Selective doping Barlowite for quantum spin liquid: a first-principles study

Barlowite $C{u}_4(OH{)}_{6}FBr$ is a newly found mineral containing $C{u}^{2+}$ kagome planes. Despite similarities in many aspects to Herbertsmithite $C{u}_{3}Zn(OH{)}_{6}C{l}_2$, the well-known quantum spin liquid (QSL) candidate, intrinsic Barlowite turns out not to be a QSL, possibly due to the presence of $C{u}^{2+}$ ions in between kagome planes that induce interkagome magnetic interaction [PRL, 113, 227203 (2014)]. Using first-principles calculation, we systematically study the feasibility of selective substitution of the interkagome Cu ions with isovalent nonmagnetic ions. Unlike previous speculation of using larger dopants, such as $C{d}^{2+}$ and $C{a}^{2+}$, we identify the most ideal stoichiometric doping elements to be Mg and Zn in forming $C{u}_{3}Mg(OH{)}_{6}FBr$ and $C{u}_{3}Zn(OH{)}_{6}FBr$ with the highest site selectivity and smallest lattice distortion. The equilibirium anti-site 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.