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.

Figures (10)

• Figure 1: Schematic illustration of the altermagnet-triplet superconductor-altermagnet junction where a finite-length spin-triplet $p$-wave superconductor (TSC) of length $L$ is sandwiched between two altermagnetic leads (AM). The transport direction is taken along the $x$ axis, while the interface planes lie in the $yz$ plane. Rashba spin--orbit coupling (RSOC) is present at both AM/TSC interfaces and is modeled by delta-function barriers. The relative Néel order parameter in the left and right AM regions are misaligned by an angle $\theta_m$. A bias voltage $V$ is applied across the junction to drive quasiparticle transport.
• Figure 2: Differential conductance $G/G_N$ as a function of $E/\Delta_0$ for AM /$p_x$-wave SC /AM system considering different AM orientations $\theta_m$. Panels (a)–(c) correspond to a nearly transparent ($Z_0 = 0.01$) while panels (d)–(f) are for opaque barrier ($Z_0 = 1$) considering different values of $Z_R$.
• Figure 3: Differential conductance $G/G_N$ as a function of $E/\Delta_0$ for AM /$p_x+ip_y$-wave SC /AM system considering different AM orientations $\theta_m$. Panels (a)–(c) correspond to a nearly transparent ($Z_0 = 0.01$) while panels (d)–(f) are for opaque barrier ($Z_0 = 1$) considering different values of $Z_R$.
• Figure 4: Zero-bias conductance as a function of the AM orientation angle $\theta_m$ for different $Z_R$ values. Panels (a) and (b) correspond to the non-chiral $p_x$-wave superconductor, while panels (c) and (d) show the chiral $p_x + i p_y$-wave case. The upper (lower) panels are for weak (strong) barrier strength $Z_0=0.01$ ($Z_0=1$).
• Figure 5: (Top panel) (a,b) Zero-bias conductance as a function of $\theta_m$ and $h_{\rm AM}/\mu$ for $Z_R=0.01$ and $Z_0=5$. (Bottom panel) (c,d) Zero-bias conductance as a function of $Z_R$ and $h_{\rm AM}/\mu$ for $Z_0=0.5$ and $\theta_m=45^\circ$. Left panels correspond to a nodal $p_x$-wave superconductor, and right panels to a chiral $p_x+ip_y$ state.