Browsing by Subject "Phase diagrams"
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Item Open Access Hard-core Yukawa model for charge-stabilized colloids(American Physical Society, 2000) Davoudi, B.; Kohandel, M.; Mohammadi, M.; Tanatar, BilalThe hypernetted chain approximation is used to study the phase diagram of a simple hardcore Yukawa model of a charge-stabilized colloids. We calculate the static structure factor, the pair distribution function, and the collective mode energies over a wide range of parameters, and the results are used for studying the freezing transition of the system. The resulting phase diagram is in good agreement with the known estimates and the Monte Carlo simulations. ©2000 The American Physical Society.Item Open Access On the stability of Fröhlich bipolarons in spherical quantum dots(Institute of Physics, 2002) Senger, R. T.; Erçelebi, A.In the strong-electron-phonon-coupling regime, we retrieve the stability criterion for bipolaron formation in a spherical quantum dot. The model that we use consists of a pair of electrons immersed in a reservoir of bulk LO phonons and confined within an isotropic parabolic potential box. In this particular quasi-zero-dimensional geometry, where the electrons do not have any free spatial direction to expand indefinitely, a plausible approach would be to treat the electrons either to form a bipolaronic bound state or enter a state of two close, but individual polarons inside the same dot. The confined two-polaron model adopted here involves the polaron-polaron separation introduced as an adjustable parameter to be determined variationally. It is found that the fundamental effect of imposing such a variational flexibility is to modify the phase diagram to a considerable extent and to sustain the bipolaron phase in a broader domain of stability.Item Open Access Phase transitions and renormalization-group theory(1989-07) Berker, A. NihatThe study of critical phenomena targets the qualitatively new phenomena that occur through the interactions of very large numbers of degrees of freedom. Such situations are typically realized near the onset of the transition between two thermodynamic phases. The special challenge of this field is thus due to the truly many-body nature of its subject. Another motivating challenge of the field has been the feasibility of immediate comparisons between the outcomes of sophisticated experiments and sophisticated theories, especially in condensed matter systems. Adding to this the wide variety of experimental and theoretical methods, it is seen that many cultures meet and exchange under the aegis of critical phenomena and phase transitions, contributing to the dynamism and intellectual enrichment of the field.Item Open Access Stepwise Positional-Orientational Order and the Multicritical-Multistructural Global Phase Diagram of the s=3/2 Ising Model From Renormalization-Group Theory(American Physical Society, 2016) Yunus, Ç.; Renklioǧlu, B.; Keskin, M.; Berker, A. N.The spin-32 Ising model, with nearest-neighbor interactions only, is the prototypical system with two different ordering species, with concentrations regulated by a chemical potential. Its global phase diagram, obtained in d=3 by renormalization-group theory in the Migdal-Kadanoff approximation or equivalently as an exact solution of a d=3 hierarchical lattice, with flows subtended by 40 different fixed points, presents a very rich structure containing eight different ordered and disordered phases, with more than 14 different types of phase diagrams in temperature and chemical potential. It exhibits phases with orientational and/or positional order. It also exhibits quintuple phase transition reentrances. Universality of critical exponents is conserved across different renormalization-group flow basins via redundant fixed points. One of the phase diagrams contains a plastic crystal sequence, with positional and orientational ordering encountered consecutively as temperature is lowered. The global phase diagram also contains double critical points, first-order and critical lines between two ordered phases, critical end points, usual and unusual (inverted) bicritical points, tricritical points, multiple tetracritical points, and zero-temperature criticality and bicriticality. The four-state Potts permutation-symmetric subspace is contained in this model.Item Open Access Synthesis of V2 O3 nanoplates for the exploration of the correlated supercritical state(American Physical Society, 2019) Rasouli, Hamid Reza; Mehmood, Naveed; Çakıroğlu, Onur; Sürmeli, Engin Can; Kasırga, T. SerkanPeculiar features exist in the stress-temperature phase stability diagram of V2O3, such as a first-order phase transition between the paramagnetic insulating and metallic phases that ends with a critical point, quantum phase transition, and a triple point. These features remain largely unexplored, and the exact nature of the phase transitions is not clear due to very limited control over the stress in bulk or film samples. Here, we show the synthesis of single-crystal V2O3 nanoplates using chemical vapor deposition via van der Waals epitaxy. Thickness of the V2O3 nanoplates range from a few to hundreds of nanometers, and they can be mechanically exfoliated from the growth substrate. Using Raman spectroscopy on the nanoplates, we reveal that, upon heating, V2O3 enters a supercritical state for both tensile strained and relaxed crystals with a similar out-of-plane response. Transmission electron microscopy on V2O3 nanoplates hints at the existence of a structural change when the crystals are heated. Our results show that V2O3nanoplates should be useful for studying the physics of the supercritical state and the phase stability of V2O3 to enable new horizons in applications.Item Open Access Vortex lattices in dipolar two-compenent Bose-Einstein condensates(American Physical Society, 2014-02-21) Ghazanfari, N.; Keles, A.; Oktel, M. O.We consider a rapidly rotating two-component Bose-Einstein condensate with short-range s-wave interactions as well as dipolar coupling. We calculate the phase diagram of vortex lattice structures as a function of the intercomponent s-wave interaction and the strength of the dipolar interaction. We find that the long-range interactions cause new vortex lattice structures to be stable and lead to a richer phase diagram. Our results reduce to the previously found lattice structures for short-range interactions and single-component dipolar gases in the corresponding limits.