Causal structure of interacting Weyl fermions in condensed matter systems

Wei Chi Chiu, Guoqing Chang, Gennevieve Macam, Ilya Belopolski, Shin Ming Huang, Robert Markiewicz, Jia Xin Yin, Zi Jia Cheng, Chi Cheng Lee, Tay Rong Chang, Feng Chuan Chuang, Su Yang Xu, Hsin Lin, M. Zahid Hasan, Arun Bansil

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


The spacetime light cone is central to the definition of causality in the theory of relativity. Recently, links between relativistic and condensed matter physics have been uncovered, where relativistic particles can emerge as quasiparticles in the energy-momentum space of matter. Here, we unveil an energy-momentum analogue of the spacetime light cone by mapping time to energy, space to momentum, and the light cone to the Weyl cone. We show that two Weyl quasiparticles can only interact to open a global energy gap if they lie in each other’s energy-momentum dispersion cones–analogous to two events that can only have a causal connection if they lie in each other’s light cones. Moreover, we demonstrate that the causality of surface chiral modes in quantum matter is entangled with the causality of bulk Weyl fermions. Furthermore, we identify a unique quantum horizon region and an associated ‘thick horizon’ in the emergent causal structure.

Original languageEnglish (US)
Article number2228
JournalNature communications
Issue number1
StatePublished - Dec 2023

All Science Journal Classification (ASJC) codes

  • General Chemistry
  • General Biochemistry, Genetics and Molecular Biology
  • General Physics and Astronomy


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