19 research outputs found
Ultrafast modulation of the chemical potential in BaFeAs by coherent phonons
Time- and angle-resolved extreme ultraviolet photoemission spectroscopy is
used to study the electronic structure dynamics in BaFeAs around the
high-symmetry points and . A global oscillation of the Fermi level
at the frequency of the (As) phonon mode is observed. It is argued that
this behavior reflects a modulation of the effective chemical potential in the
photoexcited surface region that arises from the high sensitivity of the band
structure near the Fermi level to the phonon mode combined with a low
electron diffusivity perpendicular to the layers. The results establish a novel
way to tune the electronic properties of iron pnictides: coherent control of
the effective chemical potential. The results further suggest that the
equilibration time for the effective chemical potential needs to be considered
in the ultrafast electronic structure dynamics of materials with weak
interlayer coupling.Comment: 6 pages, 3 figure
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Ultrafast modulation of the chemical potential in BaFe2As2 by coherent phonons
Time- and angle-resolved extreme ultraviolet photoemission spectroscopy is used to study the electronic structure dynamics in BaFe2As2 around the high-symmetry points Γ and M. A global oscillation of the Fermi level at the frequency of the A1g(As) phonon mode is observed. It is argued that this behavior reflects a modulation of the effective chemical potential in the photoexcited surface region that arises from the high sensitivity of the band structure near the Fermi level to the A1g(As) phonon mode combined with a low electron diffusivity perpendicular to the layers. The results establish a novel way to tune the electronic properties of iron pnictides: coherent control of the effective chemical potential. The results further suggest that the equilibration time for the effective chemical potential needs to be considered in the ultrafast electronic structure dynamics of materials with weak interlayer coupling. © 2014 American Physical Society
Additive Manufacturing Under Lunar Gravity and Microgravity
Mankind is setting to colonize space, for which the manufacturing of habitats, tools, spare parts and other infrastructure is required. Commercial manufacturing processes are already well engineered under standard conditions on Earth, which means under Earth’s gravity and atmosphere. Based on the literature review, additive manufacturing under lunar and other space gravitational conditions have only been researched to a very limited extent. Especially, additive manufacturing offers many advantages, as it can produce complex structures while saving resources. The materials used do not have to be taken along on the mission, they can even be mined and processed on-site. The Einstein-Elevator offers a unique test environment for experiments under different gravitational conditions. Laser experiments on selectively melting regolith simulant are successfully conducted under lunar gravity and microgravity. The created samples are characterized in terms of their geometry, mass and porosity. These experiments are the first additive manufacturing tests under lunar gravity worldwide
Tracking the relaxation pathway of photo-excited electrons in 1
The ultrafast dynamics of excited electrons in 1T-TiSe2 after absorption of a 390 nm light pulse is probed by time- and angle-resolved photoemission spectroscopy using femtosecond XUV pulses. It is demonstrated that the experimental approach can provide a comprehensive view of hot carrier motion in momentum space during relaxation back to equilibrium. This capability opens a new avenue in the investigation of energy dissipation processes in solids after intense optical excitation
Ultrafast Melting of a Charge-Density Wave in the Mott Insulator
Femtosecond time-resolved core-level photoemission spectroscopy with a
free-electron laser is used to measure the atomic-site specific charge-order
dynamics in the charge-density-wave/Mott insulator 1T-TaS2. After strong
photoexcitation, a prompt loss of charge order and subsequent fast
equilibration dynamics of the electron-lattice system are observed. On the time
scale of electron-phonon thermalization, about 1 ps, the system is driven
across a phase transition from a long-range charge ordered state to a
quasi-equilibrium state with domain-like short-range charge and lattice order.
The experiment opens the way to study the nonequilibrium dynamics of condensed
matter systems with full elemental, chemical, and atomic site selectivity
A direct view onto the carrier dynamics in graphite at the H point
The photophysics of charge transfer between the electron donating, surface adsorbed D149 dye and an electron accepting porous ZnO film was investigated by measuring excited state lifetimes using ultrafast transient absorption spectroscopy. We systematically varioed the production scheme of the sample including the electrolyte
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Ultrafast modulation of the chemical potential in BaFe2As2 by coherent phonons
Time- and angle-resolved extreme ultraviolet photoemission spectroscopy is used to study the electronic structure dynamics in BaFe2As2 around the high-symmetry points Γ and M. A global oscillation of the Fermi level at the frequency of the A1g(As) phonon mode is observed. It is argued that this behavior reflects a modulation of the effective chemical potential in the photoexcited surface region that arises from the high sensitivity of the band structure near the Fermi level to the A1g(As) phonon mode combined with a low electron diffusivity perpendicular to the layers. The results establish a novel way to tune the electronic properties of iron pnictides: coherent control of the effective chemical potential. The results further suggest that the equilibration time for the effective chemical potential needs to be considered in the ultrafast electronic structure dynamics of materials with weak interlayer coupling. © 2014 American Physical Society