Spin-correlation driven ferroelectric quantum criticality in a perovskite quantum spin-liquid system, Ba3CuSb2O9

Abstract

Here we have experimentally demonstrated spin-correlation-driven ferroelectric quantum criticality in a prototype quantum spin-liquid system, Ba₃CuSb₂O₉, a quantum phenomenon that is rarely observed. The dielectric constant follows a clear T² scaling, showing that the material behaves as a quantum paraelectric without developing ferroelectric order. Magnetically, the system avoids long-range order down to 1.8 K and instead displays a T^3/2 dependence in its inverse susceptibility, a hallmark of antiferromagnetic quantum critical fluctuations. Together with known spin–orbital–lattice entanglement in this compound, these signatures point to a strong interplay between spin dynamics and the polar lattice. Our pioneering work places this perovskite spin-liquid family at the forefront of this domain and suggests the flexibility of this family in a suitable environment by tuning chemical/external pressure.