Multiferroic properties of a frustrated quantum spin chain system linarite

Dielectric measurements were performed across the strongly anisotropic phase diagram of the frustrated S=1/2 spin chain compound $\mathrm{PbCuSO_4(OH)_2}$, also know as linarite. In particular, electric polarization was measured on single crystals of the titled material in 6 different geometric configurations. At least two of the magnetic phases for H$||$b-axis are revealed to be also ferroelectric \footnote{K. Yu. Povarov, Y. Feng, A. Zheludev, Multiferroic phases of the frustrated quantum spin chain compound linarite, arXive: 1609.06087.}. The observed orientation of dielectric polarization suggests that one of the previously proposed phase-coexistence regions is actually a proper thermodynamic phase, possibly with a multi-q magnetic structure.