Emergence of spin singlets with inhomogeneous gaps in the kagome Heisenberg antiferromagnets Zn-barlowite and herbertsmithite

Abstract

The kagome Heisenberg antiferromagnet formed by frustrated spins arranged in a lattice of corner-sharing triangles is a prime candidate for hosting a quantum spin liquid (QSL) ground state consisting of entangled spin singlets. But the existence of various competing states makes a convincing theoretical prediction of the QSL ground state difficult, calling for experimental clues from model materials. The kagome lattice materials Zn-barlowite ZnCu${}_3$(OD)${}_6$FBr and herbertsmithite ZnCu${}_3$(OD)${}_6$Cl${}_2$ do not exhibit long range order, and they are considered the best realizations of the kagome Heisenberg antiferromagnet known to date. Here we use ${}^{63}$Cu nuclear quadrupole resonance combined with the inverse Laplace transform (ILT) to probe locally the inhomogeneity of delicate quantum ground states affected by disorder. We present direct evidence for the gradual emergence of spin singlets with spatially varying excitation gaps, but even at temperatures far below the super-exchange energy scale their fraction is limited to approximately 60\% of the total spins. Theoretical models need to incorporate the role of disorder to account for the observed inhomogeneously gapped behaviour.

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References in corpus (10)

• Spin Dynamics of the Spin-1/2 Kagome Lattice Antiferromagnet ZnCu_3(OH)_6Cl_2
• Projected wavefunction study of Spin-1/2 Heisenberg model on the Kagome lattice
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• ^{63}Cu, ^{35}Cl, and ^{1}H NMR in the S=1/2 Kagomé Lattice ZnCu_{3}(OH)_{6}Cl_{2}
• Dynamic Scaling in the Susceptibility of the Spin-1\2 Kagome Lattice Antiferromagnet Herbertsmithite
• Pinwheel VBS state and triplet excitations in the two-dimensional deformed kagome lattice
• Symmetry Reduction in the Quantum Kagome Antiferromagnet Herbertsmithite
• Local Spin Susceptibility of the S=1/2 Kagome Lattice in ZnCu3(OD)6Cl2
• ${}^{139}$La NMR investigation of the interplay between the lattice, charge, and spin dynamics in charge ordered high $T_c$ cuprate La${}_{1.875}$Ba${}_{0.125}$CuO${}_4$
• Site-Specific Structure at Multiple Length Scales in Kagome Quantum Spin Liquid Candidates

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• Specific Heat of the Kagome Antiferromagnet Herbertsmithite in High Magnetic Fields
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• Strong relevance of Zinc impurity in the spin-$\frac{1}{2}$ Kagome quantum antiferromagnets: a variational study
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• Quantifying the Phase Diagram and Hamiltonian of $S=1/2$ Kagome Antiferromagnets: Bridging Theory and Experiment
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• Gapped magnetic ground state in the spin-liquid candidate $\kappa$-(BEDT-TTF)${}_2$Ag${}_2$(CN)${}_3$ suggested by magnetic spectroscopy
• Witnessing Disorder in Quantum Magnets
• Spinon mediation of witness spin dynamics in herbertsmithite
• Emergent Spin-Singlet Pairing in the Frustrated Kagome Metal Sc${}_3$Mn${}_3$Al${}_7$Si${}_5$
• Dynamical spin correlations in kagome antiferromagnets: comparison of Abrikosov fermion and Schwinger boson approaches beyond mean field
• Local probe investigation of the spin dynamics in the kagome and inter-layers of orthorhombic barlowite Cu${}_4$(OD)${}_6$FBr: ${}^{79}$Br and ${}^{63}$Cu NQR study
• ${}^{13}$C NMR observation of a nonmagnetic charge-ordered state in the organic conductor $\kappa$-(ET)${}_2$Hg(SCN)${}_2$Cl
• Emergence of a Fluctuating Ground State in Y-kapellasite under Pressure