Isotope effect in the work function of lithium

TL;DR

This study measures the work functions of lithium isotopes at various temperatures, revealing a significant isotope effect and complex electronic-ionic interactions that challenge simple models of quantum materials.

Contribution

It provides the first detailed experimental analysis of isotope effects on lithium's work function, highlighting the need for advanced microscopic understanding.

Findings

Marked isotope effect in temperature variation of work functions

Curvature of temperature dependence exceeds simple electron gas models

Work function slope approaches zero at low temperatures, consistent with thermodynamics

Abstract

The work functions of 7Li and 6Li metals have been measured as a function of temperature, by using photoionization of pure isolated metal nanoparticles in a beam. These data reveal a marked isotope effect in the temperature variation of these work functions. Furthermore, for both isotopes the curvature of this temperature variation is found to be significantly larger than may be ascribed purely to a change in the electron gas density. These findings enhance the characterization of lithium as a quantum material in which the interplay between electronic and ionic degrees of freedom is nontrivial, and call for a microscopic understanding beyond simple models. Additionally, the slope of the work function curves was observed to vanish in the low temperature limit, as had been predicted on the basis of the Third Law of thermodynamics.