@article {603,
	title = {Electronic and topological band evolution of VB-group transitionmetal monocarbides M$_{2}$C (M=V, Nb, or Ta) bulk and monolayer},
	journal = {Mater. Today Commun.},
	volume = {32},
	year = {2022},
	pages = {103875},
	abstract = {Two-dimensional transition metal monocarbides (2D MXenes) have attracted intense interest due to their versatility, predicted topological phase, and immense applications. In this study, we investigated the electronic and topological band evolutions of both the bulk and monolayer MXenes, M$_{2}$C (M~= V, Nb, or Ta), using first-principles calculations. Our study shows that all the three bulk M$_{2}$C are semi-metallic and host topological phases. Interestingly, our study showed pristine monolayers V$_{2}$C and Nb$_{2}$C exhibit non-trivial topological phases, while Ta$_{2}$C exhibits trivial phase. Unlike other MXenes, monolayer V$_{2}$C and Nb$_{2}$C host the quantum spin Hall effect without functionalizations. Furthermore, thickness-dependent calculations intriguingly show Lifshitz electronic transition from semi-metallic to topological insulating phase in V$_{2}$C from bilayer to monolayer with a sufficiently large bandgap of 0.32~eV. Moreover, the topological phase transition between the TI state and the trivial state in V$_{2}$C is driven by quantum size effects as the Z$_{2}$ topological invariant notably oscillates between 1 and 0 with varying thickness. Finally, our study demonstrated that VB MXenes could be promising topological materials for spintronics applications.},
	keywords = {Electronic structures, First-principles calculations, Mono-transition metal MXenes, Topological insulators, Topological phase transition, Transition metal monocarbides},
	doi = {10.1016/j.mtcomm.2022.103875},
	author = {Ali Sufyan and Aniceto B. Maghirang and Gennevieve M. Macam and Zhi-Quan Huang and Chia-Hsiu Hsu and Feng-Chuan Chuang}
}
@article {602,
	title = {Interplay between anisotropic spin texture and large gap topological insulating phases in functionalized MXenes},
	journal = {Chinese J. Phys.},
	volume = {77},
	year = {2022},
	pages = {2346},
	abstract = {Massive attention has been given to two-dimensional (2D) MXenes due to their predicted topological phase and promising diverse applications. Using first-principles with hybrid functional calculations, we systematically conducted an extensive study on M$_{2}$C (M~=~Mo, or W) in 1T and 2H structures with various surface terminations T$_{2}$ (T~=~H, O, OH, F, Cl, Br, or I). Pristine Mo$_{2}$C and W$_{2}$C compounds are in the 2H phase. Upon functionalization of H, O, OH and F, they retain the 2H structure, whereas Cl, Br, and I functionalization, the structures transform to 1T phase. Notably, M$_{2}$CO$_{2}$ are found to be 2D topological insulators (TIs) with sizable nontrivial bandgaps as large as 666~meV. Interestingly, 2H M$_{2}$CO$_{2}$ exhibits not only large-gapped Zeeman-type spin splitting at K-point but also anisotropic Rashba spin splitting at Γ-point. The successful synthesis of pristine Mo$_{2}$C and our theoretical study pave a path for future applications of MXene-based 2D TIs.},
	doi = {10.1016/j.cjph.2022.04.012},
	author = {Aniceto B. Maghirang and Gennevieve M. Macam and Ali Sufyan and Zhi-Quan Huang and Chia-Hsiu Hsu and Feng-Chuan Chuang}
}
@article {601,
	title = {Robust tunable large-gap quantum spin Hall states in monolayer Cu$_{2}$S on insulating substrates},
	journal = {ACS Omega},
	volume = {7},
	year = {2022},
	pages = {15760},
	abstract = {Quantum spin Hall (QSH) insulators with large band gaps and dissipationless edge states are of both technological and scientific interest. Although numerous two-dimensional (2D) systems have been predicted to host the QSH phase, very few of them harbor large band gaps and retain their nontrivial band topology when they are deposited on substrates. Here, based on a first-principles analysis with hybrid functional calculations, we investigated the electronic and topological properties of inversion-asymmetric monolayer copper sulfide (Cu$_{2}$S). Interestingly, we found that monolayer Cu$_{2}$S possesses an intrinsic QSH phase, Rashba spin splitting, and a large band gap of 220 meV that is suitable for room-temperature applications. Most importantly, we constructed heterostructures of a Cu$_{2}$S film on PtTe$_{2}$, h-BN, and Cu(111) substrates and found that the topological properties remain preserved upon an interface with these substrates. Our findings suggest Cu$_{2}$S as a possible platform to realize inversion-asymmetric QSH insulators with potential applications in low-dissipation electronic devices.},
	doi = {10.1021/acsomega.2c00781},
	author = {Ali Sufyan and Gennevieve M. Macam and Zhi-Quan Huang and Chia-Hsiu Hsu 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 M. 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 M. Macam and Ali Sufyan and Zhi-Quan Huang and Chia-Hsiu Hsu and Shin-Ming Huang and Hsin Lin and Feng-Chuan Chuang}
}