Hidden spin polarization in the centrosymmetric MoS2 crystal revealed via elliptically polarized terahertz emission

The spin polarization in centrosymmetric molybdenum disulfide ( MoS2 ) bulk crystal is recorded by helicity dependent photocurrent exposed as elliptically polarized terahertz (THz) emission. We assign this observation to hidden spin polarization due to the local Dresselhaus effect induced by the molybdenum atomic site asymmetry. This spin polarization induces ultrafast optically controlled circular photogalvanic current that results in elliptically polarized THz emission. Furthermore, this THz radiation exhibits a helicity dependent bleaching effect under opposite circularly polarized excitations due to the spin relaxation. Our results demonstrate the viability of all-optical control of hidden spin polarization in two-dimensional materials and propose the applicability of the THz emission spectroscopy as a sensitive and contactless method to study spintronic physics in two-dimensional materials.