A central challenge in physics, chemistry, and material science is finding accurate ab initio descriptions of materials, which are ultimately made up of quantum electrons and nuclei. While powerful numerical methods like density functional theory (DFT) have proven extremely successful in describing the quantum behavior of electrons in a computationally efficient way – unlocking applications from understanding and predicting the properties of materials to ab initio design of new materials – comparably accurate and efficient descriptions of the quantum effects of nuclei (especially light ones) have remained elusive. Their quantum effects are thus often neglected and they are instead treated as classical, point particles; even though it is known that quantum positional uncertainty and quantum tunneling of light nuclei strongly affect the structure and dynamics of important classes of advanced materials, including hydrogen-storage materials, materials with Li ions, and record high-Tc superconductors. In fact, in modern ab initio calculations the missing quantum effects of nuclei are often the dominant source of discrepancy between numerical predictions and experimental results.
In studies of magnetic and superconducting materials, we also often use muon spectroscopy (μSR), where we produce quantum particles, called muons, in particle accelerators and implant them in the studied material as uniquely sensitive local probes of internal magnetic fields. However, the interpretation of μSR experiments can often be ambiguous due to unaccounted-for quantum effects of muons (mainly, quantum uncertainty in their positions, quantum entanglement with nearby nuclear positions or spins, and random quantum tunneling events). These are even stronger than nuclear quantum effects due to the muons’ lower mass (they are ~9× lighter than hydrogen). Because μSR is one of the few techniques that can be used to study the spin dynamics of advanced quantum and topological materials, including superconductors, quantum spin liquids (QSLs; exotic dynamical spin states with long-range quantum entanglement but no long-range order, with proposed applications in robust, topological quantum computing), and skyrmions (topologically protected vortices of magnetization, with proposed applications in spintronics, a magnetic analogue of electronics) accurately capturing quantum effects of muons is crucial.
The proposed program will develop the necessary theoretical tools and numerical methods to accurately and efficiently describe the quantum effects of muons and light nuclei. It will thus unlock the full potential of the powerful μSR technique in the study of advanced materials, and finally enable reliable ab initio prediction and understanding of crucial quantum effects of nuclei in a range of quantum materials. It will also study exotic quantum and topological spin systems, including QSLs and skyrmions, using μSR and related experimental techniques, both to gain crucial new insights into these exotic states of matter and to benchmark the developed theory.
Asst. Prof. Dr. Matjaž Gomilšek
Matjaž Gomilšek is the head of the Laboratory for Numerical Physics and a member of the Laboratory for Measurements at Large-Scale User Facilities at the Department of Condensed Matter Physics F5. His research work focuses on experimental and ab initio investigations of quantum and topological magnetism and related quantum effects of light particles in matter. He is the recipient of several ARIS research projects, head of the supercomputing cluster at F5, and co-developer of the MuFinder program for ab initio analysis of muon spectroscopy measurements.
Research programme: Physics of quantum and functional materials
Training topic: Quantum effects of light particles in matter and ab initio simulations of matter