Relativistic analysis of magnetoelectric crystals:: Extracting a new 4-dimensional P odd and T odd pseudoscalar from Cr2O3 data

Earlier, the linear magnetoelectric effect of chromium sesquioxide Cr2O3 has been determined experimentally as a function of temperature. One measures the electric field-induced magnetization on Cr2O3 crystals or the magnetic field-induced polarization. From the magnetoelectric moduli of Cr2O3 we extract a 4-dimensional relativistic invariant pseudoscalar (alpha) over tilde. It is temperature dependent and of the order of similar to 10(-4)Y(0), with Y-0 as vacuum admittance. We show that the new pseudoscalar (alpha) over tilde is odd under parity transformation and odd under time inversion. Moreover, (alpha) over tilde is for Cr2O3 what Tellegen's gyrator is for two port theory, the axion field for axion electrodynamics, and the PEMC (perfect electromagnetic conductor) for electrical engineering. (C) 2007 Elsevier B.V. All rights reserved.