Olsen Thomas
CAMD, Department of Physics, Technical University of Denmark, 2800 Kgs. Lyngby Denmark.
Phys Rev Lett. 2021 Oct 15;127(16):166402. doi: 10.1103/PhysRevLett.127.166402.
We present first principles calculations of the two-particle excitation spectrum of CrI_{3} using many-body perturbation theory including spin-orbit coupling. Specifically, we solve the Bethe-Salpeter equation, which is equivalent to summing up all ladder diagrams with static screening, and it is shown that excitons as well as magnons can be extracted seamlessly from the calculations. The resulting optical absorption spectrum as well as the magnon dispersion agree very well with recent measurements, and we extract the amplitude for optical excitation of magnons resulting from spin-orbit interactions. Importantly, the results do not rely on any assumptions of the microscopic magnetic interactions such as Dzyaloshinskii-Moriya (DM), Kitaev, or biquadratic interactions, and we obtain a model independent estimate of the gap between acoustic and optical magnons of 0.3 meV. In addition, we resolve the magnon wave function in terms of band transitions and show that the magnon carries a spin that is significantly smaller than ℏ. This highlights the importance of terms that do not commute with S^{z} in any Heisenberg model description.
我们使用包括自旋轨道耦合的多体微扰理论，给出了CrI₃双粒子激发光谱的第一性原理计算。具体而言，我们求解了贝塞耳-萨尔皮特方程，该方程等同于对所有具有静态屏蔽的梯形图求和，结果表明激子以及磁振子都可以从计算中无缝提取。所得的光吸收光谱以及磁振子色散与最近的测量结果非常吻合，并且我们提取了由自旋轨道相互作用导致的磁振子光激发振幅。重要的是，结果不依赖于任何微观磁相互作用的假设，如Dzyaloshinskii-Moriya（DM）、Kitaev或双二次相互作用，并且我们获得了声学和光学磁振子之间能隙的与模型无关的估计值0.3毫电子伏特。此外，我们根据能带跃迁解析了磁振子波函数，并表明磁振子携带的自旋明显小于ℏ。这突出了在任何海森堡模型描述中与Sᴾ不共轭的项的重要性。
