Joseph Henry Laboratory of Physics, Department of Physics, Princeton University, Princeton, NJ 08544, USA.
Science. 2011 Apr 29;332(6029):560-4. doi: 10.1126/science.1201607. Epub 2011 Mar 31.
The recently discovered three-dimensional or bulk topological insulators are expected to exhibit exotic quantum phenomena. It is believed that a trivial insulator can be twisted into a topological state by modulating the spin-orbit interaction or the crystal lattice, driving the system through a topological quantum phase transition. By directly measuring the topological quantum numbers and invariants, we report the observation of a phase transition in a tunable spin-orbit system, BiTl(S(1-δ)Se(δ))(2), in which the topological state formation is visualized. In the topological state, vortex-like polarization states are observed to exhibit three-dimensional vectorial textures, which collectively feature a chirality transition as the spin momentum-locked electrons on the surface go through the zero carrier density point. Such phase transition and texture inversion can be the physical basis for observing fractional charge (±e/2) and other fractional topological phenomena.
最近发现的三维或体拓扑绝缘体有望表现出奇异的量子现象。人们相信，通过调节自旋轨道相互作用或晶体格子，平凡绝缘体可以被扭曲成拓扑状态，从而驱动系统通过拓扑量子相变。通过直接测量拓扑量子数和不变量，我们报告了在可调谐自旋轨道系统 BiTl(S(1-δ)Se(δ))(2)中观察到的相变，其中拓扑状态的形成得到了可视化。在拓扑状态中，观察到类涡旋的极化状态表现出三维向量纹理，其特征是当表面上的自旋动量锁定电子穿过零载流密度点时，手性发生转变。这种相变和纹理反转可能是观察分数电荷（±e/2）和其他分数拓扑现象的物理基础。
