Spin-liquid-like state in a spin-1/2 square-lattice antiferromagnet perovskite induced by $d^{10}$-$d^0$ cation mixing

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 dominates) antiferromagnetic order. However, there are no known compounds in this region. Here we use $d^{10}$-$d^0$ 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 Sr${}_2$Cu(Te${}_{0.5}$W${}_{0.5}$)O${}_6$, where the isostructural end phases Sr${}_2$CuTeO${}_6$ and Sr${}_2$CuWO${}_6$ are Néel and columnar type antiferromagnets, respectively. We show that magnetism in Sr${}_2$Cu(Te${}_{0.5}$W${}_{0.5}$)O${}_6$ is entirely dynamic down to 19 mK. Additionally, we observe at low temperatures for Sr${}_2$Cu(Te${}_{0.5}$W${}_{0.5}$)O${}_6$, 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 Sr${}_2$Cu(Te${}_{0.5}$W${}_{0.5}$)O${}_6$ highlight the role of disorder in addition to magnetic frustration in spin liquid physics.

19+4 pages, 4+3 figures. Accepted for publication in Nature Communications