Semimetallic nature of and magnetic polarons in EuB6 studied using angle-resolved photoemission spectroscopy

Temperature-dependent angle-resolved photoemission spectroscopy (ARPES) was carried out on single-crystalline EuB 6 samples. By measuring ARPES spectra in an extended Brillouin zone, we clearly observed a B 2 p hole pocket centered at the X point, thus proving the semimetallic nature of EuB 6 . Below the Curie temperature T C , ARPES spectra show two B 2 p bands of which separation is due to an exchange interaction between local Eu 4 f and itinerant B 2 p electrons. The exchange splitting becomes smaller as the temperature increases and disappears well above T C . Additionally, a diffuse structure near the Fermi level survives at temperatures just above T C . Such behavior is well described by using Monte Carlo simulations of a Kondo-lattice model, thus supporting the formation of magnetic polarons in EuB 6 , which accounts for the resistivity upturn slightly above T C as the temperature is lowered.