通过从头算非绝热分子动力学研究1T-VSe_(2)中的光激发诱导自旋动力学

Photoexcitation-induced spin dynamics in 1T-VSe_(2) investigated by ab initio nonadiabatic molecular dynamics

利用光激发来操控二维材料中的磁矩是实现光自旋电子学器件的基础.本工作中,我们利用从头算非绝热分子动力学模拟,研究了光激发如何改变二维铁磁金属VSe_(2)中的磁矩.我们发现自旋-轨道耦合作用和声子激发导致了自旋向上和自旋向下电子态发生混合,并在费米能级以上1.0 eV附近形成了一个自旋混合区.当自旋向上或向下的电子在弛豫过程中经过这个混合区时,它们会丢失原有的自旋方向.当电子从费米面以上2.0 eV左右向下弛豫时,自旋向下的电子发生带内弛豫,而自旋向上的电子发生带间弛豫.因此,自旋向下电子的弛豫速度比自旋向上电子高出约一个数量级.这种自旋向上和自旋向下电子的动态行为差异导致了VSe_(2)的磁矩在光激发后10 fs内先增大,这对应了自旋向下电子失去了原始的自旋方向;随后,磁矩在100 fs内减小,这对应了自旋向上电子失去了原始自旋的方向;最后,系统的总磁矩在皮秒的时间尺度内逐渐恢复到光激发前的水平.这项工作为我们了解光激发如何操控二维材料的磁性提供了理论依据.

Using photoexcitation to manipulate the magnetic moment in two-dimensional(2D)materials paves the way for the design of opto-spintronic devices.In this work,using ab initio nonadiabatic molecular dynamics simulation,we studied how photoexcitation changed the magnetic moment in the 2D ferromagnetic metal VSe_(2).The spin-orbit coupling and phonon excitation lead to the loss of the original spin orientation in both the spin-up and spin-down orbitals,forming a spin-mixing region approximately 1.0 eV above the Fermi level.When spin-up or spin-down electrons pass through this region during relaxation,they lose their original spin orientation.However,spin-down electrons relax approximately an order of magnitude faster than spin-up electrons,as the relaxation for spin-down is primarily intraband,while spin-up electrons undergo interband relaxation.Such different dynamical behaviors for spin-up and spin-down electrons result in the magnetic moment of VSe_(2) initially rising within approximately 10 fs after optical excitation,corresponding to the loss of the original spin orientation for spindown electrons.Subsequently,it decreases by approximately 1oo fs,corresponding to the loss of spin orientation for spinup electrons.Finally,the total magnetic moment of the system gradually recovers to the preexcitation level on the order of picoseconds.This work provides new insight into how photoexcitation controls the magnetic properties of 2D materials.