185 research outputs found
Evidence - The Pennsylvania Rape Shield Law - Admissibility of Evidence Concerning Sexual Conduct Offered for Purposes of Impeachment
The Pennsylvania Supreme Court held that state courts may order a school district and teachers\u27 association to participate in court-monitored negotiations when the courts grant the Secretary of Education an injunction ending a teachers\u27 strike.
Carroll v. Ringgold Educ. Ass\u27n, 680 A.2d 1137 (Pa. 1996)
Observation of antiphase coherent phonons in the warped Dirac cone of Bi2Te3
In this Rapid Communication we investigate the coupling between excited electrons and phonons in the highly anisotropic electronic structure of the prototypical topological insulator Bi2Te3. Using time and angle resolved photoemission spectroscopy we are able to identify the emergence and ultrafast temporal evolution of the longitudinal optical A1g coherent phonon mode in Bi2Te3. We observe an antiphase behavior in the onset of the coherent phonon oscillations between the amp; 915;K and the amp; 915;M high symmetry directions that is consistent with warping. The qualitative agreement between our density functional theory calculations and the experimental results reveals the critical role of the anisotropic coupling between Dirac fermions and phonon modes in the topological insulator Bi2Te
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
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
Band Renormalization of Blue Phosphorus on Au 111
Most recently, theoretical calculations predicted the stability of a novel two dimensional phosphorus honeycomb lattice named blue phosphorus. Here, we report on the growth of blue phosphorus on Au 111 and unravel its structural details using diffraction, microscopy and theoretical calculations. Most importantly, by utilizing angle resolved photoemission spectroscopy we identify its momentum resolved electronic structure. We find that Au 111 breaks the sublattice symmetry of blue phosphorus leading to an orbital dependent band renormalization upon the formation of a 4 4 superstructure. Notably, the semiconducting two dimensional phosphorus realizes its valence band maximum at 0.9 eV binding energy, however, shifted in momentum space due to the substrate induced band renormalizatio
Effect of ligand methylation on the spin-switching properties of surface-supported spin-crossover molecules
X-ray absorption spectroscopy investigations of the spin-state switching of spin-crossover (SCO) complexes adsorbed on a highly-oriented pyrolytic graphite (HOPG) surface have shown so far that HOPG is a promising candidate to realize applications such as spintronic devices because of the stability of SCO complexes on HOPG and the possibility of highly efficient thermal and light-induced spin-state switching. Herein, we present the spin switching of several Fe(II) SCO complexes adsorbed on an HOPG surface with particular emphasis on the thermally induced spin transition behaviour with respect to different structural modifications. The complexes of the type [Fe(bpz)2(L)] (bpz  =  dihydrobis(pyrazolyl)borate, L  =  1,10-phenanthroline, 2,2'-bipyridine) and their methylated derivatives exhibit SCO in the solid state with some differences regarding cooperative effects. However, in the vacuum-deposited thick films on quartz, complete and more gradual spin transition behavior is observable via UV/vis spectroscopy. In contrast to that, all complexes show large differences upon direct contact with HOPG. Whereas the unmodified complexes show thermal and light-induced SCO, the addition of e.g. two or four methyl groups leads to a partial or a complete loss of the SCO on the surface. The angle-dependent measurement of the N K-edge compared to calculations indicates that the complete SCO and HS-locked molecules on the surface exhibit a similar preferential orientation, whereas complexes undergoing an incomplete SCO exhibit a random orientation on the surface. These results are discussed in the light of molecule-substrate interactions
Anisotropic effect of warping on the lifetime broadening of topological surface states in angle-resolved photoemission from Bi2 Te3
We analyze the strong hexagonal warping of the Dirac cone of Bi2Te3 by angle-
resolved photoemission. Along Γ¯¯¯M¯¯¯, the dispersion deviates from a linear
behavior meaning that the Dirac cone is warped outwards and not inwards. We
show that this introduces an anisotropy in the lifetime broadening of the
topological surface state which is larger along Γ¯¯¯K¯¯¯. The result is not
consistent with an explanation by nesting properties. Based on the
theoretically predicted modifications of the ground-state spin texture of a
strongly warped Dirac cone, we propose spin-dependent scattering processes as
explanation for the anisotropic scattering rates. These results could help
paving the way for optimizing future spintronic devices using topological
insulators and controlling surface-scattering processes via external gate
voltages
Recommended from our members
Lifshitz transition in titanium carbide driven by a graphene overlayer
Two-dimensional (2D) Dirac materials are electronically and structurally very sensitive to proximity effects. We demonstrate, however, the opposite effect: that the deposition of a monolayer 2D material could exercise a substantial influence on the substrate electronic structure. Here we investigate TiC(111) and show that a graphene overlayer produces a proximity effect, changing the Fermi surface topology of the TiC from six electron pockets to one hole pocket on the depth of several atomic layers inside the substrate. In addition, the graphene electronic structure undergoes an extreme modification as well. While the Dirac cone remains gapless, it experiences an energy shift of 1.0 eV beyond what was recently achieved for the Lifshitz transition of overdoped graphene. Due to this shift, the antibonding π∗ band at the M¯ point becomes occupied and observable by photoemission
- …