Direct observation of the Dirac nodes lifting in semimetallic perovskite SrIrO3 thin films

Abstract

Perovskite SrIrO3 has long been proposed as an exotic semimetal induced by the interplay between the spin-orbit coupling and electron correlations. However, its low-lying electronic structure is still lacking. We synthesize high-quality perovskite SrIrO3 (100) films by means of oxide molecular beam epitaxy, and then systemically investigate their low energy electronic structure using in-situ angle-resolved photoemission spectroscopy. We find that the hole-like bands around R and the electron-like bands around U(T) intersect the Fermi level simultaneously, providing the direct evidence of the semimetallic ground state in this compound. Comparing with the density functional theory, we discover that the bandwidth of states near Fermi level is extremely small, and there exists a pronounced mixing between the Jeff = 1/2 and Jeff = 3/2 states. Moreover, our data reveal that the predicted Dirac degeneracy protected by the mirror-symmetry, which was theoretically suggested to be the key to realize the non-trivial topological properties, is actually lifted in perovskite SrIrO3 thin films. Our findings pose strong constraints on the current theoretical models for the 5d iridates.

Epitaxial growth and thermodynamic stability of SrIrO3/SrTiO3 heterostructures

“…film decreases slightly with decreasing temperature, and displays a small upturn at low temperature [13][14][15]21,22 . The small resistivity variation over the entire temperature range can be a signature of the semimetallic ground state reported in recent ARPES studies 17,18 . Interestingly, we observe a slight change of slope at T = 105 K, which is reproducible across different samples and thermal cycles and is most likely related to the structural transition of the STO substrate from cubic to tetragonal phase 28 .…”

“…This requires particular care due to the high volatility of iridium oxides and competition with other phases such as Sr 2 IrO 4 and Sr 3 Ir 2 O 7 10 . These extreme conditions can be avoided by resorting to thin film growth, where epitaxial constraint can be used to synthesize perovskite SrIrO 3 films 8,[11][12][13][14][15][16][17][18][19] . SrIrO 3 films are generally grown by pulsed laser deposition (PLD), where a relatively high oxygen pressure (0.01 -1 mbar) is required to control the Ir oxidation state 19 .…”

Symmetry demanded topological nodal-line materials

“…Orthorhombic perovskite iridates [66,67,76,139,[144][145][146][147][148][149][150][151]: AIrO 3 , where A is an alkaline-earth metal, is a class of orthorhombic perovskite iridates in space group Pbnm No. 62.…”

“…Zr(Hf)SiS, SrIrO 3 , and IrO 2 have nodal ring/ line protected by non-symmorphic symmetry that are robust against SOC [66,74,75]. SrIrO 3 , however, can gap out when magnetic ordering is included and is still being investigated [76]. All other DNLS reviewed here have nodal rings without SOC, however, including SOC turns them into Weyl semimetals or TIs.…”

Anisotropy and interaction effects of strongly strained SrIrO3 thin films

“…On GdScO 3 , which induces a small lattice extension, a recent study finds that strain may significantly alter the band structure of thin films, in particular opening a gap in place of the predicted symmetry-protected line nodes for SIO [15]. A similar opening was found, from band calculations and photoemission spectroscopy, for films on SrTiO 3 , which induces a large lattice compression [16]. Despite such an attention, it remains unclear how correlations in this semimetal actually affect the transport properties.…”