Detection of Nontrivial Topology Driven by Charge Density Wave in a Semi‐Dirac Metal

Abstract

The presence of electron correlations in a system with topological order can lead to exotic ground states. Considering single crystals of LaAgSb2 which has a square net crystal structure, one finds multiple charge density wave transitions (CDW) as the temperature is lowered. Large planar Hall (PHE) signals are found in the CDW phase, which are still finite in the high‐temperature phase though they change sign. Optimizing the structure within first‐principles calculations, one finds an unusual chiral metallic phase. This is because as the temperature is lowered, the separation between the Ag/Sb atoms on different layers decreases, leading to stronger repulsions between electrons associated with atoms on different layers. This leads to successive layers sliding with respect to each other, thereby stabilizing a chiral structure in which inversion symmetry is also broken. The large Berry curvature associated with the low‐temperature structure explains the low‐temperature PHE. At high temperature, the PHE arises from the changes induced in the anisotropic Dirac cone in presence of a magnetic field. This work represents a route toward detecting and understanding the mechanism in a correlation‐driven topological transition through electron transport measurements, complemented by ab‐initio electronic structure calculations.

Origin of the Anomalous Electrical Transports in Quasi-One-Dimensional Ta2NiSe7

“…Due to the diamagnetic nature of Ta 2 NiSe 7 , the mechanism of PHE induced by magnetic factors was excluded. In some topological insulators, the PHE is usually attributed to the resistivity anisotropy induced by the difference of field-induced anisotropic scattering in surface Dirac Fermions of various spins. − Besides, in many topological semimetals, the origin of PHE was often pinned down to the chiral anomaly of topological electrons. ,,, There are some anomalies as well: The sign change of the PHE signal around the CDW transition was reported in single crystals of LaAgSb 2 . At low temperatures it originates from large Berry curvature, while at high temperatures it arises from the changes induced in the anisotropic Dirac cone in the presence of a magnetic field.…”

“…47,49,50,56 There are some anomalies as well: The sign change of the PHE signal around the CDW transition was reported in single crystals of LaAgSb 2 . 57 At low temperatures it originates from large Berry curvature, while at high temperatures it arises from the changes induced in the anisotropic Dirac cone in the presence of a magnetic field. Higher-order oscillatory PHE was observed in topological kagome KV 3 Sb 5 below CDW transition, which can be attributed to a strong and complicated coupling between lattice symmetry and electron scatterings mediated by the CDW transition.…”