2,135 research outputs found
Suppression of electron scattering resonances in graphene by quantum dots
Transmission of low-energetic electrons through two-dimensional materials
leads to unique scattering resonances. These resonances contribute to
photoemission from occupied bands where they appear as strongly dispersive
features of suppressed photoelectron intensity. Using angle-resolved
photoemission we have systematically studied scattering resonances in epitaxial
graphene grown on the chemically differing substrates Ir(111), Bi/Ir, Ni(111)
as well as in graphene/Ir(111) nanopatterned with a superlattice of uniform Ir
quantum dots. While the strength of the chemical interaction with the substrate
has almost no effect on the dispersion of the scattering resonances, their
energy can be controlled by the magnitude of charge transfer from/to graphene.
At the same time, a superlattice of small quantum dots deposited on graphene
eliminates the resonances completely. We ascribe this effect to a
nanodot-induced buckling of graphene and its local rehybridization from
sp to sp towards a three-dimensional structure. Our results suggest
nanopatterning as a prospective tool for tuning optoelectronic properties of
two-dimensional materials with graphene-like structure.Comment: The following article has been submitted to Applied Physics Letters.
If it is published, it will be found online at http://apl.aip.or
Rashba splitting of 100 meV in Au-intercalated graphene on SiC
Intercalation of Au can produce giant Rashba-type spin-orbit splittings in
graphene but this has not yet been achieved on a semiconductor substrate. For
graphene/SiC(0001), Au intercalation yields two phases with different doping.
Here, we report the preparation of an almost pure p-type graphene phase after
Au intercalation. We observe a 100 meV Rashba-type spin-orbit splitting at 0.9
eV binding energy. We show that this giant splitting is due to hybridization
and much more limited in energy and momentum space than for Au-intercalated
graphene on Ni
Exploratory studies of contact angle hysteresis, wetting of solidified rare gases and surface properties of mercury Final report
Contact angle hysteresis, wetting of solidified rare gases, and surface properties of mercur
Laser-induced persistent photovoltage on the surface of a ternary topological insulator at room temperature
Using time- and angle-resolved photoemission, we investigate the ultrafast
response of excited electrons in the ternary topological insulator (BiSb)Te to fs-infrared pulses. We demonstrate that at the
critical concentration =0.55, where the system becomes bulk insulating, a
surface voltage can be driven at room temperature through the topological
surface state solely by optical means. We further show that such a photovoltage
persists over a time scale that exceeds 6 s, i.e, much longer than
the characteristic relaxation times of bulk states. We attribute the origin of
the photovoltage to a laser-induced band-bending effect which emerges near the
surface region on ultrafast time scales. The photovoltage is also accompanied
by a remarkable increase in the relaxation times of excited states as compared
to undoped topological insulators. Our findings are relevant in the context of
applications of topological surface states in future optical devices.Comment: 5 pages, 4 figure
Adverse Domination, Statutes of Limitations and the In Pari Delicto Defense - Application in Cases Involving Claims of Accounting Malpractice and Corporate Fraud
Ultrafast spin polarization control of Dirac fermions in topological insulators
Three-dimensional topological insulators (TIs) are characterized by
spin-polarized Dirac-cone surface states that are protected from backscattering
by time-reversal symmetry. Control of the spin polarization of topological
surface states (TSSs) using femtosecond light pulses opens novel perspectives
for the generation and manipulation of dissipationless surface spin currents on
ultrafast timescales. Using time-, spin-, and angle-resolved spectroscopy, we
directly monitor for the first time the ultrafast response of the spin
polarization of photoexcited TSSs to circularly-polarized femtosecond pulses of
infrared light. We achieve all-optical switching of the transient out-of-plane
spin polarization, which relaxes in about 1.2 ps. Our observations establish
the feasibility of ultrafast optical control of spin-polarized Dirac fermions
in TIs and pave the way for novel optospintronic applications at ultimate
speeds.Comment: 9 pages, 4 figure
RICO Extraterritoriality, RJR Nabisco and Shareholder Residence – A Key Consideration in Determining RICO Domestic Injury
Mn valence instability in La2/3Ca1/3MnO3 thin films
A Mn valence instability on La2/3Ca1/3MnO3 thin films, grown on LaAlO3
(001)substrates is observed by x-ray absorption spectroscopy at the Mn L-edge
and O K-edge. As-grown samples, in situ annealed at 800 C in oxygen, exhibit a
Curie temperature well below that of the bulk material. Upon air exposure a
reduction of the saturation magnetization, MS, of the films is detected.
Simultaneously a Mn2+ spectral signature develops, in addition to the expected
Mn3+ and Mn4+ contributions, which increases with time. The similarity of the
spectral results obtained by total electron yield and fluorescence yield
spectroscopy indicates that the location of the Mn valence anomalies is not
confined to a narrow surface region of the film, but can extend throughout the
whole thickness of the sample. High temperature annealing at 1000 C in air,
immediately after growth, improves the magnetic and transport properties of
such films towards the bulk values and the Mn2+ signature in the spectra does
not appear. The Mn valence is then stable even to prolonged air exposure. We
propose a mechanism for the Mn2+ ions formation and discuss the importance of
these observations with respect to previous findings and production of thin
films devices.Comment: Double space, 21 pages, 6 figure
Quantitative determination of spin-dependent quasiparticle lifetimes and electronic correlations in hcp cobalt
We report on a quantitative investigation of the spin-dependent quasiparticle
lifetimes and electron correlation effects in ferromagnetic hcp Co(0001) by
means of spin and angle-resolved photoemission spectroscopy. The experimental
spectra are compared in detail to state-of-the-art many-body calculations
within the dynamical mean field theory and the three-body scattering
approximation, including a full calculation of the one-step photoemission
process. From this comparison we conclude that although strong local many-body
Coulomb interactions are of major importance for the qualitative description of
correlation effects in Co, more sophisticated many-body calculations are needed
in order to improve the quantitative agreement between theory and experiment,
in particular concerning the linewidths. The quality of the overall agreement
obtained for Co indicates that the effect of non-local correlations becomes
weaker with increasing atomic number
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