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Discovery of Lorentz-violating type II Weyl fermions in LaAlGe

TitleDiscovery of Lorentz-violating type II Weyl fermions in LaAlGe
Publication TypeJournal Article
Year of Publication2017
AuthorsXu, Su-Yang, Alidoust Nasser, Chang Guoqing, Lu Hong, Singh Bahadur, Belopolski Ilya, Sanchez Daniel S., Zhang Xiao, Bian Guang, Zheng Hao, Husanu Marious-Adrian, Bian Yi, Huang Shin-Ming, Hsu Chuang-Han, Chang Tay-Rong, Jeng Horng-Tay, Bansil Arun, Neupert Titus, Strocov Vladimir N., Lin Hsin, Jia Shuang, and Hasan Zahid M.
JournalSci. Adv.
Date Published06/2017
Keywordsarcs, crystal, dirac semimetals, electron, energy-bands, hall, mote2, phase

In quantum field theory, Weyl fermions are relativistic particles that travel at the speed of light and strictly obey the celebrated Lorentz symmetry. Their low-energy condensed matter analogs are Weyl semimetals, which are conductors whose electronic excitations mimic the Weyl fermion equation of motion. Although the traditional (type I) emergent Weyl fermions observed in TaAs still approximately respect Lorentz symmetry, recently, the so-called type II Weyl semimetal has been proposed, where the emergent Weyl quasiparticles break the Lorentz symmetry so strongly that they cannot be smoothly connected to Lorentz symmetric Weyl particles. Despite some evidence of nontrivial surface states, the direct observation of the type II bulk Weyl fermions remains elusive. We present the direct observation of the type II Weyl fermions in crystalline solid lanthanum aluminum germanide (LaAlGe) based on our photoemission data alone, without reliance on band structure calculations. Moreover, our systematic data agree with the theoretical calculations, providing further support on our experimental results.


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