During my PhD research, I studied the photon statistics of light emitted by a microcavity that contains a single quantum dot (QD) on resonance. The work encompasses an experimental part,... Show moreDuring my PhD research, I studied the photon statistics of light emitted by a microcavity that contains a single quantum dot (QD) on resonance. The work encompasses an experimental part, simulations and a theoretical element. In the experimental part, we developed a fiber-coupled single-photon source, which can easily be integrated with existing quantum technologies. The developed source is state of the art in terms of single photon rate and purity. Further, I performed extensive simulations on the quantum master model. This is a theoretical model describing the interaction between light and the quantum dot in a microcavity. These simulations lead to a better theoretical understanding of the physics behind single photon light and other non- classical states of light. Through a theoretical study, we reported of an alternative way to produce single photons called unconventional photon blockade. In my PhD research, I learned to develop new quantum technologies such as single photon sources, thoroughly analyze them using numerical simulations for improvement, as well as being able to perform a theoretical analysis for physical understanding. Show less
Graphene nanoribbons (GNRs) are used as a current carrying substrate in investigation of current-induced forces in a low-temperature STM (chapter 2). We demonstrate induced migration of Co adatoms... Show moreGraphene nanoribbons (GNRs) are used as a current carrying substrate in investigation of current-induced forces in a low-temperature STM (chapter 2). We demonstrate induced migration of Co adatoms on GNRs and on Au(111) using voltage pulses from the STM tip and we argue that motion is due to thermal excitations rather than the wind force. In chapter 3 we show that voltage signal is induced in a graphene strip when a droplet of ionic liquid is moved across its surface. Here we show that even deionized water can induce voltage over charged graphene surface due to the polarizability of water molecules. In chapter 4 we present a method for fabrication of graphene nanoelectrodes which we further test electrically in a modified STM. For the first time we demonstrate that the gap between two graphene nanoelectrodes can be tuned with subnanometric precision Show less
A difficulty of studies on chemical kinetics are the reaction time scales and detection of their intermediates. Rapid Freeze-Quench (RFQ) is one of the most common techniques to investigate... Show moreA difficulty of studies on chemical kinetics are the reaction time scales and detection of their intermediates. Rapid Freeze-Quench (RFQ) is one of the most common techniques to investigate chemical kinetics. Since the intermediates of many reactions are paramagnetic, coupling RFQ to Electron Paramagnetic Resonance (EPR) is a desirable goal, especially at high-frequency (HF-EPR). HF-EPR offers high resolution and better spectral definition. However, collection of RFQ samples for HF-EPR is troublesome. In Chapter 2, the successful coupling of RFQ to HF-EPR at 275 GHz is described. Chapter 3 describes the development of Temperature-Cycle EPR (T-Cycle EPR), a novel high-frequency EPR technique that couples laser-induced T-jumps of the sample to a high-frequency 275 GHz EPR spectrometer, to detect short-lived paramagnetic intermediates and kinetics of chemical reactions in aqueous solutions. Chapter 4 discusses the application of T-Cycle EPR on a model reaction unfolding over hundreds of milliseconds, proving the technique is suitable to study many (bio)chemical systems. Chapter 5 shows an attempt to apply T-Cycle EPR to an enzymatic system on the sub-second time. T-Cycle EPR experiments at 275 GHz are performed on the reoxidation of a mutant of Small Laccase in the sub-second time regime, without making use of RFQ. Show less
Triplet superconductivity refers to a condensate of equal-spin Cooper pairs (pairs of electrons with equal spin). While exceptionally rare in nature, triplet pairing of electrons can occur if... Show moreTriplet superconductivity refers to a condensate of equal-spin Cooper pairs (pairs of electrons with equal spin). While exceptionally rare in nature, triplet pairing of electrons can occur if either the temporal or spatial component of the superconducting wavefunction can be represented by an odd function. These are often referred to as odd-frequency and odd-parity triplets, respectively. We use hybrid magnetic devices to study the former, while the latter is investigated in mesoscopic structures of strontium ruthenate (Sr\tss{2}RuO\tss{4}). Show less
This thesis discusses the discovery potential of Intensity Frontier experiments. As a particular examples of such experiment the SHiP and MATHUSLA experiments where taken. The reach of these... Show moreThis thesis discusses the discovery potential of Intensity Frontier experiments. As a particular examples of such experiment the SHiP and MATHUSLA experiments where taken. The reach of these experiments was studied for the number of specific model of the Beyond Standard Model physics, namely neutrino Minimal Standard Model, Higgs-like scalar, axion-like particles and light dark matter. Show less
In this thesis, "culture" refers to the collection of subjective human traits, such as preferences an opinions, that a given, geographically bounded population has at a given moment in time.... Show moreIn this thesis, "culture" refers to the collection of subjective human traits, such as preferences an opinions, that a given, geographically bounded population has at a given moment in time. Representative samples of individuals from such populations are studied, focusing on individual opinions expressed on various topics, present in multivariate empirical data that had been previously collected, mainly via social surveys. We propose and exploit new methods for analyzing such data, relying on mathematical notions specific to statistical mechanics and information theory, but also on agent-based models/simulations of opinion/cultural dynamics driven by social influence. These methods provide new insights about how human culture is organized. They provide indications that cultural structure has universal properties, independent of the geographical region and of the set of survey questions. Furthermore, these properties suggest that culture is shaped around a small number of "rationalities", while also having a certain hierarchical organization that is robust to social influence dynamics. Finally, we propose a method of filtering the noise in the data, which seems to allow for the identification of cultural modules that are not visible otherwise. However, we also show that visible modules may well be just artifacts of survey design. Show less
Electrons in a crystal lattice have properties that may differ from those of a free electron in vacuum. The effective mass can be different from the bare electron mass, and it may even vanish, ... Show moreElectrons in a crystal lattice have properties that may differ from those of a free electron in vacuum. The effective mass can be different from the bare electron mass, and it may even vanish, so that the electron behaves in some respects as a relativistic massless particle such as a photon. The magnetic moment of the intrinsic angular momentum, the electron spin, may be also different from that of an elementary particle. Spin-like degrees of freedom, referred to as "pseudospin" or "valley isospin", can also arise in the effective low-energy description of electrons in the lattice fields. These various degrees of freedom are of interest as ways to store and transport information: one speaks of "spintronics" and "valleytronics" as alternatives to "electronics". For these purposes it is of interest to study the interplay between the orbital motion of electrons and their spin (spin-like) degrees of freedom, the so-called "spin-orbit coupling". In some systems where this interaction is strong, it causes the electron spin to be tied to the direction of motion. This thesis contains results about the effects of this "spin-momentum locking" on two classes of materials, oxide interfaces and Weyl semimetals, with a focus on their electrical transport properties. Show less
In the first part of this thesis we study the geometry of folding patterns. Specifically, we focus on crease patterns consisting entirely of four-vertices; these are points where four fold... Show moreIn the first part of this thesis we study the geometry of folding patterns. Specifically, we focus on crease patterns consisting entirely of four-vertices; these are points where four fold lines come together. A single four-vertex is the simplest example of a foldable crease pattern that can be folded without bending the material in between the folds, and has a remarkable property: despite its single degree of freedom, it has two distinct folding motions. We make use of this property, and show how to design arbitrarily large four-vertex crease patterns, which can fold into two or more shapes. This is in contrast to other design methods, which produce patterns that can only fold into one specific shape. In the second part of this thesis, we study single four-vertices, and show a robust method to obtain four-vertices with three energy minima, which correspond to three different stable folded configurations. This too is in contrast to other experimental methods, which can only generate bistable vertices or patterns. Show less
Mechanical metamaterials are man-made materials which derive their unusual properties from their structure rather than their composition. Their structure, or architecture, often consists of... Show moreMechanical metamaterials are man-made materials which derive their unusual properties from their structure rather than their composition. Their structure, or architecture, often consists of periodically arranged building blocks whose mutual interactions realize unusual properties. In this thesis, we investigate the role of two aspects of mechanical metamaterials: The beam ligaments and the microstructures of hinging squares. Both aspects play an important role in mechanical metamaterials, but give rise simultaneously to several open problems. First, although the mechanical behaviour of slender beam ligaments is well understood, the finite-width ligaments that often occur in mechanical metamaterials lead to new physics; wide beams exhibit a negative post-buckling stiffness, characterized by a decreasing force after buckling, which is not well understood. Second, fully filled microstructures of hinging squares constitute an auxetic mechanism, but possible new zero modes derived from (diluted) microstructures with missing squares remain largely unexplored. How does the number of zero modes increases in such diluted systems, can we count these additional modes, and what is their spatial structure? Here we address these open problems, thereby providing the necessary understanding to fully leverage the characteristics of wide beam ligaments and diluted collections of hinging squares for the design of novel mechanical functionalities. Show less
In this Thesis, novel charge induction mechanisms of ionic liquids are treated, tested and experimented on complex oxides, in particular cuprates. We show that it is possible to traverse the phase... Show moreIn this Thesis, novel charge induction mechanisms of ionic liquids are treated, tested and experimented on complex oxides, in particular cuprates. We show that it is possible to traverse the phase diagram of a cuprate, albeit electrochemically. This is in turn has been used in combination with advanced lithogragphic techniques to attempt to fabricate an in-plane Josephson junction. We point out that a long-range proximity effect is observed in a number of junctions. Possible connections to the Giant Proximity Effect are evaluated in the final chapter of the Thesis. Show less
This thesis is devoted to an in-depth examination of the various effects of disorder in the cuprate high-temperature superconductors. Disorder is ubiquitous in these materials and is central to... Show moreThis thesis is devoted to an in-depth examination of the various effects of disorder in the cuprate high-temperature superconductors. Disorder is ubiquitous in these materials and is central to a number of phenomena observed in various phases. We revisit several phenomena in the cuprates in light of what is now known about the nature of disorder present in these materials. First, the phenomenon of quasiparticle scattering interference is revisited using a number of different realistic models of distributed disorder which go beyond the single-impurity paradigms used in much of the literature. Next, we study the manner in which a finite DOS at the Fermi energy, seen in a large number of experiments, is generated by various models of disorder, and consider the possibility that smooth disorder from off-plane dopants explains this phenomenon. In addition the localization properties of the superconducting quasiparticles in the presence of various types of disorder are studied. Finally, we show how a number of nontrivial interaction effects in the superconducting and normal states of the cuprates could be visualized by scanning tunneling spectroscopy experiments. Show less
This thesis describes a study from both a theoreticaL and an experimental point of view. I deveLop a new ru•deL for electron transport through networks of interconnected narnzparticLes In the... Show moreThis thesis describes a study from both a theoreticaL and an experimental point of view. I deveLop a new ru•deL for electron transport through networks of interconnected narnzparticLes In the Coulomb blockade regime and compare this ru•del tc experimental data. The main conclusion from this study is that cotunneLing does not give any significant contribution tc electron transport. Instead, transport is governed by perccIatLng paths thrcugh the netwcrk. Here, disorder In the array (in the form of variation of the Coulomb chargLng energy of the nanzparticLes) is the domLnating factor. Morecver, usLng Low—energy electron potentiometry, I visualise the f Low cf electrcns through the network. We find here that the contact resistance is negligibLe, and Chat the electi•zn flow 13 not impeded by small irregularities such as small and grain boundaries . Show less
The key characteristic of active matter is the motion of an emergent collection (such as a flock of birds), which is driven by the consumption of energy by its active components (i.e. individual... Show moreThe key characteristic of active matter is the motion of an emergent collection (such as a flock of birds), which is driven by the consumption of energy by its active components (i.e. individual birds). In this thesis, the central question I consider is: how do topology and geometry affect the motion of active and other driven systems?I answer this question by considering several examples. Starting with active nematics, I show that geometry can eliminate the threshold reported for such systems and demonstrate how this can be realised, which can be useful in designing laminar flows at low activity. I then construct a minimal hydrodynamic theory of a living liquid crystal, in which bacteria are controlled by nematic patterning on a substrate which exhibit non-trivial topology. Finally I investigate topological mechanical chains; after explaining the different phases of the chain, in the process uncovering a new superspinner phase, I go on to analyse how these chains swim at low Reynolds number, and find that this is connected to both the topology and geometry of the chain. Show less
In this thesis we study quantum transport phenomena on the nanometer scale, in two classes of materials: topological insulators with induced superconductivity and graphene superlattices. Both... Show moreIn this thesis we study quantum transport phenomena on the nanometer scale, in two classes of materials: topological insulators with induced superconductivity and graphene superlattices. Both topics are motivated by recent experimental developments: the first topic arose from the search for Majorana fermions in a quantum spin Hall insulator, the second topic arose from the search for massive Dirac fermions in the Kekulé band structure of graphene on a copper substrate. We focus on lattice models, solving them both numerically and analytically. Show less
This thesis is a collection of experimental attempts to enhance photoluminescence of fluorescent molecules and quantum dots with single gold nanorods (GNRs) and relevant applications. Special... Show moreThis thesis is a collection of experimental attempts to enhance photoluminescence of fluorescent molecules and quantum dots with single gold nanorods (GNRs) and relevant applications. Special attention is focused on the interactions between single emitters and GNRs. The idea is to increase the emission of weak emitters by the excellent optical properties of GNRs so that weak light emitters will then be bright enough to be detected and studied individually. We can thus generalize single-molecule fluorescence spectroscopy to weakly emitting species which are currently undetectable by conventional single-molecule spectroscopy. The research is important for extending the scope of single-molecule spectroscopy, which is a powerful technique for understanding the dynamic behaviors at the nanometer scale in biological systems and other materials. Show less
This PhD-thesis presents a study on micron-sized particles, so-called colloids. By controlling the chemical and physical properties of these particles, such as the interparticle interaction... Show moreThis PhD-thesis presents a study on micron-sized particles, so-called colloids. By controlling the chemical and physical properties of these particles, such as the interparticle interaction and the particles’ shape, colloids can act as building blocks that self-assembly into larger structures. This could lead to the development of materials with novel properties such as ‘smart’ materials with the ability to adapt their structure to the environment. In this thesis spherical colloids are used as a starting point to make complex colloidal building blocks and larger microstructures. Anisotropic particles were formed by introducing surface roughness, dents, protrusions and chemical functionalization on the particle surface. Complex structures were obtained by assembling and reconfiguring clusters of spheres. Here, a balance of several phenomena including, the interfacial and potential energy, entropy and geometric constraints, determined the final geometry of the assembled structure. The work also shows how anisotropic elongated particles distorted the hexagonal order in crystals of spheres, either locally or over long distances. These distortions are known to influence the optical, mechanical and electronic properties of colloidal crystals. The complex particles and assemblies made in this study are therefore an important step towards the development of materials with novel and adaptable properties. Show less
Electron microscopy has become an extremely important techniquein a wide variety of elds. The resolving power is vastly superiorto light microscopes and electron microscopy has proven tobe valuable... Show moreElectron microscopy has become an extremely important techniquein a wide variety of elds. The resolving power is vastly superiorto light microscopes and electron microscopy has proven tobe valuable in elds ranging from archaeology and geology to biology andcondensed-matter physics.A major disadvantage is that the electron energy used in conventional ElectronMicroscopy (EM) ranges from 10’s to 100’s of keV. Such energetic electronscan signicantly damage the specimen. This is especially relevant in thestudy of biological samples and organic materials in general. Major eorts arebeing made to avoid this radiation damage from interfering with the studyof such materials. There are several approaches to minimize damage in EM.These include developing better detectors such that lower electron doses aresucient to form an image, and lowering the electron energies to several keV.In this dissertation I present the development of, and measurements with, atransmission electron microscope that uses electron energies ve orders ofmagnitude lower than in conventional Transmission Electron Microscopes(TEMs). The energies we use are in the order of a few eV. Hence, we call ourtechnique ’eV-TEM’. Show less
Single-molecule fluorescence was invented in the 1990s and has quickly developed into an indispensable technique in the biomedical sciences and condensed-matter research. It has revolutionized... Show moreSingle-molecule fluorescence was invented in the 1990s and has quickly developed into an indispensable technique in the biomedical sciences and condensed-matter research. It has revolutionized the fields of molecular biology, imaging (super-resolution), and catalysis, to name a few. In this thesis, we will apply fluorescence enhancement by single gold nanorods to extend single-molecule studies to chromophores with low fluorescence quantum yields and to high concentrations of probe molecules. Following single-molecule trajectories, we will explore variations in the electron-transfer rates of the metalloprotein azurin both from molecule to molecule and for the same molecule as a function of time. Evidence for conformational substates will be discussed based on dynamic heterogeneity. Show less
Atoms and molecules are the basic units of matter. If we keep dividing a bar of gold or a glass of water into smaller parts, at the end we are left with a single gold atom or a water molecule. We... Show moreAtoms and molecules are the basic units of matter. If we keep dividing a bar of gold or a glass of water into smaller parts, at the end we are left with a single gold atom or a water molecule. We could not divide them further without them losing their identity. Molecular electronics is the study of how electrons, which are fundamental particles in nature, flow through these basic units of the matter once connected between two electrical leads. At such small dimensions matter starts to lose its macroscopic properties and its behaviour is governed by the rules of quantum mechanics. A molecule can have various electronic and mechanical degrees of freedom (or eigenstates) with discrete energies. The electrons flowing through the molecule can interact with these degrees of freedom making single molecule devices. Better control and understanding of these interactions and study of how the atomic structure of the macroscopic electrical leads affect the electronic-transport forms the main focus of this thesis. Controlled manipulation of single atoms and molecules using a low-temperature scanning tunnelling microscope, probing charge transport using high-frequency shot-noise measurement and the use of graphene as possible electrodes are the three directions which are investigated here. Show less
Scattering of light in the presence of nano-structured materials, i.e. with features in the order of the wavelength of the light or smaller, reveals details of how light interacts with matter at... Show moreScattering of light in the presence of nano-structured materials, i.e. with features in the order of the wavelength of the light or smaller, reveals details of how light interacts with matter at the nanoscale. In this dissertation we present four cases of light scattering on nano-structures. First we describe how light confined in 2D structures, namely a dielectric membrane and a metal layer, interacts with either a single nano-hole or a hole-array. Then, we study two cases of light propagating in random scattering media: we show how phase modulation can be used to measure scattering properties in a volume scatterer (e.g. white paint), and we investigate light transport in a rough thin-film silicon solar cell. Show less
