In this letter, we study the relaxation of nonequilibrium homogeneous spin distribution due to the D’yakonov-Perel’ mechanism in two-dimensional (2D) semiconductors with an elliptic band structure. Within the effective-mass approximation, the low-energy band structure is described using anisotropic in-plane effective mass of free carriers. Spin relaxation time of free carriers is calculated theoretically using the time evolution of the density matrix of a polarized spin ensemble in the strong momentum scattering regime. Results are obtained for scattering potential due to both Coulomb interaction and uncharged defects in the sample. We show that the ratio of spin relaxation time in y- and x- directions within the 2D material plane scales as a power of the corresponding effective mass ratio where the exponent depends on the details of the scattering potential. The model is applied to study spin relaxation of electrons in monolayer black phosphorus, which is known to exhibit significant band structure ellipticity. The model can also predict spin relaxation in mechanically strained 2D materials in which elliptic band structure emerges as a consequence of the modification of the lattice constants.
Published : "arXiv Mesoscale and Nanoscale Physics".