Separation of orbital contributions to the optical conductivity of BaVS$_3$

TL;DR

This study investigates the metal-insulator transition in BaVS$_3$ using polarized infrared spectroscopy, revealing the coexistence of two electron types, their transport properties, and the nature of the energy gap.

Contribution

It provides a detailed analysis of the orbital contributions to the optical conductivity and models the transition with a two-band approach.

Findings

Identification of two electron types at the Fermi level

Observation of a pseudo-gap above the transition temperature

Insulating gap follows BCS-like temperature dependence

Abstract

The correlation-driven metal-insulator transition (MIT) of BaVS$_3$ was studied by polarized infrared spectroscopy. In the metallic state two types of electrons coexist at the Fermi energy: The quasi 1D metallic transport of $A_{1g}$ electrons is superimposed on the isotropic hopping conduction of localized $E_g$ electrons. The "bad-metal" character and the weak anisotropy are the consequences of the large effective mass $m_{eff}\approx7m_e$ and scattering rate $\Gamma\geq160$ meV of the quasi-particles in the $A_{1g}$ band. There is a pseudo-gap above $T_{MI}=69$ K, and in the insulating phase the gap follows the BCS-like temperature dependence of the structural order parameter with $\Delta_{ch}\approx42$ meV in the ground state. The MIT is described in terms of a weakly coupled two-band model.