Slow magnetic quantum oscillations in the c-axis magnetoresistance of UTe$_2$

Abstract

Details of the electronic band structure in unconventional superconductors are key to the understanding of their fundamental ground state. The potential spin-triplet superconductor UTe$_2$, with $T_\mathrm{c}\approx 2.1\,$K, has attracted attention recently. Its main Fermi surface consists of weakly corrugated, two-dimensional Fermi-surface cylinders that run along the crystallographic $c$ axis. In addition, there is evidence for the presence of an additional small three-dimensional band. This has been discussed controversially as it may be essential for the realization of superconductivity in UTe$_2$. Here, we investigate the angle-resolved magnetoresistance and Hall effect in bulk crystalline samples with current along the $c$ axis in fields up to $60\,$T. We observe low-frequency magnetic quantum oscillations with light effective masses that are most pronounced for magnetic field applied along the $a$ axis. Two distinct frequencies indicate two separate changes in the Fermi-surface topology, likely connected with Lifshitz transitions. We discuss the origin of these oscillations in terms of magnetic breakdown, quantum interference, and other potential mechanisms.