9 research outputs found
Green's function formalism for spin transport in metal-insulator-metal heterostructures
We develop a Green's function formalism for spin transport through
heterostructures that contain metallic leads and insulating ferromagnets. While
this formalism in principle allows for the inclusion of various magnonic
interactions, we focus on Gilbert damping. As an application, we consider
ballistic spin transport by exchange magnons in a metal-insulator-metal
heterostructure with and without disorder. For the former case, we show that
the interplay between disorder and Gilbert damping leads to spin current
fluctuations. For the case without disorder, we obtain the dependence of the
transmitted spin current on the thickness of the ferromagnet. Moreover, we show
that the results of the Green's function formalism agree in the clean and
continuum limit with those obtained from the linearized stochastic
Landau-Lifshitz-Gilbert equation. The developed Green's function formalism is a
natural starting point for numerical studies of magnon transport in
heterostructures that contain normal metals and magnetic insulators.Comment: 13 pages, 8 figure
Large scale spatio-temporal behaviour in surface growth
This paper presents new findings concerning the dynamics of the slow height variations in surfaces produced by the two-dimensional isotropic Kuramoto-Sivashinsky equation with an additional nonlinear term. In addition to the disordered cellular patterns of specific size evident at small scales, slow height variations of scale-free character become increasingly evident when the system size is increased. This paper focuses on the parameter range in which the kinetic roughening with eventual saturation in surface roughness and coarseness is obtained, and the statistical and dynamical properties of surfaces in the long-time stationary regime are investigated. The resulting long-range scaling properties of the saturated surface roughness consistent with the power-law shape of the surface spectrum at small wave numbers are obtained in a wider parameter range than previously reported. The temporal properties of these long-range height variations are investigated by analysing the time series of surface roughness fluctuations. The resulting power-spectral densities can be expressed as a generalized Lorentzian whose cut-off frequency varies with system size. The dependence of this lower cut-off frequency on the smallest wave number connects spatial and temporal properties and gives new insight into the surface evolution on large scales
Superfluidity and spin superfluidity in spinor Bose gases
\u3cp\u3eWe show that spinor Bose gases subject to a quadratic Zeeman effect exhibit coexisting superfluidity and spin superfluidity, and study the interplay between these two distinct types of superfluidity. To illustrate that the basic principles governing these two types of superfluidity are the same, we describe the magnetization and particle-density dynamics in a single hydrodynamic framework. In this description spin and mass supercurrents are driven by their respective chemical potential gradients. As an application, we propose an experimentally accessible stationary state, where the two types of supercurrents counterflow and cancel each other, thus resulting in no mass transport. Furthermore, we propose a straightforward setup to probe spin superfluidity by measuring the in-plane magnetization angle of the whole cloud of atoms. We verify the robustness of these findings by evaluating the four-magnon collision time, and find that the time scale for coherent (superfluid) dynamics is separated from that of the slower incoherent dynamics by one order of magnitude. Comparing the atom and magnon kinetics reveals that while the former can be hydrodynamic, the latter is typically collisionless under most experimental conditions. This implies that, while our zero-temperature hydrodynamic equations are a valid description of spin transport in Bose gases, a hydrodynamic description that treats both mass and spin transport at finite temperatures may not be readily feasible.\u3c/p\u3
Large scale spatio-temporal behaviour in surface growth
This paper presents new findings concerning the dynamics of the slow height variations in surfaces produced by the two-dimensional isotropic Kuramoto-Sivashinsky equation with an additional nonlinear term. In addition to the disordered cellular patterns of specific size evident at small scales, slow height variations of scale-free character become increasingly evident when the system size is increased. This paper focuses on the parameter range in which the kinetic roughening with eventual saturation in surface roughness and coarseness is obtained, and the statistical and dynamical properties of surfaces in the long-time stationary regime are investigated. The resulting long-range scaling properties of the saturated surface roughness consistent with the power-law shape of the surface spectrum at small wave numbers are obtained in a wider parameter range than previously reported. The temporal properties of these long-range height variations are investigated by analysing the time series of surface roughness fluctuations. The resulting power-spectral densities can be expressed as a generalized Lorentzian whose cut-off frequency varies with system size. The dependence of this lower cut-off frequency on the smallest wave number connects spatial and temporal properties and gives new insight into the surface evolution on large scales
Spin hall mode in a trapped thermal rashba gas
\u3cp\u3eWe theoretically investigate a two-dimensional harmonically trapped gas of identical atoms with Rashba spin-orbit coupling and no interatomic interactions. In analogy with the spin Hall effect in uniform space, the gas exhibits a spin Hall mode. In particular, in response to a displacement of the center of mass of the system, spin-dipole moment oscillations occur. We determine the properties of these oscillations exactly and find that their amplitude strongly depends on the spin-orbit-coupling strength and the quantum statistics of the particles.\u3c/p\u3
CATARACTS: Challenge on automatic tool annotation for cataRACT surgery
Surgical tool detection is attracting increasing attention from the medical image analysis community. The goal generally is not to precisely locate
tools in images, but rather to indicate which tools are being used by the surgeon at each instant. The main motivation for annotating tool usage is
to design e_cient solutions for surgical workflow analysis, with potential applications in report generation, surgical training and even real-time
decision support. Most existing tool annotation algorithms focus on laparoscopic surgeries. However, with 19 million interventions per year, the
most common surgical procedure in the world is cataract surgery. The CATARACTS challenge was organized in 2017 to evaluate tool annotation
algorithms in the specific context of cataract surgery. It relies on more than nine hours of videos, from 50 cataract surgeries, in which the
presence of 21 surgical tools was manually annotated by two experts. With 14 participating teams, this challenge can be considered a success.
As might be expected, the submitted solutions are based on deep learning. This paper thoroughly evaluates these solutions: in particular, the
quality of their annotations are compared to that of human interpretations. Next, lessons learnt from the di_erential analysis of these solutions
are discussed. We expect that they will guide the design of e_cient surgery monitoring tools in the near future