Harnessing orbital and valley thermal transport in 2D materials: the significance of inversion symmetry

Orbitronics and valleytronics, analogous to spintronics, leverage the orbital degree of freedom and the valley degree of freedom of electrons to carry information, promising significant advancements in information processing. In this study, we disentangle the orbital and valley Nernst effect (VNE) in 2D monolayers, based on the global symmetry of the monolayers. We conduct an in-depth analysis of the orbital (valley) Nernst effect in inversion symmetric (asymmetric) monolayers, using an analytical tight binding model. Furthermore, we elucidate the dependence of the two effects on various inherent materials' parameters using the prototypical Kane-Mele model. Our calculations show that an inversion symmetric gapped Kagome lattice shows a significant orbital Nernst effect emerging from the interatomic contribution, even in the absence of both spin and VNEs. Furthermore, for the inversion asymmetric 2H-phase of TMDs, we elucidate that the valley degree of freedom encompasses the orbital degree of freedom and the VNE can be more accurately described using the orbital degree of freedom, hence termed as the valley-orbital Nernst effect.