Multiferroicity in the spin-1/2 quantum matter of LiCu2O2

Multiferroicity in LiCu2O2 single crystals is studied using resonant soft x-ray magnetic scattering, hard x-ray diffraction, heat capacity, magnetic susceptibility, and electrical polarization. Two magnetic transitions are found at 24.6 K (T1) and 23.2 K (T2). Our data are consistent with a sinusoidal spin structure at T2<T<T1 and with a helicoidal spin structure at T<T2 giving rise to ferroelectricity. Surprisingly, above T2 the correlation lengths of the spin structures increase as the temperature increases with dramatic changes of ~42% along the c-axis. Our results demonstrate the interplay of the geometrical frustration and the electronic and magnetic polarizations.