标题： 超快能量和动量分辨的拓扑绝缘体Sb$_2$Te$_3$表面狄拉克光电流 显示英文标题

标题： Ultrafast Energy- and Momentum-resolved Surface Dirac Photocurrents in the Topological Insulator Sb$_2$Te$_3$

摘要： 我们通过时间分辨和角度分辨双光子光电子能谱结合可变偏振中红外脉冲激光，展示了拓扑绝缘体Sb$_2$Te$_3$表面狄拉克光电流的能量动量映射。 结果表明，从占据态到未占据态的直接光学跃迁允许线性和圆偏振光电效应，从而使得我们可以利用激光偏振相干控制表面电流。 此外，表面电流映射直接可视化了狄拉克锥在时域中的超快电流动力学。 我们揭示了非弹性散射和动量散射的超快带内弛豫动力学。 我们的观察结果为拓扑绝缘体中表面狄拉克电子的相干光学控制开辟了道路。 显示英文摘要

摘要： We present energy-momentum mapping of surface Dirac photocurrent in the topological insulator Sb$_2$Te$_3$ by means of time- and angle-resolved two-photon photoemission spectroscopy combined with polarization-variable mid-infrared pulse laser. It is demonstrated that the direct optical transition from the occupied to the unoccupied part of the surface Dirac-cone permits the linear and circular photogalvanic effect which thereby enables us to coherently control the surface electric-current by laser polarization. Moreover, the surface current mapping directly visualizes ultrafast current dynamics in the Dirac cone in the time domain. We unravel the ultrafast intraband relaxation dynamics of the inelastic scattering and momentum scattering separately. Our observations pave the pathway for coherent optical control over surface Dirac electrons in topological insulators.