Direct measurement of interfacial Dzyaloshinskii-Moriya interaction at the few-layer MoS$_{\rm 2}$/Ni$_{80}$Fe$_{20}$ interface

We report on a direct measurement of sizable interfacial Dzyaloshinskii-Moriya interaction (iDMI) at the interface of two-dimensional transition metal dichalcogenide (2D-TMD), MoS$_{\rm 2}$ and Ni$_{80}$Fe$_{20}$ (Py) using Brillouin light scattering spectroscopy. A clear asymmetry in spin-wave dispersion is measured in MoS$_{\rm 2}$/Py/Ta, while no such asymmetry is detected in the reference Py/Ta system. A linear scaling of the DMI constant with the inverse of Py thickness indicates the interfacial origin of the observed DMI. We further observe an enhancement of DMI constant in 3-4 layer MoS$_{\rm 2}$/Py system (by 58$\%$) as compared to 2 layer MoS$_{\rm 2}$/Py which is caused by a higher density of MoO$_{\rm 3}$ defect species in the case of 3-4 layer MoS$_{\rm 2}$. The results open possibilities of spin-orbitronic applications utilizing the 2D-TMD based heterostructures.