264,942 research outputs found
Dirac spin gapless semiconductors: Ideal platforms for massless and dissipationless spintronics and new (quantum) anomalous spin Hall effects
It is proposed that the new generation of spintronics should be ideally
massless and dissipationless for the realization of ultra-fast and
ultra-low-power spintronic devices. We demonstrate that the spin-gapless
materials with linear energy dispersion are unique materials that can realize
these massless and dissipationless states. Furthermore, we propose four new
types of spin Hall effects which consist of spin accumulation of equal numbers
of electrons and holes having the same or opposite spin polarization at the
sample edge in Hall effect measurements, but with vanishing Hall voltage. These
new Hall effects can be classified as (quantum) anomalous spin Hall effects.
The physics for massless and dissipationless spintronics and the new spin Hall
effects are presented for spin-gapless semiconductors with either linear or
parabolic dispersion. New possible candidates for Dirac-type or parabolic type
spin-gapless semiconductors are demonstrated in ferromagnetic monolayers of
simple oxides with either honeycomb or square lattices.Comment: 5 pages, 7 figue
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Role of initial magnetic disorder: A time-dependent ab initio study of ultrafast demagnetization mechanisms.
Despite more than 20 years of development, the underlying physics of the laser-induced demagnetization process is still debated. We present a fast, real-time time-dependent density functional theory (rt-TDDFT) algorithm together with the phenomenological atomic Landau-Lifshitz-Gilbert model to investigate this problem. Our Hamiltonian considers noncollinear magnetic moment, spin-orbit coupling (SOC), electron-electron, electron-phonon, and electron-light interactions. The algorithm for time evolution achieves hundreds of times of speedup enabling calculation of large systems. Our simulations yield a demagnetization rate similar to experiments. We found that (i) the angular momentum flow from light to the system is not essential and the spin Zeeman effect is negligible. (ii) The phonon can play a role but is not essential. (iii) The initial spin disorder and the self-consistent update of the electron-electron interaction play dominant roles and enhance the demagnetization to the experimentally observed rate. The spin disorder connects the electronic structure theory with the phenomenological three-temperature model
Quantum Transport Calculations Using Periodic Boundary Conditions
An efficient new method is presented to calculate the quantum transports
using periodic boundary conditions. This method allows the use of conventional
ground state ab initio programs without big changes. The computational effort
is only a few times of a normal ground state calculation, thus it makes
accurate quantum transport calculations for large systems possible.Comment: 9 pages, 6 figure
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