Temperature-dependent exchange splitting of a surface state on a local-moment magnet: Tb(0001)

We have investigated the temperature-dependent binding energies of the exch ange-split Tb(0001) surface state by means of scanning tunneling spectrosco py. At T = 16 K the majority and minority part of the surface state exhibit a binding energy of -135 +/- 8 meV and +430 +/- 15 meV, respectively. Both peak positions shift with increasing temperature and continuously decrease the exchange splitting down to 200 meV at 260 K. i.e., 30 K above the bulk Neel temperature T-NB. This result is explained in terms of a decrease of helical short-range spin order with increasing temperature above T-NB.