Orbital-dependent quasiparticle scattering interference in 3R-NbS₂

We measured the quasiparticle interference (QPI) in a valleytronics-candidate material 3R-NbS₂ using spectroscopic-imaging scanning tunneling microscopy. We find that the QPI signal of the inter-valley scattering is noticeably weaker than that of the intra-valley scattering. Numerical simulations reveal that the selection rules associated with the spin and orbital degrees of freedom (DOF) suppress the QPI signal of the inter-valley scattering and that the orbital selection rule plays a major role in the QPI. These findings indicate that not only the spin but also orbital DOF should be taken into account for a better understanding of inter-valley scattering process. Our findings offer a new perspective for better understanding of the valley related phenomena and for developing a novel technique of the valley manipulation.