Doping-Induced Ferromagnetism and Possible Triplet Pairing in d4 Mott Insulators

TL;DR

This paper investigates how electron doping in d^4 Mott insulators can induce ferromagnetism and potentially lead to triplet superconductivity, revealing new magnetic and pairing phenomena driven by excitonic interactions.

Contribution

It demonstrates the emergence of ferromagnetism and possible triplet pairing in doped d^4 Mott insulators, highlighting the role of J-excitons and spin-orbit coupling effects.

Findings

Doping induces ferromagnetic metallic phases from nonmagnetic or antiferromagnetic insulators.

Strong paramagnon excitations near ferromagnetic phases may mediate triplet pairing.

Electron doping can suppress magnetic order, leading to nonmagnetic metallic states.

Abstract

We study the effects of electron doping in Mott insulators containing d^4 ions such as Ru4+, Os4+, Rh5+, and Ir5+ with J=0 singlet ground state. Depending on the strength of the spin-orbit coupling, the undoped systems are either nonmagnetic or host an unusual, excitonic magnetism arising from a condensation of the excited J=1 triplet states of t_2g^4. We find that the interaction between J-excitons and doped carriers strongly supports ferromagnetism, converting both the nonmagnetic and antiferromagnetic phases of the parent insulator into a ferromagnetic metal, and further to a nonmagnetic metal. Close to the ferromagnetic phase, the low-energy spin response is dominated by intense paramagnon excitations that may act as mediators of a triplet pairing.