Search results for " symmetry"

Quantum Dots in Magnetic Fields: Phase Diagram and Broken Symmetry at the Maximum-Density-Droplet Edge

1999

Quantum dots in magnetic fields are studied within the current spin-density-functional formalism avoiding any spatial symmetry restrictions of the solutions. We find that the maximum-density droplet reconstructs into states with broken internal symmetry: The Chamon-Wen edge coexists with a modulation of the charge density along the edge. The phase boundaries between the polarization transition, the maximum-density droplet, and its reconstruction are in agreement with recent experimental results.

Electronic structure calculations forZnFe2O4

2011

Local density approximation was applied to scrutinize the electronic structure and magnetic properties of the spinel ferrite ${\mathrm{ZnFe}}_{2}{\mathrm{O}}_{4}$. Various cation distributions were established to obtain the ground state for the system. In magnetic crystals, the position of the atoms is not enough for symmetry determination. A structure prediction by decreasing the octahedral point group symmetry ${\mathrm{O}}_{h}$ of Fe to ${\mathrm{D}}_{4h}$, ${\mathrm{C}}_{4v}$, and ${\mathrm{C}}_{3v}$ was carried out. The effect of the exchange and correlation terms on the band structure of ${\mathrm{ZnFe}}_{2}{\mathrm{O}}_{4}$ was studied by the generalized gradient approximation $+$ th…

Spin-S Kagome quantum antiferromagnets in a field with tensor networks

2016

Spin-$S$ Heisenberg quantum antiferromagnets on the Kagome lattice offer, when placed in a magnetic field, a fantastic playground to observe exotic phases of matter with (magnetic analogs of) superfluid, charge, bond or nematic orders, or a coexistence of several of the latter. In this context, we have obtained the (zero temperature) phase diagrams up to $S=2$ directly in the thermodynamic limit thanks to infinite Projected Entangled Pair States (iPEPS), a tensor network numerical tool. We find incompressible phases characterized by a magnetization plateau vs field and stabilized by spontaneous breaking of point group or lattice translation symmetry(ies). The nature of such phases may be se…

Three physical quantum manifolds from the conformal group

1987

Hyperbolic character of the angular moment equations of radiative transfer and numerical methods

2000

We study the mathematical character of the angular moment equations of radiative transfer in spherical symmetry and conclude that the system is hyperbolic for general forms of the closure relation found in the literature. Hyperbolicity and causality preservation lead to mathematical conditions allowing to establish a useful characterization of the closure relations. We apply numerical methods specifically designed to solve hyperbolic systems of conservation laws (the so-called Godunov-type methods), to calculate numerical solutions of the radiation transport equations in a static background. The feasibility of the method in any kind of regime, from diffusion to free-streaming, is demonstrat…

Asymptotic structure factor and power-law tails for phase ordering in systems with continuous symmetry.

1991

We compute the asymptotic structure factor ${\mathit{S}}_{\mathbf{k}}$(t) [=L(t${)}^{\mathit{d}}$g(kL(t)), where L(t) is a time-dependent characteristic length scale and d is the dimensionality] for a system with a nonconserved n-component vector order parameter quenched into the ordered phase. The well-known Ohta-Jasnow-Kawasaki-Yalabik-Gunton result is recovered for n=1. The scaling function g(x) has the large-x behavior g(x)\ensuremath{\sim}${\mathit{x}}^{\mathrm{\ensuremath{-}}(\mathit{d}+\mathit{n})}$, which includes Porod's law (for n=1) as a special case.

General Hartree–Fock method and symmetry breaking in quantum dots

2010

Interaction and correlation effects in quantum dots play a fundamental role in defining both their equilibrium and transport properties. Numerical methods are commonly employed to study such systems. In this paper we present a two-step approach in which a Hartree-Fock method, with explicit symmetry breaking, is followed by a projection technique for symmetry restoration. Three different Hartree-Fock implementations, with an increasing degree of symmetry breaking, are introduced and applied to the study of interacting planar dots with N = 3 and 6, electrons in the presence of a perpendicular magnetic field. In addition to the restricted and unrestricted techniques already employed for quantu…

Tools for incorporating a D-wave contribution in Skyrme energy density functionals

2015

International audience; The possibility of adding a D-wave term to the standard Skyrme effective interaction has been widely considered in the past. Such a term has been shown to appear in the next-to-next-to-leading order of the Skyrme pseudo-potential. The aim of the present article is to provide the necessary tools to incorporate this term in a fitting procedure: first, a mean-field equation written in spherical symmetry in order to describe spherical nuclei and second, the response function to detect unphysical instabilities. With these tools it will be possible to build a new fitting procedure to determine the coupling constants of the new functional.

Non-Hermitian Hamiltonian for a Modulated Jaynes-Cummings Model with PT Symmetry

2015

We consider a two-level system such as a two-level atom, interacting with a cavity field mode in the rotating wave approximation, when the atomic transition frequency or the field mode frequency is periodically driven in time. We show that in both cases, for an appropriate choice of the modulation parameters, the state amplitudes in a generic $n${-}excitation subspace obey the same equations of motion that can be obtained from a \emph{static} non-Hermitian Jaynes-Cummings Hamiltonian with ${\mathcal PT}$ symmetry, that is with an imaginary coupling constant. This gives further support to recent results showing the possible physical interest of ${\mathcal PT}$ symmetric non-Hermitian Hamilto…

Strong-interaction Isospin-symmetry Breaking Within the Density Functional Theory

2015

The conventional Skyrme interaction is generalized by adding zero-range charge-symmetry-breaking and charge-independence-breaking terms, and the corresponding energy density functional is derived. It is shown that the extended model accounts for experimental values of mirror and triplet displacement energies (MDEs and TDEs) in sd-shell isospin triplets with, on average, about 100~keV precision using only two additional adjustable coupling constants. Moreover, the model is able to reproduce, for the first time, the A=4n versus A=4n+2 staggering of the TDEs.