Interplay of Spin-Orbit Interactions, Dimensionality, and Octahedral Rotations in Semimetallic ${\mathbf{\text{SrIrO}}}_3$

We employ reactive molecular-beam epitaxy to synthesize the metastable perovskite ${\text{SrIrO}}_3$ and utilize in situ angle-resolved photoemission to reveal its electronic structure as an exotic narrow-band semimetal. We discover remarkably narrow bands which originate from a confluence of strong spin-orbit interactions, dimensionality, and both in- and out-of-plane ${\mathrm{IrO}}_6$ 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, ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$, illustrating the power of structure-property relations for manipulating the subtle balance between spin-orbit interactions and electron-electron interactions.

Figure 1

(a), (b) $E$ vs $k$ dispersions and isoenergy intensity maps of ${\text{SrIrO}}_3$ and ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ measured by ARPES at temperatures of 20 and 70 K, respectively. The isoenergy intensity maps are unsymmetrized, while the $E$ vs $k$ data have been symmetrized about $k_x=\pi /a$ for purposes of illustration. The white solid lines denote a quarter of the pseudocubic and tetragonal projected 2D Brillouin zones (2DBZs) for ${\text{SrIrO}}_3$ and ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$, respectively. (c), (d) Corresponding energy distribution curves (EDCs) along the high-symmetry directions of the 2DBZ, revealing sharp quasiparticle peaks and extremely narrow bandwidths in ${\text{SrIrO}}_3$, compared to the broader bandwidths and wider spectral features in ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$. (e) Longitudinal in-plane resistivity showing the metallic and insulating transport characteristics of ${\text{SrIrO}}_3$ and ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$, respectively. (f) The Hall resistivity of ${\text{SrIrO}}_3$ exhibits a large temperature dependence, consistent with the complex multiband electronic structure revealed by ARPES.

Figure 2

ARPES measurements of (a) two massive holelike bands at $(0,\pi )$, and (b) a light, almost linearly dispersive electron band at $(-\pi /2,\pi /2)$ along the cuts shown by red lines in the insets. In (a), the spectrum was measured at a temperature of 40 K and divided by the Fermi function to thermally populate states slightly above $E_F$. Lorentzian peak fits to (a) EDCs and (b) momentum distribution curves (MDCs) are shown as the symbols. (c)–(d) Simulated Fermi surfaces from the $\mathrm{LDA}+\mathrm{SOI}$ calculations, assuming an inner potential of 11 eV as discussed in the main text, reproduce the general features of the measured Fermi surfaces if spin-orbit interactions are included (c), but show substantial qualitative discrepancies if they are neglected (d). The dashed lines are guides to the eye, showing four-lobe shape pockets. More details in Supplemental Material, Fig. S3 [20]. (e) Simulated ARPES spectrum from the $\mathrm{LDA}+\mathrm{SOI}$ calculations show good qualitative agreement with experimental measurements (symbols).

Figure 3

Extracted band dispersions of ${\text{SrIrO}}_3$ (blue) and ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ (red) are determined by fitting both EDCs and MDCs in the raw data (circles) and estimated from peak positions in second derivative data (squares). The band dispersion of ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ is rigidly shifted in energy by 0.17 eV to align the top of the valence band with the Fermi level in ${\text{SrIrO}}_3$ for purposes of comparison.

Figure 4

(a) $\mathrm{LDA}+\mathrm{SOI}$ band structure, projected onto a $J_{\mathrm{eff}}=(1/2,3/2)$ basis, of ${\text{SrIrO}}_3$ for a perfect cubic structure, revealing broad bandwidths. (b) Including [001] octahedral rotations backfolds the bands in plane, but leads to only relatively minor changes in the degree of orbital mixing. (c) Additionally including [110] rotations, however, causes substantial further band folding along $k_z$, leading to the intersection of numerous bands of different orbital character. SOI opens hybridization gaps around the resulting band crossings, substantially narrowing the bandwidth, and leads to strong mixing of $J_{\mathrm{eff}}=(1/2,3/2)$ states. The calculations are shown along the $k$ paths (red) shown in inset. (d)–(f), Equivalent calculations of two-dimensional ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ show moderate band narrowing due to [001] rotations and only small changes due to additional artificial [110] rotations.