Profound impacts of interlayer interactions in bilayer altermagnetic V2S2O

TL;DR

This study systematically explores how interlayer interactions affect the electronic, magnetic, and quantum transport properties of bilayer V2S2O, revealing their critical role in modulating spin currents and band structures for spintronics applications.

Contribution

It provides a comprehensive analysis of interlayer effects on bilayer altermagnetic V2S2O using DFT and NEGF, highlighting their impact on band structure, magnetic effects, and spin transport.

Findings

Interlayer interactions modulate top valence bands and induce a small energy difference of 9 meV.

External electric fields weaken interlayer coupling, increasing band energy differences.

Spin current polarization decreases from nearly 100% in monolayer to 60% in bilayer.

Abstract

Two-dimensional altermagnets exhibit exceptional potential for low-power spintronics via nonrelativistic spin splitting and zero net magnetization. Here, we systematically investigate the influence of interlayer interactions on the electronic, magnetic and quantum transport properties of bilayer vanadium oxysulfide (V2S2O), a prototypical layered altermagnet, using DFT and NEGF calculations. Our results reveal that interlayer interactions predominantly modulate the p-orbital derived top valence bands, inducing a profound competitive valence band maximum position between Gamma-point pz and X/Y-point pxy orbitals, with an energy difference as small as 9 meV. Furthermore, interlayer interactions suppress the piezomagnetic effect and impose additional requirements on the type of strain for the bilayer system, compared to its monolayer counterpart. Out-of-plane external electric fields effectively weaken interlayer coupling by enlarging the energy difference of Gamma/X-Y top valence bands to 170 meV. Quantum transport simulations on a bilayer Au/V2S2O/Au two-probe device demonstrate the presence of pronounced spin current. Interlayer interactions reduce the transmission spin polarization from nearly 100% (monolayer) to 60% (bilayer) for energies above the Fermi level. Notably, gate-voltage modulation exhibits significant asymmetry in controlling charge-to-spin current conversion efficiency, originating from the out-of-plane symmetry breaking induced by the electrode geometry. Specifically, a positive gate voltage markedly enhances the contribution of the bottom layer to the overall spin polarization, while a negative gate voltage induces a marginal reduction of transmission spin polarization, attributed to the inherently weak polarization contribution of the bottom layer. These findings provide essential insights for the design and optimization of multilayer altermagnetic spintronics.