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

TL;DR

This study uses first-principles calculations to identify optimal nonmagnetic ion dopants, Mg and Zn, for Barlowite to suppress magnetic interactions and enhance its potential as a quantum spin liquid candidate.

Contribution

It systematically evaluates and proposes specific Mg and Zn doping strategies to improve Barlowite's properties for quantum spin liquid research.

Findings

Mg and Zn are ideal dopants for Barlowite with minimal lattice distortion.

Doped Barlowite shows significantly reduced anti-site disorder compared to Herbertsmithite.

Doping mitigates magnetic differences, making Barlowite more similar to Herbertsmithite.

Abstract

Barlowite $Cu_4(OH)_6FBr$ is a newly found mineral containing $Cu^{2+}$ kagome planes. Despite similarities in many aspects to Herbertsmithite $Cu_3Zn(OH)_6Cl_2$, the well-known quantum spin liquid (QSL) candidate, intrinsic Barlowite turns out not to be a QSL, possibly due to the presence of $Cu^{2+}$ 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 $Cd^{2+}$ and $Ca^{2+}$, we identify the most ideal stoichiometric doping elements to be Mg and Zn in forming $Cu_3Mg(OH)_6FBr$ and $Cu_3Zn(OH)_6FBr$ 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.