Coherent-noncoherent tunneling crossover in Nb Se3 -Nb Se3 point contacts

Abstract

Current-voltage (IV) characteristics of Nb Se3 -Nb Se3 artificial contacts (point contacts) formed along the a* axis have been investigated in a wide range of contact resistances and temperatures. Depending on the contact resistance, two types of IV characteristics have been observed: the first type observed for low contact resistance demonstrates a conducting peak at zero bias, while the second one for large contact resistance is characterized by a large resistance maximum near the zero bias voltage. Below the second charge-density wave (CDW) transition (T<59 K), CDW energy gap singularities were observed in the IV characteristics of both types of junctions at V= Δp1/e and V=2 Δp2/e, while the singularity at V= Δp2/e corresponding to the single particle tunneling of carriers noncondensed into the low-temperature CDW is absent. The experimental results are discussed in the frame of the model of interlayer coherent tunneling of the remaining charge carriers that are not condensed into the CDW. © 2007 The American Physical Society.