@article{OPUS4-12895,
  title     = {Search for second generation scalar leptoquarks in pp collisions at √s=7 TeV with the ATLAS detector},
  series = {The European Physical Journal C},
  volume    = {72},
  journal   = {The European Physical Journal C},
  number    = {2151},
  organization    = {ATLAS Collaboration},
  doi       = {10.1140/epjc/s10052-012-2151-6},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-128957},
  year      = {2012},
  abstract  = {The results of a search for the production of second generation scalar leptoquarks are presented for final states consisting of either two muons and at least two jets or a muon plus missing transverse momentum and at least two jets. A total of 1.03 fb\(^{-1}\) integrated luminosity of proton-proton collision data produced by the Large Hadron Collider at s√=7 TeV and recorded by the ATLAS detector is used for the search. The event yields in the signal regions are found to be consistent with the Standard Model background expectations. The production of second generation leptoquarks is excluded for a leptoquark mass m\(_{LQ}\)<594 (685) GeV at 95 \% confidence level, for a branching ratio of 0.5 (1.0) for leptoquark decay to a muon and a quark.},
  language  = {en}
}
@article{OPUS4-12896,
  title     = {Search for same-sign top-quark production and fourth-generation down-type quarks in pp collisions at √s=7 TeV with the ATLAS detector},
  series = {Journal of High Energy Physics},
  volume    = {04},
  journal   = {Journal of High Energy Physics},
  number    = {69},
  organization    = {ATLAS Collaboration},
  doi       = {10.1007/JHEP04(2012)069},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-128960},
  year      = {2012},
  abstract  = {A search is presented for same-sign top-quark production and down-type heavy quarks of charge -1/3 in events with two isolated leptons (e or μ) that have the same electric charge, at least two jets and large missing transverse momentum. The data are selected from pp collisions at √s=7TeV recorded by the ATLAS detector and correspond to an integrated luminosity of 1.04 fb\(^{-1}\). The observed data are consistent with expectations from Standard Model processes. Upper limits are set at 95 \% confidence level on the cross section of new sources of same-sign top-quark pair production of 1.4-2.0 pb depending on the assumed mediator mass. Upper limits are also set on the pair-production cross-section for new heavy down-type quarks; a lower limit of 450 GeV is set at 95 \% confidence level on the mass of heavy down-type quarks under the assumption that they decay 100 \% of the time to W t.},
  language  = {en}
}
@article{OPUS4-12897,
  title     = {Jet mass and substructure of inclusive jets in √s=7 TeV pp collisions with the ATLAS experiment},
  series = {Journal of High Energy Physics},
  volume    = {05},
  journal   = {Journal of High Energy Physics},
  number    = {128},
  organization    = {ATLAS Collaboration},
  doi       = {10.1007/JHEP05(2012)128},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-128970},
  year      = {2012},
  abstract  = {Recent studies have highlighted the potential of jet substructure techniques to identify the hadronic decays of boosted heavy particles. These studies all rely upon the assumption that the internal substructure of jets generated by QCD radiation is well understood. In this article, this assumption is tested on an inclusive sample of jets recorded with the ATLAS detector in 2010, which corresponds to 35 pb\(^{-1}\) of pp collisions delivered by the LHC at √s=7TeV. In a subsample of events with single pp collisions, measurements corrected for detector efficiency and resolution are presented with full systematic uncertainties. Jet invariant mass, k\(_t\) splitting scales and N-subjettiness variables are presented for anti-k\(_t\) R = 1.0 jets and Cambridge-Aachen R = 1.2 jets. Jet invariant-mass spectra for Cambridge-Aachen R = 1.2 jets after a splitting and filtering procedure are also presented. Leading-order parton-shower Monte Carlo predictions for these variables are found to be broadly in agreement with data. The dependence of mean jet mass on additional pp interactions is also explored.},
  language  = {en}
}
@phdthesis{Steinbacher2015,
  author    = {Steinbacher, Andreas Edgar},
  title     = {Circular dichroism and accumulative polarimetry of chiral femtochemistry},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-116500},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2015},
  abstract  = {This work brings forward successful implementations of ultrafast chirality-sensitive spectroscopic techniques by probing circular dichroism (CD) or optical rotation dispersion (ORD). Furthermore, also first steps towards chiral quantum control, i.e., the selective variation of the chiral properties of molecules with the help of coherent light, are presented. In the case of CD probing, a setup capable of mirroring an arbitrary polarization state of an ultrashort laser pulse was developed. Hence, by passing a left-circularly polarized laser pulse through this setup a right-circularly polarized laser pulse is generated. These two pulse enantiomers can be utilized as probe pulses in a pump--probe CD experiment. Besides CD spectroscopy, it can be utilized for anisotropy or ellipsometry spectroscopy also. Within this thesis, the approach is used to elucidate the photochemistry of hemoglobin, the oxygen transporting protein in mammalian blood. The oxygen loss can be triggered with laser pulses as well, and the results of the time-resolved CD experiment suggest a cascade-like relaxation, probably through different spin states, of the metallo-porphyrins in hemoglobin. The ORD probing was realized via the combination of common-path optical heterodyne interferometric polarimetry and accumulative femtosecond spectroscopy. Within this setup, on the one hand the applicability of this approach for ultrafast studies was demonstrated explicitly. On the other hand, the discrimination between an achiral and a racemic solution without prior spatial separation was realized. This was achieved by inducing an enantiomeric excess via polarized femtosecond laser pulses and following its evolution with the developed polarimeter. Hence, chiral selectivity was already achieved with this method which can be turned into chiral control if the polarized laser pulses are optimized to steer an enhancement of the enantiomeric excess. Furthermore, within this thesis, theoretical prerequisites for anisotropy-free pump--probe experiments with arbitrary polarized laser pulses were derived. Due to the small magnitude of optical chirality-sensitve signals, these results are important for any pump--probe chiral spectroscopy, like the CD probing presented in this thesis. Moreover, since for chiral quantum control the variation of the molecular structure is necessary, the knowledge about rearrangement reactions triggered by photons is necessary. Hence, within this thesis the ultrafast Wolff rearrangement of an α-diazocarbonyl was investigated via ultrafast photofragment ion spectroscopy in the gas phase. Though the compound is not chiral, the knowledge about the exact reaction mechanism is beneficial for future studies of chiral compounds.},
  subject      = {Ultrakurzzeitspektroskopie},
  language  = {en}
}
@misc{Gogolin2010,
  type      = {Master Thesis},
  author    = {Gogolin, Christian},
  title     = {Pure State Quantum Statistical Mechanics},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-106065},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2010},
  abstract  = {The capabilities of a new approach towards the foundations of Statistical Mechanics are explored. The approach is genuine quantum in the sense that statistical behavior is a consequence of objective quantum uncertainties due to entanglement and uncertainty relations. No additional randomness is added by hand and no assumptions about a priori probabilities are made, instead measure concentration results are used to justify the methods of Statistical Physics. The approach explains the applicability of the microcanonical and canonical ensemble and the tendency to equilibrate in a natural way. This work contains a pedagogical review of the existing literature and some new results. The most important of which are: i) A measure theoretic justification for the microcanonical ensemble. ii) Bounds on the subsystem equilibration time. iii) A proof that a generic weak interaction causes decoherence in the energy eigenbasis. iv) A proof of a quantum H-Theorem. v) New estimates of the average effective dimension for initial product states and states from the mean energy ensemble. vi) A proof that time and ensemble averages of observables are typically close to each other. vii) A bound on the fluctuations of the purity of a system coupled to a bath.},
  subject      = {Quantenstatistik},
  language  = {en}
}
@phdthesis{Dengel2013,
  author    = {Dengel, Radu-Gabriel},
  title     = {Fabrication of magnetic artificial atoms},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-103162},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2013},
  abstract  = {This thesis presents the detailed development of the fabrication process and the first observations of artificial magnetic atoms from the II-VI diluted magnetic semiconductor alloy (Zn,Cd,Be,Mn)Se. In order to manufacture the vertical quantum dot device which exhibits artificial atom behavior a number of development steps are conducted. First, the II-VI heterostructure is adjusted for the linear transport regime. Second, state of the art vertical quantum dot fabrication techniques in the III-V material system are investigated regarding their portability to the II-VI heterostructure. And third, new approaches to the fabrication process are developed, taking into account the complexity of the heterostructure and its physical properties. Finally a multi-step fabrication process is presented, which is built up from electron beam and optical lithography, dry and wet etching and insulator deposition. This process allows for the processing of pillars with diameters down to 200 nm with an insulating dielectric and gate. Preliminary transport data on the fabricated vertical quantum dots are presendted confirming the magnetic nature of the resulting artificial atoms.},
  subject      = {Zwei-Sechs-Halbleiter},
  language  = {en}
}
@phdthesis{Boariu2014,
  author    = {Boariu, Florin Loredan},
  title     = {The "Hidden-Order" Phase Transition of URu2Si2 : Investigated by Angle-Resolved Photoelectron Spectroscopy},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-98259},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2014},
  abstract  = {In 1985, an enigmatic second order phase transition was discovered in the actinide compound URu2Si2. Evading a microscopic description for nearly three decades in spite of numerous experimental and theoretical attempts, the name "hidden order Transition" was adopted for the effect. (...)},
  subject      = {Actinoide},
  language  = {en}
}
@phdthesis{Kremling2013,
  author    = {Kremling, Stefan},
  title     = {Charakterisierung von InP und InGaN Quantenpunkten als Einzelphotonenquellen sowie von AlGaInAs Quantenpunkten in Zwischenband-Solarzellen},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-101712},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2013},
  abstract  = {Die vorliegende Arbeit beschreibt die Charakterisierung von Halbleiter-Quantenpunkten (QP) in unterschiedlichen Materialsystemen. Die hier dargelegten Untersuchungen wurden mit verschiedenen Methoden der optischen Spektroskopie durchgef{\"u}hrt. Zu Beginn der Arbeit werden theoretische Grundlagen von QP hinsichtlich ihrer elektronischen Struktur und statistischen Eigenschaften erl{\"a}utert. Dar{\"u}ber hinaus wird n{\"a}her auf die Physik von Solarzellen eingegangen, in dem die relevanten Gleichungen f{\"u}r die Beschreibung des Ladungstr{\"a}gertransportes hergeleitet und diskutiert werden. Darauf folgend werden die experimentelle Methoden erkl{\"a}rt, welche zur Charakterisierung der jeweiligen Proben dienten. Besonderes Augenmerk wird auf die Methode zur Messung des Zwei-Photonen-Absorptionsprozesses gelegt. Der Abschnitt der experimentell gewonnenen Ergebnisse beginnt mit Untersuchungen an einzelnen, spektral isolierten InP QP, welche mit ultralangsamen Wachstumsraten hergestellt wurden. Aufgrund der sehr geringen Fl{\"a}chendichte konnten grundlegende physikalische Eigenschaften von QP ohne zus{\"a}tzliche laterale Strukturierungen studiert werden. Mittels Messungen in Abh{\"a}ngigkeit der Anregungsleistung und Detektion in Abh{\"a}ngigkeit der Polarisation konnten die verschiedenen Lumineszenzlinien eines QP-Spektrums den jeweiligen exzitonischen Zust{\"a}nden zugeordnet werden. Zus{\"a}tzlich wurden die QP in einem externen Magnetfeld in Faraday-Konfiguration untersucht. Abschließend durchgef{\"u}hrte Autokorrelationsmessungen erlaubten die Untersuchung der zeitlichen Statistik der QP-Photonen. Es konnte die Emission einzelner Photonen nachgewiesen werden. Anschließend folgen spektroskopische Untersuchungen von InP QP, welche mittels sequentiellen Wachstums hergestellt wurden. Anhand von Messungen in Abh{\"a}ngigkeit der Anregungsleistung und best{\"a}tigt durch zeitaufgel{\"o}ste Messungen am QP-Ensemble wurde eine bimodale QP-Verteilung mit Typ-I und Typ-II Bandverlauf bestimmt. Zus{\"a}tzlich konnten an einzelnen, spektral isolierten QP verschiedene Exziton-Zust{\"a}nde identifiziert werden, bevor abschließend Autokorrelationsmessungen die Emission einzelner Photonen demonstrierten. Zur Steigerung der Auskoppeleffizienz der Photonen wurden InP QP in Mikros{\"a}ulenresonatoren, bestehend aus zwei Bragg-Spiegeln mit einer dazwischenliegenden GaInP Kavit{\"a}t, eingebettet. Anfangs wurde die Emission der Kavit{\"a}tsmode von Strukturen mit unterschiedlichen lateralen Durchmessern charakterisiert. Mittels Temperaturverstimmung konnte die Energie eines einzelnen QP-Exzitons in Resonanz mit der Resonatormode gebracht werden. Im Regime der schwachen Wechselwirkung wurde eine signifikante {\"U}berh{\"o}hung der Lumineszenzintensit{\"a}t aufgrund des Purcell-Effektes gemessen. Zus{\"a}tzlich wurde im Regime der schwachen Kopplung die Emission einzelner Photonen anhand von Korrelationsmessungen nachgewiesen. Im zweiten Schritt wurden die QP-Mikros{\"a}ulenresonatorstrukturen elektrisch angeregt. Nach einer grundlegenden Charakterisierung konnte auch hier mittels Temperaturverstimmung die Energie der Resonatormode mit der eines Exziton in Resonanz gebracht werden. Im Regime der schwachen Wechselwirkung stieg die Intensit{\"a}t der Lumineszenz aufgrund des Purcell-Effekts signifikant an. Zum Abschluss best{\"a}tigen Korrelationsmessungen den Nachweis der Emission einzelner Photonen. In Kapitel 6 werden die Eigenschaften von InGaN QP genauer analysiert. Nitrid-Verbindungshalbleiter kristallieren vorzugsweise stabil in der Wurtzit-Kristallstruktur. Polare Kristallebenen mit fehlender Spiegelsymmetrie f{\"u}hren zu starken piezoelektrischen Feldern. Dies hat eine Lumineszenz mit ausgepr{\"a}gter linearer Polarisation zur Folge hat. Diese Eigenschaft wurde mittels statistischen Untersuchungen n{\"a}her betrachtet. Zus{\"a}tzlich erlaubten Messungen in Abh{\"a}ngigkeit der Anregungsleistung die verschiedenen Exziton-Zust{\"a}nde eines QP zu identifizieren. Zudem wurde die Emission einzelner Photonen durch InGaN QP demonstriert, erstmals sogar bis zu einer Temperatur von 50 K. Im abschliessenden Kapitel wird eine m{\"o}gliche Anwendung von QP pr{\"a}sentiert, bei der Eigenschaften in Bauteilen gezielt ausgenutzt werden, um die Bandbreite der Photonenabsorption zu erh{\"o}hen. Das Konzept der Zwischenband-Solarzellen verspricht auch Photonen mit einer Energie kleiner der Bandl{\"u}cke des umgebenden Materials aufnehmen zu k{\"o}nnen und somit den spektralen Absorptionsbereich zu erweitern. F{\"u}r eine systematische Untersuchung wurden verschiedene Proben mit integrierten AlGaInAs QP hergestellt. Anhand der Strom-Spannungs-Kennlinien der jeweiligen Proben im Dunkeln und unter Beleuchtung konnten wichtige Solarzellenparameter bestimmt werden. Spektrale Messungen liefern Informationen {\"u}ber die externe Quanteneffizienz der Proben. Entscheidend f{\"u}r den experimentellen Nachweis des Funktionsprinzips der Zwischenband-Solarzellen ist die Messung der Zwei-Photonen-Absorption f{\"u}r zwei Photonen mit jeweils kleineren Energien als der Bandl{\"u}cke des umgebenden Materials.},
  subject      = {Quantenpunkt},
  language  = {de}
}
@phdthesis{Tam2014,
  author    = {Tam, Jason},
  title     = {Search for Second Generation Scalar Leptoquarks using the ATLAS Detector},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-103451},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2014},
  abstract  = {Leptoquarks are hypothetical particles that attempt to explain the coincidental similarities between leptons and quarks included in SM. Their exact properties vary between different theoretical models, and there are no strong theoretical constraints on their possible mass values. They can possibly be produced from particle collisions, and there have already been searching efforts at previous collider experiments. Their presence have yet been observed, and this fact has been translated into lower bound exclusions on their possible mass values. The Large Hadron Collider (LHC) being the most recently constructed particle collider with the highest collision energies ever achieved experimentally, provides a new platform to continue the search for Leptoquarks at even higher mass ranges. This thesis describes a search for pair-produced second-generation Leptoquarks using 20.3 fb-1 of data recorded by the ATLAS detector of LHC at √s = 8 TeV. Events with two oppositely charged muons and two or more jets in the final state were used. Candidate leptoquark events were selected with the help of four observables: the di-muon invariant mass (Mμμ ), the sum of the pT of the two muons (LT ), the sum of the pT of the two leading jets (HT ) and the average Leptoquark mass (MLQ ). Monte Carlo simulations of SM background processes have shown to be in good agreement with data, both in the region constructed using selection requirements for candiate leptoquark events and in the designated control regions. Since no significant excess of events was observed in data, a exclusion limit was set as a function of the Leptoquark mass.},
  subject      = {Leptoquark},
  language  = {en}
}
@phdthesis{Naydenova2014,
  author    = {Naydenova, Tsvetelina},
  title     = {A Study of Seebeck and Nernst effects in (Ga,Mn)As/normal semiconductor junctions},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-101981},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2014},
  abstract  = {The discovery of the Giant Magneto Resistance (GMR) effect in 1988 by Albert Fert [Baib 88] and Peter Gr{\"u}nberg [Bina 89] led to a rapid development of the field of spintronics and progress in the information technology. Semiconductor based spintronics, which appeared later, offered a possibility to combine storage and processing in a single monolithic device. A direct result is reduced heat dissipation. The observation of the spin Seebeck effect by Ushida [Uchi 08] in 2008 launched an increased interest and encouraged research in the field of spin caloritronics. Spintronics is about the coupling of charge and spin transport. Spin caloritronics studies the interaction between heat and spin currents. In contrast to spintronics and its variety of applications, a particular spin-caloritronic device has not yet been demonstrated. However, many of the novel phenomena in spin caloritronics can be detected in most spintronic devices. Moreover, thermoelectric effects might have a significant influence on spintronic device operation. This will be of particular interest for this work. Additional knowledge on the principle of coupling between heat and spin currents uncovers an alternative way to control heat dissipation and promises new device functionalities. This thesis aims to further extend the knowledge on thermoelectrics in materials with strong spin-orbit coupling, in this case the prototypical ferromagnetic semiconductor (Ga,Mn)As. The study is focused on the thermoelectric / thermomagnetic effects at the interface between a normal metal and the ferromagnetic (Ga,Mn)As. In such systems, the different interfaces provide a condition for minimal phonon drag contribution to the thermal effects. This suggests that only band contributions (a diffusion transport regime) to these effects will be measured. Chapter 2 begins with an introduction on the properties of the studied material system, and basics on thermoelectrics and spin caloritronics. The characteristic anisotropies of the (Ga,Mn)As density of states (DOS) and the corresponding magnetic properties are described. The DOS and magnetic anisotropies have an impact on the transport prop- erties of the material and that results in effects like tunneling anisotropic magnetores- istance (TAMR) [Goul 04]. Some of these effects will be used later as a reference to the results from thermoelectric / thermomagnetic measurements. The Fingerprint tech- nique [Papp 07a] is also described. The method gives an opportunity to easily study the anisotropies of materials in different device geometries. Chapter 3 continues with the experimental observation of the diffusion thermopower of (Ga,Mn)As / Si-doped GaAs tunnel junction. A device geometry for measuring the diffusion thermopower is proposed. It consists of a Si - doped GaAs heating channel with a Low Temperature (LT) GaAs / (Ga,Mn)As contact (junction) in the middle of the channel. A single Ti / Au contact is fabricated on the top of the junction. For transport characterization, the device is immersed in liquid He. A heating current technique is used to create a temperature difference by local heating of the electron system on the Si:GaAs side. An AC current at low frequency is sent through the channel and it heats the electron population in it, while the junction remains at liquid He temperature (experimentally con- firmed). A temperature difference arises between the heating channel and the (Ga,Mn)As contact. As a result, a thermal (Seebeck) voltage develops across the junction, which we call tunnelling anisotropic magneto thermopower (TAMT), similar to TAMR. TAMT is detected by means of a standard lock-in technique at double the heating current frequency (at 2f ). The Seebeck voltage is found to be linear with the temperature difference. That dependence suggests a diffusion transport regime. Lattice (phonon drag) contribution to the thermovoltage, which is usually highly nonlinear with temperature, is not observed. The value of the Seebeck coefficient of the junction at 4.2 K is estimated to be 0.5 µV/K. It is about three orders of magnitude smaller than the previously reported one [Pu 06]. Subsequently, the thermal voltage is studied in external magnetic fields. It is found that the thermopower is anisotropic with the magnetization direction. The anisotropy is explained with the anisotropies of the (Ga,Mn)As contact. Further, switching events are detected in the thermopower when the magnetic field is swept from negative to positive fields. The switchings remind of a spin valve signal and is similar to the results from previous experiments on spin injection using a (Ga,Mn)As contacts in a non-local detection scheme. That shows the importance of the thermoelectric effects and their possible contribution to the spin injection measurements. A polar plot of the collected switching fields for different magnetization angles reveals a biaxial anisotropy and resembles earlier TAMR measurements of (Ga,Mn)As tunnel junction. A simple cartoon model is introduced to describe and estimate the expected thermopower of the studied junction. The model yields a Fermi level inside of the (Ga,Mn)As valence band. Moreover, the model is found to be in good agreement with the experimental results. The Nernst effect of a (Ga,Mn)As / GaAs tunnel junction is studied in Chapter 4. A modified device geometry is introduced for this purpose. Instead of a single contact on the top of the square junction, four small contacts are fabricated to detect the Nernst signal. A temperature difference is maintained by means of a heating current technique described in Chapter 3. A magnetic field is applied parallel to the device plane. A voltage drop across two opposite contacts is detected at 2f. It appears that a simple cosine function with a parameter the angle between the magnetization and the [100] crystal direction in the (Ga,Mn)As layer manages to describe this signal which is attributed to the anomalous Nernst effect (ANE) of the ferromagnetic contact. Its symmetry is different than the Seebeck effect of the junction. For the temperature range of the thermopower measurements the ANE coefficient has a linear dependence on the temperature difference (∆T). For higher ∆T, a nonlinear dependence is observed for the coefficient. The ANE coefficient is found to be several orders of magnitude smaller than any Nernst coefficient in the literature. Both the temperature difference and the size of the ANE coefficient require further studies and analysis. Switching events are present in the measured Nernst signal when the magnetic field is swept from positive to negative values. These switchings are related to the switching fields in the ferromagnetic (Ga,Mn)As. Usually, there are two states which are present in TAMR or AMR measurements - low and high resistance. Instead of that, the Nernst signal appears to have three states - high, middle and low thermomagnetic voltage. That behaviour is governed not only by the magnetization, but also by the characteristic of the Nernst geometry. Chapter 5 summarizes the main observations of this thesis and contains ideas for future work and experiments.},
  subject      = {Galliumarsenid},
  language  = {en}
}
@phdthesis{Hartmann2012,
  author    = {Hartmann, Fabian},
  title     = {Elektrooptische Transporteigenschaften und stochastisch aktivierte Prozesse Resonanter Tunneldioden},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-90876},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2012},
  abstract  = {Im Rahmen der vorliegenden Arbeit wurden elektrooptische Transporteigenschaften und stochastisch aktivierte Prozesse Resonanter Tunneldioden (RTDs) bei Raumtemperatur untersucht. Die RTDs wurden auf dem III-V Halbleitermaterialsystem AlGaAs/GaAs durch Molekularstrahlepitaxie, Elektronenstrahllithographie und trockenchemischen {\"A}tztechniken hergestellt. Im Bereich des negativen differentiellen Leitwerts konnte bistabi-les Schalten und hierbei stochastisch aktivierte Dynamik nichtlinearer Systeme untersucht werden. Die Fl{\"a}chenabh{\"a}ngigkeit der {\"A}tzrate konnte ausgenutzt werden, um RTDs mit einem Stamm und zwei Transport{\"a}sten zu realisieren, welche hinsichtlich ihrer optischen und elektrischen Eigenschaften untersucht wurden. Im ersten experimentellen Abschnitt 3.1 werden die elektrischen Transporteigenschaften Resonanter Tunneldioden bei Raum-temperatur und die Fl{\"a}chenabh{\"a}ngigkeit des koh{\"a}renten und nicht-koh{\"a}renten Elektronen-transports analysiert. Die Realisierung universeller logischer Gatter (NOR und NAND) und deren Rekonfigurierbarkeit durch einen externen Kontrollparameter wird in Abschnitt 3.2 gezeigt. In Abschnitt 3.3 wird die Lichtsensitivit{\"a}t Resonanter Tunneldioden als Photode-tektoren f{\"u}r den sichtbaren Wellenl{\"a}ngenbereich und in Abschnitt 3.4 f{\"u}r die Telekommu-nikationswellenl{\"a}nge bei λ = 1,3 µm demonstriert.},
  subject      = {Resonanz-Tunneldiode},
  language  = {de}
}
@phdthesis{Rauh2013,
  author    = {Rauh, Daniel},
  title     = {Impact of Charge Carrier Density and Trap States on the Open Circuit Voltage and the Polaron Recombination in Organic Solar Cells},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-90083},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2013},
  abstract  = {The focus of this work is studying recombination mechanisms occurring in organic solar cells, as well as their impact on one of their most important parameters — the open circuit voltage Voc. Firstly, the relationship between Voc and the respective charge carrier density n in the active layer under open circuit conditions is analyzed. Therefor, a model after Shockley for the open circuit voltage is used, whose validity is proven with the aid of fits to the measured data. Thereby, it is emphasized that the equation is only valid under special conditions. In the used reference system P3HT:PC61BM the fits are in agreement with the measurement data only in the range of high temperatures (150 - 300 K), where Voc increases linearly with decreasing temperature. At lower temperatures (50 - 150 K), the experiment shows a saturation of Voc. This saturation cannot be explained with the model by the measured falling charge carrier density with decreasing temperatures. In this temperature range Voc is not directly related to the intrinsic properties of the active layer. Voc saturation is due to injection energy barriers at the contacts, which is ascertained by macroscopic simulations. Furthermore, it is observed that Voc in the case of saturation is equivalent to the so-called built-in potential. The difference between the built-in potential and the energy gap corresponds thereby to the sum of the energy barriers at both contacts. With the knowledge of the Voc(n) dependency for not contact limited solar cells, it is possible to investigate the recombination mechanisms of charge carriers in the active layer. For Langevin recombination the recombination rate is Rn2 (recombination order RO = 2), for Shockley-Read-Hall (SRH) Rn1 (RO=1); in various publications RO higher than two is reported with two main explanations. 1: Trap states for charge carriers exist in the respective separated phases, i.e. electrons in the acceptor phase and holes in the donor phase, which leads to a delayed recombination of the charge carriers at the interface of both phases and finally to an apparent recombination order higher than 2. 2: The enhanced R(n) dependency is attributed to the so called recombination prefactor, which again is dependent from n dependent mobility µ. It is shown that for the system P3HT:PC61BM at room temperature the µ(n) dependency does nearly completely explain the higher RO but not at lower temperatures which in this case supports the first explanation. In the material system PTB7:PC71BM the increased RO cannot be explained by the µ(n) dependency even at room temperature. To support the importance of trap states in combination with a phase separation for the explanation of the enhanced RO, additional trap states were incorporated in the solar cells to investigate their influence on the recombination mechanisms. To achieve this, P3HT:PC61BM solar cells were exposed to synthetic air (in the dark and under illumination) or TCNQ was added in small concentrations to the active layer which act as electron traps. For the oxygen degraded solar cell the recombination order is determined by a combination of open Voc-transients and Voc(n) measurements. Thereby, a continuous increase of the recombination order from 2.4 to more than 5 is observed with higher degradation times. By the evaluation of the ideality factor it can be shown that the impact of SRH recombination is increasing with higher trap concentration in relation to Langevin recombination. A similar picture is revealed for solar cells with TCNQ as extrinsic trap states. Finally, a phenomenon called s-shaped IV-curves is investigated, which can sometimes occur for solar cells under illumination. As course of this a reduced surface recombination velocity can be found. Experimentally, the solar cells were fabricated using a special plasma treatment of the ITO contact. The measured IV-curves of such solar cells are reproduced by macroscopic simulations, where the surface recombination velocity is reduced. Hereby, it has to be distinguished between the surface recombination of majority and minority charge carriers at the respective contacts. The theory can be experimentally confirmed by illumination level dependent IV-curves as well as short circuit current density and open circuit voltage transients.},
  subject      = {Organische Solarzelle},
  language  = {en}
}
@phdthesis{Summa2014,
  author    = {Summa, Alexander},
  title     = {Modelling high-energy observables of supernova explosions},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-94608},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2014},
  abstract  = {In this work, high-energy observables arising during different phases of SN explosions are studied with respect to their potential for allowing conclusions on suggested explosion scenarios and physical mechanisms that are thought to influence the evolution of SNe in a major way. The focus on selected observables at keV and MeV energies is motivated by the appearance of large degeneracies that can even be found for disparate scenarios in many wavelength regimes. Since the discussed emission in the high-energy regime is directly linked to nuclear processes being usually very distinct for different suggested physical models, the signatures at keV and MeV energies allow for meaningful comparisons of simulations with observations.},
  subject      = {Supernova},
  language  = {en}
}
@article{OPUS4-27753,
  title     = {Search for squarks and gluinos in final states with same-sign leptons and jets using 139 fb\(^{-1}\) of data collected with the ATLAS detector},
  series = {Journal of High Energy Physics},
  journal   = {Journal of High Energy Physics},
  number    = {6},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1007/JHEP06(2020)046},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-277538},
  pages     = {46},
  year      = {2020},
  abstract  = {A search for supersymmetric partners of gluons and quarks is presented, involving signatures with jets and either two isolated leptons (electrons or muons) with the same electric charge, or at least three isolated leptons. A data sample of proton-proton collisions at root s = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider between 2015 and 2018, corresponding to a total integrated luminosity of 139 fb(-1), is used for the search. No significant excess over the Standard Model expectation is observed. The results are interpreted in simplified supersymmetric models featuring both R-parity conservation and R-parity violation, raising the exclusion limits beyond those of previous ATLAS searches to 1600 GeV for gluino masses and 750 GeV for bottom and top squark masses in these scenarios.},
  language  = {en}
}
@article{OPUS4-17369,
  title     = {A measurement of the calorimeter response to single hadrons and determination of the jet energy scale uncertainty using LHC Run-1 \(pp\)-collision data with the ATLAS detector},
  series = {European Physical Journal C},
  volume    = {77},
  journal   = {European Physical Journal C},
  number    = {26},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1140/epjc/s10052-016-4580-0},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-173690},
  year      = {2017},
  abstract  = {A measurement of the calorimeter response to isolated charged hadrons in the ATLAS detector at the LHC is presented. This measurement is performed with 3.2 nb\(^{-1}\) of proton-proton collision data at \(\sqrt{s}\) = 7 TeV from 2010 and 0.1 nb\(^{-1}\) of data at \(\sqrt{s}\) = 8 TeV from 2012. A number of aspects of the calorimeter response to isolated hadrons are explored. After accounting for energy deposited by neutral particles, there is a 5\% discrepancy in the modelling, using various sets of GEANT4 hadronic physics models, of the calorimeter response to isolated charged hadrons in the central calorimeter region. The description of the response to anti-protons at low momenta is found to be improved with respect to previous analyses. The electromagnetic and hadronic calorimeters are also examined separately, and the detector simulation is found to describe the response in the hadronic calorimeter well. The jet energy scale uncertainty and correlations in scale between jets of different momenta and pseudorapidity are derived based on these studies. The uncertainty is 2-5\% for jets with transverse momenta above 2 TeV, where this method provides the jet energy scale uncertainty for ATLAS.},
  language  = {en}
}
@article{AeschlimannBrixnerCinchettietal.2017,
  author    = {Aeschlimann, Martin and Brixner, Tobias and Cinchetti, Mirko and Frisch, Benjamin and Hecht, Bert and Hensen, Matthias and Huber, Bernhard and Kramer, Christian and Krauss, Enno and Loeber, Thomas H. and Pfeiffer, Walter and Piecuch, Martin and Thielen, Philip},
  title     = {Cavity-assisted ultrafast long-range periodic energy transfer between plasmonic nanoantennas},
  series = {Light: Science \& Applications},
  volume    = {6},
  journal   = {Light: Science \& Applications},
  doi       = {10.1038/lsa.2017.111},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-173265},
  year      = {2017},
  abstract  = {Radiationless energy transfer is at the core of diverse phenomena, such as light harvesting in photosynthesis\(^1\), energy-transfer-based microspectroscopies\(^2\), nanoscale quantum entanglement\(^3\) and photonic-mode hybridization\(^4\). Typically, the transfer is efficient only for separations that are much shorter than the diffraction limit. This hampers its application in optical communication and quantum information processing, which require spatially selective addressing. Here, we demonstrate highly efficient radiationless coherent energy transfer over a distance of twice the excitation wavelength by combining localized and delocalized\(^5\) plasmonic modes. Analogous to the Tavis-Cummings model, two whispering-gallery-mode antennas\(^6\) placed in the foci of an elliptical plasmonic cavity\(^7\) fabricated from single-crystal gold plates act as a pair of oscillators coupled to a common cavity mode. Time-resolved two-photon photoemission electron microscopy (TR 2P-PEEM) reveals an ultrafast long-range periodic energy transfer in accordance with the simulations. Our observations open perspectives for the optimization and tailoring of mesoscopic energy transfer and long-range quantum emitter coupling.},
  language  = {en}
}
@techreport{Gross2022,
  author    = {Groß, Lennart},
  title     = {Advices derived from troubleshooting a sensor-based adaptive optics direct stochastic optical reconstruction microscope},
  doi       = {10.25972/OPUS-28995},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-289951},
  pages     = {20},
  year      = {2022},
  abstract  = {One rarely finds practical guidelines for the implementation of complex optical setups. Here, we aim to provide technical details on the decision making of building and revising a custom sensor-based adaptive optics (AO) direct stochastic optical reconstruction microscope (dSTORM) to provide practical assistance in setting up or troubleshooting similar devices. The foundation of this report is an instrument constructed as part of a master's thesis in 2021, which was built for deep tissue imaging. The setup is presented in the following way: (1) An optical and mechanical overview of the system at the beginning of this internship is given. (2) The optical components are described in detail in the order at which the light passes through, highlighting their working principle and implementation in the system. The optical component include (2A) a focus on even sample illumination, (2B) restoring telecentricity when working with commercial microscope bodies, (2C) the AO elements, namely the deformable mirror (DM) and the wavefront sensor, and their integration, and (2D) the separation of wavefront and image capture using fluorescent beads and a dichroic mirror. After addressing the limitations of the existing setup, modification options are derived. The modifications include the implementation of adjustment only light paths to improve system stability and revise the degrees of freedom of the components and changes in lens choices to meet the specifications of the AO components. Last, the capabilities of the modified setup are presented and discussed: (1) First, we enable epifluorescence imaging of bead samples through 180 µm unstained murine hippocampal tissue with wavefront error correction of ~ 90 \%. Point spread function, wavefront shape and Zernike decomposition of bead samples are presented. (2) Second, we move from epifluorescent to dSTORM imaging of tubulin stained primary mouse hippocampal cells, which are imaged through up to 180 µm of unstained murine hippocampal tissue. We show that full width at half maximum (FWHM) of prominent features can be reduced in size by nearly a magnitude from uncorrected epiflourescence images to dSTORM images corrected by the adaptive optics. We present dSTORM localization count and FWHM of prominent features as as a function of imaging depth.},
  subject      = {Einzelmolek{\"u}lmikroskopie},
  language  = {en}
}
@article{OPUS4-17371,
  title     = {Search for triboson \({W^\pm}{W^\pm}{W^\mp}\) production in \(pp\) collisions at \(\sqrt{s}\) = 8 TeV with the ATLAS detector},
  series = {European Physical Journal C},
  volume    = {77},
  journal   = {European Physical Journal C},
  number    = {141},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1140/epjc/s10052-017-4692-1},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-173710},
  year      = {2017},
  abstract  = {This paper reports a search for triboson \({W^\pm}{W^\pm}{W^\mp}\) production in two decay channels (\({W^\pm}{W^\pm}{W^\mp}\) → \({ℓ^\pm}{νℓ^\pm}{νℓ^\mp}{ν}\) and \({W^\pm}{W^\pm}{W^\mp}\) → \({ℓ^\pm}{νℓ^\pm}{νjj}\) with \(ℓ=e,μ\)) in proton-proton collision data corresponding to an integrated luminosity of 20.3 fb\(^{-1}\) at a centre-of-mass energy of 8 TeV with the ATLAS detector at the Large Hadron Collider. Events with exactly three charged leptons, or two leptons with the same electric charge in association with two jets, are selected. The total number of events observed in data is consistent with the Standard Model (SM) predictions. The observed 95\% confidence level upper limit on the SM \({W^\pm}{W^\pm}{W^\mp}\) production cross section is found to be 730 fb with an expected limit of 560 fb in the absence of SM \({W^\pm}{W^\pm}{W^\mp}\) production. Limits are also set on \(WWWW\) anomalous quartic gauge couplings.},
  language  = {en}
}
@article{OPUS4-22066,
  title     = {Measurement of dijet azimuthal decorrelations in \({pp}\) collisions at root s=8 TeV with the ATLAS detector and determination of the strong coupling},
  series = {Physical Review D},
  volume    = {98},
  journal   = {Physical Review D},
  number    = {9},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1103/PhysRevD.98.092004},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-220665},
  pages     = {1-31},
  year      = {2018},
  abstract  = {measurement of the rapidity and transverse momentum dependence of dijet azimuthal decorrelations is presented, using the quantity R-Delta phi. The quantity R-Delta phi specifies the fraction of the inclusive dijet events in which the azimuthal opening angle of the two jets with the highest transverse momenta is less than a given value of the parameter Delta phi(max). The quantity R-Delta phi is measured in proton-proton collisions at root s = 8 TeV as a function of the dijet rapidity interval, the event total scalar transverse momentum, and Delta phi(max). The measurement uses an event sample corresponding to an integrated luminosity of 20.2 fb(-1) collected with the ATLAS detector at the CERN Large Hadron Collider. Predictions of a perturbative QCD calculation at next-to-leading order in the strong coupling with corrections for nonperturbative effects are compared to the data. The theoretical predictions describe the data in the whole kinematic region. The data are used to determine the strong coupling alpha(S) and to study its running for momentum transfers from 260 GeV to above 1.6 TeV. Analysis that combines data at all momentum transfers results in alpha(S) (m(Z)) = 0.1127(- 0.0027) (+0.0063).},
  language  = {en}
}
@phdthesis{Dietrich2024,
  author    = {Dietrich, Philipp},
  title     = {Traveling Wave Magnetic Particle Imaging: Visuelle Stenosequantifizierung und Perkutane Transluminale Angioplastie im Gef{\"a}ßmodell},
  doi       = {10.25972/OPUS-35251},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-352517},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2024},
  abstract  = {Magnetic Particle Imaging (MPI) ist ein innovatives tomographisches Bildgebungs­verfahren, mit dem Tracerpartikel {\"a}ußerst sensitiv und schnell mehrdimensional abgebildet werden k{\"o}nnen. Die Methode basiert auf der nichtlinearen Magnetisierungs­antwort superparamagnetischer Eisenoxidnanopartikel (SPION) in einem Messpunkt, welcher ein Messvolumen rastert. In vorliegender Arbeit wurde das sog. Traveling Wave MPI (TWMPI) Verfahren eingesetzt, wodurch im Vergleich zu konventionellen MPI-Scannern ein gr{\"o}ßeres Field of View (FOV) und eine geringere Latenz bis zur Bildanzeige erreicht werden konnte. TWMPI weist einige f{\"u}r medizinische Zwecke vielversprechende Eigenschaften auf: Es liefert zwei- und dreidimensionale Bildrekonstruktionen in Echtzeit mit hoher zeitlicher und r{\"a}umlicher Aufl{\"o}sung. Dabei ist die Bildgebung von Grund auf hintergrundfrei und erfordert keinerlei ionisierende Strahlung. Zudem ist die Technik {\"a}ußerst sensitiv und kann SPION-Tracer noch in mikromolaren Konzentrationen detektieren. Ziel dieser Arbeit war es daher zu untersuchen, inwiefern es mittels TWMPI m{\"o}glich ist, k{\"u}nstliche Stenosen im Gef{\"a}ßmodell visuell in Echtzeit darzustellen und quantitativ zu beurteilen sowie {\"u}berdies eine perkutane transluminale Angioplastie (PTA) im Gef{\"a}ßmodell unter TWMPI-Echtzeit-Bildgebung durchzuf{\"u}hren. Alle Experimente wurden in einem speziell angefertigten TWMPI-Scanner durchgef{\"u}hrt (JMU W{\"u}rzburg, Experimentelle Physik V (Biophysik), FOV: 65 x 29 x 29 mm³, Aufl{\"o}sung: ca. 1.5 - 2 mm). Die Lumen-Darstellungen erfolgten mittels des SPION-Tracers Ferucarbotran in einer Verd{\"u}nnung von 1 : 50 (entspr. 10 mmol [Fe]/l). Das PTA-Instrumentarium wurde mit eigens hergestelltem ferucarbotran­haltigem Lack (100 mmol [Fe]/l) markiert. F{\"u}r die verschiedenen Teilexperimente wurden den jeweiligen speziellen Anforderungen entsprechend mehrere Gef{\"a}ßmodelle handgefertigt. F{\"u}r die visuelle Stenosequantifizierung wurden f{\"u}nf starre Stenosephantome unterschiedlicher Stenosierung (0\%, 25\%, 50\%, 75\%, 100\%) aus Polyoxymethylen her­gestellt (l: 40 mm, ID: 8 mm). Die Gef{\"a}ßmodelle wurden mehrfach zentral im FOV platz­iert und das stenosierte Lumen mittels sog. Slice-Scanning Modus (SSM, Einzel­aufnahme inkl. 10 Mittelungen: 200 ms, Bildfrequenz: 5 Bilder pro Sekunde, Latenz: ca. 100 ms) als zweidimensionale Quasi-Projektionen abgebildet. Diese Aufnahmen (n = 80, 16 je Phantom) wurden mit einer ein­heitlichen Grauskalierung versehen und anschließend entsprechend den NASCET-Kriterien visuell ausgewertet. Alle achtzig Aufnahmen waren unabh{\"a}ngig vom Stenosegrad aufgrund einheitlicher Fensterung sowie konstanter Scannerparameter untereinander gut vergleichbar. Niedrig­gradige Stenosen konnten insgesamt genauer abgebildet werden als h{\"o}hergradige, was sich neben der subjektiven Bildqualit{\"a}t auch in geringeren Standardabweichungen zeigte (0\%: 3.70 \% ± 2.71, 25\%: 18.64 \% ± 1.84, 50\%: 52.82 \% ± 3.66, 75\%: 77.84 \% ± 14.77, 100\%: 100 \% ± 0). Mit zunehmendem Stenosegrad kam es vermehrt zu geometrischen Ver­zerrungen im Zentrum, sodass bei den 75\%-Stenosen eine breitere Streuung der Messwerte mit einer h{\"o}heren Standardabweichung von 14.77\% einherging. Leichte, randst{\"a}ndige Artefakte konnten bei allen Datens{\"a}tzen beobachtet werden. F{\"u}r die PTA wurden drei interaktive Gef{\"a}ßmodelle aus Polyvinylchlorid (l: 100 mm, ID: 8 mm) mit zu- und abf{\"u}hrendem Schlauchsystem entwickelt, welche mittels Kabelband von außen hochgradig eingeengt werden konnten. Analog zu einer konventionellen PTA mittels r{\"o}ntgenbasierter digitaler Subtraktionsangiographie (DSA), wurden alle erforder­lichen Arbeitsschritte (Gef{\"a}ßdarstellung, Drahtpassage, Ballonplatzierung, Angioplastie, Erfolgskontrolle) unter (TW)MPI-Echtzeit-Bildgebung (Framerate: 2 - 4 FPS, Latenz: ca. 100 ms) abgebildet bzw. durchgef{\"u}hrt. Im Rahmen der PTA war eine Echtzeit-Visualisierung der Stenose im Gef{\"a}ßmodell durch Tracer-Bolusgabe sowie die F{\"u}hrung des markierten Instrumentariums zum Zielort m{\"o}glich. Die Markierung der Instrumente hielt der Beanspruchung w{\"a}hrend der Prozedur stand und erm{\"o}glichte eine genaue Platzierung des Ballonkatheters. Die Stenose konnte mittels Angioplastie-Ballons unter Echtzeit-Darstellung gesprengt werden und der Interventionserfolg im Anschluss durch erneute Visualisierung des Lumens validiert werden. Insgesamt zeigt sich MPI somit als ad{\"a}quate Bildgebungstechnik f{\"u}r die beiden in der Fragestellung bzw. Zielsetzung definierten experimentellen Anwendungen. Stenosen im Gef{\"a}ßmodell konnten erfolgreich in Echtzeit visualisiert und bildmorphologisch nach NASCET-Kriterien quantifiziert werden. Ebenso war eine PTA im Gef{\"a}ßmodell unter TWMPI-Echtzeit-Bildgebung machbar. Diese Ergebnisse unter­streichen das grundlegende Potenzial von MPI f{\"u}r medizinische Zwecke. Um zu den bereits etablierten Bildgebungsmethoden aufzuschließen, ist jedoch weitere Forschung im Bereich der Scanner-Hard- und -Software sowie bez{\"u}glich SPION-Tracern n{\"o}tig.},
  subject      = {Medizinische Radiologie},
  language  = {de}
}