一般，磁场使传导电子运动局域化，引起正的磁电阻。大的负磁阻并不常见，往往代表着奇异的物理现象。负磁阻常与磁性材料联系在一起。最近在非磁性的狄拉克半金属和外尔半金属中，发现了手征反常引起的负磁阻效应。负磁阻对磁场和电场角度非常敏感，磁场平行于电场时最大。然而，在非磁性的三维拓扑绝缘体和拓扑晶体绝缘体中，也发现了类似的反常负磁阻效应和无序引起的各向同性负磁阻效应。目前，它们的物理机制还没有明确统一建立。不同实验的机理解释都存在各自的局限性，并不适用与彼此。本项目拟通过一系列对照实验研究，探明负磁阻效应与拓扑非平庸态的相关性；研究无序、载流子浓度等因素对拓扑绝缘体负磁阻的影响，为揭示隐藏的本征物理机制和建立统一理论提供实验依据。

In general, magnetic fields tend to localize electrons and lead to positive magnetoresistance. Therefore, large negative magnetoresistance is unusual and always represents some peculiar physics. Negative magnetoresistance was often associated with magnetic materials. Recently, anomalous negative magnetoresistance was observed in non-magnetic Dirac and Weyl semimetal, which is attributed to the chiral anomaly of Weyl fermions. This negative magnetoresistance is very sensitive to the angle between magnetic field and current, and the maximum value is obtained when magnetic field is parallel to the current. However, a similar negative magnetoresistance was also discovered in non-magnetic 3D topological insulator and topological crystal insulator. So far, their physical mechanisms have not yet been clearly defined. The interpretations of different experimental mechanisms have their own limitations and does not apply to each other. This project plans to determine the relationship between the anomalous negative magnetoresistance and topological non-trivial state, and research how the disorder and carrier concentration affect the negative magnetoresistance, through a series of special comparative experiments. It will provide useful experimental evidence for revealing hidden intrinsic physics and establishing a unified theory.