Selectively doping barlowite for quantum spin liquid: A first-principles study.

Barlowite Cu4(OH)6FBr is a newly found mineral containing Cu2+ kagome planes. Despite similarities in many aspects to herbertsmithite Cu3Zn(OH)6Cl2, the well-known quantum spin liquid (QSL) candidate, intrinsic barlowite turns out not to be a QSL, possibly due to the presence of Cu2+ ions in between kagome planes that induce interkagome magnetic interaction [Phys. Rev. Lett. 113, 227203 (2014)]. Using first-principles calculation, we systematically study the feasibility of selective substitution of the interkagome Cu ions with isovalent nonmagnetic ions as a function of ion concentration up to the stoichiometric limit. Unlike previous speculation of using larger dopants, such as Cd2+ and Ca2+, we identify the most ideal stoichiometric doping elements to be Mg and Zn in forming Cu3Mg(OH)6FBr and Cu3Zn(OH)6FBr with the highest site selectivity and smallest lattice distortion. The equilibrium antisite disorder in Mg/Zn-doped barlowite is estimated to be one order of magnitude lower than that in herbertsmithite. The single-electron band structure and orbital component analysis show that the proposed selective doping effectively mitigates the difference between barlowite and herbertsmithite. [ABSTRACT FROM AUTHOR]