Spin relaxation time, spin dephasing time and ensemble spin dephasing time in nn-type GaAs quantum wells

We investigate the spin relaxation and spin dephasing of $n$-type GaAs quantum wells. We obtain the spin relaxation time $T_1$, the spin dephasing time $T_2$ and the ensemble spin dephasing time $T_2^{\ast}$ by solving the full microscopic kinetic spin Bloch equations, and we show that, analogous to the common sense in an isotropic system for conduction electrons, $T_1$, $T_2$ and $T_2^{\ast}$ are identical due to the short correlation time. The inhomogeneous broadening induced by the D'yakonov-Perel term is suppressed by the scattering, especially the Coulomb scattering, in this system.Comment: 4 pages, 2 figures, to be published in Phys. Lett.

Frictional drag between non-equilibrium charged gases

The frictional drag force between separated but coupled two-dimensional electron gases of different temperatures is studied using the non-equilibrium Green function method based on the separation of center-of-mass and relative dynamics of electrons. As the mechanisms of producing the frictional force we include the direct Coulomb interaction, the interaction mediated via virtual and real TA and LA phonons, optic phonons, plasmons, and TA and LA phonon-electron collective modes. We found that, when the distance between the two electron gases is large, and at intermediate temperature where plasmons and collective modes play the most important role in the frictional drag, the possibility of having a temperature difference between two subsystems modifies greatly the transresistivity.Comment: 8figure

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time, and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space. While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes, vast areas of the tropics remain understudied. In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity, but it remains among the least known forests in America and is often underrepresented in biodiversity databases. To worsen this situation, human-induced modifications may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge, it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%–18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost

RESISTIVITY OF A DISORDERED TWO-DIMENSIONAL ELECTRON GAS UNDER MAGNETIC FIELD

On obtient la moyenne sur les impuretés de la résistivité d'un gaz d'électrons sous un champ magnétique avec la technique de la fonction mémoire-opérateurs de projection de Mori. L'hamiltonien est transformé en coordonnées relatives et de centre-de-masse. La fonction mémoire est exprimée en termes de la fonction de corrélation force-force.The impurity averaged resistivity for an electron gas under external magnetic field is obtained directly by using Mori's memory function-projector technique. The Hamiltonian is transformed into center-of-mass and relative coordinates. The memory function is expressed in terms of the force-force correlation function

A Model For Lattice Dynamics Of B.c.c. Metals

A model for b.c.c. metals is proposed by adding electron-ion interaction term from Krebs' model to the ion-ion interaction term of axially symmetric model of Lehman et al. The computed phonon frequencies of sodium are found to reproduce experimental ones within the limit of experimental error. © 1972.111014311433Lehman, Wolfram, Dewames, (1962) Phys. Rev., 128, p. 1593Bajpai, Neelakandan, (1971) Solid State. Commun., 9, p. 167Sharma, Joshi, Model for the Lattice Dynamics of Metals and Its Application to Sodium (1963) The Journal of Chemical Physics, 39, p. 2633Krebs, Dispersion Curves and Lattice Frequency Distribution of Metals (1965) Physical Review, 138, p. 143Woods, Brockhouse, March, Stewart, Bowers, (1962) Phys. Rev., 128, p. 1112Behari, Tripathi, Jr., (1970) Phys. Soc. Japan, 28, p. 346Ho, Ruoff, A Quasi-Harmonic Calculation of Lattice Dynamics for Na (1967) physica status solidi (b), 23, p. 48

Bloch Electrons In A Magnetic Field

A complete set of basis functions for the expansion of the wavefunction of a Bloch electron in a uniform magnetic field is derived. In the empty lattice limit this set gives the appropriate Landau free-electron wavefunctions, contrary to the Roth functions which in that limit are plane waves. © 1975.171215911592Misra, (1970) Phys. Rev., 2 B, p. 3906Roth, (1962) J. Phys. Chem. Solids, 23, p. 433Misra, (1970) Phys. Lett., 33, p. 33

Lattice Dynamics Of Alkali Metals

Frequency versus wave-vector dispersion relations along the three principal symmetry directions viz. ||, |ζζ0| and |ζζζ| have been computed for the alkali metals potassium, rubidium and lithium by a model developed by the present authors by combining ion-ion interaction of an axially symmetric model with electron-ion interaction from the Krebs model. The theoretical results have almost reproduced the experimental ones within the limits of the experimental errors. © 1974.721179187De, (1956) Solid State Physics, 2, p. 220. , F. Seitz, D. Turnbell, Academic Press Inc, New YorkBhatia, (1955) Phys. Rev., 97, p. 363Sharma, Joshi, Model for the Lattice Dynamics of Metals and Its Application to Sodium (1963) The Journal of Chemical Physics, 39, p. 2633Krebs, (1964) Phys. Letters, 10, p. 12Chéveau, Model for Lattice Dynamics in Metals (1968) Physical Review, 169, p. 496Shukla, Lima, Brescansin, (1972) Solid State Commun., 11, p. 1431Krebs, Hölze, (1969) Euratom Reports, p. 3621CLehman, Wolfram, DeWames, (1962) Phys. Rev., 128, p. 1593Cowley, Woods, Dolling, (1966) Phys. Rev., 150, p. 487Marquardt, Trivisonno, (1965) J. phys. Chem. Solids, 26, p. 273Smith, Dolling, Nicklov, (1962) Proc. Internat. Conf. Inelastic Neutron Scattering, IAEAC, 1, p. 149. , ViennaNash, Smith, Single-crystal elastic constants of lithium (1969) Journal of Physics and Chemistry of Solids, 9, p. 113Lähteenkorva, (1969) Ann. Acad. Sci. Fennicae, 6, p. 3Copley, Brockhouse, Chen, (1968) Proc. Internat. Conf. on Neutron Inelastic Scattering, A.A.E.A., 1, p. 209. , ViennaRoberts, Meistener, The elastic constants of rubidium (1967) Journal of Physics and Chemistry of Solids, 27, p. 1401Huntington, (1958) Solid State Phys., 7, p. 228. , F. Seitz, T. Turnbell, New YorkSharma, Singh, (1972) Physica, 59, p. 109Krebs, Dispersion Curves and Lattice Frequency Distribution of Metals (1965) Physical Review, 138, p. 143Shukla, Closs, (1973) J. Phys. F. (Metal Physics), 3, p. L

Effect of spin-polarized subbands in the inhomogeneous hole gas providing the indirect exchange in GaMnAs bilayers

The magnetic order resulting from the indirect exchange in the metallic phase of a (Ga,Mn)As/GaAs double layer structure is studied via Monte Carlo simulation. The polarization of the hole gas is taken into account, establishing a self-consistency between the magnetic order and the electronic structure. The Curie–Weiss temperatures calculated for these low-dimensional systems are in the range of 50–80 K, and the dependence of the transition temperature with the GaAs separation layer is established