Different instabilities have been confirmed to exist in the three-dimensional (3D) electron gas when it is confined to the lowest Landau level in the extreme quantum limit. The recently discovered 3D topological semimetals offer a good platform to explore these phenomena due to the small sizes of their Fermi pockets, which means the quantum limit can be achieved at relatively low magnetic fields. In this work, we report the high-magnetic-field transport properties of the Dirac semimetal state in pressurized black phosphorus. Under applied hydrostatic pressure, the band structure of black phosphorus goes through an insulator-semimetal transition. In the high pressure topological semimetal phase, anomalous behaviors are observed on both magnetoresistance and Hall resistivity beyond the relatively low quantum limit field, which is demonstrated to indicate the emergence of an exotic electronic state hosting a density wave ordering. Our findings bring the first insight into the electronic interactions in black phosphorus under intense field.

当三维（3D）电子气被限制在极端量子极限的最低朗道能级时，已经证实存在不同的不稳定性。最近发现的 3D 拓扑半金属提供了一个很好的平台来探索这些现象，因为它们的费米口袋尺寸很小，这意味着可以在相对较低的磁场下实现量子极限。在这项工作中，我们报告了狄拉克半金属态在加压黑磷中的高磁场传输特性。在施加的静水压力下，黑磷的能带结构经历绝缘体-半金属转变。在高压拓扑半金属相中，在相对较低的量子极限场之外，磁阻和霍尔电阻率均观察到反常行为，这被证明表明出现了一种具有密度波排序的奇异电子态。我们的研究结果首次深入了解了强场下黑磷中的电子相互作用。