Unusual microwave vortex dissipation of Nd1.85Ce0.15CuO4

Abstract We have measured the microwave surface impedance Z S = R S +i X S of the electron-doped cuprate Nd 1.85 Ce 0.15 CuO 4 in magnetic field perpendicular to the superconducting layers. A broad peak was observed in the field dependence of flux flow resistivity ρ f obtained from Z S . This peak shifts to higher field with increasing microwave frequency, indicating that the peak originates not from the vortex pinning effect but from the electronic excitations. We discussed several possible origins for this peak.