Transient changes in the electronic structure of Bi2Sr2CaCu2O8+x

Die vorliegende Arbeit untersucht die dynamische Antwort des elektronischen Systems des Hochtemperatursupraleiters Bi2Sr2CaCu2O8+x (Bi2212) auf die optische Anregung durch ultrakurze Laserpulse. Mittels der zeit- und winkelaufgelösten Photoemissionsspektroskopie an optimal- und unterdotiertem Bi2212 in der „Pseudogap“-Phase werden anhand von Änderungen in der elektronischen Struktur zwei Effekte diskutiert, welche aufgrund ihres unterschiedlichen Zeitverhaltens als unabhängig betrachtet werden können. Zum einen ist dies eine photoinduzierte Änderung der effektiven Masse m* im Bereich der „Kink“-Energie von E - EF = -70 meV, welche innerhalb der Zeitauflösung des Experimentes von ~100 fs auftritt und somit als eine direkt durch den Anregepuls verursachte Störung der zu dem „Kink“ führenden elektronischen Wechselwirkung interpretiert werden kann. Zum anderen wird eine Verschiebung des Fermiflächenvektors kF beobachtet, was als effektive Änderung der Dotierung interpretiert werden kann und somit neue Möglichkeiten in Bezug auf ultraschnelle optoelektronische Bauteile basierend auf photoinduzierten Phasenübergängen eröffnet. Darüber hinaus wird die energie- und fluenzabhängige Dynamik angeregter Elektronen untersucht, welche ein biexponentielles Verhalten aufweisen. Während die langsame Komponente dieses Zerfalls von der Anregefluenz unabhängig ist, zeigt die schnelle Komponente einen deutlichen Sprung in der zugehörigen Zerfallszeit ober- und unterhalb der für das Material charakteristischen Energie von 70 meV. Dieser Sprung ist für niedrige Fluenzen am deutlichsten ausgeprägt, was anhand einer theoretischen Modellrechnung diskutiert wird. Ein großer Teil der vorliegenden Arbeit bestand zudem in der Konstruktion und dem Aufbau eines von Grund auf neuen Experimentes zur Photoemissionsspektroskopie, dessen Hauptbestandteil in dem Design eines 6-Achsen Manipulators lag, mit dessen Hilfe eine Probe bei tiefen Temperaturen unter Vakuumbedingungen unabhängig in jeweils alle 3 Rotations- und Translationsrichtungen bewegt werden kann. Im Zuge dieser Arbeiten wurden mit dem Aufbau zudem erste Test- und Charakterisierungsmessungen durchgeführt.This work investigates the dynamic response of the electronic system of the high critical temperature superconductor Bi2Sr2CaCu2O8+x (Bi2212) due to the optical excitation by ultra short laser pulses. By using time- and angle-resolved photoemission spectroscopy on optimally and underdoped Bi2212 in the pseudogap phase two effects revealed by changes in the electronic structure are being discussed which, due to their different temporal behaviors, can be considered as independent. First, this is an photoinduced change of the effective mass m* around the kink energy of E - EF = -70 meV, that occurs during the experiment’s time resolution of ~100 fs and therefore can be interpreted as perturbation of the underlying electronic interaction caused directly by the pump pulse. Second, a shift of the Fermi surface vector kF is observed, that can be interpreted as an effective change of hole doping that gives rise to new opportunities for possible ultrafast optoelectronic devices based on optically induced phase transitions. Furthermore, the energy- and fluence-dependent dynamics of excited electrons are investigated, which exhibit a biexponential behavior. While the slow component of this decay seems to be independent from the excitation fluence, the fast component shows a pronounced jump in the corresponding decay time above and below the material’s characteristic energy of 70 meV. This jump is most pronounced for the low fluences, which will be discussed in the context of an appropriate theoretical model system. Moreover, a major part of this work was the construction and build up of an entirely new experimental setup for photoemission spectroscopy. The main part regarding this issue consists of the design of 6-axis manipulator which is capable of moving the sample at low temperature independently in all 3 rotational and translational degrees of freedom. In the context of this work first tests and characterization measurements has been performed using this new setup

The Chemical Signature of Dust in the Reynolds Creek Experimental Watershed, Idaho

Aeolian or wind-blown sediment redistribution in the northern Great Basin impacts landscape development, soil depths/variations, and wind erosion of semi-arid rangeland surfaces. This study evaluates the importance of aeolian processes for carbonates found in soils and analyzes the organic material (specifically post-fire) in dust deposits to help characterize aeolian processes on soils in Reynolds Creek Experimental Watershed (RCEW) southwest of Boise. Researchers hypothesize that the source of calcium found in RCEW soils must be deposited through aeolian mechanisms, because the alternate bedrock source of calcium is inconsistent with corresponding soils. It’s important to understand how calcium is introduced to RCEW soils because soils provide storage for carbon in the form of calcium carbonate. Past dust collections from passive (vertically deposited) dust traps at RCEW are analyzed for elemental and nutrient concentrations, grain size distribution, and organic material concentrations. These analyses will build upon our understanding of calcium contributed to soils by dust and indicate any post-fire signal of organic material. This study is an extension of past research, which observed suspension and deposition of local material following wildfires with increased organic material, particle size, and mass flux. Future research will use new dust capture technology to evaluate horizontal aeolian transport

Mass-spectrometric identification of primary biological particle markers and application to pristine submicron aerosol measurements in Amazonia

The detection of primary biological material in submicron aerosol by means of thermal desorption/electron impact ionization aerosol mass spectrometry was investigated. Mass spectra of amino acids, carbohydrates, small peptides, and proteins, all of which are key building blocks of biological particles, were recorded in laboratory experiments. Several characteristic marker fragments were identified. The intensity of the marker signals relative to the total organic mass spectrum allows for an estimation of the content of primary biological material in ambient organic aerosol. The developed method was applied to mass spectra recorded during AMAZE-08, a field campaign conducted in the pristine rainforest of the central Amazon Basin, Brazil, during the wet season of February and March 2008. The low abundance of identified marker fragments places upper limits of 7.5% for amino acids and 5.6% for carbohydrates on the contribution of primary biological aerosol particles (PBAP) to the submicron organic aerosol mass concentration during this time period. Upper limits for the absolute submicron concentrations for both compound classes range from 0.01 to 0.1 μg m−3. Carbohydrates and proteins (composed of amino acids) make up for about two thirds of the dry mass of a biological cell. Thus, our findings suggest an upper limit for the PBAP mass fraction of about 20% to the submicron organic aerosol measured in Amazonia during AMAZE-08

Energy dissipation in the time domain governed by bosons in a correlated material

In complex materials various interactions play important roles in determining the material properties. Angle Resolved Photoelectron Spectroscopy (ARPES) has been used to study these processes by resolving the complex single particle self energy $\Sigma(E)$ and quantifying how quantum interactions modify bare electronic states. However, ambiguities in the measurement of the real part of the self energy and an intrinsic inability to disentangle various contributions to the imaginary part of the self energy often leave the implications of such measurements open to debate. Here we employ a combined theoretical and experimental treatment of femtosecond time-resolved ARPES (tr-ARPES) and show how measuring the population dynamics using tr-ARPES can be used to separate electron-boson interactions from electron-electron interactions. We demonstrate the analysis of a well-defined electron-boson interaction in the unoccupied spectrum of the cuprate Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$ characterized by an excited population decay time constant $\tau_{QP}$ that maps directly to a discrete component of the equilibrium self energy not readily isolated by static ARPES experiments.Comment: 19 pages with 6 figure

In situ, satellite measurement and model evidence on the dominant regional contribution to fine particulate matter levels in the Paris megacity

International audiencePublished by Copernicus Publications on behalf of the European Geosciences Union. 9578 M. Beekmann et al.: Evidence for a dominant regional contribution to fine particulate matter levels Abstract. A detailed characterization of air quality in the megacity of Paris (France) during two 1-month intensive campaigns and from additional 1-year observations revealed that about 70 % of the urban background fine particulate matter (PM) is transported on average into the megacity from upwind regions. This dominant influence of regional sources was confirmed by in situ measurements during short intensive and longer-term campaigns, aerosol optical depth (AOD) measurements from ENVISAT, and modeling results from PMCAMx and CHIMERE chemistry transport models. While advection of sulfate is well documented for other megacities, there was surprisingly high contribution from long-range transport for both nitrate and organic aerosol. The origin of organic PM was investigated by comprehensive analysis of aerosol mass spectrometer (AMS), radio-carbon and tracer measurements during two intensive campaigns. Primary fossil fuel combustion emissions constituted less than 20 % in winter and 40 % in summer of carbonaceous fine PM, unexpectedly small for a megacity. Cooking activities and, during winter, residential wood burning are the major primary organic PM sources. This analysis suggests that the major part of secondary organic aerosol is of modern origin , i.e., from biogenic precursors and from wood burning. Black carbon concentrations are on the lower end of values encountered in megacities worldwide, but still represent an issue for air quality. These comparatively low air pollution levels are due to a combination of low emissions per inhabitant , flat terrain, and a meteorology that is in general not conducive to local pollution build-up. This revised picture of a megacity only being partially responsible for its own average and peak PM levels has important implications for air pollution regulation policies

In situ, satellite measurement and model evidence on the dominant regional contribution to fine particulate matter levels in the Paris megacity

A detailed characterization of air quality in the megacity of Paris (France) during two 1-month intensive campaigns and from additional 1-year observations revealed that about 70 % of the urban background fine particulate matter (PM) is transported on average into the megacity from upwind regions. This dominant influence of regional sources was confirmed by in situ measurements during short intensive and longer-term campaigns, aerosol optical depth (AOD) measurements from ENVISAT, and modeling results from PMCAMx and CHIMERE chemistry transport models. While advection of sulfate is well documented for other megacities, there was surprisingly high contribution from long-range transport for both nitrate and organic aerosol. The origin of organic PM was investigated by comprehensive analysis of aerosol mass spectrometer (AMS), radiocarbon and tracer measurements during two intensive campaigns. Primary fossil fuel combustion emissions constituted less than 20 % in winter and 40 % in summer of carbonaceous fine PM, unexpectedly small for a megacity. Cooking activities and, during winter, residential wood burning are the major primary organic PM sources. This analysis suggests that the major part of secondary organic aerosol is of modern origin, i.e., from biogenic precursors and from wood burning. Black carbon concentrations are on the lower end of values encountered in megacities worldwide, but still represent an issue for air quality. These comparatively low air pollution levels are due to a combination of low emissions per inhabitant, flat terrain, and a meteorology that is in general not conducive to local pollution build-up. This revised picture of a megacity only being partially responsible for its own average and peak PM levels has important implications for air pollution regulation policies