Department of Applied Physics, Eindhoven University of Technology, Eindhoven, Netherlands.
Phys Rev Lett. 2018 Jun 29;120(26):266801. doi: 10.1103/PhysRevLett.120.266801.
Inversion-symmetric materials are forbidden to show an overall spin texture in their band structure in the presence of time-reversal symmetry. However, in van der Waals materials which lack inversion symmetry within a single layer, it has been proposed that a layer-dependent spin texture can arise leading to a coupled spin-layer degree of freedom. Here we use time-resolved Kerr rotation in inversion-symmetric WSe_{2} and MoSe_{2} bulk crystals to study this spin-layer polarization and unveil its dynamics. Our measurements show that the spin-layer relaxation time in WSe_{2} is limited by phonon scattering at high temperatures and that the interlayer hopping can be tuned by a small in-plane magnetic field at low temperatures, enhancing the relaxation rates. We find a significantly lower lifetime for MoSe_{2} which agrees with theoretical expectations of a spin-layer polarization stabilized by the larger spin-orbit coupling in WSe_{2}.
在时间反演对称性的存在下，具有反转对称性的材料在其能带结构中被禁止显示整体自旋织构。然而，在单层内缺乏反转对称性的范德瓦尔斯材料中，已经有人提出，可能会出现依赖于层的自旋织构，从而导致耦合的自旋层自由度。在这里，我们使用反转对称的 WSe_{2}和 MoSe_{2}体块晶体中的时间分辨克尔旋转来研究这种自旋层极化，并揭示其动力学。我们的测量表明，WSe_{2}中的自旋层弛豫时间在高温下受到声子散射的限制，而低温下的小面内磁场可以调节层间跃迁，从而提高弛豫速率。我们发现 MoSe_{2}的寿命明显更短，这与 WSe_{2}中较大的自旋轨道耦合稳定的自旋层极化的理论预期一致。
