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 k(z) =pi/b plane protected by nonsynunorphic symmetry are induced from the surface nodes on the k(z) =pi/b plane. Distinct from previously reported TSMs, CaSb2 has both type-I and type-11 Dirac nodal lines. Experimentally, we observed a resistivity plateau under a weak magnetic field at 10K and nonsaturating giant magnetoresistance (GMR). The MR reaches the order of 10(3)% at 7 T below 10 K.