Abstract:A classical spin which is antiferromagnetically coupled to a system of strongly correlated conduction electrons is shown to exhibit unconventional real-time dynamics which cannot be described by Gilbert damping. Depending on the strength of the local Coulomb interaction U, the two main electronic dissipation channels, namely transport of excitations via correlated hopping and via excitations of correlation-induced magnetic moments, become active on largely different time scales. We demonstrate that correlation… Show more
“…The strong dependency on indicates, however, that the current model is not a parameter-free approach. Fortunately, the relevant parameters can be extracted from ab - initio methods 42, 43 .Figure 2Moment of inertia ι as a function of the broadening of the quasiparticle spectral function for bcc Fe (green dotes and lines), fcc Co (red dotes and lines), and fcc Ni (blue dotes and lines) and with two different methods: ( i ) the torque-torque correlation method (filled triangles) and the ( ii ) Greens function method 32 (filled circles). The dotted grey lines indicating the zero level.…”
An essential property of magnetic devices is the relaxation rate in magnetic switching which strongly depends on the energy dissipation. This is described by the Landau-Lifshitz-Gilbert equation and the well known damping parameter, which has been shown to be reproduced from quantum mechanical calculations. Recently the importance of inertia phenomena have been discussed for magnetisation dynamics. This magnetic counterpart to the well-known inertia of Newtonian mechanics, represents a research field that so far has received only limited attention. We present and elaborate here on a theoretical model for calculating the magnetic moment of inertia based on the torque-torque correlation model. Particularly, the method has been applied to bulk itinerant magnets and we show that numerical values are comparable with recent experimental measurements. The theoretical analysis shows that even though the moment of inertia and damping are produced by the spin-orbit coupling, and the expression for them have common features, they are caused by very different electronic structure mechanisms. We propose ways to utilise this in order to tune the inertia experimentally, and to find materials with significant inertia dynamics.
“…The strong dependency on indicates, however, that the current model is not a parameter-free approach. Fortunately, the relevant parameters can be extracted from ab - initio methods 42, 43 .Figure 2Moment of inertia ι as a function of the broadening of the quasiparticle spectral function for bcc Fe (green dotes and lines), fcc Co (red dotes and lines), and fcc Ni (blue dotes and lines) and with two different methods: ( i ) the torque-torque correlation method (filled triangles) and the ( ii ) Greens function method 32 (filled circles). The dotted grey lines indicating the zero level.…”
An essential property of magnetic devices is the relaxation rate in magnetic switching which strongly depends on the energy dissipation. This is described by the Landau-Lifshitz-Gilbert equation and the well known damping parameter, which has been shown to be reproduced from quantum mechanical calculations. Recently the importance of inertia phenomena have been discussed for magnetisation dynamics. This magnetic counterpart to the well-known inertia of Newtonian mechanics, represents a research field that so far has received only limited attention. We present and elaborate here on a theoretical model for calculating the magnetic moment of inertia based on the torque-torque correlation model. Particularly, the method has been applied to bulk itinerant magnets and we show that numerical values are comparable with recent experimental measurements. The theoretical analysis shows that even though the moment of inertia and damping are produced by the spin-orbit coupling, and the expression for them have common features, they are caused by very different electronic structure mechanisms. We propose ways to utilise this in order to tune the inertia experimentally, and to find materials with significant inertia dynamics.
“…Tight-binding spin dynamics.-Most (but not all) features of the transversal quantum dynamics are qualitatively captured by the numerically much cheaper "tightbinding spin dynamics" (TB-SD) [7,12], i.e., quantumclassical hybrid or Ehrenfest dynamics. TB-SD originates from the Hamiltonian Eq.…”
mentioning
confidence: 99%
“…Now, from the numerical evaluation of Eq. (5) it is well known [7,12] that, for fixed S cl. , the damping becomes stronger and the relaxation time shorter with increasing J.…”
mentioning
confidence: 99%
“…To this end we compare numerical results from exact quantum-classical hybrid theory [10,11], i.e., the TB-SD [7,12], with those of exact quantum theory, computed with time-dependent density-matrix renormalp-1 arXiv:1609.05526v1 [cond-mat.str-el] 18 Sep 2016 ization group (t-DMRG) [13,14], for different spin quantum numbers S. It turns out that even for S = 1/2 there is a surprisingly good qualitative agreement of quantum with semiclassical dynamics. However, we also identify a physical phenomenon, namely nutational motion, where remarkable differences are found:…”
-Spin dynamics in the Kondo impurity model, initiated by suddenly switching the direction of a local magnetic field, is studied by means of the time-dependent density-matrix renormalization group. Quantum effects are identified by systematic computations for different spin quantum numbers S and by comparing with tight-binding spin-dynamics theory for the classical-spin Kondo model. We demonstrate that, besides the conventional precessional motion and relaxation, the quantum-spin dynamics shows nutation, similar to a spinning top. Opposed to semiclassical theory, however, the nutation is efficiently damped on an extremely short time scale. The effect is explained in the large-S limit as quantum dephasing of the eigenmodes in an emergent two-spin model that is weakly entangled with the bulk of the system. We argue that, apart from the Kondo effect, the damping of nutational motion is essentially the only characteristics of the quantum nature of the spin. Qualitative agreement between quantum and semiclassical spin dynamics is found down to S = 1/2.Introduction.-The paradigmatic system to study the real-time dynamics of a spin-1/2 coupled to a Fermi sea is the Kondo model [1]. It is mainly considered as a generic model for the famous Kondo effect [2], namely screening of the impurity spin by a mesoscopically large number of electrons in a thermal state with temperature below the Kondo temperature T K ∼ exp(−1/Jρ), where J is the strength of the exchange coupling and ρ is the density of states. The Kondo effect is a true quantum effect which originates from the two-fold spin degeneracy and is protected by time-reversal symmetry. Longitudinal spin dynamics, such as the time-dependent Kondo screening, has been studied recently [3,4] by starting from an initial state with a fully polarized spin, which can be prepared with the help of local magnetic field. The longitudinal dynamics is initiated by suddenly switching off the field.
“…A larger electronelectron interaction has been shown to introduce a slow timescale into the electron dynamics in model condensed-phase problems, associated with exchange. [37][38][39][40] Fig. 5(a) presents the spin-trajectories for an atomic species with a larger U scattering off of a Cu surface for the same scattering conditions studied in Fig.…”
We explore model electron dynamics of an atom scattering off a surface within the time-dependent complete active space self-consistent field (TD-CASSCF) approximation. We focus especially on the scattering of a hydrogen atom and its resulting spin dynamics starting from an initially spin-polarized state. Our results reveal competing electronic time scales that are governed by the electronic structure of the surface as well as the character of the atom. The time scales and nonadiabaticity of the dynamics are reported on by the final spin polarization of the scattered atom, which may be probed in future experiments.
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