Coexistence of Weyl semimetal and Weyl nodal loop semimetal phases in a collinear antiferromagnet

Antiferromagnets (AFMs) with anomalous quantum responses have led to new progress for the understanding of their magnetic and electronic structures from symmetrical and topological points of view. Two typical topological states are the collinear antiferromagnetic Weyl semimetal (WSM) and Weyl nodal loop semimetal (WNLSM). In comparison with their counterparts in ferromagnets and noncollinear AFMs, WSMs and WNLSMs in collinear AFMs are still awaiting experimental verification. In this paper, we theoretically predict the coexistence of Weyl points (WPs) and Weyl nodal loops (WNLs) in transition metal oxide ${\mathrm{RuO}}_{2}$. Owing to the small magnetocrystalline anisotropy energy, the WPs and WNLs can transform into each other via tuning the N\'eel vector. Moreover, since the WPs are very close to the Fermi level and the WNLs are even crossing the Fermi level, the topological states in ${\mathrm{RuO}}_{2}$ can be easily probed by photoemission and scanning tunneling microscopy methods. Our result provides a promising material platform for the study of WSM and WNLSM states in collinear AFMs.