Abstract
A quantum spin liquid state has long been predicted to arise in spin-1/2 Heisenberg square-lattice antiferromagnets at the boundary region between Néel (nearest-neighbor interaction dominates) and columnar (next-nearest-neighbor interaction dominates) antiferromagnetic order. However, there are no known compounds in this region. Here we use d10–d0 cation mixing to tune the magnetic interactions on the square lattice while simultaneously introducing disorder. We find spin-liquid-like behavior in the double perovskite Sr2Cu(Te0.5W0.5)O6, where the isostructural end phases Sr2CuTeO6 and Sr2CuWO6 are Néel and columnar type antiferromagnets, respectively. We show that magnetism in Sr2Cu(Te0.5W0.5)O6 is entirely dynamic down to 19 mK. Additionally, we observe at low temperatures for Sr2Cu(Te0.5W0.5)O6—similar to several spin liquid candidates—a plateau in muon spin relaxation rate and a strong T-linear dependence in specific heat. Our observations for Sr2Cu(Te0.5W0.5)O6 highlight the role of disorder in addition to magnetic frustration in spin liquid physics.
Highlights
IntroductionA quantum spin liquid state has long been predicted to arise in spin-1/2 Heisenberg squarelattice antiferromagnets at the boundary region between Néel (nearest-neighbor interaction dominates) and columnar (next-nearest-neighbor interaction dominates) antiferromagnetic order
A quantum spin liquid state has long been predicted to arise in spin-1/2 Heisenberg squarelattice antiferromagnets at the boundary region between Néel and columnar antiferromagnetic order
The nature of the ground state in the highly frustrated region at the Néel antiferromagnetic (NAF)–columnar antiferromagnetic (CAF) boundary near J2/J1 ≈ 0.5 is under debate
Summary
A quantum spin liquid state has long been predicted to arise in spin-1/2 Heisenberg squarelattice antiferromagnets at the boundary region between Néel (nearest-neighbor interaction dominates) and columnar (next-nearest-neighbor interaction dominates) antiferromagnetic order. The region is a valence other bond ground state solid[12,13,14], in suggested for the J2/J1 ≈ which spins form dimer or plaquette singlets with a static pattern Despite these theoretical predictions for the square-lattice antiferromagnets, no experimental evidence of a compound in the J2/J1 ≈ 0.5 region exists. Recent neutron scattering studies have revealed NAF ordering at TN = 29 K with J1 = −7.18 and J2 = −0.21 meV (J2/J1 = 0.03) for Sr2CuTeO6, whereas Sr2CuWO6 has CAF ordering at TN = 24 K with J1 = –1.2 and J2 = –9.5 meV (J2/J1 = 7.92)[18, 19, 23, 24] (Fig. 1c) This dramatic change in exchange interactions is driven by differences in orbital hybridization.
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