor holds considerable promise for implementation and recognition as a glucose sensor for human serum. The discrepancy in complex permittivity as a result of enhanced capacitor was achieved for the detection and determination of random glucose concentration levels using a unique variation of capacitor that indeed results in an adequate variation of the resonance frequency. Moreover, the design and development of micro-resonator with enhanced MIS capacitor generate a resolution of 112.38 × 10 -3 pF/mg/dl, minimum detectable glucose level of 7.45mg/dl, and a limit of quantification of 22.58mg/dl. Additionally, this unique approach offers long-term reliability for mediator-free glucose sensing with a relative standard deviation of less than 0.5%. Copyright © 2017 IPEM. Published by Elsevier Ltd. All rights reserved.

  10. Controlled thermoelectric response of a tunable Rashba coupled metal-insulator-superconductor junction

    Science.gov (United States)

    Kapri, Priyadarshini; Adhikary, Priyanka; Sinha, Shubham; Basu, Saurabh

    2018-05-01

    Thermoelectric effect for metal, insulator and the superconductor junctions has been studied with Rashba spin-orbit coupling (RSOC) being present at the interfaces via modified Blonder-Tinkham-Klapwijk (BTK) theory. We find that the thermopower, as a function of an effective barrier potential that characterizes the intermediate insulating layer, displays an oscillatory behavior. Interesting interplay between the strength of RSOC and the effective barrier potential has been carried out in details in this regard. For specific ranges of the effective barrier potential, RSOC enhances the thermopower, while the reverse happens for other values. Moreover it is found that the effective barrier potential plays a crucial role in determining the thermopower spectrum. For a tunable Rashba coupling, the thermopower of the junction can be controlled with precision, which may useful for the thermoelectric applications, at low temperatures. Further the efficiency of the system is obtained for different pairing correlations of the superconducting lead where we find that the system with a d-wave symmetry is more efficient as compared to a s-wave correlation, in some selective regions of effective barrier potential. It is found that for some selective regions of effective barrier potential, the efficiency of the system increases with RSOC and the opposite happens for other values.

  11. Low dielectric constant-based organic field-effect transistors and metal-insulator-semiconductor capacitors

    Science.gov (United States)

    Ukah, Ndubuisi Benjamin

    This thesis describes a study of PFB and pentacene-based organic field-effect transistors (OFET) and metal-insulator-semiconductor (MIS) capacitors with low dielectric constant (k) poly(methyl methacrylate) (PMMA), poly(4-vinyl phenol) (PVP) and cross-linked PVP (c-PVP) gate dielectrics. A physical method -- matrix assisted pulsed laser evaporation (MAPLE) -- of fabricating all-polymer field-effect transistors and MIS capacitors that circumvents inherent polymer dissolution and solvent-selectivity problems, is demonstrated. Pentacene-based OFETs incorporating PMMA and PVP gate dielectrics usually have high operating voltages related to the thickness of the dielectric layer. Reduced PMMA layer thickness (≤ 70 nm) was obtained by dissolving the PMMA in propylene carbonate (PC). The resulting pentacene-based transistors exhibited very low operating voltage (below -3 V), minimal hysteresis in their transfer characteristics, and decent electrical performance. Also low voltage (within -2 V) operation using thin (≤ 80 nm) low-k and hydrophilic PVP and c-PVP dielectric layers obtained via dissolution in high dipole moment and high-k solvents -- PC and dimethyl sulfoxide (DMSO), is demonstrated to be a robust means of achieving improved electrical characteristics and high operational stability in OFETs incorporating PVP and c-PVP dielectrics.

  12. 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...... on fundamental physical principles. It describes essential thermodynamical properties of the system such as heat capacity, the phase transition temperature and others from the analysis of the polypeptide potential energy surface calculated as a function of two dihedral angles, responsible for the polypeptide...

  13. An objective indicator for two-phase flow pattern transition

    International Nuclear Information System (INIS)

    Hervieua, E.; Seleghim, P. Jr.

    1998-01-01

    This work concerns the development of a methodology the objective of which is to characterize and diagnose two-phase flow regime transitions. The approach is based on the fundamental assumption that a transition flow is less stationary than a flow with an established regime. During the first time, the efforts focused on: (1) the design and construction of an experimental loop, allowing to reproduce the main horizontal two-phase flow patterns, in a stable and controlled way; (2) the design and construction of an electrical impedance probe, providing an imaged information of the spatial phase distribution in the pipe; and (3) the systematic study of the joint time-frequency and time-scale analysis methods, which permitted to define an adequate parameter quantifying the unstationarity degree. During the second time, in order to verify the fundamental assumption, a series of experiments were conducted, the objective of which was to demonstrate the correlation between unstationarity and regime transition. The unstationarity degree was quantified by calculating the Gabor's transform time-frequency covariance of the impedance probe signals. Furthermore, the phenomenology of each transition was characterized by the joint moments and entropy. The results clearly show that the regime transitions are correlated with local time-frequency covariance peaks, which demonstrates that these regime transitions are characterized by a loss of stationarity. Consequently, the time-frequency covariance constitutes an objective two-phase flow regime transition indicator. (orig.)

  14. An objective indicator for two-phase flow pattern transition

    International Nuclear Information System (INIS)

    Hervieu, E.; Seleghim, P. Jr.

    1998-01-01

    This work concerns the development of a methodology which objective is to characterize and diagnose two-phase flow regime transitions. The approach is based on the fundamental assumption that a transition flow is less stationary than a flow with an established regime. In a first time, the efforts focused on: the design and construction of an experimental loop, allowing to reproduce the main horizontal two-phase flow patterns, in a stable and controlled way; the design and construction of an electrical impedance probe, providing an imaged information of the spatial phase distribution in the pipe; the systematic study of the joint time-frequency and time-scale analysis methods, which permitted to define an adequate parameter quantifying the unstationarity degree. In a second time, in order to verify the fundamental assumption, a series of experiments were conducted, which objective was to demonstrate the correlation between unstationarity and regime transition. The unstationarity degree was quantified by calculating the Gabor's transform time-frequency covariance of the impedance probe signals. Furthermore, the phenomenology of each transition was characterized by the joint moments and entropy. The results clearly show that the regime transitions are correlated with local time-frequency covariance peaks, which demonstrates that these regime transitions are characterized by a loss of stationarity. Consequently, the time-frequency covariance constitutes an objective two-phase flow regime transition indicator. (author)

  15. Magnetically inhomogeneous ground state below the first-order valence transition in (Pr1-yYy)0.7Ca0.3CoO3-δ

    Science.gov (United States)

    Phelan, D.; Bhatti, Kanwal Preet; Taylor, M.; Wang, Shun; Leighton, C.

    2014-05-01

    perovskite cobaltite magnetic phase diagram to the insulating side (where ferromagnetic clusters are well known to exist). These results thus shed significant light on the formation of the magnetically inhomogenous ground state of Pr-based cobaltites undergoing a first-order metal-insulator transition and indeed provide clear and direct evidence of such.

  16. New numerical method to study phase transitions and its applications

    International Nuclear Information System (INIS)

    Lee, Jooyoung; Kosterlitz, J.M.

    1991-11-01

    We present a powerful method of identifying the nature of transitions by numerical simulation of finite systems. By studying the finite size scaling properties of free energy barrier between competing states, we can identify unambiguously a weak first order transition even when accessible system sizes are L/ξ < 0.05 as in the five state Potts model in two dimensions. When studying a continuous phase transition we obtain quite accurate estimates of critical exponents by treating it as a field driven first order transition. The method has been successfully applied to various systems

  17. Phase diagram of compressively strained nickelate thin films

    Energy Technology Data Exchange (ETDEWEB)

    Disa, Ankit S [Yale University; Kumah, D. [Yale University; Ngai, J H [Yale University; Specht, Eliot D [ORNL; Arena, D.A. [Brookhaven National Laboratory (BNL); Walker, Frederick J. [Yale University; Ahn, Charles H. [Yale University

    2013-01-01

    The complex phase diagrams of strongly correlated oxides arise from the coupling between physical and electronic structure. This can lead to a renormalization of the phase boundaries when considering thin films rather than bulk crystals due to reduced dimensionality and epitaxial strain. The well-established bulk RNiO3 phase diagram shows a systematic dependence between the metal-insulator transition and the perovskite A-site rare-earth ion, R. Here, we explore the equivalent phase diagram for nickelate thin films under compressive epitaxial strain. We determine the metalinsulator phase diagram for the solid solution of Nd1-yLayNiO3 thin films within the range 0 y 1. We find qualitative similarity between the films and their bulk analogs, but with an overall renormalization in the metal-insulator transition to lower temperature. A combination of x-ray diffraction measurements and soft x-ray absorption spectroscopy indicates that the renormalization is due to increased Ni O bond hybridization for coherently strained thin films.

  18. On the phase transition nature in compressible Ising models

    International Nuclear Information System (INIS)

    Ota, A.T.

    1985-01-01

    The phase transition phenomenon is analysed in a compressible ferromagnetic Ising model at null field, through the mean-field approximation. The model studied is d-dimensional under the magnetic point of view and one-dimensional under the elastic point of view. This is achieved keeping the compressive interactions among the ions and rejecting annealing forces completely. The exchange parameter J is linear and the elastic potential quadratic in relation to the microscopic shifts of the lattice. In the one-dimensional case, this model shows no phase transition. In the two-dimensional case, the role of the S i spin of the i-the ion is crucial: a) for spin 1/2 the transitions are of second order; b) for spin 1, desides the second order transitions there is a three-critical point and a first-order transitions line. (L.C.) [pt

  19. No Hawking-Page phase transition in three dimensions

    International Nuclear Information System (INIS)

    Myung, Y.S.

    2005-01-01

    We investigate whether or not the Hawking-Page phase transition is possible to occur in three dimensions. Starting with the simplest class of Lanczos-Lovelock action, thermodynamic behavior of all AdS-type black holes without charge falls into two classes: Schwarzschild-AdS black holes in even dimensions and Chern-Simons black holes in odd dimensions. The former class can provide the Hawking-Page transition between Schwarzschild-AdS black holes and thermal AdS space. On the other hand, the latter class is exceptional and thus the Hawking-Page transition is hard to occur. In three dimensions, a second-order phase transition might occur between the non-rotating BTZ black hole and the massless BTZ black hole (thermal AdS space), instead of the first-order Hawking-Page transition between the non-rotating BTZ black hole and thermal AdS space

  20. Signatures of Quantum Phase Transitions via Quantum Information Theoretic Measures

    Science.gov (United States)

    Bose, I.; Tribedi, A.

    Quantum phase transitions (QPTs) in many body systems occur at T = 0 brought about by tuning a non-thermal parameter, e.g. pressure, chemical composition or external magnetic field [1, 2]. In a QPT, the ground state wave function undergoes qualitative changes at the transition point. The transition is driven by quantum fluctuations whereas ordinary phase transitions occurring at nonzero temperatures are driven by thermal fluctuations. Like a thermal phase transition, a QPT can be first order, second order or higher order. The thermal critical point, associated with a second-order phase transition, is characterized by the presence of thermal fluctuations on all length scales resulting in a divergent correlation length. The free energy and the thermodynamic functions develop singularities as temperature Trightarrow T_{textrm{c}} , the critical temperature. At the quantum critical point (QCP), quantum fluctuations occur on all length scales leading to a divergent correlation length. The ground state and related physical quantities become non-analytic as the tuning parameter g tends to the critical value g c . The influence of QPTs extends into the finite T part of the phase diagram so that experimental detection of QPTs is possible.

  1. Complexity and phase transitions in a holographic QCD model

    Science.gov (United States)

    Zhang, Shao-Jun

    2018-04-01

    Applying the "Complexity = Action" conjecture, we study the holographic complexity close to crossover/phase transition in a holographic QCD model proposed by Gubser et al. This model can realize three types of phase transition, crossover or first and second order, depending on the parameters of the dilaton potential. The re-scaled late-time growth rate of holographic complexity density for the three cases is calculated. Our results show that it experiences a fast drop/jump close to the critical point while approaching constants far beyond the critical temperature. Moreover, close to the critical temperature, it shows a behavior characterizing the type of the transition. These features suggest that the growth rate of the holographic complexity may be used as a good parameter to characterize the phase transition. The Lloyd's bound is always satisfied for the cases we considered but only saturated for the conformal case.

  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. Phase transitions in nuclear matter and consequences for neutron stars

    International Nuclear Information System (INIS)

    Kaempfer, B.

    1983-04-01

    Estimates of the minimal bombarding energy necessary to reach the quark gluon phase in heavy ion collisions are presented within a hydrodynamical scenario. Further, the consequences of first-order phase transitions from nuclear/neutron matter to pion-condensed matter or quark matter are discussed for neutron stars. (author)

  5. Observation of phase transitions in spreading activation networks.

    Science.gov (United States)

    Shrager, J; Hogg, T; Huberman, B A

    1987-05-29

    Phase transitions, similar to those seen in physical systems, are observed in spreading activation networks. Such networks are used both in theories of cognition and in artificial intelligence applications. This result confirms a predicted abrupt behavioral change as either the topology of the network or the activation parameters are varied across phase boundaries.

  6. Supercooling across first-order phase transitions in vortex matter

    Indian Academy of Sciences (India)

    Abstract. Hysteresis in cycling through first-order phase transitions in vortex matter, akin to the well-studied phenomenon of supercooling of water, has been discussed in literature. Hysteresis can be seen while varying either temperature T or magnetic field H (and thus the density of vortices). Our recent work on phase ...

  7. Chiral phase transitions in quantum chromodynamics at finite ...

    Indian Academy of Sciences (India)

    cedure the phase structure of gauge theories. At finite temperature/density, however, we should seriously ask whether the preceding results [1] of the DS equation analysis on the chiral phase transition could be relied on being the real consequences of thermal gauge theories. This is because in previous analyses the ...

  8. Commensurate-incommensurate phase transition in the deformed crystal

    International Nuclear Information System (INIS)

    Parlinski, K.; Watanabe, Y.; Ohno, K.; Kawazoe, Y.

    1995-01-01

    Using simple orthorhombic microscopic model the commensurate-incommensurate phase transition has been studied. Coupling of the order parameter with spontaneous strain may lead to process which uses the ferroelastic domain walls to introduce the discommensurations to the incommensurate phase. (author). 4 refs, 1 fig

  9. Phase transitions and topological excitations in hypergauge theories

    International Nuclear Information System (INIS)

    Nencka-Ficek, H.

    1985-01-01

    The problems connected with the phase structure of antisymmetric tensor gauge fields are investigated. (s+1)-dimensional hyperloops cannot be constructed in (s+1)-dimensional lattices. This is the cause of a lack of phase transitions in the U(1) theories with fields being sth-kind gauge invariant in the (s+1)-dimensional lattice

  10. The Physics of Weldpool Formation: Phase Transition Process In ...

    African Journals Online (AJOL)

    ... phase transition took place but did not significantly alter the microstructure of the weldment. This study also supports the claims made by different investigators about the different heat treatments given to metals to determine a particular hardenability level. This heat treatment process is an indicator of phase change.

  11. The crystal structure and the phase transitions of pyridinium trifluoromethanesulfonate

    International Nuclear Information System (INIS)

    Jesariew, Dominik; Ilczyszyn, Maria M; Pietraszko, Adam

    2014-01-01

    The calorimetric and optical studies and the structural properties of pyridinium trifluoromethanesulfonate (abbreviated as PyHOTf) are reported. A sequence of four fully reversible solid–solid phase transitions, at 223.0, 309.0, 359.9 and 394.3 K, has been discovered. The phase transition sequence was confirmed by x-ray diffraction data. The crystal structures of three phases (V, IV and III) have been determined from the single crystal x-ray diffraction data. Structural properties of the high temperature phases are characterized using powder x-ray diffraction data measured in the 290–425 K temperature range. The structural changes triggered by the temperature change are discussed in relation to the phase transitions. Two low temperature phases (V and IV) belong to the P4 3 2 1 2 space group of the tetragonal system. The intermediate phases (III and II) are monoclinic and the prototype high temperature phase (I) is a pseudo-cubic (tetragonal) one. The low temperature phases (V and IV) are well ordered. The crystal structure of intermediate (III and II) and prototype (I) phases are characterized by high disorder of the pyridinium cations and triflate anions. (papers)

  12. Phase transitions in biogenic amorphous calcium carbonate.

    Science.gov (United States)

    Gong, Yutao U T; Killian, Christopher E; Olson, Ian C; Appathurai, Narayana P; Amasino, Audra L; Martin, Michael C; Holt, Liam J; Wilt, Fred H; Gilbert, P U P A

    2012-04-17

    Crystalline biominerals do not resemble faceted crystals. Current explanations for this property involve formation via amorphous phases. Using X-ray absorption near-edge structure (XANES) spectroscopy and photoelectron emission microscopy (PEEM), here we examine forming spicules in embryos of Strongylocentrotus purpuratus sea urchins, and observe a sequence of three mineral phases: hydrated amorphous calcium carbonate (ACC · H(2)O) → dehydrated amorphous calcium carbonate (ACC) → calcite. Unexpectedly, we find ACC · H(2)O-rich nanoparticles that persist after the surrounding mineral has dehydrated and crystallized. Protein matrix components occluded within the mineral must inhibit ACC · H(2)O dehydration. We devised an in vitro, also using XANES-PEEM, assay to identify spicule proteins that may play a role in stabilizing various mineral phases, and found that the most abundant occluded matrix protein in the sea urchin spicules, SM50, stabilizes ACC · H(2)O in vitro.

  13. Theoretical Predictions of Phase Transitions at Ultra-high Pressures

    Science.gov (United States)

    Boates, Brian

    2013-06-01

    We present ab initio calculations of the high-pressure phase diagrams of important planetary materials such as CO2, MgSiO3, and MgO. For CO2, we predict a series of distinct liquid phases over a wide pressure (P) and temperature (T) range, including a first-order transition to a dense polymer liquid. We have computed finite-temperature free energies of liquid and solid CO2 phases to determine the melting curve beyond existing measurements and investigate possible phase separation transitions. The interaction of these phase boundaries with the mantle geotherm will also be discussed. Furthermore, we find evidence for a vast pressure-temperature regime where molten MgSiO3 decomposes into liquid SiO2 and solid MgO, with a volume change of approximately 1.2 percent. The demixing transition is driven by the crystallization of MgO ? the reaction only occurs below the high-pressure MgO melting curve. The predicted transition pressure at 10,000 K is in close proximity to an anomaly reported in recent laser-driven shock experiments of MgSiO3. We also present new results for the high-pressure melting curve of MgO and its B1-B2 solid phase transition, with a triple point near 364 GPa and 12,000 K.

  14. High pressure structural phase transition of neodymium mono pnictides

    International Nuclear Information System (INIS)

    Pagare, Gitanjali; Ojha, P.; Sanyal, S.P.; Aynyas, Mahendra

    2007-01-01

    We have investigated theoretically the high-pressure structural phase transition of two neodymium mono NdX (X=As, Sb) using an interionic potential theory with necessary modification to include the effect of Coulomb screening by the delocalized f electrons of Nd ion. These compounds exhibits first order crystallographic phase transition from their NaCl (B 1 ) phase to body centered tetragonal (BCT) at 27 GPa and 15.3 GPa respectively. We also calculated the Nd-Nd distance as a function of pressure. (author)

  15. Shear induced phase transitions induced in edible fats

    Science.gov (United States)

    Mazzanti, Gianfranco; Welch, Sarah E.; Marangoni, Alejandro G.; Sirota, Eric B.; Idziak, Stefan H. J.

    2003-03-01

    The food industry crystallizes fats under different conditions of temperature and shear to obtain products with desired crystalline phases. Milk fat, palm oil, cocoa butter and chocolate were crystallized from the melt in a temperature controlled Couette cell. Synchrotron x-ray diffraction studies were conducted to examine the role of shear on the phase transitions seen in edible fats. The shear forces on the crystals induced acceleration of the alpha to beta-prime phase transition with increasing shear rate in milk fat and palm oil. The increase was slow at low shear rates and became very strong above 360 s-1. In cocoa butter the acceleration between beta-prime-III and beta-V phase transition increased until a maximum of at 360 s-1, and then decreased, showing competition between enhanced heat transfer and viscous heat generation.

  16. Generalized transport model for phase transition with memory

    International Nuclear Information System (INIS)

    Chen, Chi; Ciucci, Francesco

    2013-01-01

    A general model for phenomenological transport in phase transition is derived, which extends Jäckle and Frisch model of phase transition with memory and the Cahn–Hilliard model. In addition to including interfacial energy to account for the presence of interfaces, we introduce viscosity and relaxation contributions, which result from incorporating memory effect into the driving potential. Our simulation results show that even without interfacial energy term, the viscous term can lead to transient diffuse interfaces. From the phase transition induced hysteresis, we discover different energy dissipation mechanism for the interfacial energy and the viscosity effect. In addition, by combining viscosity and interfacial energy, we find that if the former dominates, then the concentration difference across the phase boundary is reduced; conversely, if the interfacial energy is greater then this difference is enlarged.

  17. Magnetism and Microstructure Characterization of Phase Transitions in a Steel

    Directory of Open Access Journals (Sweden)

    M. Güler

    2014-01-01

    Full Text Available We present phase transitions in a low carbon steel according to existing phases and their magnetism. Scanning electron microscope employed research to clarify and evaluate the microstructural details. Additionally, we utilized from Mössbauer spectroscopy for magnetic characteristics of different existed phases. Scanning electron microscope examinations showed that the pure state of the steel was fully in the ferrite phase with equiaxed grains. Moreover, subsequent heat treatments on the studied steel also ensured the first austenite and then pearlite phase formation. Mössbauer spectroscopy of these phases appeared as a paramagnetic single-line absorption peak for the austenite phase and ferromagnetic six-line spectra for both ferrite and pearlite phases. From Mössbauer data, we determined that the internal magnetic fields of ferrite and pearlite phases were as 32.2 Tesla and 31.3 Tesla, respectively.

  18. Effects of single particle on shape phase transitions and phase coexistence in odd-even nuclei

    Science.gov (United States)

    Yu, Xiang-Ru; Hu, Jing; Li, Xiao-Xue; An, Si-Yu; Zhang, Yu

    2018-02-01

    A classical analysis of shape phase transitions and phase coexistence in odd-even nuclei has been performed in the framework of the interacting boson-fermion model. The results indicate that the effects of a single particle may influence different types of transitions in different ways. Especially, it is revealed that phase coexistence can clearly emerge in the critical region and thus be taken as a indicator of the shape phase transitions in odd-even nuclei. Supported by National Natural Science Foundation of China (11375005)

  19. Phase transitions: the lattice QCD approach

    International Nuclear Information System (INIS)

    Gavai, R.V.

    1986-01-01

    Recent results in the field of finite temperature lattice quantum chromodynamics (QCD) are presented with special emphasis on comparison of the different methods used to incorporate the dynamical fermions. Attempts to obtain a nonperturbative estimate of the velocity of sound in both the hadronic and quark-gluon phase are summarized along with the results. 15 refs., 7 figs

  20. 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.

  1. Study of the phase transition dynamics of the L to H transition

    International Nuclear Information System (INIS)

    Moyer, R.A.; Rhodes, T.L.; Rettig, C.L.

    1997-12-01

    A highly radiating zone (MARFE) just above the divertor X-point has been used to access the marginal transition regime P sep ∼ P thres to study the existence of a critical point for the L to H transition. Phase transition models predict that at the critical point, the transition duration increases and the plasma parameters vary continuously between L-mode and H-mode. In these experiments, the L to H transition duration increased 50--100 times over fast transitions. However, the evolution of E r shear, edge density gradient, H-mode pedestal, and fluctuations is essentially unchanged from that in fast transitions. The only difference is in the speed with which and the degree to which the fluctuation amplitudes are transiently reduced. This difference is understandable in terms of the time scales for fluctuation amplitude reduction (≤ 100 micros) and edge pressure gradient increase (several ms), provided the edge fluctuations are pressure-gradient driven

  2. Quantum Phase Transition and Entanglement in Topological Quantum Wires.

    Science.gov (United States)

    Cho, Jaeyoon; Kim, Kun Woo

    2017-06-05

    We investigate the quantum phase transition of the Su-Schrieffer-Heeger (SSH) model by inspecting the two-site entanglements in the ground state. It is shown that the topological phase transition of the SSH model is signified by a nonanalyticity of local entanglement, which becomes discontinuous for finite even system sizes, and that this nonanalyticity has a topological origin. Such a peculiar singularity has a universal nature in one-dimensional topological phase transitions of noninteracting fermions. We make this clearer by pointing out that an analogous quantity in the Kitaev chain exhibiting the identical nonanalyticity is the local electron density. As a byproduct, we show that there exists a different type of phase transition, whereby the pattern of the two-site entanglements undergoes a sudden change. This transition is characterised solely by quantum information theory and does not accompany the closure of the spectral gap. We analyse the scaling behaviours of the entanglement in the vicinities of the transition points.

  3. Enthalpy of phase transition and prediction of phase Equilibria in systems of glycols and glycol ethers

    OpenAIRE

    Esina, Zoya; Miroshnikov, Aleksandr; Korchuganova, Margarita

    2014-01-01

    The PCEAS model was used to study the liquid-solid and liquid-vapor phase transitions at constant pressure in systems containing glycols and glycol ethers. This method is based on minimizing the excess Gibbs energy over the solvation parameter, which takes into account the processes of association of molecules in various phases. To compute the diagrams, the data on enthalpy and phase transition temperatures of pure components are required, while the information about the interactions in the b...

  4. Metal-insulator-metal diodes with sub-nanometre surface roughness for energy-harvesting applications

    KAUST Repository

    Khan, A.A.

    2017-07-27

    For ambient radio-frequency (RF) energy harvesting, the available power levels are quite low, and it is highly desirable that the rectifying diodes do not consume any power at all. Contrary to semiconducting diodes, a tunnelling diode – also known as a metal-insulator-metal (MIM) diode – can provide zero-bias rectification, provided the two metals have different work functions. This could result in a complete passive rectenna system. Despite great potential, MIM diodes have not been investigated much in the GHz-frequency regime due to challenging nano-fabrication requirements. In this work, we investigate zero-bias MIM diodes for RF energy-harvesting applications. We studied the surface roughness issue for the bottom metal of the MIM diode for various deposition techniques such as sputtering, atomic layer deposition (ALD) and electron-beam (e-beam) evaporation for crystalline metals as well as for an amorphous alloy, namely ZrCuAlNi. A surface roughness of sub-1nm has been achieved for both the crystalline metals as well as the amorphous alloy, which is vital for the reliable operation of the MIM diode. An MIM diode comprising of a Ti-ZnO-Pt combination yields a zero-bias responsivity of 0.25V−1 and a dynamic resistance of 1200Ω. Complete RF characterisation has been performed by integrating the MIM diode with a coplanar waveguide transmission line. The input impedance varies from 100Ω to 50Ω in the frequency range of between 2GHz and 10GHz, which can be easily matched to typical antenna impedances in this frequency range. Finally, a rectified DC voltage of 4.7mV is obtained for an incoming RF power of 0.4W at zero bias. These preliminary results of zero-bias rectification indicate that complete, passive rectennas (a rectifier and antenna combination) are feasible with further optimisation of MIM devices.

  5. Antiferrodistortive phase transitions and ground state of PZT ceramics

    International Nuclear Information System (INIS)

    Pandey, Dhananjai

    2013-01-01

    The ground state of the technologically important Pb(Zr x Ti (1-x) )O 3 , commonly known as PZT, ceramics is currently under intense debate. The phase diagram of this material shows a morphotropic phase boundary (MPB) for x∼0.52 at 300K, across which a composition induced structural phase transition occurs leading to maximization of the piezoelectric properties. In search for the true ground state of the PZT in the MPB region, Beatrix Noheda and coworkers first discovered a phase transition from tetragonal (space group P4mm) to an M A type monoclinic phase (space group Cm) at low temperatures for x=0.52. Soon afterwards, we discovered yet another low temperature phase transition for the same composition in which the M A type (Cm) monoclinic phase transforms to another monoclinic phase with Cc space group. We have shown that the Cm to Cc phase transition is an antiferrodistortive (AFD) transition involving tilting of oxygen octahedra leading to unit cell doubling and causing appearance of superlattice reflections which are observable in the electron and neutron diffraction patterns only and not in the XRD patterns, as a result of which Noheda and coworkers missed the Cc phase in their synchrotron XRD studies at low temperatures. Our findings were confirmed by leading groups using neutron, TEM, Raman and high pressure diffraction studies. The first principles calculations also confirmed that the true ground state of PZT in the MPB region has Cc space group. However, in the last couple of years, the Cc space group of the ground state has become controversial with an alternative proposal of R3c as the space group of the ground state phase which is proposed to coexist with the metastable Cm phase. In order to resolve this controversy, we recently revisited the issue using pure PZT and 6% Sr 2+ substituted PZT, the latter samples show larger tilt angle on account of the reduction in the average cationic radius at the Pb 2+ site. Using high wavelength neutrons and high

  6. Topological phases and phase transitions in magnets and ice

    NARCIS (Netherlands)

    Keesman, R.

    2017-01-01

    The main focus of this Thesis is the behaviour of two-dimensional materials, namely (anti)-ferromagnetic materials in the first two chapters, which show topological phases, and energetic square ice in the third and fourth chapter. The magnetic materials are of interest in part due to foreseen

  7. Experimental First Order Pairing Phase Transition in Atomic Nuclei

    International Nuclear Information System (INIS)

    Moretto, L G; Larsen, A C; Giacoppo, F; Guttormsen, M; Siem, S

    2015-01-01

    The natural log of experimental nuclear level densities at low energy is linear with energy. This can be interpreted in terms of a nearly 1st order phase transition from a superfluid to an ideal gas of quasi particles. The transition temperature coincides with the BCS critical temperature and yields gap parameters in good agreement with the values extracted from even- odd mass differences from rotational states. This converging evidence supports the relevance of the BCS theory to atomic nuclei

  8. Gravitational radiation from first-order phase transitions

    International Nuclear Information System (INIS)

    Child, Hillary L.; Giblin, John T. Jr.

    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 using only scalar fields, 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 enhances this radiation even in the absence of a coupled fluid or 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

  9. Chirality Quantum Phase Transition in Noncommutative Dirac Oscillator

    International Nuclear Information System (INIS)

    Wang Shao-Hua; Hou Yu-Long; Jing Jian; Wang Qing; Long Zheng-Wen

    2014-01-01

    The charged Dirac oscillator on a noncommutative plane coupling to a uniform perpendicular magnetic held is studied in this paper. We map the noncommutative plane to a commutative one by means of Bopp shift and study this problem on the commutative plane. We find that this model can be mapped onto a quantum optics model which contains Anti—Jaynes—Cummings (AJC) or Jaynes—Cummings (JC) interactions when a dimensionless parameter ζ (which is the function of the intensity of the magnetic held) takes values in different regimes. Furthermore, this model behaves as experiencing a chirality quantum phase transition when the dimensionless parameter ζ approaches the critical point. Several evidences of the chirality quantum phase transition are presented. We also study the non-relativistic limit of this model and find that a similar chirality quantum phase transition takes place in its non-relativistic limit. (physics of elementary particles and fields)

  10. Novel phase transitions in B-site doped manganites

    Energy Technology Data Exchange (ETDEWEB)

    Popovic, Z.V. [Institute of Physics, P.O. Box 68, 11080 Belgrade/Zemun (Serbia and Montenegro)]. E-mail: zoran.popovic@phy.bg.ac.yu; Cantarero, A. [Materials Science Institute, University of Valencia, P.O. Box 22085, 46071 Valencia (Spain); Thijssen, W.H.A. [Kamerlingh Onnes Laboratorium, Leiden University, Postbus 9504, 2300 RA Leiden (Netherlands); Paunovic, N. [Institute of Physics, P.O. Box 68, 11080 Belgrade/Zemun (Serbia and Montenegro); Dohcevic-Mitrovic, Z. [Institute of Physics, P.O. Box 68, 11080 Belgrade/Zemun (Serbia and Montenegro); Sapina, F. [Materials Science Institute, University of Valencia, P.O. Box 22085, 46071 Valencia (Spain)

    2005-04-30

    We have examined the infrared reflectivity and the electrical resistivity of La{sub 1-} {sub x} [Sr(Ba)] {sub x} Mn{sub 1-} {sub z} [Cu(Zn)] {sub z} O{sub 3} samples in ferromagnetic metallic and insulator regime. Several phase transitions are observed, the most obvious being the transition from a ferromagnetic metallic to a ferromagnetic insulator phase that is related to the formation of short-range orbitally ordered domains. The temperature T {sub 1} of the phase transition is dependent on doping concentration and for optimally doped samples ({approx}32% of Mn{sup 4+} ions) we have found T {sub 1}{approx}0.93 T {sub C}.

  11. Non-equilibrium physics at a holographic chiral phase transition

    International Nuclear Information System (INIS)

    Evans, Nick; Kim, Keun-young; Kalaydzhyan, Tigran; Kirsch, Ingo

    2010-11-01

    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.)

  12. Non-equilibrium physics at a holographic chiral phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Evans, Nick; Kim, Keun-young [Southampton Univ. (United Kingdom). School of Physics and Astronomy; Kavli Institute for Theoretical Physics China, Beijing (China); Kalaydzhyan, Tigran; Kirsch, Ingo [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)

    2010-11-15

    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.)

  13. Phase-transition-like behaviour of quantum games

    CERN Document Server

    Du Jiang Feng; Xu Xiao Dong; Zhou Xian Yi; Han Rong Dian

    2003-01-01

    The discontinuous dependence of the properties of a quantum game on its entanglement has been shown to be very much like phase transitions viewed in the entanglement-payoff diagram (J Du et al 2002 Phys. Rev. Lett. 88 137902). In this paper we investigate such phase-transition-like behaviour of quantum games, by suggesting a method which would help to illuminate the origin of such a kind of behaviour. For the particular case of the generalized Prisoners' Dilemma, we find that, for different settings of the numerical values in the payoff table, even though the classical game behaves the same, the quantum game exhibits different and interesting phase-transition-like behaviour.

  14. Phase-transition-like behaviour of quantum games

    International Nuclear Information System (INIS)

    Du Jiangfeng; Li Hui; Xu Xiaodong; Zhou Xianyi; Han Rongdian

    2003-01-01

    The discontinuous dependence of the properties of a quantum game on its entanglement has been shown to be very much like phase transitions viewed in the entanglement-payoff diagram (J Du et al 2002 Phys. Rev. Lett. 88 137902). In this paper we investigate such phase-transition-like behaviour of quantum games, by suggesting a method which would help to illuminate the origin of such a kind of behaviour. For the particular case of the generalized Prisoners' Dilemma, we find that, for different settings of the numerical values in the payoff table, even though the classical game behaves the same, the quantum game exhibits different and interesting phase-transition-like behaviour

  15. A MATLAB GUI to study Ising model phase transition

    Science.gov (United States)

    Thornton, Curtislee; Datta, Trinanjan

    We have created a MATLAB based graphical user interface (GUI) that simulates the single spin flip Metropolis Monte Carlo algorithm. The GUI has the capability to study temperature and external magnetic field dependence of magnetization, susceptibility, and equilibration behavior of the nearest-neighbor square lattice Ising model. Since the Ising model is a canonical system to study phase transition, the GUI can be used both for teaching and research purposes. The presence of a Monte Carlo code in a GUI format allows easy visualization of the simulation in real time and provides an attractive way to teach the concept of thermal phase transition and critical phenomena. We will also discuss the GUI implementation to study phase transition in a classical spin ice model on the pyrochlore lattice.

  16. Gravitational radiation from first-order phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Child, Hillary L.; Giblin, John T. Jr., E-mail: childh@kenyon.edu, E-mail: giblinj@kenyon.edu [Department of Physics, Kenyon College, 201 North College Road, Gambier, OH 43022 (United States)

    2012-10-01

    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 using only scalar fields, 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 enhances this radiation even in the absence of a coupled fluid or 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.

  17. Phase-transition-like behaviour of quantum games

    Energy Technology Data Exchange (ETDEWEB)

    Du Jiangfeng [Department of Modern Physics, University of Science and Technology of China, Hefei, 230027 (China); Li Hui [Department of Modern Physics, University of Science and Technology of China, Hefei, 230027 (China); Xu Xiaodong [Harrison M Randall Laboratory of Physics, University of Michigan, Ann Arbor, MI 48109-1120 (United States); Zhou Xianyi [Department of Modern Physics, University of Science and Technology of China, Hefei, 230027 (China); Han Rongdian [Department of Modern Physics, University of Science and Technology of China, Hefei, 230027 (China)

    2003-06-13

    The discontinuous dependence of the properties of a quantum game on its entanglement has been shown to be very much like phase transitions viewed in the entanglement-payoff diagram (J Du et al 2002 Phys. Rev. Lett. 88 137902). In this paper we investigate such phase-transition-like behaviour of quantum games, by suggesting a method which would help to illuminate the origin of such a kind of behaviour. For the particular case of the generalized Prisoners' Dilemma, we find that, for different settings of the numerical values in the payoff table, even though the classical game behaves the same, the quantum game exhibits different and interesting phase-transition-like behaviour.

  18. Structural and topological phase transitions on the German Stock Exchange

    Science.gov (United States)

    Wiliński, M.; Sienkiewicz, A.; Gubiec, T.; Kutner, R.; Struzik, Z. R.

    2013-12-01

    We find numerical and empirical evidence for dynamical, structural and topological phase transitions on the (German) Frankfurt Stock Exchange (FSE) in the temporal vicinity of the worldwide financial crash. Using the Minimal Spanning Tree (MST) technique, a particularly useful canonical tool of the graph theory, two transitions of the topology of a complex network representing the FSE were found. The first transition is from a hierarchical scale-free MST representing the stock market before the recent worldwide financial crash, to a superstar-like MST decorated by a scale-free hierarchy of trees representing the market’s state for the period containing the crash. Subsequently, a transition is observed from this transient, (meta)stable state of the crash to a hierarchical scale-free MST decorated by several star-like trees after the worldwide financial crash. The phase transitions observed are analogous to the ones we obtained earlier for the Warsaw Stock Exchange and more pronounced than those found by Onnela-Chakraborti-Kaski-Kertész for the S&P 500 index in the vicinity of Black Monday (October 19, 1987) and also in the vicinity of January 1, 1998. Our results provide an empirical foundation for the future theory of dynamical, structural and topological phase transitions on financial markets.

  19. Infinite cascades of phase transitions in the classical Ising chain

    Science.gov (United States)

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

    2017-12-01

    We report exact results on one of the best studied models in statistical physics: the classical antiferromagnetic Ising chain in a magnetic field. We show that the model possesses an infinite cascade of thermal phase transitions (also known as disorder lines or geometric phase transitions). The phase transition is signaled by a change of asymptotic behavior of the nonlocal string-string correlation functions when their monotonic decay becomes modulated by incommensurate oscillations. The transitions occur for rarefied (m -periodic) strings with arbitrary odd m . We propose a duality transformation which maps the Ising chain onto the m -leg Ising tube with nearest-neighbor couplings along the legs and the plaquette four-spin interactions of adjacent legs. Then the m -string correlation functions of the Ising chain are mapped onto the two-point spin-spin correlation functions along the legs of the m -leg tube. We trace the origin of these cascades of phase transitions to the lines of the Lee-Yang zeros of the Ising chain in m -periodic complex magnetic field, allowing us to relate these zeros to the observable (and potentially measurable) quantities.

  20. 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.

  1. Crystal-liquid-gas phase transitions and thermodynamic similarity

    CERN Document Server

    Skripov, Vladimir P; Schmelzer, Jurn W P

    2006-01-01

    Professor Skripov obtained worldwide recognition with his monograph ""Metastable liquids"", published in English by Wiley & Sons. Based upon this work and another monograph published only in Russia, this book investigates the behavior of melting line and the properties of the coexisting crystal and liquid phase of simple substances across a wide range of pressures, including metastable states of the coexisting phases. The authors derive new relations for the thermodynamic similarity for liquid-vapour phase transition, as well as describing solid-liquid, liquid-vapor and liquid-liquid phase tra

  2. Phase transitions in glassy systems via convolutional neural networks

    Science.gov (United States)

    Fang, Chao

    Machine learning is a powerful approach commonplace in industry to tackle large data sets. Most recently, it has found its way into condensed matter physics, allowing for the first time the study of, e.g., topological phase transitions and strongly-correlated electron systems. The study of spin glasses is plagued by finite-size effects due to the long thermalization times needed. Here we use convolutional neural networks in an attempt to detect a phase transition in three-dimensional Ising spin glasses. Our results are compared to traditional approaches.

  3. Phase transition and monopole production in supergravity inflation

    International Nuclear Information System (INIS)

    Kamada, Kohei; Nakayama, Kazunori

    2011-10-01

    In F-term supergravity inflation models, scalar fields other than the inflaton generically receive a Hubble induced mass, which may restore gauge symmetries during inflation and phase transitions may occur during or after inflation as the Hubble parameter decreases. We study monopole (and domain wall) production associated with such a phase transition in chaotic inflation in supergravity and obtain a severe constraint on the symmetry breaking scale which is related with the tensor-to-scalar ratio. Depending on model parameters, it is possible that monopoles are sufficiently diluted to be free from current constraints but still observable by planned experiments. (orig.)

  4. 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.

  5. The liquid to vapor phase transition in excited nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Elliott, J.B.; Moretto, L.G.; Phair, L.; Wozniak, G.J.; Beaulieu, L.; Breuer, H.; Korteling, R.G.; Kwiatkowski, K.; Lefort, T.; Pienkowski, L.; Ruangma, A.; Viola, V.E.; Yennello, S.J.

    2001-05-08

    For many years it has been speculated that excited nuclei would undergo a liquid to vapor phase transition. For even longer, it has been known that clusterization in a vapor carries direct information on the liquid-vapor equilibrium according to Fisher's droplet model. Now the thermal component of the 8 GeV/c pion + 197 Au multifragmentation data of the ISiS Collaboration is shown to follow the scaling predicted by Fisher's model, thus providing the strongest evidence yet of the liquid to vapor phase transition.

  6. Techniques for detection of transition phases in calcined alumina

    International Nuclear Information System (INIS)

    Pandolfelli, V.C.; Folgueras-Dominguez, S.

    1987-01-01

    Detection of transition phases in alumina, is very important in the receiving control and calcination of aluminium hydroxide. The non alfa or transition phases difficults the processability and causes localized shrinkage on sintering compromising the dimensional and mechanical aspects of the product. In this research using refraction index, absorption of dyes, specific density, X-ray diffraction and scanning electron microscopy, analyses, are done in calcined hydroxides submited to different thermal treatments. The limits and facilities of each technique are discussed and compared. (Author) [pt

  7. Phase transitions induced by the Aharonov-Bohm field

    International Nuclear Information System (INIS)

    Krive, I.V.; Naftulin, S.A.

    1990-07-01

    The influence of the Aharonov-Bohm flux (φ) on the order parameters of the 3-dimensional Gross-Neveu model and CP N -model in R 2 xS 1 space is considered. It is shown that the variation of flux causes the order parameter oscillations and for the small enough length of circular coordinate l c these oscillations attended with re-ordering phase transitions (i.e. the repeating transitions between the ordered and the disordered phases of the models in question). (author). 22 refs, 3 figs

  8. Magnetic Phase Transitions of CeSb. I

    DEFF Research Database (Denmark)

    Fischer, Pernille Hertz; Lebech, Bente; Meier, G.

    1978-01-01

    The magnetic ordering of the anomalous antiferromagnet CeSb, which has a NaCl crystal structure, was determined in zero applied magnetic field by means of neutron diffraction investigations of single crystals and powder. Below the Neel temperature TN of (16.1+or-0.1)K, there exist six partially...... a first-order phase transition at TN. At approximately TN/2 there is a first-order phase transition to a FCC type IA low-temperature configuration. The unusual magnetic properties of CeSb, which result from anisotropic exchange and crystalline electric field effects, resemble those of certain actinide Na...

  9. Ferroelectric phase transition in Ga2Te3 single crystals

    Science.gov (United States)

    Gamal, G. A.; Abdalrahman, M. M.; Ashraf, M. I.; Eman, H. J.

    2005-01-01

    Measurements of the electrical conductivity and Hall effect were carried out in a wide temperature range (200-500 K) for Ga2Te3 crystals. The crystals were grown in single crystalline form by making a modification of the travelling heater method technique. The measurements revealed unusual observations in the electric conductivity and Hall mobility indicating the presence of some type of phase transitions at about 430 K. So, ferroelectric behavior was examined for confirming the presence of second-order (ferroelectric) phase transition. An energy gap of 1.21 eV and depth of the impurity center of 0.11 eV were found.

  10. Extragalactic magnetic fields unlikely generated at the electroweak phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Wagstaff, Jacques M.; Banerjee, Robi, E-mail: jwagstaff@hs.uni-hamburg.de, E-mail: banerjee@hs.uni-hamburg.de [Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, 21029 Hamburg (Germany)

    2016-01-01

    In this paper we show that magnetic fields generated at the electroweak phase transition are most likely too weak to explain the void magnetic fields apparently observed today unless they have considerable helicity. We show that, in the simplest estimates, the helicity naturally produced in conjunction with the baryon asymmetry is too small to explain observations, which require a helicity fraction at least of order 10{sup −14}–10{sup −10} depending on the void fields constraint used. Therefore new mechanisms to generate primordial helicity are required if magnetic fields generated during the electroweak phase transition should explain the extragalactic fields.

  11. Phase Transitions in Sexual Populations Subject to Stabilizing Selection

    Science.gov (United States)

    Rogers, A.

    2003-04-01

    We show that a simple model of an evolving sexual population, which dates back to some of the earliest work in theoretical population genetics, exhibits an unexpected and previously unobserved phase transition between ordered and disordered states. This behavior is not present in populations evolving asexually without recombination and is thus important in any comparison of sexual and asexual populations. In order to calculate the details of the phase transition, we use techniques from statistical physics. We introduce the correlation of the population as the order parameter of the system and use maximum entropy inference to find the state of the population at any time.

  12. Molecules ionization at phase transition in warm dense hydrogen

    Science.gov (United States)

    Norman, G. E.; Saitov, I. M.

    2018-01-01

    An idea is suggested that the fluid–fluid phase transition in warm dense hydrogen is related to the partial ionization of molecules H2 with formation of molecular ions {{{H}}}2+ {{and}} {{{H}}}3+. Conventional ab initio quantum modeling is applied. Proton pair correlation functions (PCF) obtained are used for the nonconventional diagnostics of the phase transition and elucidation of its nature for temperatures 700–1500 K. Short- and long-range changes of PCFs are studied. H2 molecules ionization and molecular ions {{{H}}}2+ {{and}} {{{H}}}3+ appearance is revealed. The validity of the soft sphere model is tested for the long-range order.

  13. The electroweak phase transition in models with gauge singlets

    International Nuclear Information System (INIS)

    Ahriche, A.

    2007-01-01

    A strong first order phase transition is needed for generating the baryon asymmetry; and also to save it during the electroweak phase transition (EWPT). However this condition is not fulfilled within the Standard Model (SM), but in its extensions. It is widely believed that the existence of singlet scalars in some Standard Model extensions can easily make the EWPT strongly first order. In this work, we will examine the strength of the EWPT in the simplest extension of the SM with a real gauge singlet using the sphaleron energy at the critical temperature. We find that the phase transition is stronger by adding a singlet; and also that the criterion for a strong phase transition Ω(T c )/T c >or similar 1, where Ω = (v 2 + (x - x 0 ) 2 ) ( 1)/(2) and x(x 0 ) is the singlet vacuum expectation value in the broken (symmetric) phase, is not valid for models containing singlets, even though often used in the literature. The usual condition v c /T c >or similar 1 is more meaningful, and it is satisfied for the major part of the parameter space for physically allowed Higgs masses. Then it is convenient to study the EWPT in models with singlets that couple only to the Higgs doublets, by replacing the singlets by their vevs. (orig.)

  14. The electroweak phase transition in models with gauge singlets

    Energy Technology Data Exchange (ETDEWEB)

    Ahriche, A.

    2007-04-18

    A strong first order phase transition is needed for generating the baryon asymmetry; and also to save it during the electroweak phase transition (EWPT). However this condition is not fulfilled within the Standard Model (SM), but in its extensions. It is widely believed that the existence of singlet scalars in some Standard Model extensions can easily make the EWPT strongly first order. In this work, we will examine the strength of the EWPT in the simplest extension of the SM with a real gauge singlet using the sphaleron energy at the critical temperature. We find that the phase transition is stronger by adding a singlet; and also that the criterion for a strong phase transition {omega}(T{sub c})/T{sub c} >or similar 1, where {omega} = (v{sup 2} + (x - x{sub 0}){sup 2}){sup (}1)/(2) and x(x{sub 0}) is the singlet vacuum expectation value in the broken (symmetric) phase, is not valid for models containing singlets, even though often used in the literature. The usual condition v{sub c}/T{sub c} >or similar 1 is more meaningful, and it is satisfied for the major part of the parameter space for physically allowed Higgs masses. Then it is convenient to study the EWPT in models with singlets that couple only to the Higgs doublets, by replacing the singlets by their vevs. (orig.)

  15. Surface phase transitions in cu-based solid solutions

    Science.gov (United States)

    Zhevnenko, S. N.; Chernyshikhin, S. V.

    2017-11-01

    We have measured surface energy in two-component Cu-based systems in H2 + Ar gas atmosphere. The experiments on solid Cu [Ag] and Cu [Co] solutions show presence of phase transitions on the surfaces. Isotherms of the surface energy have singularities (the minimum in the case of copper solid solutions with silver and the maximum in the case of solid solutions with cobalt). In both cases, the surface phase transitions cause deficiency of surface miscibility: formation of a monolayer (multilayer) (Cu-Ag) or of nanoscale particles (Cu-Co). At the same time, according to the volume phase diagrams, the concentration and temperature of the surface phase transitions correspond to the solid solution within the volume. The method permits determining the rate of diffusional creep in addition to the surface energy. The temperature and concentration dependence of the solid solutions' viscosity coefficient supports the fact of the surface phase transitions and provides insights into the diffusion properties of the transforming surfaces.

  16. The average action for scalar fields near phase transitions

    International Nuclear Information System (INIS)

    Wetterich, C.

    1991-08-01

    We compute the average action for fields in two, three and four dimensions, including the effects of wave function renormalization. A study of the one loop evolution equations for the scale dependence of the average action gives a unified picture of the qualitatively different behaviour in various dimensions for discrete as well as abelian and nonabelian continuous symmetry. The different phases and the phase transitions can be infered from the evolution equation. (orig.)

  17. Nuclear multifragmentation and phase transition for hot nuclei

    OpenAIRE

    Borderie, B.; Rivet, M.F.

    2008-01-01

    This review article is focused on the tremendous progress realized during the last fifteen years in the understanding of multifragmentation and its relationship to the liquid-gas phase diagram of nuclei and nuclear matter. The explosion of the whole nucleus, early predicted by Bohr [N. Bohr, Nature 137 (1936) 351], is a very complex and rich subject which continues to fascinate nuclear physicists as well as theoreticians who extend the thermodynamics of phase transitions to finite systems.

  18. Electric Field-Induced Phase Transitions in Ferroelectrics at Polymorphic Phase Boundaries

    Science.gov (United States)

    Iamsasri, Thanakorn

    Ferroelectric and dielectric materials are used in many applications, including capacitors, actuators, and energy harvesting. In general, the piezoelectric and dielectric properties of these materials reach a maximum at the morphotropic or polymorphic phase boundary, which lie between two different phases of the same structure type. At the phase boundary, the two coexisting phases have similar free energies. By applying external stimuli such as pressures or electric fields, the free energies of two phases can be changed, resulting in an induced phase transition. Electric field-induced phase transitions in ferroelectrics have been observed using transmission electron microscopy (TEM) and X-ray diffraction (XRD). However, there are limited studies on the field-induced phase transitions of ferroelectrics because it requires a characterization technique that can probe structural evolution under electric fields. This study investigates the field-induced phase transitions of ferroelectrics and dielectrics using a combination of synchrotron XRD techniques including in situ XRD under electric fields, high resolution XRD, and time-resolved XRD. This combination of characterization techniques allows one to observe a field-induced phase transition and also quantify it using the intensities and positions of peaks from XRD patterns. Two different material systems are investigated in this study: Li-modified Na0.5K 0.5NbO3 (LNKN) and BaTiO3-BiZn0.5Ti 0.5O3 (BT-BZT). LNKN is a ferroelectric, and BT-BZT is a relaxorferroelectric (i.e. exhibits frequency dependence of dielectric permittivity). For both LNKN and BT-BZT, the field-induced phase transition was observed only in compositions located at the polymorphic phase boundary, but never in single-phase compositions. This result shows that the field-induced phase transition is therefore closely related to the high piezoelectric properties at the phase boundary. Additionally, domain reorientation in single-phase orthorhombic LNKN

  19. Problem-solving phase transitions during team collaboration

    DEFF Research Database (Denmark)

    Wiltshire, Travis; Butner, Jonathan E.; Fiore, Stephen M.

    2018-01-01

    Multiple theories of problem-solving hypothesize that there are distinct qualitative phases exhibited during effective problem-solving. However, limited research has attempted to identify when transitions between phases occur. We integrate theory on collaborative problem-solving (CPS) with dynami......Multiple theories of problem-solving hypothesize that there are distinct qualitative phases exhibited during effective problem-solving. However, limited research has attempted to identify when transitions between phases occur. We integrate theory on collaborative problem-solving (CPS......) with dynamical systems theory suggesting that when a system is undergoing a phase transition it should exhibit a peak in entropy and that entropy levels should also relate to team performance. Communications from 40 teams that collaborated on a complex problem were coded for occurrence of problem......-solving processes. We applied a sliding window entropy technique to each team's communications and specified criteria for (a) identifying data points that qualify as peaks and (b) determining which peaks were robust. We used multilevel modeling, and provide a qualitative example, to evaluate whether phases exhibit...

  20. Kondo-Anderson transitions

    Science.gov (United States)

    Kettemann, S.; Mucciolo, E. R.; Varga, I.; Slevin, K.

    2012-03-01

    Dilute magnetic impurities in a disordered Fermi liquid are considered close to the Anderson metal-insulator transition (AMIT). Critical power-law correlations between electron wave functions at different energies in the vicinity of the AMIT result in the formation of pseudogaps of the local density of states. Magnetic impurities can remain unscreened at such sites. We determine the density of the resulting free magnetic moments in the zero-temperature limit. While it is finite on the insulating side of the AMIT, it vanishes at the AMIT, and decays with a power law as function of the distance to the AMIT. Since the fluctuating spins of these free magnetic moments break the time-reversal symmetry of the conduction electrons, we find a shift of the AMIT, and the appearance of a semimetal phase. The distribution function of the Kondo temperature TK is derived at the AMIT, in the metallic phase, and in the insulator phase. This allows us to find the quantum phase diagram in an external magnetic field B and at finite temperature T. We calculate the resulting magnetic susceptibility, the specific heat, and the spin relaxation rate as a function of temperature. We find a phase diagram with finite-temperature transitions among insulator, critical semimetal, and metal phases. These new types of phase transitions are caused by the interplay between Kondo screening and Anderson localization, with the latter being shifted by the appearance of the temperature-dependent spin-flip scattering rate. Accordingly, we name them Kondo-Anderson transitions.

  1. On the thermodynamics of phase transitions in metal hydrides

    Science.gov (United States)

    di Vita, Andrea

    2012-02-01

    Metal hydrides are solutions of hydrogen in a metal, where phase transitions may occur depending on temperature, pressure etc. We apply Le Chatelier's principle of thermodynamics to a particular phase transition in TiH x , which can approximately be described as a second-order phase transition. We show that the fluctuations of the order parameter correspond to fluctuations both of the density of H+ ions and of the distance between adjacent H+ ions. Moreover, as the system approaches the transition and the correlation radius increases, we show -with the help of statistical mechanics-that the statistical weight of modes involving a large number of H+ ions (`collective modes') increases sharply, in spite of the fact that the Boltzmann factor of each collective mode is exponentially small. As a result, the interaction of the H+ ions with collective modes makes a tiny suprathermal fraction of the H+ population appear. Our results hold for similar transitions in metal deuterides, too. A violation of an -insofar undisputed-upper bound on hydrogen loading follows.

  2. The QCD phase transition. From the microscopic mechanism to signals

    International Nuclear Information System (INIS)

    Shuryak, E.V.

    1997-01-01

    This talk consists of two very different parts: the first one deals with non-perturbative QCD and physics of the chiral restoration, the second with rather low-key (and still unfinished) work aiming at obtaining EOS and other properties of hot/dense hadronic matter from data on heavy ion collisions. The microscopic mechanism for chiral restoration phase transition is a transition from randomly placed tunneling events (instantons) at low T to a set of strongly correlated tunneling-anti-tunneling events (known as instanton-anti-instanton molecules) at high T. Many features of the transition can be explained in this simple picture, especially the critical line and its dependence on quark masses. This scenario predicts qualitative change of the basic quark-quark interactions around the phase transition line, with some states (such as pion-sigma ones) probably surviving event at T > T c . In the second half of the talk experimental data on collective flow in heavy ion collision are discussed its hydro-based description and relation to equation of state (EOS). A distinct feature of the QCD phase transition region is high degree of 'softness', (small ratio pressure/energy density). (author)

  3. Liquid-Liquid Phase Transition and Glass Transition in a Monoatomic Model System

    Directory of Open Access Journals (Sweden)

    Nicolas Giovambattista

    2010-12-01

    Full Text Available We review our recent study on the polyamorphism of the liquid and glass states in a monatomic system, a two-scale spherical-symmetric Jagla model with both attractive and repulsive interactions. This potential with a parametrization for which crystallization can be avoided and both the glass transition and the liquid-liquid phase transition are clearly separated, displays water-like anomalies as well as polyamorphism in both liquid and glassy states, providing a unique opportunity to study the interplay between the liquid-liquid phase transition and the glass transition. Our study on a simple model may be useful in understanding recent studies of polyamorphism in metallic glasses.

  4. Is there a sharp phase transition for deterministic cellular automata?

    International Nuclear Information System (INIS)

    Wootters, W.K.

    1990-01-01

    Previous work has suggested that there is a kind of phase transition between deterministic automata exhibiting periodic behavior and those exhibiting chaotic behavior. However, unlike the usual phase transitions of physics, this transition takes place over a range of values of the parameter rather than at a specific value. The present paper asks whether the transition can be made sharp, either by taking the limit of an infinitely large rule table, or by changing the parameter in terms of which the space of automata is explored. We find strong evidence that, for the class of automata we consider, the transition does become sharp in the limit of an infinite number of symbols, the size of the neighborhood being held fixed. Our work also suggests an alternative parameter in terms of which it is likely that the transition will become fairly sharp even if one does not increase the number of symbols. In the course of our analysis, we find that mean field theory, which is our main tool, gives surprisingly good predictions of the statistical properties of the class of automata we consider. 18 refs., 6 figs

  5. DECnet routing transition from PhaseIV to PhaseV/OSI in Japan

    International Nuclear Information System (INIS)

    Yuasa, F.; Hirose, H.; Ichii, S.; Karita, Y.; Miyajima, T.; Morita, Y.; Nakamura, T.

    1994-01-01

    DECnet, one of the network protocols used in world-wide HEP community, is under the way of transition to PhaseV/OSI because of lack of address space. This affects to DECnet naming, addressing and routing. The authors present the current status of the routing transition in Japan

  6. Phase transitions in coated nickel titanium arch wires: A differential ...

    Indian Academy of Sciences (India)

    Discrete crystallographic structure and absence of mul- tiple phases showed complete martensitic–austenitic transition, which authenticated the differential scanning calori- metric findings. This can earn acceptance for the new product in contemporary orthodontic practice with adequate scope for indigenization. Keywords.

  7. Quantum phase transition of a magnet in a spin bath

    DEFF Research Database (Denmark)

    Rønnow, H.M.; Parthasarathy, R.; Jensen, J.

    2005-01-01

    The excitation spectrum of a model magnetic system, LiHoF(4), was studied with the use of neutron spectroscopy as the system was tuned to its quantum critical point by an applied magnetic field. The electronic mode softening expected for a quantum phase transition was forestalled by hyperfine...

  8. High pressure phase transitions for CdSe

    Indian Academy of Sciences (India)

    Administrator

    respectively and the intermediate states between the Cmcm structure and the CsCl structure should exist. Keywords. Semiconductor; high pressure; phase transition. 1. Introduction. CdSe has become quite interesting and important because of its major applications in solar cells and other optoelec- tronic devices due to its ...

  9. Phase transitions in coated nickel titanium arch wires: A differential ...

    Indian Academy of Sciences (India)

    Abstract. Shape memory and super-elastic properties of orthodontic nickel titanium wires, which are crucial for its clinical performance are dependent on the austenitic–martensitic phase transitions in its metallic microstructure that happen as a result of temperature or stress. The objective of this study was to compare the ...

  10. Quantum chromodynamics phase transition in the early Universe ...

    Indian Academy of Sciences (India)

    number distribution of the QNs will be calculated in §2. Section 3 will be devoted to the discussion on the evolution of these nuggets to form dark matter and§4 will contain a brief conclusion. 2. The baryon number distribution of quark nuggets. The evolution of the universe during the QCD phase transition is governed by ...

  11. Shape change as entropic phase transition: A study using Jarzynski ...

    Indian Academy of Sciences (India)

    21–28. c Indian Academy of Sciences. Shape change as entropic phase transition: A study using Jarzynski relation ... cess.1–3 This occurs with enthalpic changes in the ther- modynamic system, in which the system size is ..... Ma S K 1976 Modern theory of critical phenomena. (Benjamin, Reading, MA). 3. Stanley H E 1971 ...

  12. Ultrafast Hot Electron Induced Phase Transitions in Vanadium Dioxide

    Directory of Open Access Journals (Sweden)

    Haglund R. F.

    2013-03-01

    Full Text Available The Au/Cr/VO2/Si system was investigated in pump–probe experiments. Hot-electrons generated in the Au were found to penetrate into the underlying VO2 and couple with its lattice inducing a semiconductor-to-metal phase transition in ~2 picoseconds.

  13. Luminous transmittance and phase transition temperature of VO 2 ...

    African Journals Online (AJOL)

    The phase transition temperature (τc) of the films was obtained from both the transmittance and sheet resistance against temperature curves. A change in sheet resistance of 2 to 3 orders of magnitude was observed for both undoped and Ce-doped VO2 films. Comparison between undoped and doped VO2 films revealed ...

  14. Long time behaviour of a singular phase transition model

    Czech Academy of Sciences Publication Activity Database

    Krejčí, Pavel; Sprekels, J.

    2006-01-01

    Roč. 15, č. 4 (2006), s. 1119-1135 ISSN 1078-0947 Institutional research plan: CEZ:AV0Z10190503 Keywords : phase transition * nonlocal model * integrodifferential heat equation Subject RIV: BA - General Mathematics Impact factor: 1.087, year: 2006

  15. Simple explanation for the reentrant magnetic phase transition in Pr ...

    Indian Academy of Sciences (India)

    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 ...

  16. Fatigue and phase transition in an oscillating plate

    Czech Academy of Sciences Publication Activity Database

    Bosia, S.; Eleuteri, M.; Kopfová, J.; Krejčí, Pavel

    2014-01-01

    Roč. 435, February (2014), s. 1-3 ISSN 0921-4526 R&D Projects: GA ČR GAP201/10/2315 Institutional support: RVO:67985840 Keywords : fatigue * hysteresis * phase transitions Subject RIV: BA - General Mathematics Impact factor: 1.319, year: 2014 http://www.sciencedirect.com/science/article/pii/S0921452613006042

  17. Multifragmentation and the phase transition: A systematic study of ...

    Indian Academy of Sciences (India)

    study of the multifragmentation of 1 GeV Au, La and Kr ... Department of Physics and Chemistry, Purdue University, West Lafayette, Indiana, USA. Abstract. ... power law ( ). - , with. 25 [2] generated theoretical interest in MF in terms of a continuous phase transition. A similar power law was also predicted by Fisher [3] for.

  18. Corrosion behaviour, microstructure and phase transitions of Zn ...

    Indian Academy of Sciences (India)

    This paper is aimed at investigating the corrosion behaviour, microstructure and phase transitions of Zn-based alloys with different compositions. The corrosion tests are carried out both in acidic medium using 1 N HCl solution and in temperature dependence of thermogravimetric analysis (TGA). In the two different media, ...

  19. High-temperature phase transition in hadron matter

    International Nuclear Information System (INIS)

    Bugrij, A.I.; Trushevsky, A.A.

    1976-01-01

    A possible phase transition in hadronic systems at temperatures of few of GeV is shown in the framework of the S-matrix formulation of statistical mechanics given by Dashen, Ma, Bernstein by using Regge pole model for the scattering amplitude

  20. Wet Process Induced Phase Transited Drug Delivery System as a ...

    African Journals Online (AJOL)

    Nx 6110

    The drug release was found to be independent of the pH but dependent on the osmotic pressure of the dissolution medium. The results of in vivo toxicity studies may support the use of phase transited asymmetric membrane capsules as a means for delivery of gastro-intestinal irritant drugs in a controlled manner through ...

  1. Structure determination at room temperature and phase transition ...

    Indian Academy of Sciences (India)

    Unknown

    Structure determination at room temperature and phase transition studies above Tc in ABi4Ti4O15 (A = Ba, Sr or Pb). G NALINI and T N GURU ROW*. Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India. MS received 9 May 2002. Abstract. The room temperature structure of three ...

  2. Routing strategies in traffic network and phase transition in network ...

    Indian Academy of Sciences (India)

    3Department of Electronic Engineering, City University of Hong Kong, Hong Kong SAR,. China. *Corresponding author. ... networks. Keywords. Routing strategy; network traffic flow; hysteretic loop; phase transition from ... nication networks is to control the increasing traffic congestion and improve the efficiency of information ...

  3. Simple explanation for the reentrant magnetic phase transition in

    Indian Academy of Sciences (India)

    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 ...

  4. Quantum chromodynamics phase transition in the early Universe ...

    Indian Academy of Sciences (India)

    A first-order quark hadron phase transition in the early Universe may lead to the formation of quark nuggets. The baryon number distribution of these quark nuggets have been calculated and it has been found that there are sizeable number of quark nuggets in the stable sector. The nuggets can clump and form bigger ...

  5. Nonlinear clustering during the BEC dark matter phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Freitas, Rodolfo C. de, E-mail: rodolfo.camargo@pq.cnpq.br [Universidade Federal do Espírito Santo, Av. Fernando Ferrari, Goiabeiras, Vitória (Brazil); Instituto Federal de Educação, Ciência e Tecnologia do Espírito Santo, Avenida Vitória 1729, Jucutuquara, Vitória (Brazil); Velten, Hermano, E-mail: velten@pq.cnpq.br [Universidade Federal do Espírito Santo, Av. Fernando Ferrari, Goiabeiras, Vitória (Brazil); UMR 7332, CPT, Aix Marseille Université, 13288, Marseille (France)

    2015-12-16

    Spherical collapse of the Bose–Einstein condensate (BEC) dark matter model is studied in the Thomas–Fermi approximation. The evolution of the overdensity of the collapsed region and its expansion rate are calculated for two scenarios. We consider the case of a sharp phase transition (which happens when the critical temperature is reached) from the normal dark matter state to the condensate one and the case of a smooth first order phase transition where there is a continuous conversion of “normal” dark matter to the BEC phase. We present numerical results for the physics of the collapse for a wide range of the model’s space parameter, i.e. the mass of the scalar particle m{sub χ} and the scattering length l{sub s}. We show the dependence of the transition redshift on m{sub χ} and l{sub s}. Since small scales collapse earlier and eventually before the BEC phase transition, the evolution of collapsing halos in this limit is indeed the same in both the CDM and the BEC models. Differences are expected to appear only on the largest astrophysical scales. However, we argue that the BEC model is almost indistinguishable from the usual dark matter scenario concerning the evolution of nonlinear perturbations above typical clusters scales, i.e., ≳10{sup 14}M{sub ⊙}. This provides an analytical confirmation for recent results from cosmological numerical simulations (Schive et al., Nat Phys 10:496, 2014)

  6. Multiply Degenerate Exceptional Points and Quantum Phase Transitions

    Czech Academy of Sciences Publication Activity Database

    Borisov, D.; Růžička, František; Znojil, Miloslav

    2015-01-01

    Roč. 54, č. 12 (2015), s. 4293-4305 ISSN 0020-7748 Institutional support: RVO:61389005 Keywords : quantum mechanics * Cryptohermitian observbles * spectra and pseudospectra * real exceptional points * phase transitions Subject RIV: BE - Theoretical Physics Impact factor: 1.041, year: 2015

  7. African Transitional Justice Research Network - Phase II | IDRC ...

    International Development Research Centre (IDRC) Digital Library (Canada)

    The African Transitional Justice Research Network (ATJRN) aims to strengthen the capacity of African researchers and civil society institutions to conduct effective human rights advocacy through the production of high-quality, locally based and targeted empirical research. Phase I of the project (102862) focused on creating ...

  8. Dry Process Induced Phase Transited Drug Delivery System: A ...

    African Journals Online (AJOL)

    An in-situ formed phase transited, nondisintegrating, controlled release, asymmetric membrane capsular system for the poorly water soluble model drug ketoprofen was developed and evaluated in vitro to assess for osmotic and controlled release and in vivo to assess the ability of the fabricated dosage form to control GI ...

  9. Electroweak phase transition and some related phenomena – a brief ...

    Indian Academy of Sciences (India)

    2016-08-24

    Aug 24, 2016 ... Abstract. In this article, we give a bird's eye view of the research on electroweak phase transition and some related phenomena, viz., cosmological baryogenesis, electroweak bubble dynamics and generation of gravi- tational waves. Our presentation revolves around the observation that a strong first-order ...

  10. Phase transition in L-alaninium oxalate by photoacoustics

    Indian Academy of Sciences (India)

    Unknown

    structural where one-dimensional hydrogen bonding struc- ture is formed and stacked to form a molecular layer. This work showed a solid to solid phase transition at. 363 K (90°C). Since these crystals were grown by slow evaporation method, they have taken care in omitting the occluded water, if any, during the growth by ...

  11. Phase transitions at finite chemical potential in grand unified theories

    International Nuclear Information System (INIS)

    Bailin, D.; Love, A.

    1984-01-01

    We discuss the circumstances in which non-zero chemical potentials might prevent symmetry restoration in phase transitions in the early universe at grand unification or partial unification scales. The general arguments are illustrated by consideration of SO(10) and SU(5) grand unified theories. (orig.)

  12. Electroweak phase transition and some related phenomena – a brief ...

    Indian Academy of Sciences (India)

    2016-08-24

    Aug 24, 2016 ... Centre for Advanced Studies, Department of Physics, The University of Burdwan, Burdwan 713 104, India ... tational waves. Our presentation revolves around the observation that a strong first-order electroweak phase transition cannot be obtained in the Standard Model for experimentally favoured Higgs ...

  13. Spin delocalization phase transition in a correlated electrons model

    International Nuclear Information System (INIS)

    Huerta, L.

    1990-11-01

    In a simplified one-site model for correlated electrons systems we show the existence of a phase transition corresponding to spin delocalization. The system becomes a solvable model and zero-dimensional functional techniques are used. (author). 7 refs, 3 figs

  14. First-order quantum phase transition in a finite system

    International Nuclear Information System (INIS)

    Leviatan, A.

    2006-01-01

    The dynamics at the critical point of a general first-order quantum phase transition in a finite system is examined from an algebraic perspective. Suitable Hamiltonians are constructed whose spectra exhibit coexistence of states corresponding to two degenerate minima in the energy surface separated by an arbitrary barrier. Explicit expressions are derived for wave functions and observables at the critical point

  15. Employment, Production and Consumption model: Patterns of phase transitions

    Czech Academy of Sciences Publication Activity Database

    Lavička, H.; Lin, L.; Novotný, Jan

    2010-01-01

    Roč. 389, č. 8 (2010), s. 1708-1720 ISSN 0378-4371 Institutional research plan: CEZ:AV0Z10480505 Keywords : EPC * Agent based model * Phase transition Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders Impact factor: 1.521, year: 2010

  16. Commensurate-commensurate magnetic phase transitions in CeSb

    DEFF Research Database (Denmark)

    Lebech, Bente; Broholm, C.; Clausen, K.

    1986-01-01

    The q=2/3 to q=4/7 commensurate-commensurate phase transition in CeSb has been studied by neutron diffraction. On cooling the commensurate wave vector q changes abruptly from 2/3 to a higher-order commensurate value (≈14/23) at T1

  17. Dissipative phase transition in the open quantum Rabi model

    Science.gov (United States)

    Hwang, Myung-Joong; Rabl, Peter; Plenio, Martin B.

    2018-01-01

    We demonstrate that the open quantum Rabi model (QRM) exhibits a second-order dissipative phase transition (DPT) and propose a method to observe this transition with trapped ions. The interplay between the ultrastrong qubit-oscillator coupling and the oscillator damping brings the system into a steady state with a diverging number of excitations, in which a DPT is allowed to occur even with a finite number of system components. The universality class of the open QRM, modified from the closed QRM by a Markovian bath, is identified by finding critical exponents and scaling functions using the Keldysh functional integral approach. We propose to realize the open QRM with two trapped ions where the coherent coupling and the rate of dissipation can be individually controlled and adjusted over a wide range. Thanks to this controllability, our work opens a possibility to investigate potentially rich dynamics associated with a dissipative phase transition.

  18. Entanglement growth during Van der Waals like phase transition

    Directory of Open Access Journals (Sweden)

    Hao Xu

    2017-09-01

    Full Text Available We address the problem of describing the coexistence state of two different black holes and Van der Waals like phase transition in Reissner–Nordström–AdS space–time. We start by a small charged black hole, then introduce a collapsing neutral thin-shell described by Vaidya metric to form a large one. The formation of the large black hole does not change the temperature and free energy of the initial state. We discuss the entanglement growing during the phase transition. The transition is always continuous and the saturation time is determined by the final state. It opens a possibility for studying the holography from excited states to excited states.

  19. Negative thermal expansion near two structural quantum phase transitions

    Science.gov (United States)

    Occhialini, Connor A.; Handunkanda, Sahan U.; Said, Ayman; Trivedi, Sudhir; Guzmán-Verri, G. G.; Hancock, Jason N.

    2017-12-01

    Recent experimental work has revealed that the unusually strong, isotropic structural negative thermal expansion in cubic perovskite ionic insulator ScF3 occurs in excited states above a ground state tuned very near a structural quantum phase transition, posing a question of fundamental interest as to whether this special circumstance is related to the anomalous behavior. To test this hypothesis, we report an elastic and inelastic x-ray scattering study of a second system Hg2I2 also tuned near a structural quantum phase transition while retaining stoichiometric composition and high crystallinity. We find similar behavior and significant negative thermal expansion below 100 K for dimensions along the body-centered-tetragonal c axis, bolstering the connection between negative thermal expansion and zero-temperature structural transitions. We identify the common traits between these systems and propose a set of materials design principles that can guide discovery of new materials exhibiting negative thermal expansion.

  20. Negative thermal expansion near two structural quantum phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Occhialini, Connor A.; Handunkanda, Sahan U.; Said, Ayman; Trivedi, Sudhir; Guzmán-Verri, G. G.; Hancock, Jason N.

    2017-12-01

    Recent experimental work has revealed that the unusually strong, isotropic structural negative thermal expansion in cubic perovskite ionic insulator ScF3 occurs in excited states above a ground state tuned very near a structural quantum phase transition, posing a question of fundamental interest as to whether this special circumstance is related to the anomalous behavior. To test this hypothesis, we report an elastic and inelastic x-ray scattering study of a second system Hg2I2 also tuned near a structural quantum phase transition while retaining stoichiometric composition and high crystallinity. We find similar behavior and significant negative thermal expansion below 100 K for dimensions along the body-centered-tetragonal c axis, bolstering the connection between negative thermal expansion and zero-temperature structural transitions.We identify the common traits between these systems and propose a set of materials design principles that can guide discovery of newmaterials exhibiting negative thermal expansion