Probing Te Vacancies as a Source of the Chiral Anomaly in Layered Dirac Materials ZrTe₅ and HfTe₅

The layered Dirac materials ZrTe₅and HfTe₅ have been the subject of vigorous investigation in recent years to experimentally observe signatures of quantum anomalies in their transport. These materials exhibit negative longitudinal magnetoresistance (NLMR)—a reduction in the resistivity when parallel electric and magnetic fields are applied to a sample—that is speculated to be direct evidence of an asymmetry in the number of left- and right-handed carriers, or a <i>chiral anomaly</i>. If this is indeed the case, these materials would serve as a tractable tabletop testbed to probe cosmological theories of quantum anomalies and symmetry breaking that arises when moving from classical to quantum field theories.<br/><br/>Despite a wealth of experimental evidence of NLMR in ZrTe₅and HfTe₅, in addition to a temperature-induced change in the sign of the Hall coefficient, the microscopic mechanism driving this anomalous transport behavior remains an open question. Prior first-principles calculations have demonstrated that strain drives a series of transitions between topological states, from a strong topological insulating, to a Dirac semimetallic, to a weak topological insulating state, which explains the diversity of experimental reports of different topological states in these materials. Further, it has been experimentally observed that off-stoichiometric, Te-deficient ZrTe₅exhibits a stronger NLMR than pristine stoichiometric ZrTe₅. To determine if these materials truly exhibit a chiral anomaly, a rigorous modeling of the transport properties of ZrTe₅and HfTe₅ in the presence of Te vacancies is necessary.<br/><br/>In this work we determine the effect of Te vacancies on the electronic and transport properties of ZrTe₅and HfTe₅. From a systematic series of first-principles density functional theory calculations we demonstrate the effect of Te vacancies both as a source of defect states and as an effective intrinsic source of strain. We further perform ab initio-based transport calculations in the strong magnetic field regime with an eye towards unravelling the origin of their anomalous transport properties and to probe their utility as testbeds for the observation of quantum anomalies.<br/><br/>LA-UR-23-26340