Time-resolved luminescence of high-density magnetic polarons in CdMnTe

Excitation intensity dependence of photoluminescence signals is observed in Cd _0.9Mn _0.1Te at 2 K with varying exciton density from 10 ¹⁴ to 10 ¹⁹ cm^-3. For intermediate density regime (<10 ¹⁶ cm^-3) , the transient spectral shift reflecting the magnetic polaron formation is found to decrease with an increase in density. For high-density regime (>10 ¹⁷ cm^-3) , the polaron shift disappears, and the density-dependent red shift caused by the band-gap renormalization is observed. The experimental findings demonstrate that the magnetic polaron is unstable at high-density condition.