Chiral Landau levels in Weyl semimetal NbAs with multiple topological carriers.
Chiral Landau levels in Weyl semimetal NbAs with multiple topological carriers.
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具有多个拓扑载流子的外尔半金属 NbAs 的手性朗道能级。
DOI：
10.1038/s41467-018-04080-4
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发表时间：
2018-05-10
影响因子：
16.6
通讯作者：
Xiu F
中科院分区：
文献类型：
--
作者：
Yuan X;Yan Z;Song C;Zhang M;Li Z;Zhang C;Liu Y;Wang W;Zhao M;Lin Z;Xie T;Ludwig J;Jiang Y;Zhang X;Shang C;Ye Z;Wang J;Chen F;Xia Z;Smirnov D;Chen X;Wang Z;Yan H;Xiu F
最近，在反转对称破缺和时间反转对称破缺晶体中都实验发现了Weyl半金属。Weyl半金属中的非平凡拓扑可以表现为奇异的现象，这已被光电子能谱和输运测量广泛研究。尽管对费米弧和手征反常做了大量的实验工作，但由于严格的实验要求，非常规零朗道能级的存在仍然是Weyl费米子的一个独特标志，与手征反常高度相关。在这里，我们报道了Weyl半金属NBAs中朗道量子化的磁光研究。强磁场驱动系统接近量子极限，这导致在两个不等价的Weyl节点中观察到第零个手征朗道能级。与其他朗道能级相比，第零个手征朗道能级在磁场方向上表现出明显的线性色散，并允许光学跃迁而不受零z动量或磁场演化的限制。第零个朗道能级的磁场依赖关系进一步验证了预测的Weyl锥的粒子-空穴不对称性。同时，正常朗道能级的光学跃迁显示了多个载流子的共存，其中包括意想不到的大质量狄拉克费米子，这表明在反转对称破缺的Weyl半金属中存在更复杂的拓扑性质。我们的结果为研究Weyl费米子的朗道量子化提供了见解，并为研究复杂的拓扑系统提供了一个有效的工具。如果载体占据了最低的朗道能级，那么它们在韦尔半金属中的行为仍然是难以捉摸的。在这里，作者报告了电子占据零手性朗道能级的证据，在Weyl半金属NBAs中，两个不等价的Weyl节点具有明显的线性色散行为。
Recently, Weyl semimetals have been experimentally discovered in both inversion-symmetry-breaking and time-reversal-symmetry-breaking crystals. The non-trivial topology in Weyl semimetals can manifest itself with exotic phenomena, which have been extensively investigated by photoemission and transport measurements. Despite the numerous experimental efforts on Fermi arcs and chiral anomaly, the existence of unconventional zeroth Landau levels, as a unique hallmark of Weyl fermions, which is highly related to chiral anomaly, remains elusive owing to the stringent experimental requirements. Here, we report the magneto-optical study of Landau quantization in Weyl semimetal NbAs. High magnetic fields drive the system toward the quantum limit, which leads to the observation of zeroth chiral Landau levels in two inequivalent Weyl nodes. As compared to other Landau levels, the zeroth chiral Landau level exhibits a distinct linear dispersion in magnetic field direction and allows the optical transitions without the limitation of zero z momentum or magnetic field evolution. The magnetic field dependence of the zeroth Landau levels further verifies the predicted particle-hole asymmetry of the Weyl cones. Meanwhile, the optical transitions from the normal Landau levels exhibit the coexistence of multiple carriers including an unexpected massive Dirac fermion, pointing to a more complex topological nature in inversion-symmetry-breaking Weyl semimetals. Our results provide insights into the Landau quantization of Weyl fermions and demonstrate an effective tool for studying complex topological systems. How the carriers behave in a Weyl semimetal if they occupy the lowest Landau level remains elusive. Here, the authors report evidences of electrons occupying zeroth chiral Landau levels with distinct linear dispersion behaviors for two inequivalent Weyl nodes in a Weyl semimetal NbAs.
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