Photon energy and polarization-dependent electronic structure of Cr-doped ${\mathrm{Bi}}_2{\mathrm{Se}}_3$

In this article, we report a comparative study of the electronic structure of Cr-doped and pristine ${\mathrm{Bi}}_2{\mathrm{Se}}_3$. Circular dichroism and photon-energy-dependent angle-resolved photoemission experiments were performed. Even though the surface states seen on the Cr-doped samples are gapped, they exhibit strong circular dichroism, for which we provide its origin in accordance with the nontrivial band structure of the bulk. The surface electronic structure measurements with linear and circular polarized light show signatures that the orbital composition of the surface states is changed with Cr doping. Our observations not only provide further spectroscopic information about topological materials, but also promotes an alternative experimental tool to control their spin-orbital texture.

Figure 1

(a) Systematic representation of the studied sample. (b) Experimental geometry for photoemission experiment.

Figure 2

(a) ARPES map of the ${\mathrm{Bi}}_{1.78}{\mathrm{Cr}}_{0.22}{\mathrm{Se}}_3$ thin film taken with 50-eV p-pol. light at 15 K. (b)–(e) Constant energy counters at different $E_b$.

Figure 3

(a)–(d) Photon energy-dependent surface electronic structure of ${\mathrm{Bi}}_{1.78}{\mathrm{Cr}}_{0.22}{\mathrm{Se}}_3$. (e) ARPES intensity plot in the $k_z-k_y$ plane at $E_F$.

Figure 4

(a1)–(a2) Surface electronic structure of ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ taken with p-pol. and s-pol. 50-eV photons, respectively. (a3) Corresponding MDCs obtained at $E_b=0.2$ eV. (b1)–(b3) Same as in (a1)–(a3) but for ${\mathrm{Bi}}_{1.78}{\mathrm{Cr}}_{0.22}{\mathrm{Se}}_3$.

Figure 5

(a1)–(a3) and (b1)–(b3) ARPES maps of ${\mathrm{Bi}}_{1.78}{\mathrm{Cr}}_{0.22}{\mathrm{Se}}_3$ obtained with circularly polarized 60- and 50-eV photons along with the MDCs integrated within 10 meV at the ${\mathrm{E}}_F$. (c1)–(c3) and (d1)–(d3) Same as (a1)–(a3) and (b1)–(b3) but for ${\mathrm{Bi}}_2{\mathrm{Se}}_3$.

Figure 6

(a), (b) CD-ARPES maps of ${\mathrm{Bi}}_{1.78}{\mathrm{Cr}}_{0.22}{\mathrm{Se}}_3$ taken with circularly polarized 50- and 60-eV photons, respectively. (c), (d) Same as (a1), (a2) but for ${\mathrm{Bi}}_2{\mathrm{Se}}_3$. (e) CD signal of the upper surface states along the $k_{\parallel }$ for ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ (red squares) and ${\mathrm{Bi}}_{1.78}{\mathrm{Cr}}_{0.22}{\mathrm{Se}}_3$ (black squares). The CD signal was obtained by integration over the surface states (in momentum) within 20-meV energy window. Each $k_{\parallel }$ was determined from the corresponding $E_b$.