PbCuTe2O6 is considered to be one of the rare candidate materials for a three-dimensional quantum spin
liquid (QSL). This assessment was based on the results of various magnetic experiments, performed mainly on
polycrystalline material. More recent measurements on single crystals revealed an even more exotic behavior,
yielding ferroelectric order below T_FE ≈ 1 K, accompanied by distinct lattice distortions, and a somewhat modified
magnetic response which is still consistent with a QSL. Here we report on low-temperature measurements of
various thermodynamic, magnetic, and dielectric properties of single-crystalline PbCuTe2O6 in magnetic fields
B ≤ 14.5 T. The combination of these various probes allows us to construct a detailed B-T phase diagram
including a ferroelectric phase for B ≤ 8 T and a B-induced magnetic phase at B ≥ 11 T. These phases are
preceded by or coincide with a structural transition from a cubic high-temperature phase into a distorted noncubic
low-temperature state. The phase diagram discloses a ferroelectric quantum critical point at B_c1 = 7.9 T, where
the second-order phase transition line associated with ferroelectric order is suppressed to zero. In addition, a
magnetic quantum phase transition is revealed at B_c2 = 11 T. The corresponding phase transition to a fieldinduced
magnetic order at B > B_c2 is likely to be of first order. Field-induced lattice distortions, observed in the
state at T > 1 K and which are assigned to the effect of spin-orbit interaction of the Cu2+ ions, are considered
as the key mechanism by which the magnetic field couples to the dielectric degrees of freedom in this material.

Data from the figures of the publication P. Eibisch et al., Phys. Rev. B 107, 235133 (2023)