Institute of Physics and Applied Physics, Yonsei University, Seoul 120-749, Korea.
Phys Rev Lett. 2012 Jan 27;108(4):046805. doi: 10.1103/PhysRevLett.108.046805. Epub 2012 Jan 25.
We performed angle-resolved photoemission (ARPES) experiments with circularly polarized light and first-principles density functional calculation with spin-orbit coupling to study surface states of a topological insulator Bi2Se3. We observed circular dichroism (CD) as large as 30% in the ARPES data with upper and lower Dirac cones showing opposite signs in CD. The observed CD is attributed to the existence of local orbital-angular momentum (OAM). First-principles calculation shows that OAM in the surface states is significant and is locked to the electron momentum in the opposite direction to the spin, forming chiral OAM states. Our finding opens a new possibility for strong light-induced spin-polarized current in surface states. We also provide a proof for local OAM origin of the CD in ARPES.
我们进行了角分辨光发射（ARPES）实验，使用圆偏振光和包含自旋轨道耦合的第一性原理密度泛函计算，以研究拓扑绝缘体 Bi2Se3 的表面态。我们在 ARPES 数据中观察到高达 30%的圆二色性（CD），其中上和下狄拉克锥的 CD 具有相反的符号。所观察到的 CD 归因于局部轨道角动量（OAM）的存在。第一性原理计算表明，表面态中的 OAM 非常显著，并且与电子动量锁定在与自旋相反的方向，形成手性 OAM 态。我们的发现为表面态中强光诱导的自旋极化电流开辟了新的可能性。我们还为 ARPES 中 CD 的局部 OAM 起源提供了证据。
