Dimensionality-Driven Metal-Insulator Transition in Spin-Orbit-Coupled ${\mathrm{SrIrO}}_{3}$

Dimensionality-Driven Metal-Insulator Transition in Spin-Orbit-Coupled ${SrIrO}_{3}$

P. Schütz, D. Di Sante, L. Dudy, J. Gabel, M. Stübinger, M. Kamp, Y. Huang, M. Capone, M.-A. Husanu, V. N. Strocov, G. Sangiovanni, M. Sing, and R. Claessen

Phys. Rev. Lett. 119, 256404 – Published 22 December 2017

Abstract

Upon reduction of the film thickness we observe a metal-insulator transition in epitaxially stabilized, spin-orbit-coupled ${SrIrO}_{3}$ ultrathin films. By comparison of the experimental electronic dispersions with density functional theory at various levels of complexity we identify the leading microscopic mechanisms, i.e., a dimensionality-induced readjustment of octahedral rotations, magnetism, and electronic correlations. The astonishing resemblance of the band structure in the two-dimensional limit to that of bulk ${Sr}_{2} {IrO}_{4}$ opens new avenues to unconventional superconductivity by “clean” electron doping through electric field gating.

Received 29 June 2017

DOI:https://doi.org/10.1103/PhysRevLett.119.256404

Physics Subject Headings (PhySH)

Band gap Metal-insulator transition

Iridates

Angle-resolved photoemission spectroscopy Density functional theory

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

P. Schütz¹, D. Di Sante², L. Dudy¹, J. Gabel¹, M. Stübinger¹, M. Kamp¹, Y. Huang³, M. Capone⁴, M.-A. Husanu^5,6, V. N. Strocov⁶, G. Sangiovanni², M. Sing¹, and R. Claessen¹

¹Physikalisches Institut and Röntgen Center for Complex Material Systems (RCCM), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
²Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
³Van der Waals—Zeeman Insitute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
⁴CNR-IOM-Democritos National Simulation Centre and International School for Advanced Studies (SISSA), Via Bonomea 265, I-34136 Trieste, Italy
⁵National Institute of Materials Physics, Atomistilor 405 A, 077125 Magurele, Romania
⁶Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen, Switzerland

Spin-Orbit Semimetal ${SrIrO}_{3}$ in the Two-Dimensional Limit

D. J. Groenendijk, C. Autieri, J. Girovsky, M. Carmen Martinez-Velarte, N. Manca, G. Mattoni, A. M. R. V. L. Monteiro, N. Gauquelin, J. Verbeeck, A. F. Otte, M. Gabay, S. Picozzi, and A. D. Caviglia

Phys. Rev. Lett. 119, 256403 (2017)

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Vol. 119, Iss. 25 — 22 December 2017

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Figure 1
(a) Real and (b) reciprocal space structure of strained, tetragonal ${SrIrO}_{3}$ without octahedral rotations [34]. (c),(d) $E$ vs $k$ dispersions along the high-symmetry lines $Γ - X - M - Γ$ and $Z - R - A - Z$ measured by SX ARPES ( $h ν = 745 eV$ and $h ν = 660 eV$ , respectively) and compared to $DFT + U$ calculations. The band structure was calculated for the tetragonal setting and projected onto a $J_{eff} = (1 / 2, 3 / 2)$ basis with (c) $U = 0$ and $J = 0 eV$ and (d) $U = 3.4$ and $J = 0.4 eV$ . The introduction of a sizable on-site Coulomb repulsion significantly enhances the agreement between theory and experimental results. (e),(f) Fermi surface topology without (e) and with (f) on-site Coulomb repulsion $U$ and exchange coupling $J$ .
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Figure 2
(a) Real-space lattice structure of ${SrIrO}_{3}$ including octahedral rotations ( $a^{+} b^{-} b^{-}$ in Glazer notation with the $a$ axis orthogonal to the film surface normal) and strain. The orthorhombic unit cell (blue) is enlarged by $2 \times \sqrt{2} \times \sqrt{2}$ with respect to the tetragonal unit cell (black). (b) Reciprocal space structure of the orthorhombic (blue) and tetragonal (black) structure. (c) SX-ARPES band maps along the pseudotetragonal high-symmetry lines $Γ - X - M - Γ$ and $Z - R - A - Z$ in comparison to $DFT + U$ band structure calculated in the orthorhombic setting and unfolded into the tetragonal Brillouin zone.
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Figure 3
(a) Ultraviolet photoelectron spectroscopy (UPS) of ${SrIrO}_{3}$ films with thickness $m$ (bare $Nb : SrTi O_{3}$ , $m = 1, 2, 3, 4 u . c .$ ) exhibiting the opening of a charge gap between 3 and 4 u.c. Inset: DOS from $DFT + U$ slab calculations of $m$ ${SrIrO}_{3}$ layers on 4 ${SrTiO}_{3}$ layers ( $m ⫽ 4$ ). (b) LEED and RHEED patterns of an insulating ( $m = 3$ ) and a metallic ( $m = 4$ ) ${SrIrO}_{3}$ film exhibit a structural transition from a $\sqrt{2} \times \sqrt{2}$ to a $2 \times 2$ surface periodicity across the MIT. (c) Structural model explaining the observed changes as result of suppressed in-plane octahedral rotations in thin films ( $a^{0} a^{0} b^{+ / -}$ ) as opposed to the bulk rotational pattern ( $a^{+} b^{-} b^{-}$ ) observed in thick films.
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Figure 4
(a) SX-ARPES band map of a ${SrIrO}_{3}$ monolayer grown on $Nb : SrTi O_{3}$ and $DFT + U$ band structure of a $1 ⫽ 4$ ${SrIrO}_{3} ⫽ SrTi O_{3}$ slab along the pseudotetragonal high-symmetry line $Γ - X - M - Γ$ . (b) $DFT + U$ $k$ -integrated density of states (DOS) of the $1 ⫽ 4$ slab. The antiferromagnetic solution exhibits a charge gap of $\approx 1 eV$ , while the nonmagnetic solution is in a metallic state. (c) $DFT + U$ band structure calculation for bulk ${Sr}_{2} {IrO}_{4}$ .
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Physical Review Letters

Dimensionality-Driven Metal-Insulator Transition in Spin-Orbit-Coupled ${SrIrO}_{3}$

P. Schütz, D. Di Sante, L. Dudy, J. Gabel, M. Stübinger, M. Kamp, Y. Huang, M. Capone, M.-A. Husanu, V. N. Strocov, G. Sangiovanni, M. Sing, and R. Claessen

Phys. Rev. Lett. 119, 256404 – Published 22 December 2017

Abstract

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Spin-Orbit Semimetal ${SrIrO}_{3}$ in the Two-Dimensional Limit

D. J. Groenendijk, C. Autieri, J. Girovsky, M. Carmen Martinez-Velarte, N. Manca, G. Mattoni, A. M. R. V. L. Monteiro, N. Gauquelin, J. Verbeeck, A. F. Otte, M. Gabay, S. Picozzi, and A. D. Caviglia

Phys. Rev. Lett. 119, 256403 (2017)

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Physical Review Letters

Dimensionality-Driven Metal-Insulator Transition in Spin-Orbit-Coupled SrIrO3

P. Schütz, D. Di Sante, L. Dudy, J. Gabel, M. Stübinger, M. Kamp, Y. Huang, M. Capone, M.-A. Husanu, V. N. Strocov, G. Sangiovanni, M. Sing, and R. Claessen

Phys. Rev. Lett. 119, 256404 – Published 22 December 2017

Abstract

Physics Subject Headings (PhySH)

Authors & Affiliations

See Also

Spin-Orbit Semimetal SrIrO3 in the Two-Dimensional Limit

D. J. Groenendijk, C. Autieri, J. Girovsky, M. Carmen Martinez-Velarte, N. Manca, G. Mattoni, A. M. R. V. L. Monteiro, N. Gauquelin, J. Verbeeck, A. F. Otte, M. Gabay, S. Picozzi, and A. D. Caviglia

Phys. Rev. Lett. 119, 256403 (2017)

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Dimensionality-Driven Metal-Insulator Transition in Spin-Orbit-Coupled ${SrIrO}_{3}$

Spin-Orbit Semimetal ${SrIrO}_{3}$ in the Two-Dimensional Limit