Negative thermal expansion near two structural quantum phase transitions

TL;DR

This study investigates the link between negative thermal expansion and structural quantum phase transitions by analyzing two different materials, revealing common traits and proposing design principles for new materials with this property.

Contribution

The paper demonstrates a connection between negative thermal expansion and proximity to structural quantum phase transitions in two materials, and proposes design principles for new materials.

Findings

Similar negative thermal expansion observed in Hg2I2 and ScF3.

Negative thermal expansion occurs below 100K along specific axes.

Identifies common traits and proposes design principles for new NTE materials.

Abstract

Recent experimental work has revealed that the unusually strong, isotropic structural negative thermal expansion in cubic perovskite ionic insulator ScF3 occurs in excited states above a ground state tuned very near a structural quantum phase transition, posing a question of fundamental interest as to whether this special circumstance is related to the anomalous behavior. To test this hypothesis, we report an elastic and inelastic X-ray scattering study of a second system Hg2I2 also tuned near a structural quantum phase transition while retaining stoichiometric composition and high crystallinity. We find similar behavior and significant negative thermal expansion below 100K for dimensions along the body-centered-tetragonal c axis, bolstering the connection between negative thermal expansion and zero temperature structural transitions. We identify the common traits between these systems and propose a set of materials design principles that can guide discovery of new materials exhibiting negative thermal expansion.