Some 200 years ago, physicists discovered that the interaction of light with a material provides an insight into the arrangement of atoms in a crystalline structure.
The so-called optical activity of materials has been studied extensively since then, so it is perhaps surprising that there is anything new to discover. However, José Goulon of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, and co-workers at the ESRF, the University of Paris and Purdue University in the US have recently observed a new type of optical activity using linearly polarized X-rays. The effect – known as non-reciprocal linear dichroism – was discovered in a chromium-doped vanadium-oxide crystal in which the magnetic moments of the atoms are aligned in opposite directions (J Goulon et al. 2000 Phys. Rev. Lett. 85 4385).
In the February issue of Physics World, Gerrit van der Laan of the Synchrotron Radiation Department, Daresbury Laboratory, Warrington, UK, describes the effect – which had been predicted theoretically – but has now been observed clearly for the first time.
