Spin liquid and ferroelectricity close to a quantum critical point in PbCuTe$_2$O$_6$

TL;DR

This study investigates PbCuTe$_2$O$_6$, revealing a 3D quantum spin liquid state with emergent ferroelectricity and quantum critical behavior, highlighting complex interplay between magnetic, electric, and lattice properties.

Contribution

It provides the first comprehensive experimental evidence of ferroelectricity and quantum criticality in a 3D frustrated quantum spin liquid candidate.

Findings

Single crystals exhibit ferroelectric order at ~1 K.

Lattice distortions accompany ferroelectricity.

Magnetic response shows signs of quantum critical behavior.

Abstract

Geometrical frustration among interacting spins combined with strong quantum fluctuations destabilize long-range magnetic order in favour 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 favourable 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 PbCuTe$_2$O$_6$, 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 behaviour is revealed for the single crystals. These crystals show ferroelectric order at $T_{\text{FE}} \approx 1\,\text{K}$, accompanied by strong lattice distortions, and a modified magnetic response -- still consistent with a quantum spin liquid -- but with clear indications for quantum critical behaviour.