New trend in photonics?

HFML guest researchers from the the Hungarian Academy of Sciences and the Budapest University of Technology and Economics discovered an optical phenomenon. Their results, which can open new horizons in photonics and information technology, have been published on 3 February in Nature Communications. The Hungarian researchers worked together with scientists from Estonia and Japan and with HFML-researcher Hans Engelkamp.

Memory devices
The materials studied by this research team are simultaneously ferromagnetic and ferroelectric. Such multiferroic compounds are a hot topic in current materials science, since some of them exhibit multiferroic character even at room temperature and hold promise for a new generation of memory devices. These devices would combine the best qualities of ferroelectric and magnetoresistive memories: fast low-power electrical write operation, and non-destructive non-volatile magnetic read operation. The present work demonstrates that optical studies can promote the systhematic synthesis of novel materials for such memory applications.

While usual materials absorb counter-propagating light beams with the same strength, the absorbed intensity can strongly depend on the polarization of the beams. The difference in the absorption coefficient for light beams with perpendicular polarizations is termed as dichroism and it is widely exploited in applications like liquid crystal displays.

The researchers found that in multiferroic materials the absorption coefficient can be different not only for light beams with prependicular polarizations but also for counter-propagating beams with the same polarization. They call the new phenomenon quadrochroism as all the four possible states of a photon can be distinguished by multiferroic media. The large magnitude of the effect implies the feasibility of producing new optical devices, such as directional light switches, based on multiferroics. Indeed, in several compounds they observed one-way transparency that is the absorptionless propagation of light along one direction and its strong absorption along the opposite direction. The group also demonstrated that the one-way transparency is directly related to the strength of the static magnetoelectric effect in these materials, which is the key parameter in memory applications.

These theoretical and experimental results provide guidelines for the systematic synthesis of novel materials for directional light switches and can also promote the development of a new generation of memory devices.

One-way transparency of four-coloured spin-wave excitations in multiferroic materials

Figure 1

In multiferroic materials the absorption of photons simultaneously induces a precession of the magnetization (green arrows) and an oscillation in the electric polarization (red arrows). Consequently, these compounds can distinguish between counter-propagating light beams: they are transparent from one direction and absorb light traveling in the opposite direction.