Systematic variation of magnetic-field penetration depth in high-Tc superconductors studied by muon-spin relaxation

The muon-spin relaxation rate σ has been measured in the high-Tc superconductors YBa2Cu3Ox for x=6.66, 6.95, 7.0, and La1.85Sr0.15CuO4 in transverse external magnetic fields ∼1-4 kG. We find a simple relation which connects the transition temperature Tc, the magnetic-field penetration depth λL, the carrier concentration ns, and the effective mass m* as Tc∝σ∝1λL2∝nsm*. The linear dependence Tc∝nsm* suggests a high-energy scale for the coupling between superconducting carriers.