Topological and magnetic phases of interacting electrons in the pyrochlore iridates

Abstract

We construct a model for interacting electrons with strong spin orbit coupling in the pyrochlore iridates. We establish the importance of the direct hopping process between the Ir atoms and use the relative strength of the direct and indirect hopping as a generic tuning parameter to study the correlation effects across the iridates family. We predict novel quantum phase transitions between conventional and/or topologically non-trivial phases. At weak coupling, we find topological insulator and metallic phases. As one increases the interaction strength, various magnetic orders emerge. The novel topological Weyl semi-metal phase is found to be realized in these different orders, one of them being the all-in/all-out pattern. Our findings establish the possible magnetic ground states for the iridates and suggest the generic presence of the Weyl semi-metal phase in correlated magnetic insulators on the pyrochlore lattice. We discus the implications for existing and future experiments.

Lifshitz metal–insulator transition induced by the all-in/all-out magnetic order in the pyrochlore oxide Cd2Os2O7

“…19 Moreover, in Nd 2 Ir 2 O 7 , the resistivity tends to saturate below ∼30 K and anomalous magnetoresistances are observed at lower temperatures, 22,38,39 which have been attributed to conducting domain walls. 22 The weak ferromagnetic moments and the remaining conductivity of Nd 2 Ir 2 O 7 have been discussed in terms of the MDWs of the AIAO order, 37 [40][41][42] The Weyl semimetal is theoretically predicted to have a peculiar metallic state with a Fermi arc at the surface. In addition, Yamaji and Imada note that ferromagnetic and metallic MDWs can occur in the AIAO magnetic order and survive even at low temperatures after the metallic surface state has been diminished by pair annihilation of the Weyl electrons, which may solve the experimental puzzles for R 2 Ir 2 O 7 .…”

Correlation effects in pyrochlore iridate thin films grown along the [111] direction

“…In this work, we apply the model Hamiltonian proposed for the three-dimensional materials 25,30 to the quasi-two-dimensional thin film systems. 47 Effectively integrating out the oxygen orbitals involved in indirect hopping processes between B-site ions, one obtains a model that only involves the B-sites.…”

“…17 In addition, we include an on-site Coulomb repulsion within the J eff = 1/2 pseudospin space to obtain the effective Hamiltonian for our thin films: 28,30 …”

“…The intrinsic spin-orbit coupling of the Ir local moments generally breaks the spinrotational invariance 25,30 and therefore opens the possibility of long-range magnetic order at non-zero temperatures. Therefore, we do not expect qualitative changes to the magnetic order upon the inclusion of spatial fluctuations on top of the magnetic order predicted in HF theory.…”

“…[19][20][21][22][23] Among the real-material proposals for systems expected to exhibit topological properties, transition metal oxides (TMO) are a promising candidate for realizing nontrivial interacting topological phases. [24][25][26][27][28][29][30][31][32][33][34][35][36] Among the bulk (as apposed to thin-film) TMO that have been theoretically studied in the context of topological phases, the irradiates have been particularly singled out. 17,[24][25][26][27][28][29][30][31][32][33][34][35]37 In these materials, the iridium 5d electrons typically dominate the states near the Fermi energy.…”