WAGENKNECHT, M. ... et al, 2008. Phase diagram of the electron-doped La(2-x)Ce(x)CuO(4) cuprate superconductor from Andreev bound states at grain boundary junctions. Physical Review Letters, 100 (22), 4pp.
We use quasiparticle tunneling across La2 xCexCuO4 grain boundary junctions to probe the superconducting
state and its disappearance with increasing temperature and magnetic field. A zero bias
conductance peak due to zero energy surface Andreev bound states is a clear signature of the phase
coherence of the superconducting state. Hence, such a peak must disappear at or below the upper critical
field Bc2 T . For La2 xCexCuO4 this approach sets a lower bound for Bc2 0 25 T which is substantially
higher than reported previously. The method of probing the superconducting state via Andreev
bound states should also be applicable to other cuprate superconductors.