Interaction of coherent phonons with spin-orbit coupled surface states*

Spin-polarized electronic states form at the surface of materials due to the combination of spin-orbit coupling and broken inversion symmetry. This phenomenon was first established for Shockley states at the surface of noble metals such as gold, and more recently, has been recognized as a central mechanism responsible for the formation of topologically non-trivial states. Given the fundamental significance of these states, as well as their potential role in spintronics applications, it is important to understand their interaction with collective excitations of the crystal lattice.

Here we use time- and angle-resolved photoemission spectroscopy (trARPES) to investigate electron-phonon coupling in a model system: the Rashba-split surface state of the semimetal Antimony (Sb). The simplicity of the structure permits us to coherently excite all zero-momentum optical modes of the crystal, and study their coupling to both bulk and surface electronic states. In addition, this material provides an ideal platform for testing coherent control schemes, as well as exploring excitation mechanisms for finite-momentum phonon modes. We will discuss our results in the context of similar measurements on topological insulators.