Exact description of the magnetoelectric effect in the spin-1/2   XXZ-chain with Dzyaloshinskii-Moriya interaction
  We consider a simple integrable model of a spin chain exhibiting the Magnetoelectric Effect (MEE). Starting from the periodic S=1/2 XXZ-chain with Dzyaloshinskii-Moriya terms, which we consider as a local electric polarization in the spirit of the Katsura-Nagaosa-Baladsky (KNB) mechanism, we perform the mapping onto the conventional XXZ-chain with twisted boundary conditions. Using the techniques of Quantum Transfer Matrix (QTM) and Non-Linear Integral Equations (NLIE) we obtain the magnetization, electric polarization and magnetoelectric tensor as functions of magnetic and electric field for arbitrary temperatures. We investigate these dependencies as well as the thermal behavior of the above mentioned physical quantities, especially in the low-temperature regime. We found several regimes of polarization. Adjusting the magnetic field one can switch the system from one regime to another. The features of the critical properties connected with the MEE are also illustrated. 
Michael Brockmann, Andreas Kl\"umper, and Vadim Ohanyan
cond-mat.str-el math-ph math.MP