The explosive rise of silicon photonics has led to renewed interest in the electro-optic (EO) or Pockels effect due to its potential uses in many next-generation device applications. To find materials with a strong EO response in thin-film form, which are essential for low power and small footprint devices, one needs to find a general design rule for strong Pockels materials.
To elucidate what makes the Pockels effect strong, researchers study the effect in LiB3O5 (LBO) and CsB3O5 (CBO) and use these materials as prototypical examples of where conventional wisdom breaks down. They find the Pockels tensor components to be extremely small in both materials, despite the large degree of anharmonicity in the crystals, which has been used as a proxy for the presence of nonlinear electronic effects.
The researchers relate the lack of EO response to the large optical phonon frequencies (despite the relatively large Raman susceptibility) in LBO and to the small Raman susceptibility (despite the low phonon frequencies) in CBO, respectively. They shed light on the physical phenomena behind the Raman susceptibility, which they find to be intimately linked to the electron-phonon coupling strength of the near-edge electronic states, and identify a route to discovering new strong EO materials.