Altermagnetic Proximity Effect

Abstract

Proximity effects not only complement the conventional methods of designing materials, but also enable realizing properties that are not present in any constituent region of the considered heterostructure. Here we reveal an unexplored altermagnetic proximity effect (AMPE), distinct from its ferromagnetic and antiferromagnetic counterparts. Using first-principles and model analyses of van der Waals heterostructures based on the prototypical altermagnet V$_2$Se$_2$O, we show that its hallmark momentum-alternating spin splitting can be directly imprinted onto adjacent nonmagnetic layers -- a process we term altermagnetization. This is demonstrated in a monolayer PbO through characteristic band splitting and real-space spin densities, with systematic dependence on interlayer spacing and magnetic configuration. We further predict broader AMPE manifestations: Valley-selective spin splitting in a monolayer PbS and a topological superconducting phase in monolayer NbSe$_2$, both inheriting the alternating $k$-space spin texture of the altermagnet. These results establish AMPE not only as a distinct proximity mechanism, but also as a powerful method of using altermagnetism in designing emergent phenomena and versatile applications.

Figures (4)

• Figure 1: Schematic of the AMPE. (a) Altermagnetism penetrating an NM layer. (b) Band evolution of the NM layer as it becomes a proximitized altermagnet (PAM).
• Figure 2: (a) Crystal structure of PbO/V$_2$Se$_2$O heterostructure. The spin sublattices of V$_2$Se$_2$O are connected by $\left[C_2 || C_{4z}\right]$ symmetry. (b)- (d) Calculated bands and spin densities of pristine monolayers PbO and V$_2$Se$_2$O, and their heterostructure. The inset in (b) shows the first Brillouin zone. (e) and (f) Enlarged views of the regions labeled i and ii in (d). (g) Differential charge density of the PbO/V$_2$Se$_2$O heterostructure and its planar average, $\Delta q(z)$. Green (purple) indicates charge accumulation (depletion) and the isosurface value is $5 \times 10^{-4}$ e/bohr$^3$. (h) Spin splitting $\Delta E_S$ in (f) with the spin densities, as a function of the interlayer distance $d$ in (a), where $d_0$ is the equilibrium value. (i) Same as (d) but for a proximitized AFM PbO (PAFM-PbO), realized when PbO is placed on a $\sqrt{2} \times \sqrt{2}$ V$_2$Se$_2$O supercell in a conventional AFM state. For all bands, black denotes spin-degenerate states; red and blue indicate spin-up and spin-down bands of the PAM component (PbO), while yellow and green represent the corresponding bands of the V$_2$Se$_2$O component.
• Figure 3: (a) Schematic of the PbS/V$_2$Se$_2$O heterostructure illustrating the AMPE- and strain-induced spin and valley splitting in a monolayer PbS. (b) and (c) Calculated bands of the monolayer PbS and PbS/V$_2$Se$_2$O heterostructure. (d) Bands of the AM-proximitized monolayer PbS under 3% uniaxial tensile strain along the $x$ axis, showing valley splitting, $\Delta E_V$. (e) Strain-dependent $\Delta E_V$. Band color codes as in Fig. \ref{['Figure2']}.
• Figure 4: (a) Schematic transformation of an $s$-wave superconductor NbSe$_2$ into a topological superconductor hosting edge MM (red circle) via AMPE from V$_2$Se$_2$O. (b) and (c) Bands of a NbSe$_2$ supercell and the NbSe$_2$/V$_2$Se$_2$O heterostructure. (d) Topological phase diagram of the PAM-NbSe$_2$ obtained from Eq. (\ref{['eq1']}). (e) and (f) Ribbon spectra of PAM-NbSe$_2$ showing helical and chiral MM (HMM and CMM). Parameters are $t_x=1$, $\mu=0.6$, $\lambda_R=0.2$, $J_A=0.4$, $\Delta=0.2$. $t_y=1$ in (e) and $t_y=0.8$ in (f). Band color codes as in Fig. \ref{['Figure2']}.