Speaker
Description
Lifshitz transitions of the Fermi surface are significant in a wide variety of strongly correlated and topological materials, and understanding the origin and influence of Lifshitz transitions has led to deeper understanding of key aspects of magnetic, transport or quantum critical behaviour.
In the ferromagnetic superconductor UCoGe, a magnetic field applied along the c-axis induces a series of anomalies in both transport and thermopower that may be caused by Lifshitz transitions. A need to understand the close relationship between magnetism, superconductivity and the heavy electron Fermi surface in this material makes it important to explore if and why such a series of magnetic-field-induced Lifshitz transitions occur. Lifshitz transitions are also prominent at high magnetic fields in UPt$_3$ and UTe$_2$.
I will discuss the results of magnetic susceptibility measurements of UCoGe, in magnetic fields up to 30 T, in which we observed a series of clearly-defined features in the susceptibility, and multiple sets of strongly field-dependent de Haas-van Alphen oscillations. From the experimental results complemented by DFT bandstructure calculations, we extracted detailed field-dependence of the quasiparticle properties, determined the likely shape of the Fermi surface and identified candidate Lifshitz transitions.
I will compare the results from UCoGe to other recent Fermi surface measurements of UPt$_3$ and UTe$_2$, and discuss the evolution of the Fermi surface in connection to the development of magnetisation and superconductivity in these materials.