Halide perovskites are a promising class of materials for optoelectronic and photovoltaic applications, exhibiting high power conversion efficiency due to strong light absorption and long carrier diffusion lengths. While various aspects of their crystal and electronic structure have been studied, we identify a fundamental property previously overlooked that may significantly impact their efficiency. We demonstrate that halide perovskites realize a three-dimensional (3D) Lieb lattice, giving rise to a gapped 3D Dirac cone of spin-1 fermions. This leads to a fivefold reduction in effective mass compared to a conventional cubic structure and suppressed carrier backscattering due to Klein tunneling. Our conclusions are supported by band structure calculations and angle-resolved photoemission spectroscopy from CsPbBr3 and CsSnBr3. In particular, we reveal the transformation of the flat band of the Lieb lattice and the emergence of a dark corridor effect in photoemission from the Dirac cone, which increases as the band gap is decreased from CsPbBr3 to CsSnBr3.
@article{arxiv.2503.15343,
title = {Halide Perovskites as Spin-1 Dirac Materials},
author = {Dmitry Marchenko and Maryam Sajedi and Maxim Krivenkov and Saleem Ayaz Khan and Andrei Varykhalov and Alexander Fedorov and Jaime Sánchez-Barriga and Daniel M. Többens and Thomas Unold and Ján Minár and Oliver Rader},
journal= {arXiv preprint arXiv:2503.15343},
year = {2025}
}