Quantum Dielectric Fluctuation in an Electronic Ferroelectricity studied by Variational Monte-Carlo Method

Electronic structure and dielectric property in an electronic ferroelectricty, where electric polarization is driven by an electronic charge order without inversion symmetry, are studied. Motivated from layered iron oxides, roles of quantum fluctuation on ferroelectricity in a paired-triangular lattice are focused on. Three types of the extended V-t model are examined by the variational Monte-Carlo method with the Gutzwiller-type correlation factor. It is shown that electron transfer between the triangular layers corresponding to the inter-layer polarization fluctuation promotes the three-fold charge order associated with an electric polarization. This result is in highly contrast to the usual manner of quantum fluctuation in the hydrogen-bond type ferroelectricities and the quantum paraelectric oxides. Spin degree of freedom of electron and a realistic crystal structure for the layered iron oxides further stabilize the polar charge ordered state. Implications of the numerical results for layered iron oxides are discussed.