Helmholtz-Zentrum Berlin für Materialien und Energie, Elektronenspeicherring BESSY II, Albert-Einstein-Strasse 15, 12489 Berlin, Germany.
Phys Rev Lett. 2013 May 24;110(21):216801. doi: 10.1103/PhysRevLett.110.216801. Epub 2013 May 22.
The helical Dirac fermions at the surface of topological insulators show a strong circular dichroism which has been explained as being due to either the initial-state spin angular momentum, the initial-state orbital angular momentum, or the handedness of the experimental setup. All of these interpretations conflict with our data from Bi(2)Te(3) which depend on the photon energy and show several sign changes. Our one-step photoemission calculations coupled to ab initio theory confirm the sign change and assign the dichroism to a final-state effect. Instead, the spin polarization of the photoelectrons excited with linearly polarized light remains a reliable probe for the spin in the initial state.
拓扑绝缘体表面的螺旋狄拉克费米子表现出强烈的圆二色性，这可以解释为初始态自旋角动量、初始态轨道角动量或实验装置的手性。所有这些解释都与我们从 Bi(2)Te(3)得到的数据相矛盾，Bi(2)Te(3)的数据依赖于光子能量，并显示出几个符号变化。我们的一步光电子发射计算与从头理论相结合，证实了符号的变化，并将二色性归因于末态效应。相反，用线性偏振光激发的光电子的自旋极化仍然是初始态自旋的可靠探针。
