The Discovery of Ferroelectricity in NH4CuCl3, a Gapless Quantum Magnet

Alkali metal trichlorocuprates ($M_3CuCl_3$: $M = K^+,Tl^+$ and $NH_{4}^{+}$) have received considerable attention as a unique system of gapped/gapless quantum magnets. However, their possible multiferroelectricity, as both magnets and ferroelectrics, have not been reported. Such a finding would add a new dimension to their utility as memory storage elements. Here we report the discovery of ferroelectricity in $NH_{4} CuCl_{3}$, and several of its mixed lattices with K. In this talk, we present details of our crystal growth, x-ray diffraction studies of lattice authenticity and purity, dielectric, specific heat with and without fields, magnetic susceptibility, pulsed fields, and EPR characterization of these novel materials. Theoretical studies of the new findings should be fruitful.