Spin–Orbit-Coupling-Induced Type-I/type-II Dirac Nodal-Line Metal in Nonsymmorphic CaSb2

From band structure calculations, we show that the nonsymmorphic crystal CaSb2 is a new topological semimetal (TSM) with an unprecedented band structure. In the absence of spin–orbit coupling (SOC), CaSb2 contains several Dirac nodal points, nodal lines, and a nodal surface. When the effects of SOC are taken into account, these Dirac nodes vanish, but renewed nodal lines on the kz = π/b plane protected by nonsymmorphic symmetry are induced from the surface nodes on the kz = π/b plane. Distinct from previously reported TSMs, CaSb2 has both type-I and type-II Dirac nodal lines. Experimentally, we observed a resistivity plateau under a weak magnetic field at 10 K and nonsaturating giant magnetoresistance (GMR). The MR reaches the order of 103% at 7 T below 10 K.