Search results for "Coupling"
showing 10 items of 1862 documents
Alignment-orientation transition at optical excitation of molecules in magnetic field
1995
Abstract Angular momentum alignment-orientation transition is analyzed for the ground state of diatomic or linear molecules subjected to the dynamic Stark effect. Analytical expressions are derived for the orientation value. It is shown that, first, orientation of angular momenta resulting from the action of the dynamic Stark effect is a nonlinear process which depends quadratically on the intensity of the irradiating light; second, it is a quantum effect and disappears for the states with large angular momenta; and, third, it occurs only in the presence of an external magnetic field.
Carrier-induced ferromagnetism in two-dimensional magnetically doped semiconductor structures
2021
We show theoretically that the magnetic ions, randomly distributed in a two-dimensional (2D) semiconductor system, can generate a ferromagnetic long-range order via the RKKY interaction. The main physical reason is the discrete (rather than continuous) symmetry of the 2D Ising model of the spin-spin interaction mediated by the spin-orbit coupling of 2D free carriers, which precludes the validity of the Mermin-Wagner theorem. Further, the analysis clearly illustrates the crucial role of the molecular field fluctuations as opposed to the mean field. The developed theoretical model describes the desired magnetization and phase-transition temperature ${T}_{c}$ in terms of a single parameter, na…
Experimental determination of single molecule toroic behaviour in a Dy8 single molecule magnet
2019
The enhancement of toroic motifs through coupling toroidal moments within molecular nanomagnets is a new, interesting and relevant approach for both fundamental research and potential quantum computation applications. We investigate a Dy8 molecular cluster and discover it has a antiferrotoroic ground state with slow magnetic relaxation. The experimental characterization of the magnetic anisotropy axes of each magnetic center and their exchange interactions represents a considerable challenge due to the non-magnetic nature of the toroidal motif. To overcome this and obtain access to the low energy states of Dy8 we establish a multi-orientation single-crystal micro Hall sensor magnetometry ap…
Spectroscopy of Hexafluorides with an Odd Number of Electrons: The Vibronic Bands of IrF6
1996
Abstract The low resolution absorption spectroscopy of the first five excited electronic states of IrF 6 has made possible some new assignments for the vibronic transitions of this molecule, and the determination of new vibronic parameter values. They are more accurate than those found in the literature. In this aim, we introduce a simplified tensorial formulation for the linear Jahn–Teller terms in a fourfold degenerate electronic state of an XY 6 -type molecule, which allows easier computation of matrix elements and avoids the use of perturbation theory. Methods for IrF 6 synthesis (using a dynamical flow system) and purification are also presented.
Transplanckian masses in inflation
2016
AbstractWe explore the possibility that the transplanckian field values needed to accommodate the experimental results in minimally coupled single-field inflation models are only due to our insistence of imposing a minimal coupling of the inflaton field to gravity. A simple conformal transformation can bring the field values below the Planck mass without changing the physics at the expense of having a richer gravitational sector. Transplanckian field values may be the signal that we are (miss)interpreting phenomena due to gravity as being originated exclusively in the scalar sector.
Dynamics of a Supercooled Lennard-Jones System: Qualitative and Quantitative Tests of Mode-Coupling Theory
1997
Using a molecular dynamics computer simulation we investigate the dynamics of a supercooled binary Lennard-Jones mixture. At low temperatures this dynamics can be described very well by the ideal version of mode-coupling theory. In particular we find that at low temperatures the diffusion constants show a power-law behavior, that the intermediate scattering functions obey the time temperature superposition principle, and that the various relaxation times show a power-law behavior. By solving the wave-vector dependent mode-coupling equations we demonstrate that the prediction of the theory for the wave-vector dependence of the nonergodicity parameters and the r-dependence of the critical amp…
Structural relaxation in a binary metallic melt: Molecular dynamics computer simulation of undercooledAl80Ni20
2008
Molecular dynamics computer simulations are performed to study structure and structural relaxation in the glassforming metallic alloy ${\text{Al}}_{80}{\text{Ni}}_{20}$. The interactions between the particles are modeled by an effective potential of the embedded atom type. Our model of ${\text{Al}}_{80}{\text{Ni}}_{20}$ exhibits chemical short-range order (CSRO) that is reflected in a broad prepeak around a wave number of $1.8\text{ }{\text{\AA{}}}^{\ensuremath{-}1}$ in the partial static structure factor for the Ni-Ni correlations. The CSRO is due to the preference of Ni atoms to have Al rather than Ni atoms as nearest neighbors. By analyzing incoherent and coherent intermediate scattering…
Understanding the glass transition and the amorphous state of matter: can computer simulation solve the challenge?
1999
The glass transition of supercooled fluids is one of the big puzzles of condensed matter physics, because there occurs a dramatic slowing down (the viscosity η can increase from about η = 1 Poise at the melting transition to η 10 13 Poise at the glass transition temperature T g ), but one hardly sees any accompanying change in the static structure. Theoretical concepts are very controversial - e.g., the Gibbs-di Marzio theory attributes glassy freezing to an underlying entropy catastrophe (the entropy of the supercooled fluid would fall below the crystal entropy at the Kauzmann temperature T 0 T g . Computer simulations offer the advantage that atomistically detailed information on structur…
A mode coupling analysis of the central peak at order disorder phase transitions
1993
The influence of local and translation invariant memory effects on the critical dynamics of a model undergoing a continous structural phase transition from a disordered (T>Tc) to an ordered distorted phase (T>Tc) is studied by mode coupling theory above the critical temperatureTc. It is shown that besides the existence of critical slowing-down modes there also exists a central peak as a consequence of correlations of the critical modes, increasing with the critical exponent γ when approachingTc. The dependence of the central peak on the wavevector\(\vec q\), temperatureT and on the spatial dimensiond is investigated. Ford=3 a scenario withlocal long time memory correlations is compared with…
High-precision measurement of the atomic mass of the electron
2014
A very precise measurement of the magnetic moment of a single electron bound to a carbon nucleus, combined with a state-of-the-art calculation in the framework of bound-state quantum electrodynamics, gives a new value of the atomic mass of the electron that is more precise than the currently accepted one by a factor of 13. The atomic mass of the electron is a key parameter for fundamental physics. A precise determination is a challenge because the mass is so low. Sven Sturm and colleagues report on a new determination of the electron's mass in atomic units. The authors measured the magnetic moment of a single electron bound to a reference ion (a bare nucleus of carbon-12). The results were …