Quantum fluctuation and geometrical frustration effects on electric polarization

We examine theoretically the possibility of ferroelectricity caused by electronic charge order without inversion symmetry motivated by layered iron oxides. Quantum electronic models in a paired-triangular lattice are analyzed by utilizing the variational Monte Carlo simulation. Our calculations demonstrate that the combined effects of electron transfer between the layers, corresponding to quantum fluctuation between the potential minima, and geometrical frustration promote the appearance of electric polarization. Our results contrast with the conventional manner of quantum fluctuation in ferroelectricity.