From antiferromagnetic insulator to correlated metal in pressurized and doped LaMnPO

TL;DR

This study demonstrates that modest pressure can induce a transition in LaMnPO from an antiferromagnetic insulator to a correlated metal, revealing potential pathways to high-temperature superconductivity in Mn-based compounds.

Contribution

It challenges previous beliefs by showing that only modest pressures are needed to induce electronic delocalization in LaMnPO, a Mn-based compound structurally similar to known superconductors.

Findings

LaMnPO transitions from insulator to metal under modest pressure.

Structural change from tetragonal to orthorhombic occurs with pressure.

Proximity to delocalization transition creates a highly interacting metallic state.

Abstract

Widespread adoption of superconducting technologies requires the discovery of new materials with enhanced properties, especially higher superconducting transition temperatures T$_{c}$. The unexpected discovery of high T$_{c}$ superconductivity in cuprates and in materials as diverse as heavy fermions, organic conductors, and endohedrally-doped fullerenes suggests that the highest T$_{c}$s occur when pressure or doping transform the localized and moment-bearing electrons in antiferromagnetic insulators into itinerant and weakly magnetic metals. The absence of this delocalization transition in Fe-based superconductors may limit their T$_{c}$s, but even larger T$_{c}$s may be possible in their isostructural Mn analogs, which are antiferromagnetic insulators like the cuprates. It is generally believed that prohibitively large pressures would be required to suppress the strong Hund's rule coupling in these Mn-based compounds, collapsing the insulating gap and enabling superconductivity. Indeed, no Mn-based compounds are known to be superconductors. The electronic structure calculations and x-ray diffraction measurements presented here challenge these long held beliefs, finding that only modest pressures are required to transform LaMnPO, isostructural to superconducting host LaFeAsO, from an insulating tetragonal structure with a large Mn moment to a gapless orthorhombic structure with a small Mn moment. Proximity to this electronic delocalization transition in LaMnPO results in a highly interacting metallic state, the familiar breeding ground of superconductivity.