Emergence of topological and trivial interface states in $\mathrm{V}{\mathrm{Se}}_2$ films coupled to ${\mathrm{Bi}}_2{\mathrm{Se}}_3$

Coupling ordinary metals with topological ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ can instigate the long-range migration of the spin-polarized Dirac states. Instead, for trivial metallic $\mathrm{V}{\mathrm{Se}}_2$ films on ${\mathrm{Bi}}_2{\mathrm{Se}}_3$, topological and trivial Rashba-type interface states emerge, each strongly localized at the $\mathrm{V}{\mathrm{Se}}_2/{\mathrm{Bi}}_2{\mathrm{Se}}_3$ interface. Their rapidly decaying spectral weights are uncovered by thickness-dependent band mappings of $\mathrm{V}{\mathrm{Se}}_2$ films and replicated by a phenomenological first-principles model of the spectral function. The results are pertinent to spintronic devices requiring spin transmission across metal/topological insulator interfaces.

Figure 1

Contrasting components in $\mathrm{V}{\mathrm{Se}}_2/{\mathrm{Bi}}_2{\mathrm{Se}}_3$. (a) Unit cell for $\mathrm{V}{\mathrm{Se}}_2$ TL. (b) Atomic structure of ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ (QL identified with green dashed rectangle). (c) Comparisons between surface Brillouin zones of $\mathrm{V}{\mathrm{Se}}_2$ (turquoise) and ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ (violet); $\overline{\mathrm{\Gamma }M}$ lengths are $1.081{\AA }^{–1}$ for $\mathrm{V}{\mathrm{Se}}_2$ and $0.875{\AA }^{–1}$ for ${\mathrm{Bi}}_2{\mathrm{Se}}_3$. (d) Second-derivative spectra near the Fermi level (left) and wide-range band mapping (right) for 10 QL ${\mathrm{Bi}}_2{\mathrm{Se}}_3/\mathrm{BLG}$, taken at 30 K with 21.218-eV photons. The topological Dirac cone (red arrow) and trivial Rashba spin-split surface states (cyan arrow) are marked. (e) Same as (d) but for 1 TL $\mathrm{V}{\mathrm{Se}}_2/10\mathrm{QL} {\mathrm{Bi}}_2{\mathrm{Se}}_3$; Dirac-cone-like (red arrow) and $\mathsf{V}$-shaped (cyan arrow) features are distinguished. (f) Same as (e) but for 1 TL $\mathrm{V}{\mathrm{Se}}_2/\mathrm{BLG}$. In (d)–(f), second derivatives are taken along the in-plane momentum direction; $\overline{M}$ points of ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ and $\mathrm{V}{\mathrm{Se}}_2$ are designated.

Figure 2

Topological and trivial interface states in $\mathrm{V}{\mathrm{Se}}_2/{\mathrm{Bi}}_2{\mathrm{Se}}_3$. (a), (b) ARPES maps near the Fermi level along $\overline{\mathrm{\Gamma }K}$ and corresponding second derivatives with respect to the in-plane momentum for $N=0–3\mathrm{TL} \mathrm{V}{\mathrm{Se}}_2/\mathrm{BLG}$, respectively, taken at 30 K using 21.218-eV photons. (c), (d) Same as (a), (b) but for $N=0–3\mathrm{TL} \mathrm{V}{\mathrm{Se}}_2/10\mathrm{QL} {\mathrm{Bi}}_2{\mathrm{Se}}_3$; interfacial bands TISs (red arrow) and SISs (cyan arrow) are marked in (d).

Figure 3

Thickness-dependent ARPES versus simulated maps. (a), (b) Photoemission mappings and corresponding second derivatives for $N=0–2\mathrm{TL} \mathrm{V}{\mathrm{Se}}_2/10\mathrm{QL} {\mathrm{Bi}}_2{\mathrm{Se}}_3$, respectively, measured along $\overline{\mathrm{\Gamma }K}$ at 30 K with 21.218-eV photons. (c), (d) Theoretical spectral functions and their second derivatives for $N=0–2\mathrm{TL} \mathrm{V}{\mathrm{Se}}_2/6\mathrm{QL} {\mathrm{Bi}}_2{\mathrm{Se}}_3$, respectively, calculated parallel to $\overline{\mathrm{\Gamma }K}$. In (b), (d), second derivatives are along the in-plane momentum direction; TISs (red arrow) and SISs (cyan arrow) are flagged.

Figure 4

Spatial charge densities for interface states. (a) Simulated mapping (left) along $\overline{\mathrm{\Gamma }K}$ and its second derivative with respect to the in-plane momentum (right) for 1 TL $\mathrm{V}{\mathrm{Se}}_2/6\mathrm{QL} {\mathrm{Bi}}_2{\mathrm{Se}}_3$, wherein TISs (red arrow) and SISs (cyan arrow) are identified. (b) Similar to (a) but for 2 TL $\mathrm{V}{\mathrm{Se}}_2/6\mathrm{QL} {\mathrm{Bi}}_2{\mathrm{Se}}_3$. (c) Integrated charge densities ρ for TISs (left) and SISs (right) of 1 TL $\mathrm{V}{\mathrm{Se}}_2/6\mathrm{QL} {\mathrm{Bi}}_2{\mathrm{Se}}_3$ at the $\overline{\mathrm{\Gamma }}$ point graphed versus the spatial coordinate $z$ along the $c$ axis, where $z=0$ is at the top Se layer of ${\mathrm{Bi}}_2{\mathrm{Se}}_3$. Each curve is normalized to its maximum; colored rectangles mark regions occupied by atomic layers of ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ (lavender) and $\mathrm{V}{\mathrm{Se}}_2$ (turquoise). (d) Same as (c) but for 2 TL $\mathrm{V}{\mathrm{Se}}_2/6\mathrm{QL} {\mathrm{Bi}}_2{\mathrm{Se}}_3$. (e) Side view of 2 TL $\mathrm{V}{\mathrm{Se}}_2/6\mathrm{QL} {\mathrm{Bi}}_2{\mathrm{Se}}_3$ lattice overlaid with turquoise and lavender rectangles for select $\mathrm{V}{\mathrm{Se}}_2$ and ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ atomic-layer sets, respectively, acting as guides to those in (c), (d).