Strain-Modulated Slater-Mott Crossover of Pseudospin-Half Square-Lattice in $({\mathrm{SrIrO}}_{3}{)}_{1}/({\mathrm{SrTiO}}_{3}{)}_{1}$ Superlattices

Strain-Modulated Slater-Mott Crossover of Pseudospin-Half Square-Lattice in $({SrIrO}_{3})_{1} / ({SrTiO}_{3})_{1}$ Superlattices

Junyi Yang, Lin Hao, Derek Meyers, Tamene Dasa, Liubin Xu, Lukas Horak, Padraic Shafer, Elke Arenholz, Gilberto Fabbris, Yongseong Choi, Daniel Haskel, Jenia Karapetrova, Jong-Woo Kim, Philip J. Ryan, Haixuan Xu, Cristian D. Batista, Mark P. M. Dean, and Jian Liu

Phys. Rev. Lett. 124, 177601 – Published 29 April 2020

Abstract

We report on the epitaxial strain-driven electronic and antiferromagnetic modulations of a pseudospin-half square-lattice realized in superlattices of $({SrIrO}_{3})_{1} / ({SrTiO}_{3})_{1}$ . With increasing compressive strain, we find the low-temperature insulating behavior to be strongly suppressed with a corresponding systematic reduction of both the Néel temperature and the staggered moment. However, despite such a suppression, the system remains weakly insulating above the Néel transition. The emergence of metallicity is observed under large compressive strain but only at temperatures far above the Néel transition. These behaviors are characteristics of the Slater-Mott crossover regime, providing a unique experimental model system of the spin-half Hubbard Hamiltonian with a tunable intermediate coupling strength.

Received 16 October 2019
Accepted 3 April 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.177601

Physics Subject Headings (PhySH)

Iridates Thin films Two-dimensional electron system

Resonant elastic x-ray scattering X-ray absorption near-edge spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Junyi Yang ^1,*, Lin Hao ^1,†, Derek Meyers^2,§, Tamene Dasa³, Liubin Xu³, Lukas Horak⁴, Padraic Shafer⁵, Elke Arenholz^5,6, Gilberto Fabbris ⁷, Yongseong Choi ⁷, Daniel Haskel⁷, Jenia Karapetrova⁷, Jong-Woo Kim⁷, Philip J. Ryan⁷, Haixuan Xu³, Cristian D. Batista¹, Mark P. M. Dean ², and Jian Liu ^1,‡

¹Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA
²Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973, USA
³Department of Material Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA
⁴Department of Condensed Matter Physics, Charles University, Ke Karlovu 5, 121 16 Prague, Czech Republic
⁵Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
⁶Department of Materials Science & Engineering, University of California, Berkeley, California 94720, USA
⁷Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, 60439, USA

^*Corresponding author. jyang43@vols.utk.edu
^†Corresponding author. lhao3@utk.edu
^‡Corresponding author. jianliu@utk.edu
^§Present address: Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078, USA.

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Vol. 124, Iss. 17 — 1 May 2020

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Figure 1
(a) A schematic of the $({SrIrO}_{3})_{1} / ({SrTiO}_{3})_{1}$ superlattice grown on a substrate with compressive epitaxial strain. Because of the in-plane compression, the lattice structure is elongated along the out-of-plane [001] direction. The black arrow denotes the spin. Bottom panel shows the top view of the square lattice of ${IrO}_{6}$ octahedra. Rotation around the $c$ axis causes a $\sqrt 2 \times \sqrt 2$ cell expansion of the square lattice. (b)–(d) XRD patterns along the (0 0 $L$ ) direction for SLs grown on STO, LSAT, and NGO, respectively. The supercell $a \times a \times 2 c$ ( $a$ and $c$ are pseudocubic in-plane and out-of-plane lattice parameters, respectively) is used for the notation. The blue, green, and red dashed lines represent the (0 0 4) film peak position of SL-NGO, SL-LSAT, and SL-STO, respectively. (e)–(g) Reciprocal space mappings around the film (106) or (116) reflection of SL-STO, SL-LSAT, and SL-NGO. The same in-plane $Q$ vectors of the SLs and the corresponding substrates demonstrates that all the SLs are fully strained within the experimental resolution.
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Figure 2
(a) Temperature dependent resistivity of SL-STO (red circles), SL-LSAT (green diamonds) and SL-NGO (blue triangles). The inset shows an enlarged view of the highlighted portion (dashed box) of the resistivity curve for the SL-NGO. (b) Temperature dependence of the normalized (0.5 0.5 2) magnetic peak intensity of SL-STO, SL-LSAT, and SL-NGO. The superlattice cell $a \times a \times 2 c$ was used to define the reciprocal space. (c) The evolution of staggered moment and resistivity increases are plotted against the Néel temperature $T_{N}$ . (d) A summary diagram of the phase evolution of the SL with respect to temperature and in-plane lattice constant. The green region denotes antiferromagnetic (AFM) insulating state with the green dashed line being the phase boundary, while the white and red regions represent nonmagnetic (NM) insulating and metallic states, respectively.
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Figure 3
Schematic diagram of linearly dependent XAS measurement at O $K$ edge. (a) Out-of-plane channel. (b),(c) In-plane channel. (d) Polarization dependent O $K$ edge x-ray absorption (XAS) spectra of SL-STO (red), SL-LSAT (green), and SL-NGO (blue). The solid (dashed) line denotes XAS from out-of-plane (in-plane) measurement. The absorption is shifted vertically for clarity. (e) X-ray linear dichroism extracted from (d). Density of states (DOS) of the planar oxygen ions (f) and apical oxygen ions (g). (h) The projected DOS difference (PDOS Diff.) extracted from (f) and (g).
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Physical Review Letters

Strain-Modulated Slater-Mott Crossover of Pseudospin-Half Square-Lattice in (SrIrO3)1/(SrTiO3)1 Superlattices

Junyi Yang, Lin Hao, Derek Meyers, Tamene Dasa, Liubin Xu, Lukas Horak, Padraic Shafer, Elke Arenholz, Gilberto Fabbris, Yongseong Choi, Daniel Haskel, Jenia Karapetrova, Jong-Woo Kim, Philip J. Ryan, Haixuan Xu, Cristian D. Batista, Mark P. M. Dean, and Jian Liu

Phys. Rev. Lett. 124, 177601 – Published 29 April 2020

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Strain-Modulated Slater-Mott Crossover of Pseudospin-Half Square-Lattice in $({SrIrO}_{3})_{1} / ({SrTiO}_{3})_{1}$ Superlattices