Spin transistor operation driven by the Rashba spin-orbit coupling in the gated nanowire

The theoretical description has been proposed for the operation of the spin transistor in the gate-controlled InAs nanowire. The calculated current-voltage characteristics show that the current flowing from the source (spin injector) to the drain (spin detector) oscillates as a function of the gate voltage, which results from the precession of the electron spin caused by the Rashba spin-orbit interaction in the vicinity of the gate. We have studied two operation modes of the spin transistor: (A) the ideal operation mode with the full spin polarization of electrons in the contacts, the zero temperature, and the single conduction channel corresponding to the lowest-energy subband of the transverse motion and (B) the more realistic operation mode with the partial spin polarization of the electrons in the contacts, the room temperature, and the conduction via many transverse subbands taken into account. For mode (A) the spin-polarized current can be switched on/off by the suitable tuning of the gate voltage, for mode (B) the current also exhibits the pronounced oscillations but with no-zero minimal values. The computational results obtained for mode (B) have been compared with the recent experimental data and a good agreement has been found.Comment: 8 pages, 11 figure

Spin filter effect at room temperature in GaN/GaMnN ferromagnetic resonant tunneling diode

We have investigated the spin current polarization without the external magnetic field in the resonant tunneling diode with the emitter and quantum well layers made from the ferromagnetic GaMnN. For this purpose we have applied the self-consistent Wigner-Poisson method and studied the spin-polarizing effect of the parallel and antiparallel alignment of the magnetization in the ferromagnetic layers. The results of our calculations show that the antiparallel magnetization is much more advantageous for the spin filter operation and leads to the full spin current polarization at low temperatures and 35 % spin polarization of the current at room temperature.Comment: 4 pages, 5 figure

Hamiltonian Dynamics and the Phase Transition of the XY Model

A Hamiltonian dynamics is defined for the XY model by adding a kinetic energy term. Thermodynamical properties (total energy, magnetization, vorticity) derived from microcanonical simulations of this model are found to be in agreement with canonical Monte-Carlo results in the explored temperature region. The behavior of the magnetization and the energy as functions of the temperature are thoroughly investigated, taking into account finite size effects. By representing the spin field as a superposition of random phased waves, we derive a nonlinear dispersion relation whose solutions allow the computation of thermodynamical quantities, which agree quantitatively with those obtained in numerical experiments, up to temperatures close to the transition. At low temperatures the propagation of phonons is the dominant phenomenon, while above the phase transition the system splits into ordered domains separated by interfaces populated by topological defects. In the high temperature phase, spins rotate, and an analogy with an Ising-like system can be established, leading to a theoretical prediction of the critical temperature $T_{KT}\approx 0.855$.Comment: 10 figures, Revte

Multifractal analysis of the electronic states in the Fibonacci superlattice under weak electric fields

Influence of the weak electric field on the electronic structure of the Fibonacci superlattice is considered. The electric field produces a nonlinear dynamics of the energy spectrum of the aperiodic superlattice. Mechanism of the nonlinearity is explained in terms of energy levels anticrossings. The multifractal formalism is applied to investigate the effect of weak electric field on the statistical properties of electronic eigenfunctions. It is shown that the applied electric field does not remove the multifractal character of the electronic eigenfunctions, and that the singularity spectrum remains non-parabolic, however with a modified shape. Changes of the distances between energy levels of neighbouring eigenstates lead to the changes of the inverse participation ratio of the corresponding eigenfunctions in the weak electric field. It is demonstrated, that the local minima of the inverse participation ratio in the vicinity of the anticrossings correspond to discontinuity of the first derivative of the difference between marginal values of the singularity strength. Analysis of the generalized dimension as a function of the electric field shows that the electric field correlates spatial fluctuations of the neighbouring electronic eigenfunction amplitudes in the vicinity of anticrossings, and the nonlinear character of the scaling exponent confirms multifractality of the corresponding electronic eigenfunctions.Comment: 10 pages, 9 figure

Technical Breakthrough Points and Opportunities in Transition Scenarios for Hydrogen as Vehicular Fuel

This technical reports is about investigating a generic case of hydrogen production/delivery/dispensing pathway evolution in a large population city, assuming that hydrogen fuel cell electric vehicles (FCEV) will capture a major share of the vehicle market by the year 2050. The range of questions that are considered includes (i) what is the typical succession of hydrogen pathways that minimizes consumer cost? (ii) what are the major factors that will likely influence this sequence

Niche Construction and the Evolution of Leadership

We use the concept of niche construction - the process whereby individuals, through their activities, interactions, and choices, modify their own and each other\u27s environments - as an example of how biological evolution and cultural evolution interacted to form an integrative foundation of modern organizational leadership. Resulting adaptations are formal structures that facilitate coordination of large, postagrarian organizational networks. We provide three propositions explaining how leadership processes evolve over time within and between organizations in order to solve specific coordination problems. We highlight the balancing act between self-interests and group interests in organizations and show how leadership must regulate this tension to maintain organizational fitness. We conclude with predictions about the future evolution of leadership in organizations

Reading the face of a leader: women with low facial masculinity are perceived as competitive

In competitive settings, people prefer leaders with masculine faces. But is facial masculinity a trait that is similarly desired in men and women leaders? Across three studies, we discovered that people indeed prefer men and women leaders who have faces with masculine traits. But surprisingly, we find that people also prefer women with low facial masculinity as leaders in competitive contexts (Study 1). Our findings indicate that low facial masculinity in women, but not in men is perceived to indicate competitiveness (Study 2). Thus, in contrast to men, women leaders who rate high in facial masculinity as well as those low in facial masculinity are both selected as leaders in competitive contexts. Indeed, among CEOs of S&P 500 companies, we find a greater range of facial masculinity amongwomen CEOs than among men CEOs (Study 3). Our results suggest that traits of facial masculinity in men and women are interpreted differently. Low facial masculinity in women is linked to competitiveness and not only to cooperativeness as suggested by prior research