Naturally occurring in-plane hyperbolic response, where metallic and dielectric response along orthogonal crystal axes coexists, is rarely observed in nature. Here, the authors find that in an anisotropic transition metal dichalcogenide (i.e., the 1 phase of WTe), a pair of nested bands around its Fermi level provides the conditions for hyperbolicity to occur. The band-nesting induced resonant interband optical transitions, which in conjunction with the strong in-plane anisotropic optical processes, leads to hyperbolic plasmons in the near-infrared spectral regime. The physical principle is general, and the authors demonstrate similar hyperbolic response in other 1 transition metal dichalcogenides by modulating the degree of band nesting through strain engineering.
