Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 27 for “"collective excitations"”.
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Ultrafast Terahertz Spectroscopy of Collective Excitations in Correlated Materials
… complex ground state phases. The lowest-energy collective excitations of a particular ground state serve as a fingerprint of the phase of matter, and revealing such collective modes can therefore provide crucial information for understanding the underlying microscopic interactions. A powerful …
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Collective excitations in layered materials with momentum-resolved electron energy loss spectroscopy
… Lastly, the observation of a novel electronic collective mode in TiSe2 is presented as strong evidence for an excitonic insulator phase in this compound.
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Self -assembly on strained metallic interfaces, and, Novel collective excitations on metal surfaces
… spectroscopy on Be(0001). This new mode is a collective excitation of the surface electrons. This discovery goes against the traditional wisdom that on metal surfaces only regular (optical) surface plasmons can exist. First-principles calculations show that this mode is caused by the …
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Collective excitations in low dimensional systems and stochastic control of population growth in a fluctuating environment
… I study several problems in the following areas: collective excitations in condensed matter physics, noise in gene network and stochastic control in biophysics. In the first area, I construct an effective field theory to describe Bose-Einstein Condensate (BEC) realized in an external potential. …
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Carrier momentum relaxation in highly doped polar semiconductors and semiconductor heterostructures
… such structures. In doped polar semiconductors, collective excitations of the carriers (plasmons) and the atoms (polar phonons) couple. These coupled collective excitations affect the electrical conductivity, here quantified through the carrier mobility. In scattering events, the carriers and the …
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Collective Phenomena in Excitonic Quantum Matter
… pairs, known as excitons, are fundamental excitations of solids, and are expected to realise a rich phase diagram of quantum phases in- and out-of-equilibrium: a hypothesized pairing instability leads to the macroscopic condensation of “excitonic insulators” in small-bandgap materials, with …
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Study of Plasmon Resonances in Single Photoionization of Carbon Fullerene Molecular Ions
… surface and volume plasmon resonances due to collective excitations of valence electrons were characterized and quantified by Lorentzian fits. Resonance parameters such as lifetimes and oscillator strengths were calculated and compared. Results for the photoionization of C60+ were compared to …
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Testing the vibrational nature of 100Ru
… in the exploration of the nature of low-lying collective excitations in nuclei, as several recent studies have posed serious questions regarding the veracity of multiphonon quadrupole vibrations. A recent survey of nuclei with previously assumed low-lying spherical vibrational structure showed …
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Properties and dynamics of hot nuclei
… state and Skyrme interaction. The properties of collective excitations of various multipolarity and the transition strength to excite them are investigated. The evolution of a hot and/or compressed nucleus is analyzed within the adiabatic approximation using a constrained FTHF method to describe …
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Tuning the coherent electron-nuclear interaction in a semiconductor quantum dot
… to implement a multi-qubit register formed by collective excitations of the nuclei surrounding the electron, or to probe fundamental many-body physics through engineering of collective states. However, a tuneable interaction between the electron and the nuclear ensemble is required to fully …
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Nuclear structure in 16O measured with (e,e´γ) coincident electron scattering
… the nuclear transition currents characterizing collective excitations in doubly closed shell nuclei. This observation was achieved by studying the transverse-longitudinal form factor ratios for the excitations to the 2+ (6.92 MeV) and 3- (6.13 MeV) states of 160. At the same time, we established …
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X-Ray scattering investigations of subtle ordering in correlated materials
… new phases of matter whose properties and collective excitations bear little resemblance to the individual particles and interactions. Understanding how the macroscopic state transforms from one phase to another provides key insights into the underlying physics. In this thesis, we study two …
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Effective interactions and pairing correlations: from nuclei to compact stars
… the mixed isoscalar-isovector character of their collective excitations. In particular, we address some of the open questions concerning the nature of the low-lying isovector dipole strength experimentally observed in neutron-rich nuclei and known in literature as pygmy dipole resonance (PDR). We …
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Interactive Spin Dynamics in Magnon and Quantum Spin Systems
… directed toward two types of spin-based systems: collective excitations of spins, known as spin waves or magnons, in magnetic materials, and optically active spin defects as represented by nitrogen-vacancy (NV) centers in diamond, leading to the prosperity of magnonics, quantum sensing, and …
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Femtosecond spectroscopy of coherent phenomena in quantum materials : a dissertation
… quasi-particles and/or exciting specific collective modes. The resulting dynamic changes are then tracked as a function of time by using two different spectroscopic tools: transient reflectivity and time and angle resolved photoemission (Tr-ARPES). One approach is to perturb the system …
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Spektroskopie im superdeformierten Minimum von 240 Pu
… and the derived conclusions on the structure of collective excitation modes in deformed nuclei. From the combined analysis of γ-decay and conversion electron measurements and an experiment on the transmission resonances in the prompt fission probability a detailed level scheme for the second …
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Controlling and probing nonlinear collective mode dynamics in quantum materials
… In particular, the excitation of low-energy collective modes in solids—such as lattice vibrations (phonons) and spin precessions (magnons)—to large amplitudes opens fundamentally new pathways for controlling and probing material properties that are otherwise inaccessible under thermal …
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Coupling of single proton con_gurations to collective core excitations in 162Yb: the nucleus 161Tm.
… In attempt to understand the true nature of the collective vibrations in relation to the \pairing theory" a suitable approach is studying nuclei in the N = 88 90 region containing the [505]11=2 orbital. The current work seeks to get more insight on the microscopic nature of the aforementioned …
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Structural and electronic properties of noble metals on metal oxide surfaces
… properties of larger Ag clusters show strong collective excitations at ~ 3.8eV, in the UV part of the solar spectrum. We have found that when we encapsulated the titania supported Ag clusters in a thin titania overcapping layer, the nanoclusters retain their structural integrity and we find …
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Engineering light-matter interaction using two dimensional materials
… coupling of electromagnetic waves with various collective excitations such as plasmons and phonons, and carries great potential for nanophotonics across the long sought after terahertz to mid-infrared spectrum. In this thesis, I will show a few examples of how light-matter interaction can be …
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