We find ourselves in an era of transition, not just towards a more computing- and data-driven society but also away from unsustainable fossil fuels as an energy source. This leads to a rapidly... Show moreWe find ourselves in an era of transition, not just towards a more computing- and data-driven society but also away from unsustainable fossil fuels as an energy source. This leads to a rapidly increasing demand for computing power on an ever more tight energy budget. Therefore, it is imperative to investigate novel energy-efficient computing techniques, like superconducting spintronics or neuromorphic computing using correlated electron matter. Naturally, understanding the physics governing these processes at the sub-micrometer (i.e., device) scale is crucial for this development to succeed. This thesis examines the effects of size reduction and geometry on ferromagnetic Josephson junctions and highly correlated electron matter through transport experiments. Specifically, it describes how spin-polarized supercurrents can be generated using spin texture, stabilized by carefully tuning the geometry of planar Josephson junctions, and how the bistability of these spin textures can be employed to create non-volatile superconducting memory elements. Furthermore, it reports a strong size dependence of the current density that drives the Mott-insulating-to-metal transition in Ca2RuO4 and shows how various constricted geometries can be used to localize and examine the properties of superconducting chiral domain walls in Sr2RuO4. Show less
Fermin, R.; Scheinowitz, N.M.A.; Aarts, J.; Lahabi, K. 2022
With the ever-increasing energy need to process big data, the realization of low-power computing technologies, such as superconducting logic and memories, has become a pressing issue. Developing... Show moreWith the ever-increasing energy need to process big data, the realization of low-power computing technologies, such as superconducting logic and memories, has become a pressing issue. Developing fast and nonvolatile superconducting memory elements, however, remains a challenge. Superconductor-ferromagnet hybrid devices offer a promising solution, as they combine ultrafast manipulation of spins with dissipationless readout. Here, we present a type of nonvolatile Josephson junction memory that utilizes the bistable magnetic texture of a single mesoscopic ferromagnet. We use micromagnetic simulations to design an ellipse-shaped planar junction structured from a Co/Nb bilayer. The ellipse can be prepared as uniformly magnetized or as a pair of vortices at zero applied field. The two states yield considerably different critical currents, enabling reliable electrical readout of the element. We describe the mechanism that controls the critical current by applying numerical calculations to quantify the local stray field from the ferromagnet, which shifts the superconducting interference pattern. Our approach presents a route towards realizing superconducting memory applications by combining micromagnetic modeling with bistable spin-textured junctions. Show less
Fermin, R.; Dinter, D. van; Hubert, M.; Woltjes, B.; Silaev, M.; Aarts, J.; Lahabi, K. 2022
The surprisingly low current density required for inducing the insulator to metal transition has made Ca2RuO4 an attractive candidate material for developing Mott-based electronics devices. The... Show moreThe surprisingly low current density required for inducing the insulator to metal transition has made Ca2RuO4 an attractive candidate material for developing Mott-based electronics devices. The mechanism driving the resistive switching, however, remains a controversial topic in the field of strongly correlated electron systems. Here we probe an uncovered region of phase space by studying high-purity Ca2RuO4 single crystals, using the sample size as principal tuning parameter. Upon reducing the crystal size, we find a four orders of magnitude increase in the current density required for driving Ca2RuO4 out of the insulating state into a non-equilibrium phase which is the precursor to the fully metallic phase. By integrating a microscopic platinum thermometer and performing thermal simulations, we gain insight into the local temperature during simultaneous application of current and establish that the size dependence is not a result of Joule heating. The findings suggest an inhomogeneous current distribution in the nominally homogeneous crystal. Our study calls for a reexamination of the interplay between sample size, charge current, and temperature in driving Ca2RuO4 towards the Mott insulator to metal transition. Show less
