188 research outputs found
Spin-torque driven magnetic vortex self-oscillations in perpendicular magnetic fields
We have employed complete micromagnetic simulations to analyze dc current
driven self-oscillations of a vortex core in a spin-valve nanopillar in a
perpendicular field by including the coupled effect of the spin-torque and the
magnetostatic field computed self-consistently for the entire spin-valve. The
vortex in the thicker nanomagnet moves along a quasi-elliptical trajectory that
expands with applied current, resulting in blue-shifting of the frequency,
while the magnetization of the thinner nanomagnet is non-uniform due to the
bias current. The simulations explain the experimental magnetoresistance-field
hysteresis loop and yield good agreement with the measured frequency vs.
current behavior of this spin-torque vortex oscillator.Comment: 10 pages, 3 figures, to be appear on AP
Spin transport in ferromagnet-InSb nanowire quantum devices
Signatures of Majorana zero modes (MZMs), which are the building blocks for
fault-tolerant topological quantum computing, have been observed in
semiconductor nanowires (NW) with strong spin-orbital-interaction (SOI), such
as InSb and InAs NWs with proximity-induced superconductivity. Realizing
topological superconductivity and MZMs in this most widely-studied platform
also requires eliminating spin degeneracy, which is realized by applying a
magnetic field to induce a helical gap. However, the applied field can
adversely impact the induced superconducting state in the NWs and also places
geometric restrictions on the device, which can affect scaling of future
MZM-based quantum registers. These challenges could be circumvented by
integrating magnetic elements with the NWs. With this motivation, in this work
we report the first experimental investigation of spin transport across InSb
NWs, which are enabled by devices with ferromagnetic (FM) contacts. We observe
signatures of spin polarization and spin-dependent transport in the
quasi-one-dimensional ballistic regime. Moreover, we show that electrostatic
gating tunes the observed magnetic signal and also reveals a transport regime
where the device acts as a spin filter. These results open an avenue towards
developing MZM devices in which spin degeneracy is lifted locally, without the
need of an applied magnetic field. They also provide a path for realizing
spin-based devices that leverage spin-orbital states in quantum wires.Comment: 30 pages, 12 figure
Analytical approximations to the core radius and energy of magnetic vortex in thin ferromagnetic disks
The energy of magnetic vortex core and its equilibrium radius in thin
circular cylinder were first presented by N.A. Usov and S.E. Peschany in 1994.
Yet, the magnetostatic function, entering the energy expression, is hard to
evaluate and approximate. In this communication precise and explicit analytical
approximations to this function (as well as equilibrium vortex core radius and
energy) are derived in terms of elementary functions. Also, several simplifying
approximations to the magnetic Hamiltonian and their impact on theoretical
stability of magnetic vortex state are discussed.Comment: 5 pages, 1 figur
Spectroscopy of spin-orbit quantum bits in indium antimonide nanowires
Double quantum dot in the few-electron regime is achieved using local gating
in an InSb nanowire. The spectrum of two-electron eigenstates is investigated
using electric dipole spin resonance. Singlet-triplet level repulsion caused by
spin-orbit interaction is observed. The size and the anisotropy of
singlet-triplet repulsion are used to determine the magnitude and the
orientation of the spin-orbit effective field in an InSb nanowire double dot.
The obtained results are confirmed using spin blockade leakage current
anisotropy and transport spectroscopy of individual quantum dots.Comment: 5 pages, supplementary material available at
http://link.aps.org/supplemental/10.1103/PhysRevLett.108.16680
Suppression of Zeeman gradients by nuclear polarization in double quantum dots
We use electric dipole spin resonance to measure dynamic nuclear polarization
in InAs nanowire quantum dots. The resonance shifts in frequency when the
system transitions between metastable high and low current states, indicating
the presence of nuclear polarization. We propose that the low and the high
current states correspond to different total Zeeman energy gradients between
the two quantum dots. In the low current state, dynamic nuclear polarization
efficiently compensates the Zeeman gradient due to the -factor mismatch,
resulting in a suppressed total Zeeman gradient. We present a theoretical model
of electron-nuclear feedback that demonstrates a fixed point in nuclear
polarization for nearly equal Zeeman splittings in the two dots and predicts a
narrowed hyperfine gradient distribution
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