Anomalous Microwave Response and Upper Critical Field in Overdoped Tl2Ba2CuO6+δ

The transmittivity T H and microwave surface impedance Zs = Rs+iXs have been measured in order to clarify the unusual dc resistive transition of overdoped Tl2Ba2Cu2O6+δ in magnetic field. The transition field H* is enhanced by the columnar defect, indicating that H * is not the mean-field upper critical field but the depinning point of the vortices. Rs shows unusual field dependence which is quite different from that expected from the result of the dc resistivity.