High pressure superconducting phase diagram of 6Li: anomalous isotope effects in dense lithium

TL;DR

This study investigates the superconducting phase diagram of the light isotope 6Li under high pressure, revealing anomalous isotope effects that suggest quantum solid effects influence its low-temperature properties.

Contribution

It provides the first detailed comparison of superconductivity in 6Li and 7Li under high pressure, highlighting unusual isotope effects and their implications for quantum solid behavior.

Findings

6Li becomes superconducting between 16-26 GPa

Unusual large isotope effect observed below 21.5 GPa

Inverse isotope effect appears between 21.5-26 GPa

Abstract

We report the superconducting transition temperature of 6Li between 16-26 GPa, the lightest system to exhibit superconductivity to date. The superconducting phase diagram of 6Li is compared to that of 7Li through simultaneous measurement in a diamond anvil cell (DAC) 1, 2. Below 21.5 GPa, Li exhibits a direct, but unusually large isotope effect, while between 21.5-26 GPa, lithium shows an inverse superconducting isotope effect. The unusual dependence of the superconducting phase diagram of lithium on its atomic mass provides evidence that quantum solid effects dominate the low temperature properties of dense lithium leading to anomalous differences in the structures and/or in electronic properties of the isotopes through zero point effects.