Emergence of spin singlets with inhomogeneous gaps in the kagome lattice Heisenberg antiferromagnets ZnCu₃(OD)₆FBr and ZnCu₃(OD)₆Cl₂

The kagome Lattice Heisenberg Antiferromagnet (KLHA) formed from a corner-sharing triangular lattice of frustrated spins serves as one of the best candidates in the search for a quantum spin liquid ground state. Zn-barlowite (ZnCu₃(OD)₆FBr) and herbertsmithite (ZnCu₃(OD)₆Cl₂) are two highly promising realizations of the KLHA and have been shown to remain paramagnetic even at T ≈ 10^-4J, where J ≈ 190 K is the Cu-Cu super-exchange interaction energy. However, the reproducible contributions from interlayer defects obscure the intrinsic behavior, thus making theoretical predictions difficult to verify.  In this presentation, we will explain how ⁶³Cu and ⁷⁹Br nuclear quadrupole resonance and ¹⁹F nuclear magnetic resonance were used along with inverse Laplace transform T₁ analysis to locally probe the quantum ground states of these kagome materials and elucidate the nature of their magnetic inhomogeneity. We present direct evidence for the gradual emergence of spin singlets with spatially varying excitation gaps and show that their fraction is limited to ~60% even at temperatures far below J.