Photoemission Spectroscopy of Magnetic and Nonmagnetic Impurities on the Surface of the ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ Topological Insulator

Dirac-like surface states on surfaces of topological insulators have a chiral spin structure that suppresses backscattering and protects the coherence of these states in the presence of nonmagnetic scatterers. In contrast, magnetic scatterers should open the backscattering channel via the spin-flip processes and degrade the state’s coherence. We present angle-resolved photoemission spectroscopy studies of the electronic structure and the scattering rates upon the adsorption of various magnetic and nonmagnetic impurities on the surface of ${\mathrm{Bi}}_2{\mathrm{Se}}_3$, a model topological insulator. We reveal a remarkable insensitivity of the topological surface state to both nonmagnetic and magnetic impurities in the low impurity concentration regime. Scattering channels open up with the emergence of hexagonal warping in the high-doping regime, irrespective of the impurity’s magnetic moment.

Figure 1

Surface doping of ${\mathrm{Bi}}_2{\mathrm{Se}}_3$. (a) to (d) ARPES spectra from ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ at various stages of Rb deposition, showing the Fermi surface (upper panels) and the ($E,k$) dispersion of photoemission intensity along the momentum line slightly off the $\Gamma M$ line in the surface Brillouin zone (lower panels). (a) pristine surface, (b) intermediate doping, and (c) maximal doping, taken at $h\nu =21.3\mathrm{eV}$ and at $h\nu =18.7\mathrm{eV}$ (d). (e) Fermi surface area of the TSS and of the lower Rashba doublet (bottom), charge doped into these states (middle) and the work function (top) as functions of Rb deposition time.

Figure 2

Development of the surface electronic structure with Cesium (a), Gadolinium (b), and Rubidium (c) adsorption at the surface of ${\mathrm{Bi}}_2{\mathrm{Se}}_3$. The spectra were recorded along the $\Gamma M$ line in the surface Brillouin zone and at $h\nu =18.7\mathrm{eV}$ for Cs and Gd, and along the $\Gamma K$ line and at $h\nu =21.3\mathrm{eV}$ for Rb. The leftmost panels correspond to the pristine surface, while the rightmost panels show the electronic structure near the maximal doping achieved with each dopand.

Figure 3

$\mathrm{Im}\Sigma (\omega )$ of the topological surface state upon adsorption of Rubidium (a) and Gadolinium (b) for several different doping levels, as indicated. (c) and (d) show $\mathrm{Im}\Sigma (\omega )$ of the lower Rashba-split doublet for Rb and Gd doped surfaces, respectively, near the maximum doping.

Figure 4

(a) Development of the surface electronic structure with Cs doping. The middle panel shows the shift of the states at $k_x=0.05\AA$, while the right panel shows the $\Gamma$ point in the surface BZ during Cs deposition. (b) Surface electronic structure upon Gd doping. The middle (right) panel represents the $k_x=0.03\AA (k_x=0)$ point.