Effects of Isotope Substitution on Local Heating and Inelastic current in Hydrogen Molecular Junctions

TL;DR

This study uses first-principles methods to explore how isotope substitution affects local heating and inelastic current in hydrogen molecular junctions, revealing significant variations in vibrational energies, electron-vibration interactions, and junction stability.

Contribution

It provides new insights into isotope effects on molecular junctions, highlighting how mass differences influence vibrational properties, electron interactions, and device stability.

Findings

Heavier molecules have smaller vibrational energies and onset biases.

Electron-vibration interaction magnitude decreases with increasing molecular mass.

HD junction exhibits the largest conductance discontinuity and heating effects.

Abstract

Using first principle approaches, we investigate the effects of isotope substitution on the inelastic features in the hydrogen molecular junction. We observe thatlocal heating and inelastic current have significant isotope-substitution effects. Due to the contact characters, the energies of excited molecular vibrationsare inverse proportional to the square root of the mass. The heavier the molecule, the smaller the onset bias. In the $H_{2}$ and $D_{2}$ junctions, the heavier molecule has a smaller magnitude of electron-vibration interaction. Consequently, there is a crossing in the local temperature around $80 K$. In the HD junction, the electron-vibration interaction is enhanced by asymmetric distribution in mass. It leads to the largest discontinuity in the differential conductance and the most prominent heating in the HD junction. We predict that the junction instability is relevant to isotope substitution. The HD junction has the smallest breakdown voltage compared with the $H_{2}$ and $D_{2}$ junction.