Topological Dirac semimetals (TDSs) are three-dimensional analogs of graphene, with carriers behaving like massless Dirac fermions in three dimensions. In graphene, substrate disorder drives fluctuations in Fermi energy, necessitating construction of heterostructures of graphene and hexagonal boron nitride (h-BN) to minimize the fluctuations. Three-dimensional TDSs obviate the substrate and should show reduced E_F fluctuations due to better metallic screening and higher dielectric constants. We map the potential fluctuations in TDS Na₃Bi using a scanning tunneling microscope. The rms potential fluctuations are significantly smaller than the thermal energy room temperature (ΔE_F,rms = 4 to 6 meV = 40 to 70 K) and comparable to the highest-quality graphene on h-BN. Surface Na vacancies produce a novel resonance close to the Dirac point with surprisingly large spatial extent and provide a unique way to tune the surface density of states in a TDS thin-film material. Sparse defect clusters show bound states whose occupation may be changed by applying a bias to the scanning tunneling microscope tip, offering an opportunity to study a quantum dot connected to a TDS reservoir.

中文翻译：

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Na3Bi拓扑Dirac半金属薄膜中的空间电荷非均质性和缺陷状态。

拓扑狄拉克半金属（TDS）是石墨烯的三维类似物，其载流子的行为类似于三维中无质量的狄拉克费米子。在石墨烯中，衬底无序驱动费米能量的波动，因此必须构造石墨烯和六方氮化硼（h-BN）的异质结构以最大程度地减少波动。三维TDS消除了基板，并且由于更好的金属屏蔽和更高的介电常数而应显示出减小的E _F波动。我们使用扫描隧道显微镜绘制了TDS Na ₃ Bi中的潜在波动图。均方根电势波动明显小于室温下的热能（ΔE _F，rms= 4至6 meV = 40至70 K），可与h-BN上最高质量的石墨烯相媲美。表面Na空位在狄拉克点附近产生了新颖的共振，其空间范围出乎意料地大，并提供了一种独特的方式来调节TDS薄膜材料中态的表面密度。稀疏的缺陷簇显示出束缚态，通过向扫描隧道显微镜的尖端施加偏压可以改变其占据状态，从而为研究与TDS储集层相连的量子点提供了机会。