Reentrant superconductivity from competing spin-triplet instabilities

Reentrant superconductivity in strong magnetic fields challenges the conventional expectation that magnetic fields necessarily suppress superconductivity. We show that reentrant superconducting instability can arise from the competition between spin-unpolarized and spin-polarized superconducting channels. Using a minimal Ginzburg--Landau theory with two coupled spin-triplet order parameters, we demonstrate that a magnetic field can reorganize the hierarchy of superconducting instabilities, yielding a characteristic reentrant instability curve over a broad parameter range.