Electronic temperature and two-electron processes in overbias plasmonic emission from tunnel junctions

TL;DR

This paper introduces a method to accurately measure electronic temperature in tunnel junctions using electroluminescence emission shape, revealing deviations from lattice temperature below 30 K due to two-electron processes that excite plasmon modes.

Contribution

It demonstrates a new technique for determining electronic temperature via emission spectra and explains overbias emission through two-electron plasmon excitation processes.

Findings

Electronic temperature can be deduced from emission edge shape.

Deviations between electronic and lattice temperatures occur below 30 K.

Two-electron processes contribute to overbias plasmonic emission.

Abstract

The accurate determination of electronic temperatures in metallic nanostructures is essential for many technological applications, like plasmon-enhanced catalysis or lithographic nanofabrication procedures. In this Letter we demonstrate that the electronic temperature can be accurately measured by the shape of the tunnel electroluminescence emission edge in tunnel plasmonic nanocavities, which follows a universal thermal distribution with the bias voltage as the chemical potential of the photon population. A significant deviation between electronic and lattice temperatures is found below 30 K for tunnel currents larger than 15 nA. This deviation is rationalized as the result of a two-electron process in which the second electron excites plasmon modes with an energy distribution that reflects the higher temperature following the first tunneling event. These results dispel a long-standing controversy on the nature of overbias emission in tunnel junctions and adds a new method for the determination of electronic temperatures and quasiparticle dynamics.