409 research outputs found
Electric control of optically-induced magnetization dynamics in a van der Waals ferromagnetic semiconductor
Electric control of magnetization dynamics in two-dimensional (2D) magnetic
materials is an essential step for the development of novel spintronic
nanodevices. Electrostatic gating has been shown to greatly affect the static
magnetic properties of some van der Waals magnets, but the control over their
magnetization dynamics is still largely unexplored. Here we show that the
optically-induced magnetization dynamics in the van der Waals ferromagnet
CrGeTe can be effectively controlled by electrostatic gates, with a
one order of magnitude change in the precession amplitude and over 10% change
in the internal effective field. In contrast to the purely thermally-induced
mechanisms previously reported for 2D magnets, we find that coherent
opto-magnetic phenomena play a major role in the excitation of magnetization
dynamics in CrGeTe. Our work sets the first steps towards electric
control over the magnetization dynamics in 2D ferromagnetic semiconductors,
demonstrating their potential for applications in ultrafast opto-magnonic
devices
Magnetic field control of light-induced spin accumulation in monolayer MoSe
Semiconductor transition metal dichalcogenides (TMDs) have equivalent
dynamics for their two spin/valley species. This arises from their
energy-degenerated spin states, connected via time-reversal symmetry. When an
out-of-plane magnetic field is applied, time-reversal symmetry is broken and
the energies of the spin-polarized bands shift, resulting in different bandgaps
and dynamics in the K and K valleys. Here, we use time-resolved Kerr
rotation to study the magnetic field dependence of the spin dynamics in
monolayer MoSe. We show that the magnetic field can control the
light-induced spin accumulation of the two valley states, with a small effect
on the recombination lifetimes. We unveil that the magnetic field-dependent
spin accumulation is in agreement with hole spin dynamics at the longer
timescales, indicating that the electron spins have faster relaxation rates. We
propose a rate equation model that suggests that lifting the energy-degeneracy
of the valleys induces an ultrafast spin-flip toward the stabilization of the
valley with the higher valence band energy. Our results provide an experimental
insight into the ultrafast charge and spin dynamics in TMDs and a way to
control it, which will be useful for the development of new spintronic and
valleytronic applications.Comment: 6 pages, 4 figure
Charge dynamics in the 2D/3D semiconductor heterostructure WSe/GaAs
Understanding the relaxation and recombination processes of excited states in two-dimensional (2D)/three-dimensional (3D) semiconductor heterojunctions is essential for developing efficient optical and (opto)electronic devices which integrate new 2D materials with more conventional 3D ones. In this work, we unveil the carrier dynamics and charge transfer in a monolayer of WSe on a GaAs substrate. We use time-resolved differential reflectivity to study the charge relaxation processes involved in the junction and how they change when compared to an electrically decoupled heterostructure, WSe/hBN/GaAs. We observe that the monolayer in direct contact with the GaAs substrate presents longer optically-excited carrier lifetimes (3.5 ns) when compared with the hBN-isolated region (1 ns), consistent with a strong reduction of radiative decay and a fast charge transfer of a single polarity. Through low-temperature measurements, we find evidence of a type-II band alignment for this heterostructure with an exciton dissociation that accumulates electrons in the GaAs and holes in the WSe. The type-II band alignment and fast photo-excited carrier dissociation shown here indicate that WSe/GaAs is a promising junction for new photovoltaic and other optoelectronic devices, making use of the best properties of new (2D) and conventional (3D) semiconductors
Charge dynamics in the 2D/3D semiconductor heterostructure WSe/GaAs
Understanding the relaxation and recombination processes of excited states in two-dimensional (2D)/three-dimensional (3D) semiconductor heterojunctions is essential for developing efficient optical and (opto)electronic devices which integrate new 2D materials with more conventional 3D ones. In this work, we unveil the carrier dynamics and charge transfer in a monolayer of WSe on a GaAs substrate. We use time-resolved differential reflectivity to study the charge relaxation processes involved in the junction and how they change when compared to an electrically decoupled heterostructure, WSe/hBN/GaAs. We observe that the monolayer in direct contact with the GaAs substrate presents longer optically-excited carrier lifetimes (3.5 ns) when compared with the hBN-isolated region (1 ns), consistent with a strong reduction of radiative decay and a fast charge transfer of a single polarity. Through low-temperature measurements, we find evidence of a type-II band alignment for this heterostructure with an exciton dissociation that accumulates electrons in the GaAs and holes in the WSe. The type-II band alignment and fast photo-excited carrier dissociation shown here indicate that WSe/GaAs is a promising junction for new photovoltaic and other optoelectronic devices, making use of the best properties of new (2D) and conventional (3D) semiconductors
Charge dynamics in the 2D/3D semiconductor heterostructure WSe/GaAs
Understanding the relaxation and recombination processes of excited states in two-dimensional (2D)/three-dimensional (3D) semiconductor heterojunctions is essential for developing efficient optical and (opto)electronic devices which integrate new 2D materials with more conventional 3D ones. In this work, we unveil the carrier dynamics and charge transfer in a monolayer of WSe on a GaAs substrate. We use time-resolved differential reflectivity to study the charge relaxation processes involved in the junction and how they change when compared to an electrically decoupled heterostructure, WSe/hBN/GaAs. We observe that the monolayer in direct contact with the GaAs substrate presents longer optically-excited carrier lifetimes (3.5 ns) when compared with the hBN-isolated region (1 ns), consistent with a strong reduction of radiative decay and a fast charge transfer of a single polarity. Through low-temperature measurements, we find evidence of a type-II band alignment for this heterostructure with an exciton dissociation that accumulates electrons in the GaAs and holes in the WSe. The type-II band alignment and fast photo-excited carrier dissociation shown here indicate that WSe/GaAs is a promising junction for new photovoltaic and other optoelectronic devices, making use of the best properties of new (2D) and conventional (3D) semiconductors
Charge dynamics in the 2D/3D semiconductor heterostructure WSe/GaAs
Understanding the relaxation and recombination processes of excited states in two-dimensional (2D)/three-dimensional (3D) semiconductor heterojunctions is essential for developing efficient optical and (opto)electronic devices which integrate new 2D materials with more conventional 3D ones. In this work, we unveil the carrier dynamics and charge transfer in a monolayer of WSe on a GaAs substrate. We use time-resolved differential reflectivity to study the charge relaxation processes involved in the junction and how they change when compared to an electrically decoupled heterostructure, WSe/hBN/GaAs. We observe that the monolayer in direct contact with the GaAs substrate presents longer optically-excited carrier lifetimes (3.5 ns) when compared with the hBN-isolated region (1 ns), consistent with a strong reduction of radiative decay and a fast charge transfer of a single polarity. Through low-temperature measurements, we find evidence of a type-II band alignment for this heterostructure with an exciton dissociation that accumulates electrons in the GaAs and holes in the WSe. The type-II band alignment and fast photo-excited carrier dissociation shown here indicate that WSe/GaAs is a promising junction for new photovoltaic and other optoelectronic devices, making use of the best properties of new (2D) and conventional (3D) semiconductors
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