Landau band crossings typically stem from the intra-band evolution of electronic states in magnetic fields and enhance the interaction effect in their vicinity. Here in the extreme quantum limit of topological insulator HfTe₅, we report the observation of a topological Lifshitz transition from inter-band Landau level crossings using magneto-infrared spectroscopy. By tracking the Landau level transitions, we demonstrate that band inversion drives the zeroth Landau bands to cross with each other after 4.5 T and forms a one-dimensional Weyl mode with the fundamental gap persistently closed. The unusual reduction of the zeroth Landau level transition activity suggests a topological Lifshitz transition at 21 T, which shifts the Weyl mode close to the Fermi level. As a result, a broad and asymmetric absorption feature emerges due to the Pauli blocking effect in one dimension, along with a distinctive negative magneto-resistivity. Our results provide a strategy for realizing one-dimensional Weyl quasiparticles in bulk crystals.

朗道带交叉通常源于磁场中电子态的带内演化，并增强了它们附近的相互作用效应。_{这里是拓扑绝缘体 HfTe 5}的极限量子极限，我们报告了使用磁红外光谱从带间 Landau 水平交叉口观察到的拓扑 Lifshitz 跃迁。通过跟踪 Landau 能级跃迁，我们证明能带反转驱动第 0 个 Landau 能带在 4.5 T 后相互交叉，并形成基本间隙持续闭合的一维 Weyl 模式。第 0 个 Landau 能级跃迁活动的异常减少表明 21 T 处的拓扑 Lifshitz 跃迁，这将 Weyl 模式移动到接近费米能级。结果，由于一维泡利阻塞效应以及独特的负磁阻效应，出现了广泛且不对称的吸收特征。我们的结果提供了一种在块状晶体中实现一维外尔准粒子的策略。