Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 75 for “"Mean-Field Theory"”.
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The Study of Transition Metal Oxides using Dynamical Mean Field Theory
… phases not observed in bulk systems. Dynamical mean-field theory (DMFT) emerges as a successful numerical method to treat the strong correlation. The combination of density functional and dynamical mean-field theory (DFT+DMFT) is a prospective ab initio approach for studying realistic strongly …
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Mean-field theory for the dynamics of superfluid fermions in the BCS-BEC crossover
We use mean-field theory to investigate the dynamics of superfluid fermions. This thesis includes our two works. The first one is to study Josephson oscillations and self-trapping of superfluid fermions in a double-well potential with time-dependent Bogoliubov-de Gennes equations. We investigate …
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Cluster Dynamical Mean-Field Theory: Applications to High-Tc Cuprates and to Quantum Chemistry
… thesis we use the recently developed dynamical mean-field approximation to study problems in strongly correlated electron systems, including high-Tc cuprate superconductors as well as a few quantum chemical reference systems. We start with an introduction to the background of the interacting …
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Density-Functional Theory+Dynamical Mean-Field Theory Study of the Magnetic Properties of Transition-Metal Nanostructures
In this thesis, Density Functional Theory (DFT) and Dynamical Mean-Field Theory (DMFT) approaches are applied to study the magnetic properties of transition metal nanosystems of different sizes and compositions. In particular, in order to take into account dynamical electron correlation effects …
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Scaling of Steady States in a Simple Driven Three-State Lattice Gas
… a sufficiently large external "electric" field <I>E</I> induces the phase segregation, by separating the charges into two strips and "trapping" the hole at an interface between them. Focusing on the steady state, the scaling properties of an appropriate order parameter, depending on drive …
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Experimental study of the spin-glass phase diagram
… examined as a function of temperature, magnetic field, random anisotropy, and uniaxial anisotropy and the results are compared to recent mean-field theories. It is clearly demonstrated through measurements of the magnetic relaxation processes in the amorphous spin-glass (FeO.64MnO.36)75P16B6A13 …
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Force-response statistics of semiflexible polymers
… of histone-DNA complexes. The worm-like chain theory is a polymer-physics-based model and has been successfully applied to predict force-extension relations, bond correlations, and dynamics of semiflexible biopolymers. Despite these successes, the effects of non-uniform forces are not well …
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Physics under extreme conditions: Magnetized atoms and hot dense plasmas
… isolated atoms in very strong magnetic fields and the behavior of the electron gas near its crystallization point. For the atoms we consider a range of theoretical approaches, from mean field theory (Hartree-Fock) to an exact method using stochastic random walks (correlation function …
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Physics under extreme conditions: Magnetized atoms and hot dense plasmas
… isolated atoms in very strong magnetic fields and the behavior of the electron gas near its crystallization point. For the atoms we consider a range of theoretical approaches, from mean field theory (Hartree-Fock) to an exact method using stochastic random walks (correlation function …
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Control, Dynamics, and Epidemic Spreading in Complex Systems
… relaxation time. (c) Finally, we provide a mean field theory for a discrete time-step model of epidemic spreading on uncorrelated networks. The effect of degree distribution, time delays, and infection rate on the stability of oscillating and fixed point solutions is examined through …
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Liquid state theory of the local and long wavelength structure and thermodynamic properties of block copolymer liquids
… reference interaction site model"" (PRISM) theory to AB copolymers is presented. Within a simple ""symmetric"" model, analytical and numerical predictions are made for the fluctuation stabilization, peak scattering wavevector, and effective chi-parameter. The conditions for contact with …
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Disentangle model differences and fluctuation effects in DPD simulations of diblock copolymers
… interactions obtained from self-consistent field (SCF) calculations. Since SCF theory is a mean-field theory neglecting system fluctuations/correlations while DPD simulations fully incorporate such effects, the model differences are mixed with the fluctuation/correlation effects in their …
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Strongly Correlated Electrons on a Triangular Lattice
… energy effective theories by using perturbation theory. In chapter 3, we point out potential problems with perturbative techniques used to construct low energy theories for SCES. In chapter 4, we introduce an important class of materials, namely the cobaltates NaxCoO2 and we discuss the …
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Chiral symmetry restoration in the three-dimensional four-fermion model at non-zero temperature and density
… species N in the system can be described by mean field theory. It is also shown both analytically and numerically that the width of the region where non-trivial critical behavior sets in is suppressed by a certain power of 1/ N. At finite N, Monte Carlo simulations confirm the dimensional …
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Anistropic phenomena in strongly correlated electron systems
… Hubbard model within two-site cluster dynamical mean field theory (DMFT), at zero temperature. The "two-site" approach provides a drastically simplified but physically motivated self-consistency scheme for DMFT. This is combined for the first time with cluster DMFT, within which different …
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Effective action approach to quantum phase transitions in bosonic lattices
In this thesis, I develop a new, field-theoretic method for describing the quantum phase transition between Mott insulating and superfluid states observed in bosonic optical lattices. I begin by adding to the Hamiltonian of interest a symmetry breaking source term. Using time-dependent perturbation …
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Quasi-one-dimensional magnetism in TiOCl and a theory of a lightly doped dimerized insulator
… the main reason for the failure of conventional mean-field theory to describe the details of the transition such as its first order character. It will be shown that a simple Ginzburg-Landau theory which takes proper account of interchain-frustration is capable of explaining this unconventional …
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Pair density wave superconducting states and statistical mechanics of dimers
… octahedron equation. In chapter 2 we present a theory of superconducting states where the Cooper pairs have a nonzero center-of-mass momentum, inhomogeneous superconducting states known as a pair-density-waves (PDWs) states. We show that in a system of spin-1/2 fermions in two dimensions in an …
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Cluster mean-field dynamics of the long-range interacting Ising chain
… interacting Ising chain using a cluster mean-field approach, a mean-field theory that accounts for short range correlations. The principal result is that, if the system is isolated from an external environment, the model exhibits two different behaviors depending on the range of the …
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Fluctuation conductivity from charge density waves in pseudo-one-dimensional systems
… results is discussed. The use of mean-field theory in one dimension limits the validity of these calculations to several degrees above the transition temperature.
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