Electronic structure and open-orbit Fermi surface topology in isostructural semimetals NbAs₂ and W₂As₃ with extremely large magnetoresistance

In transition-metal dipnictides TmPn₂ (Tm = Ta and Nb; Pn = P, As, and Sb), the origin of extremely large magnetoresistance (XMR) is yet to be studied by the direct visualization of the experimental band structures. Here, using angle-resolved photoemission spectroscopy, we map out the three-dimensional electronic structure of NbAs₂. The open-orbit topology contributes to a non-negligible part of the Fermi surfaces (FSs), like that of the isostructural compound MoAs₂, where the open FS is proposed to likely explain the origin of XMR. We further demonstrate the observation of open characters in the overall FSs of W₂As₃, which is also a XMR semimetal with the same space group of C12/m1 as the TmPn₂ family and MoAs₂. Our results suggest that the open-orbit FS topology may be a shared feature between XMR materials with the space group of C12/m1 and, thus, could possibly play a role in determining the corresponding XMR effect together with the electron–hole compensation.