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

TL;DR

This study demonstrates that cation mixing in a double perovskite induces a spin-liquid-like state in a square-lattice antiferromagnet, highlighting the combined role of disorder and magnetic frustration in spin liquid physics.

Contribution

It introduces a new method of tuning magnetic interactions via $d^{10}$-$d^0$ cation mixing to realize spin-liquid-like behavior in a previously unobserved compound.

Findings

Spin-liquid-like behavior observed in Sr$_2$Cu(Te$_{0.5}$W$_{0.5}$)O$_6$

Magnetism remains dynamic down to 19 mK in the compound

Presence of a T-linear specific heat and relaxation rate plateau

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 N\'eel (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 N\'eel 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.