Signatures of spin-liquid-like state and spin-phonon coupling in square lattice Sr2CuTe0.5W0.5O6

A spin-liquid state can be induced by uncompensated interactions in the spin lattice due to disorder or randomness in exchange pathways. Sr₂CuTeO₆ and Sr₂CuWO₆ are square-lattice antiferromagnetic double perovskites (A₂BB′O₆) with dominant nearest-neighbor (Néel-type) and next-nearest neighbor (Columnar-type) magnetic interactions, respectively. Random distribution of these interactions in a system has been theoretically predicted to be a way to induce the spin-liquid state. Here, we have synthesized a spin-liquid candidate Sr₂CuTe_0.5W_0.5O₆ with B′-site mixing of its parent systems (Sr₂CuTeO₆ and Sr₂CuWO₆) to explore the phonon properties and their correlations with the liquid-like magnetic interactions. Our measurements reveal the presence of a broad continuum in the Raman spectrum of Sr₂CuTe_0.5W_0.5O₆, instead of the well-defined spin-wave excitations (magnon) observed in the parent systems. Observation of continuum feature in the Raman spectrum in conjunction with the lack of long-range magnetic order provide the signatures of liquid-like correlations. On the other hand, phonon anomalies are observed below the short-ranged magnetic ordering temperature indicating the onset of spin-phonon coupling.