Persistent coherence and spin polarization of topological surface states on topological insulators

Gapless surface states on topological insulators are protected from elastic scattering on nonmagnetic impurities, which makes them promising candidates for low-power electronic applications. However, for widespread applications, these states should remain coherent and significantly spin polarized at ambient temperatures. Here, we studied the coherence and spin structure of the topological states on the surface of a model topological insulator, Bi${}_2$Se${}_3$, at elevated temperatures in spin- and angle-resolved photoemission spectroscopy. We found an extremely weak broadening and essentially no decay of spin polarization of the topological surface state up to room temperature. Our results demonstrate that the topological states on surfaces of topological insulators could serve as a basis for room-temperature electronic devices.

Figure 1

Temperature effects on the spectra of the topological surface state on Bi${}_2$Se${}_3$. (a) ARPES intensity along the $\Gamma$$K$ line in the surface Brillouin zone at 20 K and (b) at 280 K. The top panels show the MDCs at the Fermi level, with two Lorentzian-shaped peaks, corresponding to $\pm k_F$. (c) Temperature dependence of Im$\Sigma \left(0\right)$ for TSS on Bi${}_2$Se${}_3$. Im$\Sigma \left(0\right)$ is obtained by fitting the MDC peaks with Lorentzian line shape. The error bars represent standard deviation from the fitting. The dashed line is the linear fit of Im$\Sigma \left(0\right)$.

Figure 2

Spin-resolved ARPES spectra from Bi${}_2$Se${}_3$. (a) Fermi surface and (b) spin-integrated photoemission intensity from the momentum region marked with the blue rectangle in (a). (c) Spin-up and (d) spin-down spectra from the same region, with the polarization vector along the $y$ direction. (e) Spin polarization in the $y$ direction. (f) Spin polarization in the $x$ direction. All the spectra were taken at 300 K with 50-eV photons. The arrows in (a) represent the obtained spin direction.

Figure 3

Spin-resolved ARPES spectra from Bi${}_2$Se${}_3$. (a)–(h) Spin-up (red) and spin-down (blue) EDCs and (i)–(p) spin polarization along the $y$ direction, corresponding to the spectra from Fig. 3. (q)–(x) Spin-up (green) and spin-down (red) EDCs for the spin polarization in the $x$ direction.