Precessionless spin transport wire confined in quasi-two-dimensional electron systems

We demonstrate that in an inversion-asymmetric two-dimensional electron system 2DES with both Rashba and Dresselhaus spin-orbit couplings taken into account, certain transport directions on which no spin precession occurs can be found when the injected spin is properly polarized. By analyzing the expectation value of spin with respect to the injected electron state on each space point in the 2DES, we further show that the adjacent regions with technically reachable widths along these directions exhibit nearly conserved spin. Hence a possible application in semiconductor spintronics, namely, precessionless spin transport wire, is proposed.Comment: 3 pages, 4 figures, to be appeared in Journal of Applied Physics, Proceedings of the 50th MMM Conferenc

Local spin density in two-dimensional electron gas with hexagonal boundary

The intrinsic spin-Hall effect in hexagon-shaped samples is investigated. To take into account the spin-orbit couplings and to fit the hexagon edges, we derive the triangular version of the tight-binding model for the linear Rashba [Sov. Phys. Solid State 2, 1109 (1960)] and Dresselhaus [Phys. Rev. 100, 580 (1955)] [001] Hamiltonians, which allow direct application of the Landauer-Keldysh non-equilibrium Green function formalism to calculating the local spin density within the hexagonal sample. Focusing on the out-of-plane component of spin, we obtain the geometry-dependent spin-Hall accumulation patterns, which are sensitive to not only the sample size, the spin-orbit coupling strength, the bias strength, but also the lead configurations. Contrary to the rectangular samples, the accumulation pattern can be very different in our hexagonal samples. Our present work provides a fundamental description of the geometry effect on the intrinsic spin-Hall effect, taking the hexagon as the specific case. Moreover, broken spin-Hall symmetry due to the coexistence of the Rashba and Dresselhaus couplings is also discussed. Upon exchanging the two coupling strengths, the accumulation pattern is reversed, confirming the earlier predicted sign change in spin-Hall conductivity.Comment: 7 pages, 4 figure

Spin precession due to spin-orbit coupling in a two-dimensional electron gas with spin injection via ideal quantum point contact

We present the analytical result of the expectation value of spin resulting from an injected spin polarized electron into a semi-infinitely extended 2DEG plane with [001] growth geometry via ideal quantum point contact. Both the Rashba and Dresselhaus spin-orbit couplings are taken into account. A pictorial interpretation of the spin precession along certain transport directions is given. The spin precession due to the Rashba term is found to be especially interesting since it behaves simply like a windshield wiper which is very different from the ordinary precession while that due to the Dresselhaus term is shown to be crystallographic-direction-dependent. Some crystallographic directions with interesting and handleable behavior of spin precession are found and may imply certain applicability in spintronic devices.Comment: 5 pages, 2 figures, submitted to Phys. Rev.

Social Science Considerations for Integrating Aviation Technology, Emergency Services, and Human Resilience

Unmanned aerial systems (UAS) have a range of innovative applications within the field of disaster management, underscoring the potential to enhance human security by integrating UAS across phases of disasters. This paper highlights important social science challenges that must be addressed to ensure the effective integration of UAS, the complex team of teams that respond to disasters, and the populations affected by disasters. Expanding upon points of intersection between UAS capabilities and disaster management identified in recent research, UAS uses in disaster management and corresponding psychosocial considerations are discussed. Broadly, these considerations focus on the training and development of the disaster management multiteam system (MTS) as well as the well-being of disaster responders and the populations they serve. Considerations for mitigation (resilient team infrastructure), preparation (education and training), response (an integrated MTS; responder health), and recovery (population resilience) phases of disaster management are discussed to pave the way for future research and application in this area

Spin and charge transport in U-shaped one-dimensional channels with spin-orbit couplings

A general form of the Hamiltonian for electrons confined to a curved one-dimensional (1D) channel with spin-orbit coupling (SOC) linear in momentum is rederived and is applied to a U-shaped channel. Discretizing the derived continuous 1D Hamiltonian to a tight-binding version, the Landauer-Keldysh formalism (LKF) for nonequilibrium transport can be applied. Spin transport through the U-channel based on the LKF is compared with previous quantum mechanical approaches. The role of a curvature-induced geometric potential which was previously neglected in the literature of the ring issue is also revisited. Transport regimes between nonadiabatic, corresponding to weak SOC or sharp turn, and adiabatic, corresponding to strong SOC or smooth turn, is discussed. Based on the LKF, interesting charge and spin transport properties are further revealed. For the charge transport, the interplay between the Rashba and the linear Dresselhaus (001) SOCs leads to an additional modulation to the local charge density in the half-ring part of the U-channel, which is shown to originate from the angle-dependent spin-orbit potential. For the spin transport, theoretically predicted eigenstates of the Rashba rings, Dresselhaus rings, and the persistent spin-helix state are numerically tested by the present quantum transport calculation.Comment: 16 pages, 7 figure

Integrating Aviation Technology, Emergency Services, and Human Resilience: Considerations from Social Scientists

Unmanned aerial systems (UAS) have a range of applications within the field of disaster response. This presentation offers a novel framework of psychosocial considerations designed to advance UAS and disaster management integration. Social scientists highlight important challenges to the effective integration of three primary entities: UAS, the team of teams that responds to disasters, and populations affected by disasters. The presentation adopts an emerging theoretical perspective on the intersection between UAS capabilities and disaster phases and extends it by bringing necessary attention to social science issues. Specifically, the framework outlines psychosocial considerations and areas of improvement for preparation (training), response (incident command), and recovery (occupational health; population resilience) phases of disaster management. First, training curricula must involve the full disaster response multiteam system (MTS; i.e., team of teams) in cross-training that builds a shared identity by operationalizing UAS as a component team. Second, disaster response MTSs must establish incident command structures that incorporate UAS into team communication and coordination networks. Third, the implications of stressors unique to UAS operation need to be better understood in the context of existing cyclical effects of work stress on disaster responder performance and well-being. Finally, as crisis communication affects disaster-impacted communities, populations must be able to leverage UAS as a mechanism for, and not a barrier against, recovery from disaster. Across the globe, disasters threaten human security. This presentation provides a necessary interdisciplinary perspective on implementing UAS in disaster management to help the world better prepare for, respond to, recover from, and mitigate disasters

Differential electrophysiological response during rest, self-referential, and non-self-referential tasks in human posteromedial cortex

The electrophysiological basis for higher brain activity during rest and internally directed cognition within the human default mode network (DMN) remains largely unknown. Here we use intracranial recordings in the human posteromedial cortex (PMC), a core node within the DMN, during conditions of cued rest, autobiographical judgments, and arithmetic processing. We found a heterogeneous profile of PMC responses in functional, spatial, and temporal domains. Although the majority of PMC sites showed increased broad gamma band activity (30-180 Hz) during rest, some PMC sites, proximal to the retrosplenial cortex, responded selectively to autobiographical stimuli. However, no site responded to both conditions, even though they were located within the boundaries of the DMN identified with resting-state functional imaging and similarly deactivated during arithmetic processing. These findings, which provide electrophysiological evidence for heterogeneity within the core of the DMN, will have important implications for neuroimaging studies of the DMN