Coherent-noncoherent tunneling crossover inNbSe3−NbSe3point contacts

Abstract

Current-voltage ͑IV͒ characteristics of NbSe 3 -NbSe 3 artificial contacts ͑point contacts͒ 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 ͑CDW͒ transition ͑T Ͻ 59 K͒, CDW energy gap singularities were observed in the IV characteristics of both types of junctions at V = ⌬ p1 / e and V =2⌬ p2 / e, while the singularity at V = ⌬ p2 / 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.

Electronic crystals: an experimental overview

“…Figure 9.17 shows the bias dependence of the differential resistance R d (V ) measured at T = 4.2 K for several NbSe 3 -NbSe 3 point contacts with different zero bias resistance R d0 from 10 Ω to 400 Ω. Curves with a large contact resistance R d0 > 100 Ω exhibit a behaviour with a large zero bias resistance peak while, on the contrary, those with a low contact resistance are characterised by a deep minimum of R d0 . Independently of their contact resistances all the curves show gap singularities [855] for both CDWs. Contacts with high and low zero bias resistances have a different temperature dependence.…”

“…CDW/CDW junctions I-V characteristics were measured on NbSe 3 -NbSe 3 contacts (point contacts) formed along the a * axis. To form a NbSe 3 -NbSe 3 contact [855,856], two bent crystals with parallel b-axis were brought together (see inset of figure 9.17) with the help of a precise mechanical motion transfer system. Two different behaviours in the I-V curves were observed depending on the contact resistance of the contact.…”

“…In the opposite, for low contact resistances, R d0 decreases when T is reduced. The low resistance point contacts were considered [855] to correspond to coherent interlayer tunnelling similar to properties of mesa-type junctions as described in the following section 9.6. 9.5.2.d.…”