Bertoni R, Nicholson C W, Waldecker L, Hübener H, Monney C, De Giovannini U, Puppin M, Hoesch M, Springate E, Chapman R T, Cacho C, Wolf M, Rubio A, Ernstorfer R
Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany.
Nano-Bio Spectroscopy Group and ETSF, Universidad del Pais Vasco, CFM CSIC-UPV/EHU, 20018 San Sebastian, Spain.
Phys Rev Lett. 2016 Dec 30;117(27):277201. doi: 10.1103/PhysRevLett.117.277201.
We report the spin-selective optical excitation of carriers in inversion-symmetric bulk samples of the transition metal dichalcogenide (TMDC) WSe_{2}. Employing time- and angle-resolved photoelectron spectroscopy (trARPES) and complementary time-dependent density functional theory (TDDFT), we observe spin-, valley-, and layer-polarized excited state populations upon excitation with circularly polarized pump pulses, followed by ultrafast (<100 fs) scattering of carriers towards the global minimum of the conduction band. TDDFT reveals the character of the conduction band, into which electrons are initially excited, to be two-dimensional and localized within individual layers, whereas at the minimum of the conduction band, states have a three-dimensional character, facilitating interlayer charge transfer. These results establish the optical control of coupled spin-, valley-, and layer-polarized states in centrosymmetric materials with locally broken symmetries and suggest the suitability of TMDC multilayer and heterostructure materials for valleytronic and spintronic device concepts.
我们报道了在过渡金属二硫属化物（TMDC）WSe₂的体反演对称样品中载流子的自旋选择性光激发。利用时间分辨和角分辨光电子能谱（trARPES）以及互补的含时密度泛函理论（TDDFT），我们观察到在用圆偏振泵浦脉冲激发后，自旋、谷和层极化的激发态布居，随后载流子朝着导带的全局最小值进行超快（<100 fs）散射。TDDFT揭示了电子最初被激发进入的导带的特征是二维的且局限在单个层内，而在导带最小值处，态具有三维特征，有利于层间电荷转移。这些结果确立了对具有局部对称性破缺的中心对称材料中耦合的自旋、谷和层极化态的光学控制，并表明TMDC多层和异质结构材料适用于谷电子学和自旋电子学器件概念。
