Interplay of Spin-Orbit Interactions, Dimensionality, and Octahedral Rotations in SemimetallicSrIrO3

Abstract

We employ reactive molecular-beam epitaxy to synthesize the metastable perovskite SrIrO3 and utilize in situ angle-resolved photoemission to reveal its electronic structure as an exotic narrowband semimetal. We discover remarkably narrow bands which originate from a confluence of strong spin-orbit interactions, dimensionality, and both in-and out-of-plane IrO6 octahedral rotations. The partial occupation of numerous bands with strongly mixed orbital characters signals the breakdown of the single-band Mott picture that characterizes its insulating two-dimensional counterpart, Sr2IrO4, illustrating the power of structure-property relations for manipulating the subtle balance between spin-orbit interactions and electron-electron interactions. PACS numbers: Keywords:The combination of strong spin-orbit interactions (SOIs) with electron-electron correlations has recently been predicted to realize a variety of novel quantum states of matter, including topological Mott insulators [1, 2], quantum spin Hall, quantum anomalous Hall, and axion insulators [3-6], Weyl semimetals [7], and even high temperature superconductors [8]. Although typically viewed to be disparate properties, the recent discovery that SOI can sufficiently enhance the effective role of electron correlations to stabilize a Mott-like insulating state in the quasi-two-dimensional 5d transition metal oxide Sr 2 IrO 4 [9, 10] has opened a new frontier for exploring the rare interplay between these 2 degrees of freedom. Its three-dimensional perovskite analogue, SrIrO 3 , has been theoretically proposed as a key building block for engineering topological phases at interfaces and in superlattices [3,11,12]. In bulk, SrIrO 3 is believed to lie in close proximity to a metal-insulator transition [13,14], yet little is known of its electronic structure to date.Here we reveal the momentum-resolved electronic structure of SrIrO 3 using a combination of reactive oxide molecular-beam epitaxy (MBE) and in situ angleresolved photoemission spectroscopy (ARPES). Our measurements uncover an exotic semimetallic ground state, hosting an unusual coexistence of heavy holelike and light electronlike bands. Contrary to conventional expectations that increased coordination leads to broader bands in higher-dimensional materials [13], we find that the bandwidths of SrIrO 3 are, instead, narrower than its insulating two-dimensional counterpart. By combining first-principles calculations with spectroscopic measurements, we uncover the surprising interplay of spinorbit interactions, dimensionality, and octahedral rotations which drives the narrow-band, semimetallic state in SrIrO 3 . Our results indicate that subtle changes in the structure and rotation angles should drive substantial changes in the electronic structure and physical properties of SrIrO 3 . This highlights the important structure-property relationships in correlated quantum materials [15,16], much like in ferroelectrics and multiferroics [17]. This Letter also underscores that simple toy models which neglect these str...

Synthesis, Crystal Structure, and Physical Properties of the Perovskite Iridates

“…Recent angle-resolved photoemission spectroscopy on Pv SrIrO 3 films by Nie et al [42] has uncovered such an exotic semimetallic state with very narrow bands near the Fermi surface consisting of heavy hole-like pockets around (±π, 0) and (0, 0) and light electron-like pockets at (±π/2, ±π/2). Surprisingly, the bandwidth of Pv SrIrO 3 is found to be narrower than that of Sr 2 IrO 4 , in contrary to the general expectations of broaden bandwidth with increasing dimensionality [7].…”

“…Since the Pv phase is metastable, it remains a challenge to obtain sizable bulk single crystals under HP conditions. However, Pv SrIrO 3 films and superlattices have been stabilized at ambient pressure via applying the epitaxial strain with various techniques, including the metalorganic chemical vapour deposition [9], pulsed laser deposition [45], and reactive oxide molecular-beam expitaxy [42]. As discussed below, given the tolerance factor t < 1, it is unusual for SrIrO 3 to adopt the 6H structure at ambient pressure.…”

“…The former is a rare stoichiometric oxide exhibiting non-Fermi-liquid behaviours near a ferromagnetic quantum critical point [11]. The latter was recently found to be an exotic narrow-band semimetal that may harvest many topological and magnetic insulating phases [10,41,42].…”

Wide gap Chern Mott insulating phases achieved by design

“…Interest in 5d ions on the honeycomb lattice has focused primarily on the Ir ion, 10,11,18,21 which is not a part of this study. We consider specifically the 3d→4d→5d sequence of ions; for d 4 Nonzero Chern numbers and corresponding gaps are in boldface, zero Chern numbers and corresponding gaps are in italic.…”

“…A number of model [6][7][8][9] and materialspecific studies [10][11][12][13][14][15][16] have probed the possibilities that such systems may offer. The advent of (111)-oriented growth of oxides [17][18][19][20][21][22][23][24][25] provides a new platform for design of new materials, and especially Chern insulators.…”