Revealing the bandstructure of UTe₂ through quantum interference oscillations

Detailed knowledge of the geometry and topology of the Fermi surface of a strongly correlated metal is a key piece in the puzzle of understanding any emergent phenomena that it may exhibit. In the case of UTe₂, this emergent state is its superconductivity. Superconductivity in UTe₂ not only exhibits extreme field resilience, suggesting that UTe₂ is a spin triplet superconductor, but also, it is comprised of multiple, distinct states as a function of applied magnetic field and pressure. Recently, high quality samples with long mean free paths have become available, enabling quantum oscillation measurements to directly probe its Fermi surface and carrier mass renormalisations. This talk will describe our recent high magnetic field measurements of the magnetoconductance of UTe₂. At applied fields above 36 T, we observed oscillations in contactless resistivity with frequencies and effective masses that differ markedly from prior de Haas-van Alphen effect studies, which observed quasi-2D Fermi surface sections. We find that these magnetoconductance oscillations can be well understood as a quantum interference effect stemming from quasiparticles tunnelling across the Fermi surface sheets at high magnetic fields. A large variation in the apparent effective masses for the various interference paths yields valuable insight into the electronic bandstructure underpinning unconventional superconductivity in UTe₂, which offers a route to understanding its multiple superconducting order parameters.