Regensburg 2013 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 64: Focus Session: Frontiers of electronic structure theory V (O, joinly with HL, TT)

HL 64.5: Talk

Wednesday, March 13, 2013, 17:15–17:30, H36

Spontaneous Electric Polarisation from a Classical Perspective. — •Paul Tangney — Imperial College London, London, UK

Spontaneous polarisation is a quantity attributed to noncentrosymmetric crystals and is often associated with a macroscopic electric field permeating the bulk of a sample. Its time derivative is measured as a current density during application of an external stimulus, such as temperature, strain, or an electric field. I will argue that such currents do not require the existence of a spontaneous polarisation field or a macroscopic electric field in the bulk of a polar material. They can be explained by symmetry arguments within a purely classical picture and should be calculable from the time dependence of the many-particle position probability density function of the material's constituent charges - a classical quantity. The only macroscopic electric field across any bulk crystal arises from the charges on its surfaces, which in most cases are strongly influenced by surface relaxation/reconstruction and chemical environment and unlikely to be determined by polarization currents. I will show how the classical picture of polarisation presented is consistent with the Modern Theory of Polarisation[1], in all but interpretation. I will illustrate my arguments with simulations of a toy system.

[1] R. Resta and D. Vanderbilt, "Theory of Polarization: A Modern Approach", in Physics of Ferroelectrics: a Modern Perspective C.H. Ahn, K.M. Rabe, and J.M. Triscone, Eds. Springer-Verlag, (2007).