115 research outputs found
Effect of iron thicknesses on spin transport in a Fe/Au bilayer system
This paper is concerned with a theoretical analysis of the behavior of
optically excited spin currents in bilayer and multilayer systems of
ferromagnetic and normal metals. As the propagation, control and manipulation
of the spin currents created in ferromagnets by femtosecond optical pulses is
of particular interest, we examine the influence of different thicknesses of
the constituent layers for the case of electrons excited several electronvolts
above the Fermi level. Using a Monte-Carlo simulation framework for such highly
excited electrons, we first examine the spatio-temporal characteristics of the
spin current density driven in a Fe layer, where the absorption profile of the
light pulses plays an important role. Further, we examine how the combination
of light absorption profiles, spin-dependent transmission probabilities, and
iron layer thicknesses affect spin current density in a Fe/Au bilayer system.
For high-energy electrons studied here, the interface and secondary electron
generation have a small influence on spin transport in the bilayer system.
However, we find that spin injection from one layer to another is most
effective within a certain range of iron layer thicknesses
Direct evidence for efficient ultrafast charge separation in epitaxial WS/graphene heterostructure
We use time- and angle-resolved photoemission spectroscopy (tr-ARPES) to
investigate ultrafast charge transfer in an epitaxial heterostructure made of
monolayer WS and graphene. This heterostructure combines the benefits of a
direct gap semiconductor with strong spin-orbit coupling and strong
light-matter interaction with those of a semimetal hosting massless carriers
with extremely high mobility and long spin lifetimes. We find that, after
photoexcitation at resonance to the A-exciton in WS, the photoexcited holes
rapidly transfer into the graphene layer while the photoexcited electrons
remain in the WS layer. The resulting charge transfer state is found to
have a lifetime of \,ps. We attribute our findings to differences in
scattering phase space caused by the relative alignment of WS and graphene
bands as revealed by high resolution ARPES. In combination with spin-selective
excitation using circularly polarized light the investigated WS/graphene
heterostructure might provide a new platform for efficient optical spin
injection into graphene.Comment: 28 pages, 14 figure
Direct evidence for efficient ultrafast charge separation in epitaxial WS<sub>2</sub>/graphene heterostructures
We use time- and angle-resolved photoemission spectroscopy (tr-ARPES) to investigate ultrafast charge transfer in an epitaxial heterostructure made of monolayer WS2 and graphene. This heterostructure combines the benefits of a direct-gap semiconductor with strong spin-orbit coupling and strong light-matter interaction with those of a semimetal hosting massless carriers with extremely high mobility and long spin lifetimes. We find that, after photoexcitation at resonance to the A-exciton in WS2, the photoexcited holes rapidly transfer into the graphene layer while the photoexcited electrons remain in the WS2 layer. The resulting charge-separated transient state is found to have a lifetime of ∼1 ps. We attribute our findings to differences in scattering phase space caused by the relative alignment of WS2 and graphene bands as revealed by high-resolution ARPES. In combination with spin-selective optical excitation, the investigated WS2/graphene heterostructure might provide a platform for efficient optical spin injection into graphene
Structure and electronic properties of the () SnAu/Au(111) surface alloy
We have investigated the atomic and electronic structure of the
() SnAu/Au(111) surface alloy. Low
energy electron diffraction and scanning tunneling microscopy measurements show
that the native herringbone reconstruction of bare Au(111) surface remains
intact after formation of a long range ordered () SnAu2/Au(111) surface alloy. Angle-resolved
photoemission and two-photon photoemission spectroscopy techniques reveal
Rashba-type spin-split bands in the occupied valence band with comparable
momentum space splitting as observed for the Au(111) surface state, but with a
hole-like parabolic dispersion. Our experimental findings are compared with
density functional theory (DFT) calculation that fully support our experimental
findings. Taking advantage of the good agreement between our DFT calculations
and the experimental results, we are able to extract that the occupied Sn-Au
hybrid band is of (s, d)-orbital character while the unoccupied Sn-Au hybrid
bands are of (p, d)-orbital character. Hence, we can conclude that the
Rashba-type spin splitting of the hole-like Sn-Au hybrid surface state is
caused by the significant mixing of Au d- to Sn s-states in conjunction with
the strong atomic spin-orbit coupling of Au, i.e., of the substrate.Comment: Copyright:
https://journals.aps.org/authors/transfer-of-copyright-agreement; All
copyrights by AP
Ultrafast optically induced spin transfer in ferromagnetic alloys
The vision of using light to manipulate electronic and spin excitations in materials on their fundamental time and length scales requires new approaches in experiment and theory to observe and understand these excitations. The ultimate speed limit for all-optical manipulation requires control schemes for which the electronic or magnetic subsystems of the materials are coherently manipulated on the time scale of the laser excitation pulse. In our work, we provide experimental evidence of such a direct, ultrafast, and coherent spin transfer between two magnetic subsystems of an alloy of Fe and Ni. Our experimental findings are fully supported by time-dependent density functional theory simulations and, hence, suggest the possibility of coherently controlling spin dynamics on subfemtosecond time scales, i.e., the birth of the research area of attomagnetism
Ultrafast optically induced spin transfer in ferromagnetic alloys
The vision of using light to manipulate electronic and spin excitations in materials on their fundamental time and length scales requires new approaches in experiment and theory to observe and understand these excitations. The ultimate speed limit for all-optical manipulation requires control schemes for which the electronic or magnetic subsystems of the materials are coherently manipulated on the time scale of the laser excitation pulse. In our work, we provide experimental evidence of such a direct, ultrafast, and coherent spin transfer between two magnetic subsystems of an alloy of Fe and Ni. Our experimental findings are fully supported by time-dependent density functional theory simulations and, hence, suggest the possibility of coherently controlling spin dynamics on subfemtosecond time scales, i.e., the birth of the research area of attomagnetism
A case study for the formation of stanene on a metal surface
The discovery and realization of graphene as an ideal two-dimensional (2D) material has triggered extensive efforts to create similar 2D materials with exciting spin-dependent properties. Here, we report on a novel Sn 2D superstructure on Au(111) that shows similarities and differences to the expected electronic features of ideal stanene. Using spin- and angle-resolved photoemission spectroscopy, we find that a particular Sn/Au superstructure reveals a linearly dispersing band centered at the Γ-point and below the Fermi level with antiparallel spin polarization and a Fermi velocity of vF ≈ 1×106 m/s, the same value as for graphene. We attribute the origin of the band structure to the hybridization between the Sn and the Au orbitals at the 2D Sn-Au interface. Considering that free-standing stanene simply cannot exist, our investigated structure is an important step towards the search of useful stanene-like overstructures for future technological applications
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