Pressure induced suppression of the singlet insulator phase in BaVS$_3$: infrared optical study

TL;DR

This study investigates how hydrostatic pressure affects the metal-insulator transition in BaVS$_3$, revealing that pressure suppresses the insulating phase and alters the charge gap behavior without pseudogap formation.

Contribution

It provides the first infrared optical measurements of BaVS$_3$ under pressure, showing pressure-independent charge gap ratio and the suppression of the insulating phase beyond a critical pressure.

Findings

Charge gap ratio remains constant with pressure.

Metallic spectra observed above critical pressure.

No pseudogap detected at any pressure.

Abstract

The metal-insulator (MI) transition in BaVS$_3$ has been studied at ambient pressure and under hydrostatic pressure up to $p=26 $kbar in the frequency range of $20-3000 $cm$^{-1}$. The charge gap determined from the optical reflectivity is enhanced, $\Delta_{ch}(p)/k_BT_{MI}(p)\sim 12$. This ratio is independent of pressure indicating that the character of the transition does not vary along the $p-T$ phase boundary. Above the critical pressure, $p_{cr}\sim20$ kbar, metallic spectra were recorded in the whole temperature range, as expected from the shape of the phase diagram. Our results exclude the opening of a pseudogap above $T_{MI}$ at any pressure. Below $T_{MI}$ an unusually strong temperature dependence of the charge gap was observed, resulting in a $\Delta_{ch}(T)$ deviating strongly from the mean field-like variation of the structural order parameter.