Magnetic-field induced multiferroicity in a quantum critical frustrated   spin liquid
  Dielectric spectroscopy is used to check for the onset of polar order in the quasi one-dimensional quantum spin system Sul-Cu2Cl4 when passing from the spin-liquid state into the ordered spiral phase in an external magnetic field. We find clear evidence for multiferroicity in this material and treat in detail its H-T phase diagram close to the quantum-critical regime. 
F. Schrettle, S. Krohns, P. Lunkenheimer, A. Loidl, E. Wulf, T.   Yankova, and A. Zheludev
cond-mat.str-el