Geometrical frustration among interacting spins combined with strong quantum fluctuations destabilize long-range magnetic order in favor of more exotic states such as spin liquids. By following this guiding principle, a number of spin liquid candidate systems were identified in quasi-two-dimensional (quasi-2D) systems. For 3D, however, the situation is less favorable as quantum fluctuations are reduced and competing states become more relevant. Here we report a comprehensive study of thermodynamic, magnetic and dielectric properties on single crystalline and pressed-powder samples of PbCuTe₂O₆, a candidate material for a 3D frustrated quantum spin liquid featuring a hyperkagome lattice. Whereas the low-temperature properties of the powder samples are consistent with the recently proposed quantum spin liquid state, an even more exotic behavior is revealed for the single crystals. These crystals show ferroelectric order at T_FE ≈ 1 K, accompanied by strong lattice distortions, and a modified magnetic response—still consistent with a quantum spin liquid—but with clear indications for quantum critical behavior.

相互作用的自旋之间的几何挫折与强量子涨落相结合，破坏了远程磁序的稳定性，有利于更奇异的状态，如自旋液体。通过遵循这一指导原则，在准二维（准 2D）系统中确定了许多自旋液体候选系统。然而，对于 3D，随着量子波动的减少和竞争状态变得更加相关，情况就不那么好了。在这里，我们报告了 PbCuTe ₂ O ₆单晶和压粉样品的热力学、磁性和介电性能的综合研究，具有超kagome晶格的3D受挫量子自旋液体的候选材料。尽管粉末样品的低温特性与最近提出的量子自旋液态一致，但单晶显示出更加奇特​​的行为。这些晶体在T _FE  ≈ 1 K 时显示铁电有序，伴随着强烈的晶格畸变和修改后的磁响应——仍然与量子自旋液体一致——但具有量子临界行为的明确迹象。