Topological superconductivity is a novel phenomenon, that has recently been predicted to exist in quantum wires. The first signatures of this new superconducting state have recently been reported.... Show moreTopological superconductivity is a novel phenomenon, that has recently been predicted to exist in quantum wires. The first signatures of this new superconducting state have recently been reported. The difference with usual superconductors is the appearance of conducting edge states. It is of interest to investigate how all the well-known effects of superconductivity, including Andreev reflection and Josephson effect, are modified by these edge states, and also to discover new effects that appear only in topological superconductors. This investigation is the main topic of the thesis. Show less
Imaging subsurface structures with nanometer resolution has been a long-standing desire in science and industry. To obtain subsurface information one usually applies ultrasound, like e.g. in... Show moreImaging subsurface structures with nanometer resolution has been a long-standing desire in science and industry. To obtain subsurface information one usually applies ultrasound, like e.g. in echocardiography. Implementing ultrasound in an Atomic Force Microscope, a setup that is capable of imaging surfaces with atomic resolution, gives access to additional information. In particular, it is possible to image subsurface structures with nanometer resolution. However, it is not known why the subsurface structures become visible when applying ultrasound during the imaging with an Atomic Force Microscope. Based on a special excitation scheme, which makes use of two ultrasound excitations (one through the sample and one through the cantilever), Heterodyne Force Microscopy seems to be the most promising candidate for imaging deeply buried objects or structures with nanometer resolution. This thesis focuses on the poorly understood elements in Heterodyne Force Microscopy. We studied the ultrasound propagation in the sample, the dynamics of an ultrasonically excited cantilever near a sample that is also vibrating at a slightly diff erent frequency, and the generation of the heterodyne signal. The insight we gained in these matters allowed us to determine the contrast mechanism in a very well-de fined model sample, which contains gold nanoparticles buried in a soft polymer matrix. We show that the contrast in this system is determined by “friction at shaking nanoparticles”. Show less
We study the dynamics of single molecules and individual gold nanorods in glycerol at variable temperatures. We demonstrate temperature-cycle microscopy on FRET-labeled polyproline and double... Show moreWe study the dynamics of single molecules and individual gold nanorods in glycerol at variable temperatures. We demonstrate temperature-cycle microscopy on FRET-labeled polyproline and double-stranded DNA molecules to access micro-second dynamics of single molecules, and reveal the influences of dye-dye interaction at short interdye distances on the observed FRET values. We use neutron-scattering techniques to examine the origin of solid-like structures suggested in previous reports and the influence of the thermal history. We find that crystal nucleation takes place in glycerol at temperatures very close to the glass transition temperature. This observation suggests that the thermal history of the glycerol sample needs to be controlled for studying dynamical heterogeneity in supercooled liquids. For the first time, we demonstrate gold nanorods as local viscosity reporter to study heterogeneity in supercooled liquids. Following rotational dynamics of individual gold nanorods in glycerol upon cooling below 226K, we start to observe deviations of local viscosity from the bulk viscosity of glycerol. Our observation suggests heterogeneity on relatively large length scale exists at surprisingly high temperatures. In the end, we demonstrate gold nanorods for enhancing fluorescence from single molecules and for fluorescence correlation spectroscopy at micromolar concentrations with single-molecule sensitivity. Show less
In this thesis, we study energy transport and fluctuations in simple models of fragile matter : a unique state of matter that has a vanishingly small window of linear response since one or both of... Show moreIn this thesis, we study energy transport and fluctuations in simple models of fragile matter : a unique state of matter that has a vanishingly small window of linear response since one or both of its elastic moduli (shear and bulk) are nearly zero. As a consequence, even the tiniest perturbations travel as nonlinear waves. In addition, most models of fragile matter have an amorphous structure. It is the interaction of the non-linear waves with the underlying disorder and the resulting fluctuations, that constitutes the unifying theme explored in this thesis. There are at least two seemingly distinct sources of fragility: a local source stemming from the strongly non-linear interaction potential between particles so that one can not expand around a potential minimum to define a spring constant, and a second, global source, whereby the collective response of the sample can be considered weakly linear. As a model of the first kind, we consider a two dimensional packing of soft frictionless elastic disks that are just touching their nearest neighbours. The interaction potential between elastic disks is given by the nonlinear Hertz law that has no harmonic part. Consequently, for a packing in this state, the bulk modulus is vanishingly small and the smallest compressions imparted at the edges leads to nonlinear solitary like waves. As a model of the second kind, we consider a two dimensional random network of harmonic springs where each node has on average around four nearest neighbours. Here, despite the contact interaction being harmonic, the network has a vanishingly small shear modulus. Consequently, even the tiniest shear strains elicit non-linear waves. There are many important similarities and differences between the nature of non-linear waves and the role played by disorder in the two models described above, which we are gradually beginning to understand. Show less
Magnetic resonance force microscopy (MRFM) is a powerful technique to detect a small number of spins that relies on force detection by an ultrasoft magnetically tipped cantilever and selective... Show moreMagnetic resonance force microscopy (MRFM) is a powerful technique to detect a small number of spins that relies on force detection by an ultrasoft magnetically tipped cantilever and selective magnetic resonance manipulation of the spins. MRFM would greatly benefit from ultralow temperature operation, because of lower thermomechanical noise and increased thermal spin polarization. Here we demonstrate MRFM operation at temperatures as low as 30 mK, thanks to a recently developed superconducting quantum interference device (SQUID)-based cantilever detection technique, which avoids cantilever overheating. In our experiment, we detect dangling bond paramagnetic centres on a silicon surface down to millikelvin temperatures. Fluctuations of such defects are supposedly linked to 1/f magnetic noise and decoherence in SQUIDs, as well as in several superconducting and single spin qubits. We find evidence that spin diffusion has a key role in the low-temperature spin dynamics Show less
Many materials, like foams, emulsions, suspensions and granular media obtain finite rigidity once their constituent particles are brought in contact. Nevertheless, all these materials can be made... Show moreMany materials, like foams, emulsions, suspensions and granular media obtain finite rigidity once their constituent particles are brought in contact. Nevertheless, all these materials can be made to flow by the application of relatively small stresses. By varying thermodynamic (temperature or density) and mechanical (applied stress) variables, one can bring about a transition from a freely flowing to a jammed state. What is the elastic response of foams close to the jamming point? How much can these materials be loaded before they flow? What is their behavior like in the bulk? These problems are of great interest in academics, as well as industrial applications (oil/gas extraction, cosmetics, pharmaceuticals and food processes). I study the transition from the flowing to the non-flowing regime in foams and analyze the non-affine behavior at this critical point. Additionally, whereas the usual rheological approach is to study the shear, I have developed a technique to measure compressive response in a real-world, foam system, taking gravity and temperature fluctuations into account. Show less
We study the technique of photothermal microscopy by which we can detect single nano-objects by their absorption at room temperature. We optimize the sensitivity of this technique and demonstrate... Show moreWe study the technique of photothermal microscopy by which we can detect single nano-objects by their absorption at room temperature. We optimize the sensitivity of this technique and demonstrate the first optical detection of a single molecule by its absorption at room temperature. Moreover, we combine photothermal, luminescence and scattering of individual nano-objects (organic dye nanoparticles and gold nanoparticles) at single-particle level to gain insight into their radiative and nonradiative properties. Single organic nanoparticles exhibit a complex excitation power-dependent luminescence quantum yield due to singlet-singlet or singlet-triplet annihilation, and their luminescence quantum yield can be as high as 10^(__2). In contrast to organic dye nanoparticles, gold nanoparticles yield very stable optical signals. Gold nanoparticles are also easily detectable by their photoluminescence. We find that the luminescence quantum yield of single gold nanoparticles is nearly independent of their volumes and can be as high as ~10^(-5) for nanorods with a plasmon resonance of ~650 nm. We further investigate the sensitivity of a single gold nanorod to an approaching dielectric surface. We show that the nanorod exhibits significant red-shift in its plasmon resonance wavelength for distances less than 400 nm pointing the way towards the possible application of nanorods as distance sensors. Show less
In this thesis, two routes towards high-speed scanning tunneling microscopy (STM) are described. The first possibility for high-speed scanning that is discussed is the use of MEMS (Micro-Electro... Show moreIn this thesis, two routes towards high-speed scanning tunneling microscopy (STM) are described. The first possibility for high-speed scanning that is discussed is the use of MEMS (Micro-Electro Mechanical Systems) devices as high-speed add-ons in STM microscopes. The functionality of these devices is shown using finite-element simulations, combined with measurements of their resonance frequency and actuation range. Tip deposition was done using EBID (Electron-Beam Induced Deposition) which allowed the first tunneling experiments with these high-speed STM scanners. Next, a dedicated STM design is presented that allows incorporation of a counter piezo element, which allows both force and torque compensation during STM measurements. The mechanical behaviour of the scanner as a function of scanning- and counter-piezo actuation is discussed. It is shown how image deformation, induced by internal scanner vibrations that are excited by the scanning motion of the piezo element, can be reduced using force- or torque compensation. We show that, using Fourier analysis, it is possible to determine the optimal compensation scheme for each excited internal resonance of the scanner. Show less
A surface plasmon is light that is bound to a metal surface. The main merit of a surface plasmon is that is provides confinement below the diffraction limit. In this thesis, we first study the... Show moreA surface plasmon is light that is bound to a metal surface. The main merit of a surface plasmon is that is provides confinement below the diffraction limit. In this thesis, we first study the excitation and scattering of surface plasmons by subwavelength holes in the metal. Thereafter we show that an array of these hole acts as a surface plasmon laser when the surface plasmons are sufficiently amplified using a semiconductor gain medium Show less
At any given time, cosmic rays constantly shower the Earth from all direction. The origin of cosmic rays is still a mystery as their paths are deflected by magnetic fields to random directions. The... Show moreAt any given time, cosmic rays constantly shower the Earth from all direction. The origin of cosmic rays is still a mystery as their paths are deflected by magnetic fields to random directions. The most likely sources of cosmic rays are Gamma-Ray Bursts (GRB). As the most energetic events known in the universe, GRBs are the death throes of massive stars that end in the explosion of stellar materials into interstellar matters. The interactions between cosmic rays and materials surrounding the GRB can produce neutrinos and very-high energy gamma-rays. Studying these high-energy neutrinos and gamma-rays can enlighten us further on the origin of cosmic rays. Very-high energy gamma rays can be observed by very large volume neutrino telescopes such as ANTARES in the Mediterranean Sea and IceCube in the South Pole. This dissertation focuses on ANTARES telescope operated as a gamma-ray telescope, which is possible by searching for downgoing muons produced from the interaction of gamma-rays with the Earth's atmosphere. Analytical calculations necessary to estimate the rate of photon-induced muons from GRBs has been performed. The responses of the detector to downgoing muons have been understood by using Monte Carlo simulations. The findings also provide a discussion on the future prospect of this venture. Show less
We employ the novel method of AdS/CFT correspondence to study strongly correlated fermions, their ground states and the phase transitions between them. AdS/CFT maps the quantum many-body problem to... Show moreWe employ the novel method of AdS/CFT correspondence to study strongly correlated fermions, their ground states and the phase transitions between them. AdS/CFT maps the quantum many-body problem to a classical gravity problem, making it more tractable. We find a holographic description of Fermi liquids and then proceed to find novel non-Fermi liquid ground states. In the future one can expect AdS/CFT to contribute toward our understanding of real world materials. Show less
A microscopic origin of dark matter phenomenon is the most plausible hypothesis to explain the mystery of dark matter. The dark matter particle hypothesis necessarily implies an extension of the... Show moreA microscopic origin of dark matter phenomenon is the most plausible hypothesis to explain the mystery of dark matter. The dark matter particle hypothesis necessarily implies an extension of the Standard Model. In this thesis, we undertook a systematic model-independent program of studying the properties of decaying dark matter. By analyzing the experimental data for dwarf spheroidal galaxies it was shown that the X-ray energy range is a preferred region when searching for radiatively decaying dark matter. By analyzing dark matter distributions in different types of galaxies and in galaxy clusters we show that the expected dark matter signal increases slowly with the mass of the object. Therefore, dwarf and spiral galaxies are the observational targets with the optimal signal-to-noise ratio. To probe the theoretically interesting regions of particle physics models we performed a combined analysis of a very large dataset of archival XMM-Newton observations of galaxies. Finally, we discussed an ultimate way to probe the whole parameter space of minimal models of decaying dark matter. We argue that a new X-ray telescope with the narrow energy resolution (comparable to internal width of the line) and large field-of-view is required. Show less
This thesis deals with the properties of doped perovskite manganites in the form of thin films, and with interfaces between insulating perovskites. The first question we investigate has to do with... Show moreThis thesis deals with the properties of doped perovskite manganites in the form of thin films, and with interfaces between insulating perovskites. The first question we investigate has to do with the strong reduction of the metal-insulator (MI) transition temperature when the films are strained.In particular,we investigate whether there is an influence of a change in carrier density due to strain. The data shows that the carrier density averaged over the film thickness decreases when the films become very thin. This we ascribe to the effects of the interface, and of magnetically dead layers which form close to the interface, in which charge discontinuities probably play a role. The second question, addressed in this thesis, is why the interface between two band insulators LaAlO3 and SrTiO3 is not conducting grown by sputtering, whereas many groups find conducting interfaces when growing by pulsed laser deposition (PLD). A detailed study indicates that the deposition pressure, La/Al ratio and conductivity are strongly related and play a vital role in defining the conductance of the interface. The sputter-grown non-conducting interfaces were also found to be nonmagnetic which once more emphasizes the importance of the interface oxygen stoichiometry in the mechanisms for conductance and magnetism. Show less
Phenomenologically, cosmic inflation is a satisfying and well-tested description of the physics of the very early universe. During this epoch, the universe was dominated by high energy phenomena... Show morePhenomenologically, cosmic inflation is a satisfying and well-tested description of the physics of the very early universe. During this epoch, the universe was dominated by high energy phenomena that can only be truly understood in a quantum gravity theory such as string theory. In this thesis we show that the embedding of inflation in a string theoretic framework is very sensitive to the details of the theory. We consider both the low energy supergravity limit as well as a worldsheet set-up. Moreover, we investigate the constraints imposed by supersymmetry and conformal symmetry. Conformal symmetry is important both in the worldsheet theory as well as in a holographic description of inflation. In the latter case we investigate the imprints of conformal invariance on the (observable) statistical correlations in the cosmic microwave background radiation. Show less
The work described in this thesis was aimed at the study of the functional properties of (isolated and purified) biomolecular systems at the single-molecule level. Two prerequisites are essential... Show moreThe work described in this thesis was aimed at the study of the functional properties of (isolated and purified) biomolecular systems at the single-molecule level. Two prerequisites are essential for successfully achieving this goal. First of all, single biomolecules should be observable, which means that they should be natively fluorescent or they should be rendered fluorescent by suitable biochemical or biomolecular 12 engineering. The other challenge is to engineer the system in such a way that the fluorescence intensity reports the actual, functional state of the biomolecule. Show less
Charge counting statistics (C.S.) of traversing electron in quantum devices like atomic-molecular junctions is sensitive to the local perturbation in the charge field at the contact and in the... Show moreCharge counting statistics (C.S.) of traversing electron in quantum devices like atomic-molecular junctions is sensitive to the local perturbation in the charge field at the contact and in the quantum channels. The first cumulant of C.S. i.e. current-voltage characteristic of such devices has been tool for such investigation since long time. Here we have used the second cumulant i.e. shot noise to study the electron-electron and electron-phonon interaction in the atomic contacts. The shot noise measurement on the Au atomic chain reveals the inelastic scattering in the noise. These signatures can provide vital information on the feedback of the local phonon population on electron transport. The current-voltage characteristic of the ferromagnetic atomic contacts unexpectedly shows zero bias anomalies. This observation is attributed to the interaction of traversing electron with localized magnetic moments within same host species. The observed connection between the Fano factor and the weight of the zero bias anomalies supports the view that the zero bias anomaly originates from spin scattering by localized magnetic moments. However, whether this is true Kondo scattering as suggested by Calvo et al. cannot be stated conclusively from our data. At the end of thesis we have presented a low noise high frequency broadband noise measurement setup suitable for break junction setup. Show less
A study of the effect of chloride and sulfate anions, as well as of SPS molecules on Cu electrodeposition is presented in this thesis. The deposition process was analyzed by means of a home-built... Show moreA study of the effect of chloride and sulfate anions, as well as of SPS molecules on Cu electrodeposition is presented in this thesis. The deposition process was analyzed by means of a home-built fast electrochemical STM in situ after and during deposition. Show less
Topological phases of matter are exceptional because they do not arise due to a symmetry breaking mechanism. Instead they are characterized by topological invariants -- integer numbers that are... Show moreTopological phases of matter are exceptional because they do not arise due to a symmetry breaking mechanism. Instead they are characterized by topological invariants -- integer numbers that are insensitive to small perturbations of the Hamiltonian. As a consequence they support conducting surface states that are protected against disorder and other imperfections. Furthermore, a variety of unusual transport properties arise due to the presence of topology. In this work the interplay between topology and sample imperfections is investigated with a focus on transport phenomena. Show less
In this thesis, the formation of hexagonal boron nitride (h-BN) __nanomesh__ structures and of graphene on Rhodium (111) is studied experimentally. The structures of h-BN and graphene are extremely... Show moreIn this thesis, the formation of hexagonal boron nitride (h-BN) __nanomesh__ structures and of graphene on Rhodium (111) is studied experimentally. The structures of h-BN and graphene are extremely similar: both of them are single atomic layers with a honeycomb lattice, and the lattice constants are nearly identical. Both materials introduce novel properties and have the potential for a variety of applications. In this thesis, the layers were grown by chemical vapor deposition (CVD) on Rh(111). During growth, the formation processes were tracked by scanning tunneling microscopy (STM). This was performed in situ, namely during deposition at the elevated temperatures, required for the growth. In this way, we have obtained detailed knowledge of the formation mechanisms. In this thesis, basic surface science principles are employed to explain the observed, special growth behavior. Our understanding of the mechanisms at play has enabled us to compose new, improved deposition recipes that result in higher quality nanomesh and graphene layers. This knowledge is not only valuable for these specific systems, but it also deepens our general insights into deposition and growth of atomically thin layers. Show less
