Raman Study of High T_c Superconductors (La_1-xSr_x)₂CuO₄

Abstract

Lattice vibrations in high T c superconductors (La 1- x Sr x ) 2 CuO 4 are investigated by Raman scattering using single crystals. In La 2 CuO 4 the 664 and 153 cm -1 peaks are resonantly enhanced at low temperatures. The enhancement is caused by the electronic transition spanning the quasi-square Fermi surface to the nesting directions. The 664 cm -1 mode is assigned to the planar breathing mode which strongly interacts with electrons at the Fermi level and the 796 cm -1 mode in (La 0.925 Sr 0.075 ) 2 CuO 4 is tentatively assigned to the axial breathing mode.