Pressure Effects on the Exchange Integral of Nd_2CuO_4

Abstract

Pressure dependence of the exchange integral J in Nd_2CuO_4 was investigated by high-pressure two-magnon Raman scattering. The superconducting transition temperatures T_C in electron-doped high T_C superconductors are known to be almost independent of pressure in contrast with hole-doped ones. The obtained dJ/dP=12.4, cm^-1/GPa is, however, nearly the same as those in the insulating phases of hole-doped high T_C superconductors.The pressure dependence of the hopping integral t_pd is much larger than those of hole-doped ones, because the pressure coefficient of the charge-transfer gap energy has an opposite sign from that of hole-dopable structure.