Main research interests:
1 New materials with unusual and correlated electronic behavior
2 Quantum materials on sub-micrometer length scales
3 Topological semi-metals, unconventional and high-Tc superconductors
Developing a new material to a technologically useful grade is often a decade-long task. Silicon, the most successful electronic material today, has been perfected over almost a century to reach the high level of purity and crystallinity that enables modern computing power. When a novel or less common material is discovered, a clear technological and economical use-case is required before this type of investment of time and resources is warranted. What if we could build prototypes of such new technology already today, with the lower quality materials we have now? This is the main technological challenge of our research. We advance micro- and nanofabrication technologies to combine micrometer-sized crystalline circuits from exotic materials with Si chips and demonstrate their performance. The key idea is that current materials may not be clean or large enough to build a million transistors but, with proper nanoanalysis, even in powdered samples a micron-sized grain of high enough purity can be found from which a single element can be built and tested. We use Focused Ion Beam machining to isolate this grain, cut it into a functional form, and electrically connect it to the chip.
We focus these research efforts on quantum materials. Quantum mechanics dictates the world we live in, and no material object, chemical reaction or light would even exist without it. It has been hugely successful at describing materials, for example at explaining why some materials are insulators, some are metals, and some semi-conductors. Yet in special materials, interesting material behaviour arises from quantum mechanics that goes beyond these traditional quantum pictures. In this context, the term “Quantum Materials” has been born – a loosely defined term describing those materials where quantum mechanics leads to new behaviour and properties beyond those of Silicon and Copper.
The main material classes we are interested in are topological semi-metals, unconventional and high-Tc superconductors and exotic strongly correlated electron systems. In topological semi-metals, the electronic dispersion mathematically mimics the Weyl equation, the formalism originally invented to describe massless Fermions in high energy physics. While these were never found as elementary particles, their appearance now in metals leads to signatures of relativistic behaviour. We explore how these fundamentally distinct electrons behave in electric devices, and search for ways to utilize this in novel technology. Unconventional superconductors and non-superconducting strongly correlated electron systems, for example heavy-fermion metals, exhibit a variety of interacting ground states. While these states have been the center of research for decades, their application potential in quantum technology remains largely unexplored. Using the phase information for computation is a very challenging task, and complex quantum circuits need to be built to preserve and manipulate quantum states. We research if nature has already gifted us more exotic materials, in which quantum phenomena are more pronounced and more robust, thus facilitating these quantum applications.
Magnetic electron collimation in three-dimensional semi-metals
—New Nature paper published on using magnetic field to focus electron beams in 3d semi-metals.