Abstract-Terahertz dynamics of ferroelectric vortices from first principles

Zhigang Gui and L. Bellaiche

Accepted Thursday Jan 23, 2014

http://prb.aps.org/accepted/a9072Y9fT041eb4375b770829a54d2f8474086e83

A first-principles-based effective Hamiltonian is used to reveal dynamics of vortices in ferroelectrics. In addition to the ``usual'' dielectric modes that are generated by the fluctuation of the electrical polarization, novel toroidic modes, resulting from the electric toroidal moment fluctuations, are also discovered in the THz regime. Such latter modes can have their own dynamics, with a resonant frequency that softens via a square-root law when the temperature approaches the critical temperature at which electric vortices form. These dynamics are also found to be governed by the fluctuation of the self-organized {\it azimuthal} component of individual electric dipoles. Toroidic modes thus behave as pendulums, in contrast to springs that represent polarization dynamics.}

Abstract-TERAHERTZ DIELECTRIC RESPONSE AND COUPLED DYNAMICS OF FERROELECTRICS AND MULTIFERROICS FROM EFFECTIVE HAMILTONIAN SIMULATIONS

DAWEI WANG

Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, Xi'an Jiaotong University, Xi'an 710049, P. R. China

JEEVAKA WEERASINGHE

Physics Department, University of North Texas, Denton, Texas 76205, USA

ABDULLAH ALBARAKATI

Physics Department, The University College at Al-Gammom, Umm Al-Qura University Makkah, Saudi Arabia

L. BELLAICHE

Physics Department and Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, Arkansas 72701, USA

http://www.worldscientific.com/doi/abs/10.1142/S0217979213300168

Ferroelectric and multiferroic materials form an important class of functional materials. Over the last 20 years, first-principles-based effective Hamiltonian approaches have been successfully developed to simulate these materials. In recent years, effective Hamiltonian approaches were combined with molecular dynamics (MD) methods to investigate terahertz dynamical properties of various perovskites. With this combination, a variety of ferroelectric and multiferroic materials, including BaTiO₃, Ba(Sr, Ti)O₃, Pb(Zr, Ti)O₃, BiFeO₃ and SrTiO₃ bulks and films have been simulated, which led to the understanding of complex phenomena and discovery of novel effects. In this paper we first provide technical details about effective Hamiltonians and MD simulation method. Then, we present applications of the combination of these two techniques to different perovskites. Finally, we briefly discuss possible future directions of this approach.

Read More: http://www.worldscientific.com/doi/abs/10.1142/S0217979213300168