I am an experimental physicist at the Van der Waals-Zeeman Institute which is part of the IoP. My field of research is Quantum Electron Matter, with a focus on the investigation and understanding of collective phenomena in novel materials, for example quantum phase transitions and unconventional superconductivity. The research has a strong fundamental component, but in the long term may lead to new functional materials in the fields of energy and spintronics. My experimental expertise is in measuring the transport, magnetic and thermal properties of bulk and 2D materials under extreme conditions, such as very low temperatures, high pressures and very strong magnetic fields. In addition, I use muon spin rotation/relaxation and neutron scattering techniques at large scale facilities to investigate quantum matter on the microscopic scale. I closely collaborate with the dr. Huang Ying Kai (single crystal growth), dr. Erik van Heumen (optical spectroscopy) and prof.dr. Mark Golden (ARPES and STM) and together we form the Quantum Electron Matter research group.
Quantum phase transitions: Correlated electron systems can easily be driven to an antiferromagnetic or ferromagnetic quantum phase transition by using mechanical or chemical pressure. In the quantum regime, close to absolute zero of temperature, thermal fluctuations are absent, and the transition is driven wholly by quantum fluctuations. At the quantum critical point the standard Fermi liquid theory for metals breaks down and new forms of matter may emerge.
Unconventional superconductivity: In a ferromagnetic metal superconductivity should not exist, since ferromagnetic order impedes phonon-mediated pairing of electrons in singlet states. But several years ago we discovered that, in the correlated metal UCoGe, in a twist of nature, superconductivity and ferromagnetism coexist. Such an unconventional superconducting state calls for an exotic explanation: on the verge of magnetism critical magnetic fluctuations mediate superconductivity by pairing the electrons in triplet states.
Topological insulators and superconductors: As regards charge transport, materials are divided into conductors and insulators. A few years ago a new class of materials was discovered: topological insulators. Topological insulators have the extraordinary property that they are insulating in the bulk, but conducting on the surface. The surface states are protected by topology and consequently scattering processes are absent, which makes them potential candidates for applications in spintronics. Moreover, some topological insulators can quite easily be transformed into a superconductor, e.g. half-Heuslers. Topological superconductors are predicted to host Majorana zero mode states, which in turn may form a platform for quantum computation.
Apart from supervising bachelor and master students for their final research projects, and PhD students, I am co-coordinator of the course “Oriëntatie Natuur- en Sterrenkunde” for second and third year bachelor students and I teach “Superconductivity: Fundamentals and Applications” in the AMEP track of the Physics Master.
I am co-author of over 260 publications in international refereed journals. For a complete updated list, including links to pfd’s, please visit my homepage.