Symmetry-Enforced Dirac Fermions and Structural Metastability in Pentagonal Monolayers of Transition-Metal Ditellurides
Abstract
The recent synthesis of pentagonal PdTe2 monolayer motivates broader research interests in transition-metal ditellurides whose electronic phases are governed by symmetry and structural reconstruction. The pentagonal phase of transition-metal ditellurides exhibits electronic properties that are dramatically different from those of its hexagonal counterpart due to its lower crystalline symmetry. Using first-principles calculations, we study monolayer XTe2 (X=Pd,Pt,Ni) in both hexagonal and pentagonal polymorphs. By constructing a continuous structural interpolation between the hexagonal and pentagonal phases, we show that the semimetal (hex)-to-semiconductor (penta) transition occurs only after an intermediate structural threshold rather than at the onset of symmetry reduction. The gap opening coincides with the formation of Te--Te dimers, which drive the bonding--antibonding splitting of the Te p states and reorganize the band edges. In addition, the nonsymmorphic symmetry of the pentagonal phase enforces band degeneracies at the Brillouin-zone boundary, leading to symmetry-protected two-dimensional (2D) Dirac states. These results establish pentagonal XTe2 monolayers as a new class of 2D semiconductors in which symmetry constraints and local bonding collectively shape the unconventional semiconducting electronic structure.
Versions
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BibTeX
@misc{gadtoula2026symmetryenforced,
title = {{Symmetry-Enforced Dirac Fermions and Structural Metastability in Pentagonal Monolayers of Transition-Metal Ditellurides}},
author = {Manoj Gadtoula and Clayton Conner and Avinash Sah and Ronghao Luo and Guang Bian},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2607.15580},
eprint = {2607.15580},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.15580},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Symmetry-Enforced Dirac Fermions and Structural Metastability in Pentagonal Monolayers of Transition-Metal Ditellurides
AU - Manoj Gadtoula
AU - Clayton Conner
AU - Avinash Sah
AU - Ronghao Luo
AU - Guang Bian
PY - 2026
DA - 2026/10/04
PB - arXiv
DO - 10.48550/arxiv.2607.15580
UR - https://arxiv.org/abs/2607.15580
AB - The recent synthesis of pentagonal PdTe_2 monolayer motivates broader research interests in transition-metal ditellurides whose electronic phases are governed by symmetry and structural reconstruction. The pentagonal phase of transition-metal ditellurides exhibits electronic properties that are dramatically different from those of its hexagonal counterpart due to its lower crystalline symmetry. Using first-principles calculations, we study monolayer XTe_2 (X=Pd,Pt,Ni) in both hexagonal and pentagonal polymorphs. By constructing a continuous structural interpolation between the hexagonal and pentagonal phases, we show that the semimetal (hex)-to-semiconductor (penta) transition occurs only after an intermediate structural threshold rather than at the onset of symmetry reduction. The gap opening coincides with the formation of Te--Te dimers, which drive the bonding--antibonding splitting of the Te p states and reorganize the band edges. In addition, the nonsymmorphic symmetry of the pentagonal phase enforces band degeneracies at the Brillouin-zone boundary, leading to symmetry-protected two-dimensional (2D) Dirac states. These results establish pentagonal XTe_2 monolayers as a new class of 2D semiconductors in which symmetry constraints and local bonding collectively shape the unconventional semiconducting electronic structure.
ER -