Recently, the Leiden group has developed a completely novel type of superconducting Josephson junctions (JJ), which we call a ‘spin texture junction’ (STJJ). The junction is disk-shaped, it has a ferromagnetic weak link, and the supercurrent is carried by spin-triplet correlations. None of this is standard, but the truly novel part is the presence of a magnetic vortex core in the center of the disk. The core can be moved about with an in-plane magnetic field, and in doing so the critical current of the junction changes reproducibly in ways which are very different from standard junction behavior. We find hysteretic behavior, but also indications of a non-zero phase difference over the junction even in its ground state. The physics of the system is very rich and the possibility of tuning it to multiple different critical current states makes it of strong interest for superconducting memory applications and more generally for novel devices based on superconductor-ferromagnet hybrids. The vortex is the spin-texture referred to in the title, but other types of inhomogeneous ordered spin structures, such as domain walls or skyrmions, should give rise to similar effects. We are the first group to go in this direction with the vortex disk as a model system. STJJ’s could become important building blocks for superconducting electronics, and we want to keep the lead we currently have. We shall focus on two issues in particular: (i) understand what phase relations exist, and can exist, over the junction; in other words, can we make 0-, π- or even so-called -junctions ? (ii) can we stabilize other vortex positions than the disk center, by other geometries or by making artificial pinning sites ? In doing this, we shall make extensive use of micromagnetic simulations, going hand in hand with device fabrication. For displacing the core we both want to use static fields and microwave pulses to move the core by so-called gyroscopic motion. Recently, the Leiden group has developed a completely novel type of superconducting Josephson junctions (JJ), which we call a ‘spin texture junction’ (STJJ). The junction is disk-shaped, it has a ferromagnetic weak link, and the supercurrent is carried by spin-triplet correlations. None of this is standard, but the truly novel part is the presence of a magnetic vortex core in the center of the disk. The core can be moved about with an in-plane magnetic field, and in doing so the critical current of the junction changes reproducibly in ways which are very different from standard junction behavior. We find hysteretic behavior, but also indications of a non-zero phase difference over the junction even in its ground state. The physics of the system is very rich and the possibility of tuning it to multiple different critical current states makes it of strong interest for superconducting memory applications. The vortex is the spin-texture referred to in the title, but other types of inhomogeneous ordered spin structures, such as domain walls or skyrmions, should give rise to similar effects. We are the first group to go in this direction with the vortex disk as a model system. STJJ’s could become important building blocks for superconducting electronics, and we want to keep the lead we currently have. We shall focus on two issues in particular: (i) understand what phase relations exist, and can exist, over the junction; in other words, can we make 0-, π- or even so-called -junctions ? (ii) can we stabilize other vortex positions than the disk center, by other geometries or by making artificial pinning sites ? In doing this, we shall make extensive use of micromagnetic simulations, going hand in hand with device fabrication. For displacing the core we both want to use static fields and microwave pulses to move the core by so-called gyroscopic motion.

The DNA molecules in our cells are several centimeters long and need to fit into the cell nucleus. To do this, DNA segments are wrapped around protein cylinders to form nucleosomes. To access the DNA, nucleosomes must be shifted to alternating positions in a process known as nucleosome sliding, in which the nucleosomes move along the DNA in a corkscrew fashion. We discovered that this process can be mapped onto a generalized version of a fundamental model of low-dimensional nonlinear physics, the Frenkel-Kontorova model. In this model, we discovered surprising phenomena, including an acceleration of diffusion for longer DNA segments.

High temperature superconductivity arises as a result of strong interaction between the charge carriers. This proposal will describe such strongly interacting systems by relating their dynamics to that of weakly coupled string theories.

Iron is a crucial bio-metal due to its involvement in many fundamental biological processes. In the brain, cellular iron balance is strictly regulated to avoid neurotoxicity. In fact, excessive iron is linked to the production of reactive oxygen species, lipid peroxidation, neuroinflammation and ferroptosis, a form of cell death characterized by phospholipid oxidation. Many neurodegenerative diseases show brain iron accumulation, which is -not surprisingly- thought to exacerbate disease progression. An example is Huntington’s disease, where iron accumulates in the striatum and the degree of iron load is associated with the disease progression. At least 80% of non-heme brain iron is bound to ferritin: a hollow nanosphere which stores iron in a non-toxic mineral resembling ferrihydrite. Since the core of ferritin can accommodate up to 5000 iron atoms, the particle’s magnetic moment may reach high values (~ 300 µB), which has important implications for imaging. The mapping of ferritin-bound iron can allow us to track important changes occurring at the onset and/or during the progression of brain diseases. Magnetic Resonance Imaging is very sensitive to the magnetic field perturbation caused by superparamagnetic nanoparticles like ferritin. R2* (=1/T2*) and Quantitative Susceptibility Mapping (QSM) are examples of parameters which are critically influenced by tissue iron status. However, these methods are also susceptible to factors such as myelin, tissue microstructure and fiber orientation. A different approach is to use a technique termed off-resonance saturation (ORS) to obtain iron maps in the post-mortem brain. This method is not influenced by myelin and returns a metrics which is directly related to the absolute amount of ferritin-iron. With this project, I aim to: i) Benchmark the performance of the ORS method against conventional parametric iron mapping in vivo; ii) Assess the ability of ORS to follow brain-iron changes occurring during the progression of Huntington’s disease.

Human life as we know it would be impossible without bioelectricity. Fundamental life processes, from the communication between our brain cells to the contraction of our muscles, depend on the creation and sensing of electrical signals. Recent pioneering studies revealed that bioelectricity has another, vastly underappreciated role: guiding embryonic development and tissue regeneration. The electric potential across the cell membrane (Vmem) was shown to influence crucial developmental processes, like left-right patterning or control of organ size. Even more excitingly, perturbation of Vmem was able to trigger regeneration of severed limbs in adult organisms. However, these studies were all carried out in non-mammalian species. Here, I suggest to elucidate the role of bioelectricity in mammalian development. To achieve this challenging goal we have to understand, at a fundamental level, how bioelectricity can influence gene expression and hence shape the composition of tissues. My research group uses embryonic stem cells as an in vitro model to study mammalian development. Our pilot experiments revealed that perturbation of Vmem can influence cell type specification in vitro. This encouraging result hints at important, undiscovered functions of bioelectricity. In the project described here we will first define the “electrome”, the body of molecular processes that influence Vmem. We will explore how Vmem impacts gene expression and cell type specification in embryonic stem cells, gastruloids and mouse embryos. To reveal the underlying mechanisms, we will study the influence of Vmem on cell signaling at the membrane and subcellular compartments. In particular, we will develop a super-resolution imaging approach to measure, for the first time, the spatial heterogeneity of Vmem with near-nanometer accuracy. Our interdisciplinary study, which employs tools from biophysics and molecular biology, aims to pave the way for the application of bioelectric signals in regenerative medicine.