Competing magnetic orders and multipolar Weyl fermions in 227 pyrochlore iridates

TL;DR

This paper explores the complex magnetic orders and emergent Weyl fermions in 227 pyrochlore iridates, revealing how different magnetic phases support various types of Weyl quasiparticles influenced by strong interactions.

Contribution

It identifies the dominant magnetic orders and their associated Weyl fermions in 227 pyrochlore iridates, highlighting the role of Hubbard interaction and magnetic doping in phase transitions.

Findings

All-in all-out (AIAO) order supports octupolar Weyl fermions.

Three-in one-out (3I1O) order supports dipolar Weyl fermions.

Coplanar order acts as an intermediate phase with octupolar Weyl fermions.

Abstract

Owing to comparably strong spin-orbit coupling and Hubbard interaction, iridium based 227 pyrochlore oxides harbor a rich confluence of competing magnetic orders and emergent multipolar Weyl quasiparticles. Here we show that this family of materials is predominantly susceptible toward the nucleation of electronic noncoplanar all-in all-out (AIAO) and three-in one-out (3I1O) orders, respectively transforming under the singlet $A_{2u}$ and triplet $T_{1u}$ representations, supporting octupolar and dipolar Weyl fermions, and favored by strong on-site Hubbard and nearest-neighbor ferromagnetic interaction. Furthermore, a coplanar magnetic order generically appears as an intermediate phase between them. This order transforms under the triplet $T_{2u}$ representation and also hosts octupolar Weyl fermions. With the AIAO and 3I1O phases possibly being realized in (Nd$_{1-x}$Pr$_{x}$)$_2$Ir$_2$O$_7$ when $x=0$ and 1, respectively, the intervening $T_{2u}$ order can in principle be found at an intermediate doping ($0<x<1$) or in pressured (hydrostatic) Nd$_2$Ir$_2$O$_7$.