High-Field Superconducting Halo in UTe2
Abstract
Heavy fermion UTe2 is a promising candidate for topological superconductivity that also exhibits multiple high-field superconducting phases. The SCFP phase has only been observed in off-axis magnetic fields in the bc plane at fields greater than 40 teslas, a striking scale given its critical temperature of only 2 kelvins. Here, we extend measurements of this unique superconducting state outside of the bc plane and reveal its core structure. The SCFP phase is not confined to fields in the bc plane and in fact wraps around the b axis in a halo-like fashion. In other words, this superconducting state, which exists in fields above 73 teslas, is stabilized by a field component perpendicular to the magnetic easy axis. These remarkable field scales further underscore UTe2's unique magnetophilic superconducting tendencies and suggest an underlying pairing mechanism that is qualitatively distinct from known theories for field-enhanced superconductivity. Phenomenological modeling points to a two-component, non-unitary spin triplet order parameter with finite orbital momentum of the Cooper pairs as a natural explanation for the field-angle dependence of the upper critical field of the SCFP phase.