Raman scattering excitation spectroscopy in monolayer WS2_2

Resonant Raman scattering is investigated in monolayer WS$_2$ at low temperature with the aid of an unconventional spectroscopy technique, $i.e.$, Raman scattering excitation (RSE). The RSE spectrum is made up by sweeping the excitation energy, when the detection energy is fixed in resonance with excitonic transitions related to neutral and/or charged excitons. We demonstrate that the shape of the RSE spectrum strongly depends on a selected detection energy. The out-going resonance with the neutral exciton leads to an extremely rich RSE spectrum displaying several Raman scattering features not reported so far, while no clear effect on the associated background photoluminescence is observed. Instead, a strong enhancement of the emission due to the negatively charged exciton is apparent when the out-going photons resonate with this exciton. Presented results show that the RSE spectroscopy can be a useful technique to study electron-phonon interactions in thin layers of transition metal dichalcogenides.Comment: 9 pages, 5 figure

Locking entanglement measures with a single qubit

We study the loss of entanglement of bipartite state subjected to discarding or measurement of one qubit. Examining the behavior of different entanglement measures, we find that entanglement of formation, entanglement cost, and logarithmic negativity are lockable measures in that it can decrease arbitrarily after measuring one qubit. We prove that any convex and asymptotically non-continuous measure is lockable. As a consequence, all the convex roof measures can be locked. Relative entropy of entanglement is shown to be a non-lockable measure.Comment: 5 pages, RevTex

Tuning carrier concentration in a superacid treated MoS2_2 monolayer

The effect of bis(trifluoromethane) sulfonimide (TFSI, superacid) treatment on the optical properties of MoS$_2$ monolayers is investigated by means of photoluminescence, reflectance contrast and Raman scattering spectroscopy employed in a broad temperature range. It is shown that when applied multiple times, the treatment results in progressive quenching of the trion emission/absorption and in the redshift of the neutral exciton emission/absorption associated with both the A and B excitonic resonances. Based on this evolution, a trion complex related to the B exciton in monolayer MoS$_2$ is unambiguously identified. A defect-related emission observed at low temperatures also disappears from the spectrum as a result of the treatment. Our observations are attributed to effective passivation of defects on the MoS$_{2}$ monolayer surface. The passivation reduces the carrier density, which in turn affects the out-of-plane electric field in the sample. The observed tuning of the carrier concentration strongly influences also the Raman scattering in the MoS$_2$ monolayer. An enhancement of Raman scattering at resonant excitation in the vicinity of the A neutral exciton is clearly seen for both the out-of-plane A$_1^{'}$ and in-plane E$^{'}$ modes. On the contrary, when the excitation is in resonance with a corresponding trion, the Raman scattering features become hardly visible. These results confirm the role of the excitonic charge state plays in the resonance effect of the excitation energy on the Raman scattering in transition metal dichalcogenides.Comment: 8 pages, 4 figure

Subnormalized states and trace-nonincreasing maps

We investigate the set of completely positive, trace-nonincreasing linear maps acting on the set M_N of mixed quantum states of size N. Extremal point of this set of maps are characterized and its volume with respect to the Hilbert-Schmidt (Euclidean) measure is computed explicitly for an arbitrary N. The spectra of partially reduced rescaled dynamical matrices associated with trace-nonincreasing completely positive maps belong to the N-cube inscribed in the set of subnormalized states of size N. As a by-product we derive the measure in M_N induced by partial trace of mixed quantum states distributed uniformly with respect to HS-measure in $M_{N^2}$.Comment: LaTeX, 21 pages, 4 Encapsuled PostScript figures, 1 tabl

Magnetic field induced polarization enhancement in monolayers of tungsten dichalcogenides: Effects of temperature

Optical orientation of localized/bound excitons is shown to be effectively enhanced by the application of magnetic fields as low as 20 mT in monolayer WS$_2$. At low temperatures, the evolution of the polarization degree of different emission lines of monolayer WS$_2$ with increasing magnetic fields is analyzed and compared to similar results obtained on a WSe$_2$ monolayer. We study the temperature dependence of this effect up to $T=60$ K for both materials, focusing on the dynamics of the valley pseudospin relaxation. A rate equation model is used to analyze our data and from the analysis of the width of the polarization deep in magnetic field we conclude that the competition between the dark exciton pseudospin relaxation and the decay of the dark exciton population into the localized states are rather different in these two materials which are representative of the two extreme cases for the ratio of relaxation rate and depolarization rate

Production of Bc mesons in photon-photon and hadron-hadron collisions

We discuss two-photon and hadronic production of Bc mesons in nonrelativistic bound state approximation and to lowest order in the coupling constants a and a s . It is shown that in photon-photon collisions, heavy quark fragmentation is dominated by recombination of b and c quarks up to the highest accessible transverse momenta. In contrast, in hadroproduction, which at high energies mainly involves gluon-gluon collisions, the fragmentation mechanism dominates at transverse momenta py > mRc, providing a simple and satisfactory approximation of the complete 0(a ) ) results in the high-px regime. Contradictions in previous publications on hadroproduction of Bc mesons are clarified. We also present predictions for cross sections and differential distributions at present and future accelerators

Ein Arbeitsbericht

Das Grab des Konrad von Burgsdorff (gest. 1652) wurde im Jahr 2008 in einer Gruft im Bereich des alten Berliner Doms, dem Areal des ehemaligen Dominikaner Klosters in Berlin-Mitte, entdeckt und freigelegt. Der Tote wurde in einem Sarkophag in einer Gruft am Rande der Klosterkirche mit 17 weiteren Bestattungen beigesetzt. Aufgrund des schlechten Erhaltungszustands der Metallbleche entschieden sich die Ausgräber für eine Blockbergung. In den Restaurierungslaboren der HTW Berlin wurde eine detaillierte Zustandsdokumentation erstellt. Dabei war es das Ziel, jegliche aufliegenden Verzierungen, Farbfassungen, Metall- oder Stoffapplikationen in situ zu erhalten. Es stellte sich heraus, dass der Sarkophag aus zwei großen Teilen aufgebaut war – einer unteren Wanne und einem oberen Deckel, die beide aus an den Kanten verlöteten Blechen hergestellt waren. Die Außenseiten waren mit Metallverzierungen besetzt: Löwenköpfe mit Ringen als Handgriffe, Metallborten in Akanthusmotiven, zwei Engelköpfe und einige runde Medaillons. Ein hölzerner Sarg, innen mit Textilien ausgekleidet, barg den Verstorbenen. Die Füllung der Gruft mit Bauschutt hatte den Sarkophag, der unter dieser Last eingebrochen war, stark beschädigt. Aufgrund der durchgeführten Analysen und anhand von Vergleichen mit zeitgleichen Sarkophagen aus der Hohenzollern-Gruft im Berliner Dom konnte eine überzeugende virtuelle Rekonstruktion des Sarkophags von Konrad von Burgsdorff erarbeitet werden