Thin films promise new opportunities for the manipulation of surface states of topological semimetals with the potential to realize new states that cannot be obtained in bulk materials. Here, we report transport studies of gated Hall bar structures fabricated from approximately 50-nm-thick, (001)-oriented epitaxial films of cadmium arsenide, a prototype three-dimensional Dirac semimetal, in magnetic fields up to 45 T. The films exhibit a quantized Hall effect with pronounced odd-integer plateaus that is strikingly different from that of the more widely studied (112)-oriented films. We show that the unusual quantum Hall effect is a consequence of the inverted bulk band structure of cadmium arsenide that creates topological-insulator-like states at the bottom and top interfaces, each exhibiting a half-integer quantum Hall effect. A small potential offset between the two surfaces results in the crossing of the Landau levels and gives rise to the filling factor sequences observed in the experiments. Moreover, at large negative values of gate bias, the filling factor $\nu =1$ is abruptly preempted by an insulating state that is accompanied by the collapse of the well-developed quantum Hall effect. We suggest that this new phase cannot be explained within a single-particle picture and discuss the role of Coulomb interactions between spatially separated surface states.

中文翻译：

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三维狄拉克半金属异质结中的拓扑绝缘体状态和量子霍尔效应的崩溃

薄膜为操纵拓扑半金属的表面状态提供了新的机会，并有望实现散装材料无法获得的新状态。在这里，我们报道了在大约45 T的磁场中，由大约50纳米厚的（001）取向外延砷化镉薄膜（三维Dirac半金属原型）制造的门控霍尔棒结构的运输研究。具有明显的奇整数平稳期的量化霍尔效应，与更广泛研究的（112）取向的电影的霍尔效应明显不同。我们显示出异常的量子霍尔效应是砷化镉的反向体能带结构的结果，该结构在底部和顶部界面处创建了类似于拓扑绝缘体的状态，每个状态都表现出半整数量子霍尔效应。两个表面之间的小电位偏移导致Landau水平的交叉，并导致实验中观察到的填充因子序列。此外，在栅极偏置的负值较大时，填充系数$\nu =\mathrm{1个}$突然被绝缘状态所取代，伴随着发达的量子霍尔效应的崩溃。我们建议不能在单粒子图片中解释这个新阶段，并讨论空间分离的表面状态之间库仑相互作用的作用。