Electronic phase separation in lightly doped (formula presented)

The hole concentration dependence of the magnetic correlations is studied in very lightly doped (formula presented) (formula presented) which shows coexistence of a three-dimensional antiferromagnetic long-range-ordered phase and a spin-glass phase at low temperatures. It is found that the spin-glass phase in the coexistence region also shows a diagonal spin modulation as in the pure spin-glass phase in (formula presented) (formula presented) Below (formula presented) the diagonal stripe structure is the same as that in (formula presented) with a volume fraction almost proportional to hole concentration, suggesting that electronic phase separation of the doped holes occurs so that some regions with hole concentration (formula presented) and the rest with (formula presented) are formed. To our best knowledge, this represents the most direct observation to date of electronic phase separation in lightly doped antiferromagnets. Such phase separation has been predicted by a number of theories.