Discovery of Lorentz-violating type II Weyl fermions in LaAlGe

Su Yang Xu, Nasser Alidoust, Guoqing Chang, Hong Lu, Bahadur Singh, Ilya Belopolski, Daniel S. Sanchez, Xiao Zhang, Guang Bian, Hao Zheng, Marious Adrian Husanu, Yi Bian, Shin Ming Huang, Chuang Han Hsu, Tay Rong Chang, Horng Tay Jeng, Arun Bansil, Titus Neupert, Vladimir N. Strocov, Hsin LinShuang Jia, M. Zahid Hasan

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Abstract

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.

Original languageEnglish (US)
Article numbere1603266
JournalScience Advances
Volume3
Issue number6
DOIs
StatePublished - Jun 2017

All Science Journal Classification (ASJC) codes

  • General

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