@article {618,
	title = {Causal structure of interacting Weyl fermions in condensed matter systems},
	journal = {Nat. Commun.},
	volume = {14},
	year = {2023},
	pages = {2228},
	abstract = {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{\textquoteright}s energy-momentum dispersion cones{\textendash}analogous to two events that can only have a causal connection if they lie in each other{\textquoteright}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 {\textquoteright}thick horizon{\textquoteright} in the emergent causal structure.},
	doi = {10.1038/s41467-023-37931-w},
	url = {https://www.nature.com/articles/s41467-023-37931-w},
	author = {Wei-Chi Chiu and Guoqing Chang and Gennevieve Macam and Ilya Belopolski and Shin-Ming Huang and Robert Markiewicz and Jia-Xin Yin and Zi-Jia Cheng and Chi-Cheng Lee and Tay-Rong Chang and Feng-Chuan Chuang and Su-Yang Xu and Hsin Lin and M. Zahid Hasan and Arun Bansil}
}
@article {611,
	title = {Spin-orbit quantum impurity in a topological magnet},
	journal = {Nat. Commun.},
	volume = {11},
	year = {2020},
	pages = {4415},
	abstract = {Quantum states induced by single-atomic impurities are at the frontier of physics and material science. While such states have been reported in high-temperature superconductors and dilute magnetic semiconductors, they are unexplored in topological magnets which can feature spin-orbit tunability. Here we use spin-polarized scanning tunneling microscopy/spectroscopy (STM/S) to study the engineered quantum impurity in a topological magnet Co$_{3}$Sn$_{2}$S$_{2}$. We find that each substituted In impurity introduces a striking localized bound state. Our systematic magnetization-polarized probe reveals that this bound state is spin-down polarized, in lock with a negative orbital magnetization. Moreover, the magnetic bound states of neighboring impurities interact to form quantized orbitals, exhibiting an intriguing spin-orbit splitting, analogous to the splitting of the topological fermion line. Our work collectively demonstrates the strong spin-orbit effect of the single-atomic impurity at the quantum level, suggesting that a nonmagnetic impurity can introduce spin-orbit coupled magnetic resonance in topological magnets.},
	doi = {10.1038/s41467-020-18111-6},
	author = {Jia-Xin Yin and Nana Shumiya and Yuxiao Jiang and Huibin Zhou and Gennevieve Macam and Hano Omar Mohammad Sura and Songtian S. Zhang and Zi-Jia Cheng and Zurab Guguchia and Yangmu Li and Qi Wang and Maksim Litskevich and Ilya Belopolski and Xian P. Yang and Tyler A. Cochran and Guoqing Chang and Qi Zhang and Zhi-Quan Huang and Feng-Chuan Chuang and Hsin Lin and Hechang Lei and Brian M. Andersen and Ziqiang Wang and Shuang Ji and M. Zahid Hasan}
}
