Li doping kagome spin liquid compounds

TL;DR

This study uses first-principles calculations to analyze Li doping effects in kagome spin liquid compounds herbertsmithite and Zn-doped barlowite, revealing why they remain insulating and suggesting alternative doping strategies.

Contribution

It provides detailed atomic-level insights into Li doping effects, explaining the persistent insulating state and challenging the pursuit of metallic states via Li doping in these materials.

Findings

Li prefers the Cl-(OH)$_3$-Cl site in herbertsmithite.

Li doping reduces saturation magnetization linearly.

Li forms chemical bonds that trap electrons, maintaining insulating behavior.

Abstract

Herbertsmithite and Zn-doped barlowite are two compounds for experimental realization of twodimensional gapped kagome spin liquid. Theoretically, it has been proposed that charge doping a quantum spin liquid gives rise to exotic metallic states, such as high-temperature superconductivity. However, one recent experiment about herbertsmithite with successful Li-doping shows surprisingly the insulating state even under the heavy doped scenario, which can hardly be explained by many-body physics. Using first-principles calculation, we performed a comprehensive study about the Li intercalated doping effect of these two compounds. For the Li-doped herbertsmithite, we identified the optimized Li position at the Cl-(OH)$_3$-Cl pentahedron site instead of previously speculated Cl-(OH)$_3$ tetrahedral site. With the increase of Li doping concentration, the saturation magnetization decreases linearly due to the charge transfer from Li to Cu ions. Moreover, we found that Li forms chemical bonds with the nearby (OH)$^-$ and Cl$^-$ ions, which lowers the surrounding chemical potential and traps the electron, as evidenced by the localized charge distribution, explaining the insulating behavior measured experimentally. Though with different structure from herbertsmithite, Zn-doped Barlowite shows the same features upon Li doping. We conclude that Li doping this family of kagome spin liquid cannot realize exotic metallic states, other methods should be further explored, such as element substitution with different valence electrons.