Complex structure due to As bonding and interplay with electronic structure in superconducting BaNi2As2

Abstract

$\mathrm{Ba}{\mathrm{Ni}}_{2}{\mathrm{As}}_{2}$ is a superconductor chemically related to the Fe-based superconductors, with a complex and poorly understood structural phase transition. We show, based on first-principles calculations, that, in fact, there are two distinct competing structures. These structures are different from the electronic, transport, and bonding points of view but are close in energy. These arise due to complex As bonding patterns and drive distortions of the Ni layers. This is supported by photoemission experiments. This is very distinct from views of the distortion as being primarily driven by electrons at the Fermi surface as in a classical charge density wave, or by correlated electron physics associated with the Ni $d$ electrons and the Ni $d$ orbitals. The structural distortion, although connected with As does lead to an interplay of electronic and structural behavior including induced anisotropic electronic transport. The local bonding nature of the instabilities and the competition between distortions is discussed in the context of the complex behavior observed in $\mathrm{Ba}{\mathrm{Ni}}_{2}{\mathrm{As}}_{2}$ samples.