Electronic phase separation in lightly dopedLa2−xSrxCuO4

Abstract

The hole concentration dependence of the magnetic correlations is studied in very lightly doped ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ $(x<0.02),$ 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 ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ $(0.02<~x<~0.055).$ Below $x\ensuremath{\sim}0.02$ the diagonal stripe structure is the same as that in $x\ensuremath{\sim}0.02$ 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 ${c}_{h}\ensuremath{\sim}0.02$ and the rest with ${c}_{h}\ensuremath{\sim}0$ 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.