Dwell-time distributions in quantum mechanics

Some fundamental and formal aspects of the quantum dwell time are reviewed, examples for free motion and scattering off a potential barrier are provided, as well as extensions of the concept. We also examine the connection between the dwell time of a quantum particle in a region of space and flux-flux correlations at the boundaries, as well as operational approaches and approximations to measure the flux-flux correlation function and thus the second moment of the dwell time, which is shown to be characteristically quantum, and larger than the corresponding classical moment even for freely moving particles.Comment: To appear in "Time in Quantum Mechanics, Vol. 2", Springer 2009, ed. by J. G. Muga, A. Ruschhaupt and A. del Camp

Current-induced domain wall motion : Comparison of STT and SHE

In this work, the current-induced domain wall (DW) motion driven by spin Hall effect (SHE) is theoretically investigated via an atomistic model. The SHE is taken into account in the atomistic model as a Slonczewski torque term. We first consider a bilayer system consisting of a ferromagnetic layer (FM) adjacent to a heavy metal (HM). To study the effect of spin Hall angle and FM thickness on DW motion in perpendicularly magnetized FM, an in-plane current is injected into HM. The results show that the critical current density, DW velocity and DW displacement strongly depend on the spin Hall angle and thickness of FM. To demonstrate the efficiency of SOT, we also study the DW motion driven by spin-transfer torque (STT) in a FM/NM/FM system by injecting a charge current perpendicularly to the plane of the structure. The DW velocity and DW displacement of two cases are compared. At the same current density, it is clearly observed that the DW in the presence of SOT is more easily moved with higher velocity and DW displacement. In addition, the critical current density of SHE driven case is smaller compared with spin torque case. To move the DW with the velocity of 100 m/s, the injected current density required for the STT case could be 10 times as high as the SHE case. The proposed model can be used to optimize all factors for spintronic device design with low power consumption, fast speed and high endurance such as the DW-based devices and the perpendicularly magnetized SOT-MRAM