Pressure tuning of charge density wave ordering in BaNi2As2

Abstract: Superconducting BaNi2As2 (Tc = 0.6 K) can be viewed as a non-magnetic isostructural analogue to the parent compound of the Fe-based superconductors BaFe2As21. Instead of magnetic ordering, an incommensurate charge density wave (CDW) order sets in when BaNi2As2 is cooled to low temperatures and triggers a very small orthorhombic distortion. This is rapidly followed by a commensurate CDW order accompanied by a triclinic distortion2. The incommensurate CDW order was suggested to play a similar role to that of magnetism in the Fe-based superconductors setting BaNi2As2 as a candidate system for charge-driven electronic nematicity3,4. CDW ordering in this system was shown to be strongly dependent on isoelectronic substitutions3,4,5, therefore indicating that modifications in the crystal lattice can efficiently tune its electronic ground state and can provide important input on the structural parameters controlling it.
We performed a detailed x-ray diffraction study of the crystal structure and CDW instabilities of BaNi2As2 as a function of temperature (down to 30 K) and quasihydrostatic pressure (up to 12 GPa)6. The experimentally observed cascade of pressure-induced structural phase transitions and accompanying CDW modulations is presented together with the lattice instabilities predicted by our first-principles calculations. ... mehrThe structural polymorphs and charge ordering patterns discovered in the pressure-temperature phase diagram of BaNi2As2 are discussed, also with respect to the importance of the relative Ni-Ni and Ni-As bond lengths in controlling the electronic ground state of this compound.

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