Electron Doping a Kagome Spin Liquid

TL;DR

This study synthesized electron-doped kagome spin liquid ZnLi$_x$Cu$_3$(OH)$_6$Cl$_2$ and found that doping suppresses magnetic behavior without inducing metallicity or superconductivity, challenging existing theoretical predictions.

Contribution

It provides the first systematic experimental investigation of electron doping effects on a kagome spin liquid, revealing unexpected suppression of magnetism and highlighting the need for refined theories.

Findings

No metallicity or superconductivity observed upon doping

Magnetic behavior systematically suppressed with increased doping

Doping did not induce the predicted Dirac metal state

Abstract

Herbertsmithite, ZnCu$_3$(OH)$_6$Cl$_2$, is a two dimensional kagom\'{e} lattice realization of a spin liquid, with evidence for fractionalized excitations and a gapped ground state. Such a quantum spin liquid has been proposed to underlie high temperature superconductivity and is predicted to produce a wealth of new states, including a Dirac metal at $1/3$rd electron doping. Here we report the topochemical synthesis of electron-doped ZnLi$_x$Cu$_3$(OH)$_6$Cl$_2$ from $x$ = 0 to $x$ = 1.8 ($3/5$th per Cu$^{2+}$). Contrary to expectations, no metallicity or superconductivity is induced. Instead, we find a systematic suppression of magnetic behavior across the phase diagram. Our results demonstrate that significant theoretical work is needed to understand and predict the role of doping in magnetically frustrated narrow band insulators, particularly the interplay between local structural disorder and tendency toward electron localization, and pave the way for future studies of doped spin liquids.