Strain-tunable half-metallicity in ${\mathrm{VSe}}_2/{\mathrm{Sc}}_2{\mathrm{CO}}_2$ van der Waals heterostructures

The quest for advancing the development of next-generation nanospintronic devices has propelled extensive research into the realization and control of half-metallicity in 2D materials. Here, the multiferroic ${\mathrm{VSe}}_2/{\mathrm{Sc}}_2{\mathrm{CO}}_2$ vdW heterostructures are theoretically investigated by using density functional theory to search for half-metallicity. Our theoretical exploration reveals that the ${\mathrm{VSe}}_2$ layer showcases a unique capability to transit between semiconducting and half-metallic behavior by precisely manipulating the ferroelectric polarization states of the ${\mathrm{Sc}}_2{\mathrm{CO}}_2$ layer. We further delve into the diverse electronic properties of the ${\mathrm{VSe}}_2$ layer within the heterostructure, employing uniaxial tensile strain engineering to investigate its behavior in both the semiconductor and half-metallic states. In the semiconductor state, this electronic property of the ${\mathrm{VSe}}_2$ layer remains unchanged with strain. In contrast, in the half-metallic state, the ${\mathrm{VSe}}_2$ layer undergoes a fascinating modulation, transiting from the spin-down half-metal to the metal and then to the spin-up half-metal as the strain increases from $0\%$ to $6\%$. This intriguing phenomenon is elucidated by the intricate rearrangement of the inner V atomic orbitals in response to strain.

Figure 1

The top and side views of the 2D structure of monolayer 2H-${\mathrm{VSe}}_2$ (a) and monolayer ${\mathrm{Sc}}_2{\mathrm{CO}}_2$ (b), respectively. The unit cell is denoted by a rectangle drawn with solid grey lines. All structures have undergone complete optimization. Band structure of monolayer 2H-${\mathrm{VSe}}_2$ (c) and monolayer ${\mathrm{Sc}}_2{\mathrm{CO}}_2$ (d). The Fermi level is set to zero. (e) The effective potentials (${\mathrm{V}}_{\mathrm{eff}}$) along the vertical $z$ direction to the monolayer ${\mathrm{Sc}}_2{\mathrm{CO}}_2$, in which $\mathrm{\Delta }\mathrm{\Phi }$ represent potential difference.

Figure 2

[(a)–(f)] ${\mathrm{VSe}}_2/{\mathrm{Sc}}_2{\mathrm{CO}}_2$ vdW heterostructures featuring diverse stacking configurations under different polarization states. For A, B, and C stacking configurations, the P $\uparrow$ and the P $\downarrow$ states are shown in (a)–(c) and (d)–(f), respectively.

Figure 3

Different magnetic couplings between V atoms in the ${\mathrm{VSe}}_2$ monolayer and the proposed ${\mathrm{VSe}}_2/{\mathrm{Sc}}_2{\mathrm{CO}}_2$ heterostructures. The red and blue arrows represent the spin-up and spin-down directions of V atoms, respectively. (a) The FM, and the two AFM configurations: (b) stripe-AFM, (c) zigzag-AFM.

Figure 4

(a) and (b) are the top and side views of A configuration of ${\mathrm{VSe}}_2/{\mathrm{Sc}}_2{\mathrm{CO}}_2\mathrm{P}\uparrow$ vdW heterostructures and C configuration of ${\mathrm{VSe}}_2/{\mathrm{Sc}}_2{\mathrm{CO}}_2\mathrm{P}\downarrow$ vdW heterostructures, respectively. Spin-resolved projected band structure of (c) A configuration of ${\mathrm{VSe}}_2/{\mathrm{Sc}}_2{\mathrm{CO}}_2\mathrm{P}\uparrow$ vdW heterostructure and (d) C configuration of ${\mathrm{VSe}}_2/{\mathrm{Sc}}_2{\mathrm{CO}}_2\mathrm{P}\downarrow$ vdW heterostructure. The Fermi level is set to zero.

Figure 5

The three-dimensional isosurface of the electron density difference of the multiferroic system with $\mathrm{P}\uparrow$ (a) and $\mathrm{P}\downarrow$ (b) states, respectively, where the yellow and blue areas represent electron accumulation and depletion, respectively. Band alignments for ${\mathrm{VSe}}_2/{\mathrm{Sc}}_2{\mathrm{CO}}_2$ with ferroelectric polarization of $\mathrm{P}\uparrow$ (c) and $\mathrm{P}\downarrow$ (d), respectively, of isolated layers (left panel) and that after forming heterostructure (right panel). The energies are displayed in the unit of eV.

Figure 6

Band structure of ${\mathrm{VSe}}_2/{\mathrm{Sc}}_2{\mathrm{CO}}_2\mathrm{P}\uparrow$ and ${\mathrm{VSe}}_2/{\mathrm{Sc}}_2{\mathrm{CO}}_2\mathrm{P}\downarrow$ at uniaxial tensile strains of (a), (f) $0\%$; (b), (g) $2\%$; (c), (h) $4\%$; and (d), (i) $6\%$. The dependence of band edges of ${\mathrm{VSe}}_2$ layer in (e) the ${\mathrm{VSe}}_2/{\mathrm{Sc}}_2{\mathrm{CO}}_2\mathrm{P}\uparrow$ and (j) ${\mathrm{VSe}}_2/{\mathrm{Sc}}_2{\mathrm{CO}}_2\mathrm{P}\downarrow$ heterostructure. The Fermi level is set to zero.

Figure 7

Band structure of monolayer ${\mathrm{VSe}}_2$ and ${\mathrm{Sc}}_2{\mathrm{CO}}_2$ at uniaxial tensile strains of (a), (f) $0\%$; (b), (g) $2\%$; (c), (h) $4\%$; and (d), (i) $6\%$. The dependence of band edges of ${\mathrm{VSe}}_2$ layer in (e) the ${\mathrm{VSe}}_2$ monolayer and (j) the ${\mathrm{Sc}}_2{\mathrm{CO}}_2$ monolayer. The Fermi level is set to zero. The red (blue) lines represent spin-up (spin-down) bands, the green lines represent ${\mathrm{Sc}}_2{\mathrm{CO}}_2$ bands, and square (triangle) lines represent the energy position of the CBM (VBM) bands.

Figure 8

(a) Structure of $V^{4+}$ ions at the crystallographic site of $D_{3h}$ symmetry. (b) Schematic diagram of the evolution of $V^{4+}$ d orbitals splitting in monolayer ${\mathrm{VSe}}_2$ under the influence of uniaxial strain. (c) Orbital resolved (left) spin-up and (right) spin-down band structures of ${\mathrm{VSe}}_2$. (d) The partial density of states (PDOS) of (left) $d$-resolved orbitals (right) $p$-resolved orbitals of ${\mathrm{VSe}}_2$.