Negative Differential Resistance and Ultrahigh TMR in Altermagnetic Tunnel Junctions

Abstract

Altermagnets can replace ferromagnets in tunnel junctions, yielding a large tunneling magnetoresistance, ultrafast switching, and low-power functionality. While most studies explore the linear-response regime, interesting features emerge at finite bias, with their peculiar electronic structure giving rise to complex nonlinear behavior. Using density functional theory and nonequilibrium Green’s functions, we predict a pronounced low-bias negative differential resistance in an altermagnetic tunnel junction, incorporating orbital-ordered KV2Se2O. This is ascribed to KV2Se2O’s altermagnetic quasi-2D Fermi surface. Upon application of a finite-bias voltage, the current in the parallel configuration first increases sharply before decreasing and becoming almost completely suppressed at around 0.14 V, whereas the antiparallel configuration displays monotonic current–voltage characteristics. This behavior, together with the negative differential resistance, produces a large tunneling magnetoresistance with sign inversion at 0.13 V. Our results validate altermagnetic tunnel junctions as a platform for applications requiring low-bias strongly nonlinear responses.