Valley field mechanics: a local perspective beyond valley flavor

Abstract

Valleytronics in 2D materials - primarily graphene and transition metal dichalcogenides is rooted in the existence of valley flavor but extends far out to the rich dimension of local physics, as reviewed, extensively studied and demonstrated in this work, in terms of a local, Ginzburg-Landau order parameter type field - valley field. A theoretical framework - valley field mechanics thus arises to address the local physics and opens a path to local valley control. Numerical and analytical results are presented for various structures. A spectrum of novel local phenomena are revealed with characteristics in apparent contradiction to valley flavor-based expectations or constraints, enabling flexible valley control - for example, both symmetry and material restrictions previously established are relaxed, with gapless, single-layer graphene, a material with inversion symmetry now added to the material list for a relatively simple realization of valleytronics. Non-valley targeted applications can also benefit from local valley physics, with an access given to electrical switch between direct and indirect gaps. Last, the framework of valley field mechanics is applied to valley-controlled quantum transport. Overall, the diverse local valley phenomena revealed suggest the new exciting direction of valley field engineering - design and search for quantum structures to tailor local valley physics for applications.