Sharp Negative Differential Resistance from Vibrational Mode Softening in Molecular Junctions
Author(s):
Junjie Liu, Dvira Segal
Journal:
Nano Letters
Year:
2020
Volume:
20
Pages
6128–6134
DOI:
10.1021/acs.nanolett.0c02230
Abstract:
We unravel the critical role of vibrational mode softening in single-molecule electronic devices at high bias. Our theoretical analysis is carried out with a minimal model for molecular junctions, with mode softening arising due to quadratic electron-vibration couplings, and by developing a mean-field approach. We discover that the negative sign of the quadratic electron-vibration coupling coefficient can realize, at high voltage, a sharp negative differential resistance (NDR) effect with a large peak-to-valley ratio. Calculated current–voltage characteristics, obtained based on physical parameters for a nitro-substituted oligo(phenylene ethynylene) junction, agree very well with the measurements. Our results establish that vibrational mode softening is a crucial effect at high voltage, underlying NDR, a substantial diode effect, and the breakdown of current-carrying molecular junctions.