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Zero Magnetic Field (zero + magnetic_field)
Selected AbstractsRestricted and unrestricted Hartree,Fock approaches applied to spherical quantum dots in a magnetic fieldINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 9 2006C. F. Destefani Abstract The Roothaan and Pople,Nesbet approaches for real atoms are adapted to quantum dots in the presence of a magnetic field. Single-particle Gaussian basis sets are constructed, for each dot radius, under the condition of maximum overlap with the exact functions. The chemical potential, charging energy, and total spin expected values are calculated, and we have verified the validity of the quantum dot energy shell structure as well as Hund's rule for electronic occupation at zero magnetic field. At finite field, we have observed the violation of Hund's rule and studied the influence of magnetic field on the closed and open energy shell configurations. We have also compared the present results with those obtained within the LS-coupling scheme for low electronic occupation numbers. We focus only on ground-state properties and consider quantum dots populated up to 40 electrons, constructed by GaAs or InSb nanocrystals. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Low magnetic fields behavior of photon echo in LuLiF4:Er3+LASER PHYSICS LETTERS, Issue 9 2006V. N. Lisin Abstract It is reported about the first observation and studying of the photon echo in LuLiF4:Er3+. The energy transition is 4I15/2 , 4F9/2 (, = 6536 Å). The density of ErF3 is 0.025 wt%. The operation temperature is 1.9 K. Measurements were spent at low (up to 1200 Oe) and even zero external magnetic fields. It was studied a behavior of the photon echo intensity versus the magnetic field magnitude and direction about the crystal axis C and versus the laser pulse separation t12. It was observed an exponential growth and then, after some plateau, an exponential decreasing of the photon echo intensity as a function of magnetic field with increasing of the magnetic field from zero value. The parameters describing the exponential growth and decreasing are not depended on direction of magnetic field. Value of a magnetic field at which the echo intensity accepts the maximum, and quantity of this maximum decrease with increased the pulse separation t12 and the angle , between the magnetic field and crystal axis. The echo intensity exponentially decreases with increased , . The parameter describing the exponential decreasing is not depended on the magnitude of the field. The echo intensity as a function of pulse separation shows exponential decay. The phase relaxation time is depended on the magnitude and direction of the magnetic field. T2 is equal to 202 ± 16 ns at zero magnetic field. Phenomenological formula is suggested, which qualitatively presents the mentioned dependencies. Polarization properties of the backward photon echo in this crystal are studied also. (© 2006 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Peculiar manifestation of the dipole,dipole interaction between non-Kramers paramagnetic centers as studied by tunable high-frequency EPR spectroscopy,MAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2005K. M. Salikhov Abstract EPR spectral shape of non-Kramers paramagnetic centers (PCs) is theoretically analyzed under conditions of saturation. The analysis is performed in a model that includes the spectral diffusion process induced by a random modulation of the dipole,dipole interaction of the paramagnetic centers, by reorientations of magnetic moments. It is shown that around zero magnetic field, a ,hole' might appear in the EPR spectrum. We have also studied experimentally the saturation behavior of the EPR spectrum in Cr2+ : Mg2SiO4. The experimental results are interpreted in the framework of the model considered. By comparing simulated and experimental spectra, the paramagnetic relaxation times and the characteristic rate of the spectral diffusion are estimated. Copyright © 2005 John Wiley & Sons, Ltd. [source] Optical spin orientation of a single manganese atomPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2010C. Le Gall Abstract An optical spin orientation is achieved for a Mn atom localized in a semiconductor quantum dot using quasiresonant excitation at zero magnetic field. Optically created spin polarized carriers generate an energy splitting of the Mn spin and enable magnetic moment orientation controlled by the photon helicity and energy. The dynamics and the magnetic field dependence of the optical pumping mechanism shows that the spin lifetime of an isolated Mn atom at zero magnetic field is controlled by a magnetic anisotropy induced by the built-in strain in the quantum dots. Relaxation times exceeding the micro-second range are measured (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Single-particle state mixing and Coulomb localization in two-electron realistic coupled quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007Dmitriy V. Melnikov Abstract The exchange coupling in a realistic double quantum dot system is computed as a function of the gate confinement and magnetic field using a hybrid multiscale approach where the many-body Schrödinger equation is solved exactly within the full quantum dot device environment. It is found that at zero magnetic field the exchange energy varies from meV to sub-,eV value as the confinement gate biases (tunneling barrier) are changed and the system is driven from a single quantum dot to two coupled quantum dots. At the same time the magnetic field of the singlet-triplet transition is weakly affected by the changes and remains at about 1 T in the same range of the gate biases. The small values of the exchange coupling in this structure are attributed to the large inter-electron separation arising when the Coulomb repulsion dominates tunneling. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Mechanisms of exciton spin relaxation in quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2003E. Tsitsishvili Abstract We study the phonon-assisted relaxation processes (longitudinal relaxation time T1) within the radiative doublet of the heavy-hole-exciton in asymmetrical quantum dots. Two different relaxation mechanisms are considered: the exciton spin,acoustic phonon coupling via the strain-dependent short-range exchange interaction and the second-order quasielastic interaction between charge carriers and LO phonons. For zero magnetic fields and low temperatures, the calculated relaxation times for typical QDs are very long compared to the exciton lifetime yet they are strongly reduced in high magnetic fields (of the order of a few Tesla) and high temperatures T , 100 K. [source] | |||||||||||||