Reentrant Superconductivity from Competing Spin-Triplet Instabilities

Abstract: Reentrant superconductivity in strong magnetic fields challenges the conventional expectation that magnetic fields necessarily suppress superconductivity. We show that reentrant superconductivity arises generically from the competition between spinful and spin-polarized superconducting instabilities. 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 independent of microscopic details.