The interplay between strong electron interactions and band topology is a new frontier in the search for exotic quantum phases. The Kondo insulator SmB₆ has emerged as a promising platform because its correlation-driven bulk gap is predicted to host topological surface modes entangled with f electrons, spawning heavy Dirac fermions^1,2,3,4. Unlike the conventional surface states of non-interacting topological insulators, heavy Dirac fermions are expected to harbour spontaneously generated quantum anomalous Hall states⁵, non-Abelian quantum statistics^6,7, fractionalization⁸ and topological order^6,7,8. However, the small energy scales required to probe heavy Dirac fermions have complicated their experimental realization. Here we use high-energy-resolution spectroscopic imaging in real and momentum space on SmB₆. On cooling below 35 K, we observe the opening of an insulating gap that expands to 14 meV at 2 K. Within the gap, we image the formation of linearly dispersing surface states with effective masses reaching 410 ± 20 m_e (where m_e is the mass of the electron). Our results demonstrate the presence of correlation-driven heavy surface states in SmB₆, in agreement with theoretical predictions^1,2,3,4. Their high effective mass translates to a large density of states near zero energy, which magnifies their susceptibility to the anticipated novel orders and their potential utility.

强电子相互作用和能带拓扑之间的相互作用是寻找异质量子相的新前沿。Kondo绝缘子SmB ₆已成为有前途的平台，因为它的相关性驱动的体隙被预测为包含与f电子纠缠的拓扑表面模式，从而产生重的Dirac费米子^1,2,3,4。与非相互作用的拓扑绝缘子的常规表面状态不同，重型狄拉克费米子有望自发产生量子异常霍尔态⁵，非阿贝尔量子统计量^6,7，分数化⁸和拓扑阶数^6,7,8。然而，探测重狄拉克费米子所需的小能量尺度使它们的实验实现变得复杂。在这里，我们在SmB _6的真实空间和动量空间中使用高能分辨率光谱成像。在低于35 K的冷却条件下，我们观察到绝缘间隙在2 K处扩展至14 meV。在该间隙内，我们成像了线性分散的表面态，有效质量达到410±20  m _e（其中m _e为电子的质量）。我们的结果证明了SmB _6中存在相关驱动的重表面态，与理论预测^{1,2,3,4一致}。它们的高有效质量转化为接近零能量的大状态密度，这放大了它们对预期的新颖阶数及其潜在效用的敏感性。