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, at 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 bottom and top interfaces, each exhibiting a half-integer quantum Hall effect. A small potential offset between the two surfaces results in crossing of the Landau levels and gives rise to the filling factor sequences observed in the experiments. Moreover, at large negative gate biases, the filling factor {$$} $=$ 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，并有可能实现散装材料无法获得的新状态。在这里，我们报道了由砷化镉（一种原型的三维狄拉克半金属）在大约45 T的磁场下由约50 nm厚，（001）取向的外延膜制成的门控霍尔棒结构的传输研究。具有明显的奇整数平稳期的量化霍尔效应，这与更广泛研究的（112）取向电影的显着不同。我们显示出异常的量子霍尔效应是砷化镉的倒置体结构的结果，该结构在底部和顶部界面处形成了拓扑绝缘体状的状态，每个状态都表现出半整数的量子霍尔效应。两个表面之间的小电位偏移会导致Landau水平的交叉，并导致实验中观察到的填充因子序列。此外，在较大的负栅极偏置下，填充因子{$$}$=$ 图1突然被绝缘状态所取代，同时伴随着发达的量子霍尔效应的崩溃。我们建议不能在单个粒子图片中解释这个新相，并讨论空间分离的表面状态之间库仑相互作用的作用。