144,446 research outputs found

    Plasmons of a two-dimensional electron gas in the presence of spin orbit interaction

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    A theoretical study of the collective excitation associated with plasmon modes is presented for a two-dimensional electron gas in the presence of spin orbit (SO) interaction induced by the Rashba effect. In such a case, the plasmon excitation can be achieved via intra- and inter-SO electronic transitions. As a result, three branches of the plasmon oscillations can be observed. It is found that inter-SO plasmons depend strongly on sample parameters and, at a long-wavelength limit, are optic-like, in contrast to intra-SO ones. The interesting features of these plasmon modes are examined.The author is a Research Fellow of the Australian Research Council. Discussions with P. Vasilopoulos (Concordia, Canada) and M. P. Das (ANU, Australia) are gratefully acknowledged

    Large scale behaviour of 3D continuous phase coexistence models

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    We study a class of three dimensional continuous phase coexistence models, and show that, under different symmetry assumptions on the potential, the large-scale behaviour of such models near a bifurcation point is described by the dynamical Φ3p\Phi^p_3 models for p{2,3,4}p \in \{2,3,4\}. This result is specific to space dimension 33 and does not hold in dimension 22

    Geometric model for the critical-value problem of nucleation phenomena containing the size effect of nucleating agent

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    Nucleation is of great concern in many cases—for example, the production of artificial rainfall and the synthesis of advanced amorphous alloys. Although exact solutions have been well known to both homogeneous nucleation and heterogeneous nucleation occurring on a large flat container wall, yet in more general situations the actual nucleation takes place around finite-sized heterogeneous particles. The understanding of nucleation in such situations requires a more extended model which considers the size effect of nucleating agents. Partially motivated by our research on bulk metallic glasses, we construct such a geometric model. Also we derive an exact solution to the model and discuss briefly its physical implications. A previously presumed relation between the critical energy barrier (Ec) and the volumetric Gibbs free energy of the critical nucleus (Gc)—i.e., Ec=(1/2)Gc—is found to be not true for general cases, although it is correct for the limiting cases

    Linear Vlasov theory of a magnetised, thermally stratified atmosphere

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    The stability of a collisionless, magnetised plasma to local convective disturbances is examined, with a focus on kinetic and finite-Larmor-radius effects. Specific application is made to the outskirts of galaxy clusters, which contain hot and tenuous plasma whose temperature increases in the direction of gravity. At long wavelengths (the "drift-kinetic" limit), we obtain the kinetic version of the magnetothermal instability (MTI) and its Alfv\'enic counterpart (Alfv\'enic MTI), which were previously discovered and analysed using a magnetofluid (i.e. Braginskii) description. At sub-ion-Larmor scales, we discover an overstability driven by the electron temperature gradient of kinetic-Alfv\'en drift waves -- the electron MTI (eMTI) -- whose growth rate is even larger than the standard MTI. At intermediate scales, we find that ion finite-Larmor-radius effects tend to stabilise the plasma. We discuss the physical interpretation of these instabilities in detail, and compare them both with previous work on magnetised convection in a collisional plasma and with temperature-gradient-driven drift-wave instabilities well-known to the magnetic-confinement-fusion community. The implications of having both fluid and kinetic scales simultaneously driven unstable by the same temperature gradient are briefly discussed.Comment: 51 pages, 9 figures; to appear in Journal of Plasma Physic

    Energy levels of a parabolically confined quantum dot in the presence of spin-orbit interaction

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    We present a theoretical study of the energy levels in a parabolically confined quantum dot in the presence of the Rashba spin-orbit interaction (SOI). The features of some low-lying states in various strengths of the SOI are examined at finite magnetic fields. The presence of a magnetic field enhances the possibility of the spin polarization and the SOI leads to different energy dependence on magnetic fields applied. Furthermore, in high magnetic fields, the spectra of low-lying states show basic features of Fock-Darwin levels as well as Landau levels.Comment: 6 pages, 4 figures, accepted by J. Appl. Phy

    The Extended Regularized Dual Averaging Method for Composite Optimization

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    We present a new algorithm, extended regularized dual averaging (XRDA), for solving composite optimization problems, which are a generalization of the regularized dual averaging (RDA) method. The main novelty of the method is that it allows more flexible control of the backward step size. For instance, the backward step size for RDA grows without bound, while XRDA the backward step size can be kept bounded