Existence of a new surface mode with transverse electric field

Surface acoustic waves, in particular Rayleigh waves near the surface of a piezoelectric material, have attracted a lot of attention lately through their abilities to carry electrons and to couple strongly with superconducting qubits. Here we report the study of a surface mode in a piezoelectric material with transverse electric field, which has not been explored in previous studies of surface acoustic waves. This transverse mode is different from both the well-understood Rayleigh wave that contains a longitudinal component, and the Bleustein-Gulyaev wave, which has been actively studied recently. In order to describe surface modes with transverse electric field, we develop a theory of elastic waves coupled with electromagnetic field, and find among its solutions the Rayleigh wave, the Bleustein-Gulyaev wave, and the new transverse mode. We clarify properties of this mode, such as its polarization, dispersion, and speed of sound. While this surface mode cannot be used to carry an electron, it could play an important role when surface acoustic phonons are used as quantum bus to convey information between quantum dots.