This project follows a design that aims at enabling multi-frequency readout of STM current noise in the MHz regime, with future prospects to amplify and record such signals with a SQUID amplifier....Show moreThis project follows a design that aims at enabling multi-frequency readout of STM current noise in the MHz regime, with future prospects to amplify and record such signals with a SQUID amplifier. The design consists of multiple LC resonators to allow multi-frequency readout. Design choices, freedoms and restrictions are noted and a method to built and test the model is given. Steps are taken to allow testing of a SQUID readout experiment inside a dry dilution cryostat and the dynamic range of the SQUID is calculated and compared to typical STM (noise) currents. Mainly the feasibility of the design is studied and further effort to quantitatively explore the design is suggested.Show less
Magnetic Resonance Force Microscopy (MRFM) is a sensitive method to investigate spin systems, which uses a flexible cantilever as mechanical amplifier of the forces on its magnetic tip. However,...Show moreMagnetic Resonance Force Microscopy (MRFM) is a sensitive method to investigate spin systems, which uses a flexible cantilever as mechanical amplifier of the forces on its magnetic tip. However, MRFM is generally limited in its application at milliKelvin temperatures because existing devices rely on laser interferometry to detect cantilever deflection, which heats the cantilever, leaving many condensed matter systems out of reach for MRFM. Furthermore, lower temperatures correspond to lower cantilever force noise, so samples with more diluted spins could be investigated. SQUID-detected MRFM, using the flux induced by a moving cantilever tip, does allow for operation at milliKelvin temperatures. Yet, SQUID-detecting setups have still been limited in sample accessibility because the detection loop is printed on the sample. This thesis reports on the construction of a SQUID-detected MRFM device that employs a single probe head design to overcome the issue. The design choices and assembly methods for this device, called the easyMRFM, are discussed, as well as models to predict the sensitivity. It was found that the coupling is large enough to do optimisations in liquid helium dipstick experiments, although the thermal cantilever motion signal will only barely rise above the flux noise level. Lastly, a room-temperature magnetometry setup for cantilever chips is discussed that has proven useful in characterising cantilevers before mounting them in more permanent setups.Show less
In this research, we aim to achieve sub-mK effective electron measurements to better analyze effects that occur at these very low temperatures. We do this by using a Faraday cage, through which we...Show moreIn this research, we aim to achieve sub-mK effective electron measurements to better analyze effects that occur at these very low temperatures. We do this by using a Faraday cage, through which we send a signal using sets of inductors. In order to test this, we define an effective frequency range for our signal by analyzing the theoretical electrical side effects that occur in our system. We perform multiple room temperature tests on our system within the defined frequency range, and work towards testing the effectiveness of our system at millikelvin temperatures as well.Show less
A common problem in Magnetic Resonance Force Microscopy (MRFM) is the spin-induced damping of the cantilever, which drastically limits the sensitivity to spin signals. In order to solve this...Show moreA common problem in Magnetic Resonance Force Microscopy (MRFM) is the spin-induced damping of the cantilever, which drastically limits the sensitivity to spin signals. In order to solve this problem, we have developed improvements to a Persistent Current Switch (PCS) that make it less dissipative and capable of creating a stronger magnetic field at the sample. On top of this, the low noise level that our detection setup requires is conserved. The improvements are based on the use of a low-temperature magnetic core material called MetGlas [1]. We have measured the full B-H curve of the MetGlas and verified that it decreases the current required to switch a Niobium wire to the resistive state by a factor of 30. Furthermore, we have used this data to calculate the performance of a transformer made using this material, and we have calculated the expected extremely low noise level that this circuit will cause in our SQUID.Show less
In this work, we measure the internal magnetic field of a 100nm iron-doped palladium film by means of transversal field muon spin spectroscopy. The internal field and field inhomogeneity were...Show moreIn this work, we measure the internal magnetic field of a 100nm iron-doped palladium film by means of transversal field muon spin spectroscopy. The internal field and field inhomogeneity were measured in the bulk of the film from 3.5K to 100K and compared to measurements in a pure Pd film in order to investigate the effect of iron-doping. Furthermore, we compared these temperature sweeps to existing μSR measurements on bulk PdFe [1], in order to verify the quality of the film. Finally, we measured the internal field and field inhomogeneity at 3.5K as a function of muon implantation energy, in order to learn more about the spatial variation of the internal magnetic field. Ultimately, by doing this characterization, we hope that PdFe can serve as a testbed for other local magnetic field probe techniques.Show less
Deep reinforcement learning has solved the game of Go, along with all other board games. Can it also be applied to real-world use cases? This research combines a literature study and experimental...Show moreDeep reinforcement learning has solved the game of Go, along with all other board games. Can it also be applied to real-world use cases? This research combines a literature study and experimental evaluation, focusing on the case of automation for tele-operated robotics. This is necessary because tele-operation of robots is slow and cumbersome. Classical robotics solutions are expensive, and limited in precision, but deep reinforcement learning provides an opportunity for learning visuomotor skills using partial information.Show less
In the vicinity of the superconducting dome in the phase diagram of iron-pnictides there exist a magnetically ordered phase accompanied by a nematic phase and a structural transition. Since all...Show moreIn the vicinity of the superconducting dome in the phase diagram of iron-pnictides there exist a magnetically ordered phase accompanied by a nematic phase and a structural transition. Since all three phases belong to the same point group symmetry, it is a priori difficult to establish which of these phases is dominant. The fluctuations associated with the energetically dominant transition have been proposed as the driving force behind electronic pairing in the superconducting state. Therefore the identification of this transition is essential for further understanding the physics behind superconductivity in iron-pnictides. This thesis explores the relation between nematic strength and the superconducting critical temperatures in the pnictides. The in-plane resistivity anisotropy of single crystal SmFeAsO (Tc =55 K in optimally F-doped SmFeAs[O,F]) was investigated using four different sample geometries structured by focused ion beam methods. The results are compared to other iron-pnictides and it was observed that the maximal resistivity anisotropy is similar as to that in other iron-pnictides. These initial results clearly lay the groundwork for future experimental studies, in particular probing the relation between the crystal lattice and the nematicity.Show less
A low field MRI software and hardware acquisition system has been designed and characterized. The transmit-receive is not custom built. Instead, a low cost, commercially available Software Defined...Show moreA low field MRI software and hardware acquisition system has been designed and characterized. The transmit-receive is not custom built. Instead, a low cost, commercially available Software Defined Radio (SDR) capable of transmission and reception of RF signals was used. An application for the SDR was built using the opensource program GNURadio. The custom built, relevant hardware was a Transmit-Receive switch, a RF probe, and a Halbach array of permanent magnets. The result is a system that can serve as a proof of concept for a low cost, portable, customizable MRI scanner. However, a NMR signal in the form of a Free Induction Decay (FID) remains yet to be detected.Show less
One of the limiting factors for improving the sensitivity towards single spin detection using Magnetic Resonance Force Microscopy is the working temperature. A component limiting this working...Show moreOne of the limiting factors for improving the sensitivity towards single spin detection using Magnetic Resonance Force Microscopy is the working temperature. A component limiting this working temperature is the radio frequent (RF) source. The use of a superconducting NbTiN instead of a copper RF-source improves this working temperature and theory suggests that the dissipation of such a NbTiN RF-source is geometry dependent. The dissipation of 9 NbTiN RF-sources with different geometries was measured using two different methods. First a four-point measurement was used that returned inductive effects obscuring the dissipation of the RF-source. Secondly a calorimetric measurement was tried that returned dissipation originating in the supply cables overshadowing the dissipation of the RF-source. The dissipation of these supply cables corresponds very well with the dissipation attributed to the RF-source by our predecessors. The dissipation of the RF-source is thus found to be much lower than previously thought.Show less
Experimental diffusion-weighted MRI measurements of a fiber phantom were compared to signals generated using a Monte-Carlo diffusion simulation. The diffusion simulation was combined with a...Show moreExperimental diffusion-weighted MRI measurements of a fiber phantom were compared to signals generated using a Monte-Carlo diffusion simulation. The diffusion simulation was combined with a generally applicable MRI simulation. We performed simulations for square packed and random packed cylinders that model the fibers. Good agreement was found between the simulated signal and the measured signal for a specific random packing type (the relative error was 0.09+-0.06). Follow-up simulations that use larger system sizes are needed to improve the accuracy. The simulation method presented here can be used to study changes in microstructural properties and to compare the efficiency of different MRI protocols in detecting these changes.Show less
In this proposal an experiment is envisioned that is principally able to determine whether there exists a fundamental transition between quantum mechanics (QM) and classical mechanics (CM). In the...Show moreIn this proposal an experiment is envisioned that is principally able to determine whether there exists a fundamental transition between quantum mechanics (QM) and classical mechanics (CM). In the quantum realm spatial superpositions of a particle may exist, whereas these superpositions are not observed in the classical world. Many theories have been put forward to explain this difference. Of these, decoherence theories state that there is no explicit difference between QM and CM, but that quantum phenomena are extinguished upon increasing the coupling of the studied object to its environment. Other theories, however, predict that there is a fundamental scale - apart from the environmental coupling - at which spontaneous collapse of a superposition occurs. To test whether such a scale exists, it is proposed to build an interferometer that has a tuneable, coherent amplifier in each of its two arms. The interferometer is fed by a microwave single photon source that yields an entangled superposition of zero and one photon in the arms. The advantage of using microwave photons in a transmission line is that these are carried by electrons, which have a rest mass. Therefore, spontaneous collapse may be expected upon amplifying the superposition of the single photon to such an extent, that the QM-CM transition scale is exceeded. This set-up circumvents the limitation of contemporary experiments that study superpositions of objects fixed in size. By tuning the amplifiers one is now able to smoothly vary the size of the superposition, so that studying the transition scale and its nature becomes experimentally feasible. After introducing the theoretical ideas and the experimental status of the topic, this proposal elaborates on the research goal of the proposed experiment. Then, the method is presented including the experiment's preliminary design options and considerations as well as research steps and risks. Furthermore, the proposal includes a four-year plan of work, discusses the facilities and resources of the host group and stresses collaborations with both theorists and experimentalists.Show less
