@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 {604,
	title = {Band engineering and van Hove singularity on HfX$_{2}$ thin films (X = S, Se, or Te)},
	journal = {ACS Appl. Electron. Mater.},
	volume = {3},
	year = {2021},
	pages = {1071},
	abstract = {Two-dimensional transition metal dichalcogenides (TMDs) have become well-known due to their versatile and tunable physical properties for potential applications, specifically on low-power and optical devices. Here, we explored the structural stability and electronic properties of bulk and thin-film (from 1 up to 6 layers) structures of hafnium dichalcogenides (HfX$_{2}$, X = S, Se, or Te) using first-principles calculations. Our calculations reveal that the most stable phase is 1T for both thin films and bulk. The bulk and thin-film structures of HfTe$_{2}$ are semimetallic, while those of HfS$_{2}$ and HfSe$_{2}$ are insulating. Both HfS$_{2}$ and HfSe$_{2}$ thin films exhibit a decreasing band gap with increasing thickness, while HfTe$_{2}$ thin films remain semimetallic with increasing number of layers. Moreover, van Hove singularity (vHs), due to the contribution of the pz orbital from S atoms, is observed in 3L-HfS$_{2}$ at the valence band maximum, which can be further enhanced by applying an in-plane biaxial strain, suggesting possible superconductivity. Finally, the bulk and monolayer band structures of HfTe$_{2}$, under HSE06 and GGA + U with the effective Hubbard U parameter of 4.6 eV, are in good agreement with the experimental ARPES data. Our results indeed show that HfX$_{2}$ have sensitive and tunable electronic properties through film thickness control and strain for future potential applications.},
	doi = {10.1021/acsaelm.0c00907},
	author = {Harvey N. Cruzado and John Symon C. Dizon and Gennevieve M. Macam and Rovi Angelo B. Villaos and Thi My Duyen Huynh and Liang-Ying Feng and Zhi-Quan Huang and Chia-Hsiu Hsu and Shin-Ming Huang and Hsin Lin and Feng-Chuan Chuang}
}
@article {605,
	title = {Theoretical prediction of topological insulators in two-dimensional ternary transition metal chalcogenides (MM{\textquoteright}X$_{4}$, M~=~Ta, Nb, or V; M{\textquoteright}= Ir, Rh, or Co; X~=~Se or Te)},
	journal = {Chinese J. Phys.},
	volume = {73},
	year = {2021},
	pages = {95},
	abstract = {Ternary transition metal chalcogenides (TTMCs) have attracted interest due to the discovery of their Weyl semimetallic property and the recent synthesis of layered TTMCs which are regarded as potential candidates for two-dimensional (2D) topological insulators. Here, employing first-principles calculations, we predicted the emergence of non-trivial band topologies in the monolayer MM{\textquoteright}X$_{4}$ family (M= V, Nb, or Ta; M{\textquoteright}~=~Co, Rh, or Ir; and X~=~Se or Te) within hybrid functional calculations. Five of eighteen 2D materials were found to be topological insulators, while four of them are magnetic thin films. The nontrivial topologies were verified via the calculated Z$_{2}$ topological invariant and topologically protected edge states. Further calculations showed a strain-induced phase transition in VCoTe$_{4}$ from a magnetic phase to a nonmagnetic topological insulating phase. Our comprehensive study revealed a diverse family of monolayer ternary transition metal chalcogenides adding new members to the current catalog of 2D topological insulators and 2D magnetic materials.},
	doi = {10.1016/j.cjph.2021.06.014},
	author = {Ali Sufyan and Gennevieve Macam and Chia-Hsiu Hsu and Zhi-Quan Huang and Shin-Ming Huang and Hsin Lin and Feng-Chuan Chuang}
}
@article {607,
	title = {Tuning topological phases and electronic properties of monolayer ternary transition metal chalcogenides (ABX$_{4}$, A/B = Zr, Hf, or Ti; X = S, Se, or Te)},
	journal = {Appl. Phys. Lett.},
	volume = {118},
	year = {2021},
	pages = {111901},
	abstract = {Topological materials are very promising materials for technological applications ranging from spintronics to quantum computation. Here, based on first-principles calculations, we predict a family of two-dimensional (2D) topological materials in nine ternary transition metal chalcogenides (TTMCs) ABX$_{4}$, where A/B = Zr, Hf, or Ti and X = S, Se, or Te. A total of three compounds (ZrTiTe$_{4}$, HfZrTe$_{4}$, and HfTiTe$_{4}$) are identified to be nontrivial within a hybrid functional calculation. The nontrivial phase originated from the p-d band inversion at the Г point with spin-orbit coupling. The structural stability of these monolayers is confirmed by phonon spectrum analysis, showing no negative phonon frequencies. The diversity of TTMCs will open a wide possibility for tuning the bandgap and will provide a variety of opportunities for 2D and topological materials research.},
	doi = {10.1063/5.0036838},
	author = {Gennevieve Macam and Ali Sufyan and Zhi-Quan Huang and Chia-Hsiu Hsu and Shin-Ming Huang and Hsin Lin and Feng-Chuan Chuang}
}
@article {612,
	title = {Prediction of quantum anomalous hall effect in MBi and MSb (M: Ti, Zr, and Hf) honeycombs},
	journal = {Nanoscale Res. Lett.},
	volume = {13},
	year = {2018},
	pages = {43},
	abstract = {The abounding possibilities of discovering novel materials has driven enhanced research effort in the field of materials physics. Only recently, the quantum anomalous hall effect (QAHE) was realized in magnetic topological insulators (TIs) albeit existing at extremely low temperatures. Here, we predict that MPn (M =Ti, Zr, and Hf; Pn =Sb and Bi) honeycombs are capable of possessing QAH insulating phases based on first-principles electronic structure calculations. We found that HfBi, HfSb, TiBi, and TiSb honeycomb systems possess QAHE with the largest band gap of 15 meV under the effect of tensile strain. In low-buckled HfBi honeycomb, we demonstrated the change of Chern number with increasing lattice constant. The band crossings occurred at low symmetry points. We also found that by varying the buckling distance we can induce a phase transition such that the band crossing between two Hf d-orbitals occurs along high-symmetry point K2. Moreover, edge states are demonstrated in buckled HfBi zigzag nanoribbons. This study contributes additional novel materials to the current pool of predicted QAH insulators which have promising applications in spintronics.},
	doi = {10.1186/s11671-017-2424-y},
	author = {Zhi-Quan Huang and Wei-Chih Chen and Gennevieve M. Macam and Christian P. Crisostomo and Shin-Ming Huang and Rong-Bin Chen and Marvin A. Albao and Der-Jun Jang and Hsin Lin and Feng-Chuan Chuang}
}
