Band dependence of charge density wave in quasi-one-dimensional Ta2NiSe7 probed by orbital magnetoresistance

Abstract

Ta 2 NiSe 7 is a quasi-one-dimensional (quasi-1D) transition-metal chalcogenide with Ta and Ni chain structure. An incommensurate charge-density wave (CDW) in this quasi-1D structure was well studied previously using tunnelling spectrum, X-ray and electron diffraction, whereas its transport property and the relation to the underlying electronic states remain to be explored. Here we report our results of magnetoresistance (MR) on Ta 2 NiSe 7 . A breakdown of the Kohler's rule is found upon entering the CDW state. Concomitantly, a clear change of curvature in the field dependence of MR is observed. We show that the curvature change is well described by two-band orbital MR, with the hole density being strongly suppressed in the CDW state, indicating that the p orbitals from Se atoms dominate the change in transport through the CDW transition.Low-dimensional transition-metal chalcogenides (TMC) garnered great interests due to their rich physical properties 1,2 , including the recent discovery of valley dependent transport 3 and superconductivity 4 in MoS 2 , extremely large MR in WTe 2 5 and the stunning topological phases 6 . The low dimensionality and high structural symmetry makes TMC ideal for studying the structure-property relation.Uniquely, the electron-electron interaction in 1D metals causes strong perturbations, in sharp contrast to the case in the 2D and 3D Fermi-liquid counter parts, and leads to Luttinger liquid (LL) behavior 7 . On the other hand, CDW in the quasi-1D metal can be viewed as a classical analogue of a LL state 8 . These facts raise special interests in the study of CDW in 1D metallic systems for exploring emergent behaviours. In addition, strong nonlinear electrical transport due to CDW sliding in 1D chain systems leads to high dielectric constants 9 and narrow-band noise 10 , both of which may find interesting use in applications.Ta 2 NiSe 7 is a quasi-1D ternary TMC showing an incommensurate CDW 11 . Its quasi-1D structure is illustrated in Fig. 1(a). Similar to FeNb 3 Se 10 12 , the unit cell of Ta 2 NiSe 7 consists of double rows of tantalum atoms (Ta1) in bicapped trigonal prismatic selenium coordination, and the other double rows of tantalum atoms (Ta2) in octahedral selenium coordination; nickel atoms are in highly distorted octahedral coordination. Band structure calculations showed that the Fermi surface consists of contribution from Ta2 d orbitals in the octahedral chains and Se2 p orbitals from trigonal prismatic columns 13 . At around 52 K, an incommensurate CDW occurs. Interestingly, the CDW formation mechanism a)