Symmetry-Enforced Topology and Van Hove Saddle Points in Hexagonal TiAs
Abstract
We report the first successful growth of stoichiometric hexagonal TiAs single crystals (space group P63/mmc) using chemical vapor transport and investigate their vibrational, electronic, topological, and magnetotransport properties. Polarized Raman spectroscopy identifies all four Raman-active phonon modes (A1g + E1g + 2E2g), consistent with the hexagonal crystal symmetry. First-principles calculations reveal nontrivial band topology characterized by a symmetry indicator ℤ4 = 2 and a strong topological index ν0 = 1, together with symmetry-protected fourfold band degeneracies at the nonsymmorphic Brillouin-zone boundary. The Fermi surface exhibits an orbital-dependent crossover from quasi-two-dimensional cylindrical sheets to a corrugated three-dimensional structure along kz. A Van Hove saddle point approximately 0.5 eV below the Fermi level along Γ−−K is associated with a neck-disrupting Lifshitz transition and enhanced density of states. Magnetotransport measurements reveal a pronounced twofold angular magnetoresistance, consistent with anisotropic Fermi-surface geometry and open cyclotron orbits. Hall measurements indicate uncompensated, hole-dominated transport, accounting for the absence of extreme magnetoresistance and contributing to the field-orientation-dependent Hall response. These results establish hexagonal TiAs as a platform for exploring the interplay of nonsymmorphic band topology, Van Hove singularities, and anisotropic electronic transport in transition-metal monopnictides.
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BibTeX
@misc{rahman2026symmetryenforced,
title = {{Symmetry-Enforced Topology and Van Hove Saddle Points in Hexagonal TiAs}},
author = {Azizur Rahman and Shashi B Mishra and Sheraz Khan and Khushnood Shah and Xun Ma and Xiaoyang Lin and Tomasz Sobol and Lei Zhang and Weisheng Zhao and Min Zhang and Zahir Muhammad},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.12925},
eprint = {2610.12925},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.12925},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Symmetry-Enforced Topology and Van Hove Saddle Points in Hexagonal TiAs
AU - Azizur Rahman
AU - Shashi B Mishra
AU - Sheraz Khan
AU - Khushnood Shah
AU - Xun Ma
AU - Xiaoyang Lin
AU - Tomasz Sobol
AU - Lei Zhang
AU - Weisheng Zhao
AU - Min Zhang
AU - Zahir Muhammad
PY - 2026
DA - 2026/10/09
PB - arXiv
DO - 10.48550/arxiv.2610.12925
UR - https://arxiv.org/abs/2610.12925
AB - We report the first successful growth of stoichiometric hexagonal TiAs single crystals (space group P6_3/mmc) using chemical vapor transport and investigate their vibrational, electronic, topological, and magnetotransport properties. Polarized Raman spectroscopy identifies all four Raman-active phonon modes (A_1g + E_1g + 2E_2g), consistent with the hexagonal crystal symmetry. First-principles calculations reveal nontrivial band topology characterized by a symmetry indicator ℤ_4 = 2 and a strong topological index ν_0 = 1, together with symmetry-protected fourfold band degeneracies at the nonsymmorphic Brillouin-zone boundary. The Fermi surface exhibits an orbital-dependent crossover from quasi-two-dimensional cylindrical sheets to a corrugated three-dimensional structure along k_z. A Van Hove saddle point approximately 0.5 eV below the Fermi level along Γ−−K is associated with a neck-disrupting Lifshitz transition and enhanced density of states. Magnetotransport measurements reveal a pronounced twofold angular magnetoresistance, consistent with anisotropic Fermi-surface geometry and open cyclotron orbits. Hall measurements indicate uncompensated, hole-dominated transport, accounting for the absence of extreme magnetoresistance and contributing to the field-orientation-dependent Hall response. These results establish hexagonal TiAs as a platform for exploring the interplay of nonsymmorphic band topology, Van Hove singularities, and anisotropic electronic transport in transition-metal monopnictides.
ER -