Enhanced Magnetoresistance in Nanostructures with a Single Ferromagnet

It is commonly assumed that multiple ferromagnets are required to realize large spin-valve effects. In contrast, we reveal that the interplay between the proximity-induced magnetization and Rashba spin-orbit coupling (SOC) in a two-dimensional electron gas (2DEG), or in a conventional superconductor, can lead to a large magnetoresistance even with one ferromagnet [1-4]. However, such enhanced magnetoresistance in nanostructures is not generic. For an in-plane rotation of magnetization, it is typically negligibly small for 2DEG and depends on the tunneling resonances which emerge from a novel spin-parity-time symmetry of the scattering states, while this symmetry is generally absent from the Hamiltonian of the system [1]. The key difference from considering the normal-state magnetoresistance is the presence of the spin-dependent Andreev reflection at superconducting interfaces. In magnetic nanostructures Rashba SOC can reduce the effective barrier strength for a given helicity [2] and support elusive equal-spin-triplet superconductivity. This mechanism explains an observed huge increase of magnetoresistance in all-epitaxial MgO-based nanostructures with a superconductor [5] as well as in junctions of quasi-2D van der Waals ferromagnets with conventional s-wave superconductors (Fe0.29TaS2/Nb) [3]. Realizing this enhanced magnetoresistance and spin-triplet superconductivity is an important building block for superconducting spintronics [6].