Yan Mingzhe, Huang Huaqing, Zhang Kenan, Wang Eryin, Yao Wei, Deng Ke, Wan Guoliang, Zhang Hongyun, Arita Masashi, Yang Haitao, Sun Zhe, Yao Hong, Wu Yang, Fan Shoushan, Duan Wenhui, Zhou Shuyun
State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, 100084, China.
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashihiroshima, Hiroshima, 739-0046, Japan.
Nat Commun. 2017 Aug 15;8(1):257. doi: 10.1038/s41467-017-00280-6.
Topological semimetals have recently attracted extensive research interests as host materials to condensed matter physics counterparts of Dirac and Weyl fermions originally proposed in high energy physics. Although Lorentz invariance is required in high energy physics, it is not necessarily obeyed in condensed matter physics, and thus Lorentz-violating type-II Weyl/Dirac fermions could be realized in topological semimetals. The recent realization of type-II Weyl fermions raises the question whether their spin-degenerate counterpart-type-II Dirac fermions-can be experimentally realized too. Here, we report the experimental evidence of type-II Dirac fermions in bulk stoichiometric PtTe single crystal. Angle-resolved photoemission spectroscopy measurements and first-principles calculations reveal a pair of strongly tilted Dirac cones along the Γ-A direction, confirming PtTe as a type-II Dirac semimetal. Our results provide opportunities for investigating novel quantum phenomena (e.g., anisotropic magneto-transport) and topological phase transition.Whether the spin-degenerate counterpart of Lorentz-violating Weyl fermions, the Dirac fermions, can be realized remains as an open question. Here, Yan et al. report experimental evidence of such type-II Dirac fermions in bulk PtTe single crystal with a pair of strongly tilted Dirac cones.
拓扑半金属作为最初在高能物理中提出的狄拉克费米子和外尔费米子的凝聚态物理对应物的主体材料，最近引起了广泛的研究兴趣。尽管在高能物理中需要洛伦兹不变性，但在凝聚态物理中并不一定遵守，因此违反洛伦兹的II型外尔/狄拉克费米子可以在拓扑半金属中实现。最近II型外尔费米子的实现提出了一个问题，即它们的自旋简并对应物——II型狄拉克费米子——是否也能通过实验实现。在这里，我们报告了体相化学计量比的PtTe单晶中II型狄拉克费米子的实验证据。角分辨光电子能谱测量和第一性原理计算揭示了沿Γ-A方向的一对强烈倾斜的狄拉克锥，证实PtTe为II型狄拉克半金属。我们的结果为研究新型量子现象（如各向异性磁输运）和拓扑相变提供了机会。违反洛伦兹的外尔费米子的自旋简并对应物——狄拉克费米子——是否能够实现仍然是一个悬而未决的问题。在这里，闫等人报告了在具有一对强烈倾斜狄拉克锥的体相PtTe单晶中存在这种II型狄拉克费米子的实验证据。
