Microscopic description of insulator-metal transition in high-pressure oxygen

TL;DR

This paper investigates the insulator-metal transition in high-pressure oxygen using first-principles and many-body calculations, revealing an orbital-selective Mott transition and proposing a new pairing mechanism involving coexisting electronic states.

Contribution

It introduces the first theoretical evidence of an orbital-selective Mott transition in pure p-band oxygen and connects it to experimental observations and superconductivity.

Findings

Discovery of an orbital-selective Mott transition in pure p-band oxygen.

Application of combined first-principles and many-body calculations to understand the transition.

Proposal of a novel pairing mechanism involving coexisting itinerant and localized states.

Abstract

Unusual metallic states involving breakdown of the standard Fermi-liquid picture of long-lived quasiparticles in well-defined band states emerge at low temperatures near correlation-driven Mott transitions. Prominent examples are ill-understood metallic states in $d$- and $f$-band compounds near Mott-like transitions. Finding of superconductivity in solid O$_{2}$ on the border of an insulator-metal transition at high pressures close to 96~GPa is thus truly remarkable. Neither the insulator-metal transition nor superconductivity are understood satisfactorily. Here, we undertake a first step in this direction by focussing on the pressure-driven insulator-metal transition using a combination of first-principles density-functional and many-body calculations. We report a striking result: the finding of an orbital-selective Mott transition in a pure $p$-band elemental system. We apply our theory to understand extant structural and transport data across the transition, and make a specific two-fluid prediction that is open to future test. Based thereupon, we propose a novel scenario where soft multiband modes built from microscopically coexisting itinerant and localized electronic states are natural candidates for the pairing glue in pressurized O$_{2}$.