Intrinsic Spin Filter Effect in a $d$-wave altermagnet KV$_2$Se$_2$O with Open Fermi Surface

TL;DR

This paper demonstrates that the d-wave altermagnet KV2Se2O can achieve giant tunneling magnetoresistance through orientation-dependent spin filtering, enabling high-performance, thermally stable spintronic devices.

Contribution

It introduces a novel altermagnetic heterostructure with symmetry-protected spectral gaps that enable high TMR and robust spin filtering at room temperature.

Findings

Achieved high tunneling magnetoresistance in KV2Se2O-based junctions.

Demonstrated thermally driven spin filtering and spin Seebeck effect at room temperature.

Established a pathway for scalable, field-free spin logic devices.

Abstract

Altermagnets offer a unique pathway to functional spintronics by combining vanishing magnetization with large spin splitting. Here, we demonstrate that the canonical d-wave altermagnet KV2Se2O can deliver giant tunneling magnetoresistance through orientation-dependent spin filtering. By analyzing the crystallographic spin segregation, we show that transport along specific crystallographic axes is nearly fully spin-polarized within the symmetry-protected ballistic channels. We implement this mechanism in a lattice-matched KV2Se2O/Bi2O2Se/KV2Se2O magnetic tunnel junction, which achieves a robust half-metallic transport regime. The symmetry-protected spectral gap in the parallel/anti-parallel configuration ensures a high tunneling magnetoresistance ratio, resulting in substantial tunneling magnetoresistance, robust thermally driven spin filtering, and spin Seebeck effect at room temperature. These findings provide a path of altermagnetic heterostructures as a high-performance platform for scalable, field-free, and thermally stable spin logic.