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

Abstract

Over the past few years bulk pyrochlore iridates of the form A2Ir2O7 (where A is a rare earth element, Ir is iridium, and O is oxygen) have been studied as model systems for investigating the interplay of electronic correlations and strong spin-orbit coupling, particularly with the aim of finding correlation-driven topological phases. In this work, we use cellular dynamical mean field theory (CDMFT) to study effects of electronic correlations beyond Hartree-Fock theory in thin films of pyrochlore irradiates grown along the [111] direction. We focus on the bilayer and trilayer systems, and compute the phase diagrams of these systems as a function of electron-electron interaction strength, which is modeled by an on-site Hubbard interaction. By evaluating the Z2 invariant and Chern number using formulas based on the single-particle Green's function and the quasiparticle effective Hamiltonian, we show that on-site correlations can drive an interaction-induced topological phase transition, turning a time-reversal invariant topological insulator and a nearly flat band metal to a correlated Chern insulator (CI) in bilayer and trilayer systems, respectively. By comparing with the Hartree-Fock results, the CDMFT results show that quantum fluctuations enhance the robustness of the interaction-driven CI phase in the thin films. Furthermore, our numerical analysis of the quasiparticle spectrum reveals that the topological phases we find in our many-body calculations are adiabatically connected to those in the single-particle picture.

Topological Magnon Bands and Unconventional Superconductivity in Pyrochlore Iridate Thin Films

“…Alternatively, one can view our work as a study of spin (local moment) models with SOC on decorated kagome lattices, possibly artificially created in an optical lattice using artificial gauge fields to realize the SOC and spin interaction terms [58][59][60][61]. While experiments on Eu 2 Ir 2 O 7 provide evidence for an AIAO order in thicker thin films [62][63][64], theoretical studies on atomically thin bilayers and trilayers are less conclusive [41,52,53]. We find that, in the strong coupling limit and on the mean field level, the magnetic ground state is AIAO in the trilayer system, and closely related to it in the bilayer.…”

“…As for electronic phases, there are many theoretical possibilities, including axion insulators [32,34,50], topological Mott insulators [11,16], topological crystalline insulators [10], other varieties of correlated topological insulators [8], and Weyl semimetals [31,32,34,51]. Thin films grown along high symmetry directions have been shown to offer further possible phases, that are not readily inferred from the bulk ones [41,[52][53][54][55][56].…”

“…Along this axis, the pyrochlore lattice consists of alternating triangular and kagome layers. We focus on triangular-kagome-triangular (TKT) trilayers and kagometriangular (KT) bilayers [41,52,53], as shown in Fig. 1.…”

“…In this work we focus on thin films of pyrochlore iridates with non-magnetic A site ions [69] grown [70] in the [111] direction [41,[52][53][54][55][56]. Along this axis, the pyrochlore lattice consists of alternating triangular and kagome layers.…”

“…Following bulk results [34,66] as well as thin film predictions [41,[52][53][54][55], we assume a q = 0 (translationally invariant) structure and solve the model variationally on the meanfield level. In the case of the TKT trilayer, we generically find the AIAO state, as shown in Fig.…”