Magnetic field and temperature dependence of the intrinsic resistance steps in the mixed state of the cuprate superconductor Nd2-xCexCuOy

In epitaxial c-axis oriented films of the cuprate superconductor Nd2-xCexCu Oy we have studied the magnetic field and temperature dependence of the two intrinsic steps of the flux flow resistance appearing under current bias. The two steps are explained in terms of the field induced energy shift of t he normal excitations in the superconducting mixed state. Because of the st rong interaction between vortices in the magnetic fields used in our experi ments, we propose that narrow subbands develop between the Fermi energy and the energy gap, and that the quasiparticles undergo Bloch oscillations in the subbands, thereby leading to the first resistance step. The second step , appearing at electric fields about a thousand times higher than the field s of the first step, may be explained in terms of a second subband at highe r energy or, alternatively, by a sharp upturn of the density of states near the gap energy and of the corresponding phase space available for quasipar ticle scattering. [S0163-1829(99)02341-3].