Unconventional spin valve effect in altermagnets induced by Rashba spin orbit coupling and triplet superconductivity

Abstract

We theoretically investigate spin dependent transport in altermagnet/triplet superconductor/altermagnet (AM/TSC/AM) junctions in the presence of interfacial Rashba spin orbit coupling (RSOC). Within a microscopic Bogoliubov de Gennes scattering formalism, we compute angle and energy resolved conductance, spin polarization, zero bias response, and tunneling magnetoresistance (TMR) for nodal $p_x$ and chiral $p_x+ip_y$ superconductors. Although altermagnets carry no net magnetization, the momentum dependent spin splitting, combined with RSOC, enables a pronounced spin valve effect without ferromagnetic electrodes. We show that conductance, spin polarization, and TMR exhibit distinct and robust fingerprints of the triplet pairing symmetry. For nodal $p_x$ superconductor, sign change induced surface Andreev bound states dominate subgap transport, producing strongly anisotropic conductance, giant zero bias spin polarization, and a monotonic enhancement of TMR with increasing RSOC. In contrast, the chiral $p_x+ip_y$ state exhibits smoother conductance and polarization profiles governed by topological edge modes, resulting in broader, lobe like TMR patterns with weaker sensitivity to interface transparency. Moreover, RSOC can acts as an electrically tunable spin-mixing knob, while the barrier strength controls coherence and energy selectivity, together enabling large, symmetry controlled spin filtering and magnetoresistance. Our results establish AM/TSC/AM junctions as a symmetry sensitive transport platform for realizing electrically tunable spin valve functionality and probing triplet pairing without ferromagnetic components.