Transport Studies Of Quasi-one-dimensional Charge Density Wave Material Ta₂NiSe₇

Low-dimensional transitional metal chalcogenides(TMCs)garnered great interest due to their rich physical properties.Because of their unique low-dimensional structure,they displayed interesting properties that can hardly be found in three-dimensional materials.Including su-perconductivity in MoS2,[1]extremely large magnetoresistance(MR)in WTe2,[2]and the strong increase in charge density wave(CDW)state in single-layer NbSe2.[3]The low dimensionality and high structural symmetry make TMC ideal for study structure-property relationship.Charge density wave,being one of the most heated topics in low-dimensional condensed matter physics,have made great progress both theoretically and experimentally.However,the mechanism re-garding the formation of CDW remains largely unknown,making transport study of CDW very important.In this study,we conducted electrical transport measurement in quasi-one-dimensional TMC Ta2NiSe7.By study the MR with changing magnetic field under different temperature near CDW transition,we observed a sizable change in MR curvature upon entering the CDW state.A break down of Kohler’s rule is also found,indicating the possible change of carrier under CDW transition.We showed that such curvature change can be well described by the two-band orbital MR with the hole density strongly suppressed in the CDW state,indicating the p orbitals from Se atoms dominate the change in MR through CDW transition.Furthermore,we observed a rotation of the symmetry axis of MR upon entering CDW state only when the mag-netic field is rotating in the ac plane.We showed that the rotation is not related to the amplitude of applied magnetic field and the temperature dependence of the symmetry axis angle indicated such rotation might strongly related to CDW state.