  Spin polarization of a topological surface state for GeBi$_2$Te$_4$, the
newly discovered three-dimensional topological insulator, has been studied by
means of the state of the art spin- and angle-resolved photoemission
spectroscopy. It has been revealed that the disorder in the crystal has a minor
effect on the surface state spin polarization and it exceeds 75% near the Dirac
point in the bulk energy gap region ($\sim$180 meV). This new finding for
GeBi$_{2}$Te$_{4}$ promises not only to realize a highly spin polarized surface
isolated transport but to add new functionality to its thermoelectric and
thermomagnetic properties.
