Doping Dependence of the Electric Field Gradient at La Site in La2-xMxCuO4(M=Sr, Ba) –La-NQR Study–

Abstract

The nuclear quadrupole resonance (NQR) frequency, ν Q , of 139 La in La 2- x M x CuO 4 (M=Sr, Ba) was systematically measured in the Sr or Ba content range of \(0\;\raisebox{-0.4em}{\)\stackrel<=\(}\;x\; \raisebox{-0.4em}{\)\stackrel<=\(}\;0.20\) at 1.4 and 4.2 K in zero field. ν Q , which is the principal component of the electric field gradient (EFG) tensor, decreases linearly with increasing x for both compounds, showing no appreciable change even around x ∼1/8 for Ba doping where the structural phase transition from orthorhombic to tetragonal structure occurs at low temperature.