Estimation of magnetic penetration depth in Li-doped polycrystalline Bi-2212; an ESR study

Abstract

We report on the electron spin resonance (ESR) study of the paramagnetic probe DPPH adsorbed on the surface of Li-doped polycrystalline Bi 2Sr 2CaCu 2− x Li x O 8+δ ( x = 0.5–0.7) carried out in the temperature range 77–300 K. The T c of the samples are found to increase with Cu (Li) subtraction (addition). From the model of Brandt for a triangular vortex lattice, the widths of the observed ESR lines below T c are related to the penetration depth. From the analysis of the temperature dependence of A, the penetration depth at zero temperature ( λ 0) is estimated and the observed increase in the penetration depth is explained.