Many target properties (such as band gap, topological states, and spin texture) are not readily available for pure components AX or BX but do exist in alloys of (AX)_x(BX)_1-x. Substitutional alloy disorder generally results in the distribution of local environments as well as symmetry-breaking atomic displacements as seen in SPXRD and EXAFS, leading to the removal of band degeneracies and the lack of meaning of sharp wavevectors k hence E vs k band dispersion. These effects are not treatable by single-site disorder theories such as CPA. Supercells do retain atomic resolution of disorder but do not readily produce E vs k dispersion needed to judge the target properties such as topological states. We combine supercells with band unfolding in alloys, leading to Effective Band Structure [1] which recognizes local symmetry yet informs about the extent to which the long-range translational symmetry is retained. Our method reveals how the scale of disorders in alloy systems, such as PbS-PbTe, PbSe-SnSe, CdTe-HgTe [2][3], and para-magnetic phase ABO₃ perovskite and iron-based superconductor [4], affects the electronic properties, and how the restored band dispersion helps us to understand experimental observations.

References:

[1] V. Popescu and A. Zunger, Phys. Rev. Lett. 104, 236403 (2010).

[2] Zhi Wang, Jun-Wei Luo, and Alex Zunger, Phys. Rev. Materials 3, 044605 (2019).

[3] Zhi Wang, Qihang Liu, Jun-Wei Luo and Alex Zunger, Materials Horizons, 2019, 6, 2124 – 2134.

[4] Zhi Wang, Xingang Zhao, Robert Koch, Simon J. L. Billinge, Alex Zunger, arXiv:1911.02670.

Zhi Wang (王峙) earned his PhD degree in 2015 at the Institute of Semiconductor, Chinese Academy of Sciences. After that he was at a post-doctoral position in the Hamburg Center of Ultrafast Imaging, Germany from 2015 to 2018. Since then, he joined Prof. Alex Zunger’s Matter by Design group in University of Colorado Boulder, USA in 2018, as a post-doctor. He has worked on the theory of ab initio non-equilibrium time-dependent calculation, with publications on Phys. Rev. Lett., Phys. Rev. X, Materials Horizons, Materials Today, and Nature Communications. His current interest concentrates on the theory to describe disorders and to restore the band dispersions in substitutionally and magnetically disordered systems, including topological alloys, para-magnetic Mott insulators and ABO₃ perovskites.