Authors Referees APS Members |
December 2007, to be published in Physical Review A
Relativistic nature of a magnetoelectric modulus of Cr$_2$O$_3$ crystals:
A four-dimensional pseudoscalar and its measurement
The magnetoelectric effect of chromium sesquioxide Cr$_2$O$_3$ has been determined experimentally as a function of temperature. One measures the electric field-induced magnetization on Cr$_2$O$_3$ crystals or the magnetic field-induced polarization. From the magnetoelectric moduli of Cr$_2$O$_3$ we extract a 4-dimensional relativistic invariant pseudoscalar $\widetilde{\a}$. It is temperature dependent and of the order of $\sim 10^{-4}/Z_0$, with $Z_0$ as vacuum impedance. We show that the new pseudoscalar is odd under parity transformation and odd under time inversion. Moreover, $\widetilde{\a}$ is for Cr$_2$O$_3$ what Tellegen's {\it gyrator} is for two port theory, the {\it axion} field for axion electrodynamics, and the PEMC (perfect electromagnetic conductor) for electrical engineering. © 2008 The American Physical Society.
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