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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Sr2IrO4 by Materials Project

Sr2IrO4 is (La,Ba)CuO4 structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Sr2+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of Sr–O bond distances ranging from 2.44–2.80 Å. Ir4+ is bonded to six O2- atoms to form corner-sharing IrO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (1.98 Å) and two longer (2.08 Å) Ir–O bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to five equivalent Sr2+ and one Ir4+ atom to form distorted OSr5Ir octahedra that share corners with seventeen OSr5Ir octahedra, edges with eight equivalent OSr5Ir octahedra, and faces with four equivalent OSr4Ir2 octahedra. The corner-sharing octahedra tilt angles range from 0–56°. In the second O2- site, O2- is bonded to four equivalent Sr2+ and two equivalent Ir4+ atoms to form distorted OSr4Ir2 octahedra that share corners with fourteen OSr5Ir octahedra, edges with two equivalent OSr4Ir2 octahedra, and faces with eight OSr5Ir octahedra. The corner-sharing octahedra tilt angles range from 0–56°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr2IrO4 by Materials Project

Sr2IrO4 crystallizes in the tetragonal I4_1/acd space group. The structure is three-dimensional. Sr2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Sr–O bond distances ranging from 2.46–2.77 Å. Ir4+ is bonded to six O2- atoms to form corner-sharing IrO6 octahedra. The corner-sharing octahedral tilt angles are 27°. There are four shorter (2.01 Å) and two longer (2.09 Å) Ir–O bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Sr2+ and two equivalent Ir4+ atoms. In the second O2- site, O2- is bonded to five equivalent Sr2+ and one Ir4+ atom to form a mixture of edge and corner-sharing OSr5Ir octahedra. The corner-sharing octahedra tilt angles range from 0–5°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr2IrO4 by Materials Project

Sr2IrO4 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are sixteen inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded to six O2- atoms to form distorted SrO6 pentagonal pyramids that share a cornercorner with one OSr4O trigonal bipyramid and an edgeedge with one SrO7 pentagonal bipyramid. There are a spread of Sr–O bond distances ranging from 2.46–2.72 Å. In the second Sr2+ site, Sr2+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Sr–O bond distances ranging from 2.45–2.67 Å. In the third Sr2+ site, Sr2+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Sr–O bond distances ranging from 2.50–3.20 Å. In the fourth Sr2+ site, Sr2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Sr–O bond distances ranging from 2.44–2.97 Å. In the fifth Sr2+ site, Sr2+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Sr–O bond distances ranging from 2.41–2.85 Å. In the sixth Sr2+ site, Sr2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Sr–O bond distances ranging from 2.38–2.87 Å. In the seventh Sr2+ site, Sr2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Sr–O bond distances ranging from 2.41–2.82 Å. In the eighth Sr2+ site, Sr2+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Sr–O bond distances ranging from 2.43–3.09 Å. In the ninth Sr2+ site, Sr2+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Sr–O bond distances ranging from 2.41–3.07 Å. In the tenth Sr2+ site, Sr2+ is bonded to seven O2- atoms to form distorted SrO7 pentagonal bipyramids that share a cornercorner with one OSr4O trigonal bipyramid and an edgeedge with one SrO6 pentagonal pyramid. There are a spread of Sr–O bond distances ranging from 2.41–2.80 Å. In the eleventh Sr2+ site, Sr2+ is bonded in a 7-coordinate geometry to six O2- atoms. There are a spread of Sr–O bond distances ranging from 2.37–2.77 Å. In the twelfth Sr2+ site, Sr2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Sr–O bond distances ranging from 2.43–2.92 Å. In the thirteenth Sr2+ site, Sr2+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Sr–O bond distances ranging from 2.47–2.52 Å. In the fourteenth Sr2+ site, Sr2+ is bonded in a distorted pentagonal bipyramidal geometry to seven O2- atoms. There are a spread of Sr–O bond distances ranging from 2.39–2.80 Å. In the fifteenth Sr2+ site, Sr2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Sr–O bond distances ranging from 2.32–2.88 Å. In the sixteenth Sr2+ site, Sr2+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Sr–O bond distances ranging from 2.38–2.74 Å. There are eight inequivalent Ir4+ sites. In the first Ir4+ site, Ir4+ is bonded in a square co-planar geometry to four O2- atoms. There are a spread of Ir–O bond distances ranging from 1.83–2.02 Å. In the second Ir4+ site, Ir4+ is bonded in a T-shaped geometry to three O2- atoms. There are a spread of Ir–O bond distances ranging from 1.90–2.02 Å. In the third Ir4+ site, Ir4+ is bonded in a bent 120 degrees geometry to two O2- atoms. There is one shorter (1.86 Å) and one longer (1.92 Å) Ir–O bond length. In the fourth Ir4+ site, Ir4+ is bonded in a rectangular see-saw-like geometry to four O2- atoms. There are a spread of Ir–O bond distances ranging from 1.90–1.99 Å. In the fifth Ir4+ site, Ir4+ is bonded in a T-shaped geometry to three O2- atoms. There are a spread of Ir–O bond distances ranging from 1.89–2.08 Å. In the sixth Ir4+ site, Ir4+ is bonded in a T-shaped geometry to three O2- atoms. There are a spread of Ir–O bond distances ranging from 1.95–2.13 Å. In the seventh Ir4+ site, Ir4+ is bonded in a T-shaped geometry to three O2- atoms. There are a spread of Ir–O bond distances ranging from 1.81–2.00 Å. In the eighth Ir4+ site, Ir4+ is bonded in a bent 120 degrees geometry to two O2- atoms. There is one shorter (1.84 Å) and one longer (1.93 Å) Ir–O bond length. There are thirty-two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 5-coordinate geometry to three Sr2+ and two Ir4+ atoms. In the second O2- site, O2- is bonded in a 4-coordinate geometry to three Sr2+ and one O2- atom. The O–O bond length is 1.49 Å. In the third O2- site, O2- is bonded in a 4-coordinate geometry to three Sr2+ and one Ir4+ atom. In the fourth O2- site, O2- is bonded in a distorted linear geometry to one Sr2+ and two Ir4+ atoms. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to two Sr2+ and one Ir4+ atom. In the sixth O2- site, O2- is bonded to four Sr2+ atoms to form distorted OSr4 trigonal pyramids that share a cornercorner with one OSr4O trigonal bipyramid and an edgeedge with one OSr3Ir tetrahedra. In the seventh O2- site, O2- is bonded in a 5-coordinate geometry to four Sr2+ and one O2- atom. The O–O bond length is 1.51 Å. In the eighth O2- site, O2- is bonded to three Sr2+ and one Ir4+ atom to form distorted OSr3Ir trigonal pyramids that share a cornercorner with one OSr4O trigonal bipyramid, an edgeedge with one OSr3Ir tetrahedra, and an edgeedge with one OSr3Ir trigonal pyramid. In the ninth O2- site, O2- is bonded in a 4-coordinate geometry to three Sr2+ and one Ir4+ atom. In the tenth O2- site, O2- is bonded to three Sr2+ and one Ir4+ atom to form distorted OSr3Ir tetrahedra that share a cornercorner with one OSr3Ir tetrahedra, corners with two equivalent OSr4O trigonal bipyramids, and an edgeedge with one OSr4 trigonal pyramid. In the eleventh O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Sr2+ and one Ir4+ atom. In the twelfth O2- site, O2- is bonded in a 3-coordinate geometry to two Sr2+ and two Ir4+ atoms. In the thirteenth O2- site, O2- is bonded to three Sr2+ and one Ir4+ atom to form distorted OSr3Ir tetrahedra that share a cornercorner with one OSr3Ir tetrahedra, a cornercorner with one OSr4O trigonal bipyramid, a cornercorner with one OSr3Ir trigonal pyramid, and an edgeedge with one OSr3Ir trigonal pyramid. In the fourteenth O2- site, O2- is bonded in a 4-coordinate geometry to three Sr2+ and one O2- atom. In the fifteenth O2- site, O2- is bonded in a 4-coordinate geometry to three Sr2+ and one O2- atom. The O–O bond length is 1.50 Å. In the sixteenth O2- site, O2- is bonded in a 3-coordinate geometry to three Sr2+ and one Ir4+ atom. In the seventeenth O2- site, O2- is bonded in a 4-coordinate geometry to three Sr2+ and one O2- atom. In the eighteenth O2- site, O2- is bonded to four Sr2+ and one O2- atom to form distorted OSr4O trigonal bipyramids that share a cornercorner with one SrO7 pentagonal bipyramid, a cornercorner with one SrO6 pentagonal pyramid, corners with three OSr3Ir tetrahedra, and corners with three OSr3Ir trigonal pyramids. The O–O bond length is 1.51 Å. In the nineteenth O2- site, O2- is bonded in a 4-coordinate geometry to three Sr2+ and one O2- atom. The O–O bond length is 1.50 Å. In the twentieth O2- site, O2- is bonded in a 1-coordinate geometry to one Sr2+ and one Ir4+ atom. In the twenty-first O2- site, O2- is bonded in a 5-coordinate geometry to four Sr2+ and one O2- atom. In the twenty-second O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Sr2+ and one Ir4+ atom. In the twenty-third O2- site, O2- is bonded in a 5-coordinate geometry to four Sr2+ and one Ir4+ atom. In the twenty-fourth O2- site, O2- is bonded in a 5-coordinate geometry to five Sr2+ atoms. In the twenty-fifth O2- site, O2- is bonded in a 4-coordinate geometry to three Sr2+ and one Ir4+ atom. In the twenty-sixth O2- site, O2- is bonded in a 5-coordinate geometry to four Sr2+ and one O2- atom. In the twenty-seventh O2- site, O2- is bonded in a 1-coordinate geometry to two Sr2+ and one Ir4+ atom. In the twenty-eighth O2- site, O2- is bonded in a 4-coordinate geometry to two Sr2+ and two Ir4+ atoms. In the twenty-ninth O2- site, O2- is bonded in a 3-coordinate geometry to two Sr2+ and one Ir4+ atom. In the thirtieth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Sr2+ and one O2- atom. In the thirty-first O2- site, O2- is bonded to three Sr2+ and one Ir4+ atom to form OSr3Ir trigonal pyramids that share a cornercorner with one OSr3Ir tetrahedra, a cornercorner with one OSr4O trigonal bipyramid, and an edgeedge with one OSr3Ir trigonal pyramid. In the thirty-second O2- site, O2- is bonded in a 4-coordinate geometry to three Sr2+ and one Ir4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Strain engineering of the charge and spin-orbital interactions in Sr2IrO4

In the high spin–orbit-coupled Sr 2 IrO 4 , the high sensitivity of the ground state to the details of the local lattice structure shows a large potential for the manipulation of the functional properties by inducing local lattice distortions. We use epitaxial strain to modify the Ir–O bond geometry in Sr 2 IrO 4 and perform momentum-dependent resonant inelastic X-ray scattering (RIXS) at the metal and at the ligand sites to unveil the response of the low-energy elementary excitations. Furthermore, we observe that the pseudospin-wave dispersion for tensile-strained Sr 2 IrO 4 films displays large softening along the [h,0] direction, while along the [h,h] direction it shows hardening. This evolution reveals a renormalization of the magnetic interactions caused by a strain-driven cross-over from anisotropic to isotropic interactions between the magnetic moments. Moreover, we detect dispersive electron–hole pair excitations which shift to lower (higher) energies upon compressive (tensile) strain, manifesting a reduction (increase) in the size of the charge gap. This behavior shows an intimate coupling between charge excitations and lattice distortions in Sr 2 IrO 4 , originating from the modified hopping elements between the t 2g orbitals. Our work highlights the central role played by the lattice degrees of freedom in determining both the pseudospin and charge excitations of Sr 2 IrO 4 and provides valuable information toward the control of the ground state of complex oxides in the presence of high spin–orbit coupling.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Pseudospin-lattice coupling and electric control of the square-lattice iridate Sr2IrO4

Sr 2 IrO 4 is an archetypal spin-orbit-coupled Mott insulator and has been extensively studied in part because of a wide range of predicted states. Limited experimental characterization of these states thus far brings to light the extraordinary susceptibility of the physical properties to the lattice, particularly, the Ir-O-Ir bond angle. Here, we report a microscopic rotation of the IrO 6 octahedra below 50 K measured by single crystal neutron diffraction. Overall, this sharp lattice anomaly provides keys to understanding the anomalous low-temperature physics and a direct confirmation of a crucial role that the Ir-O-Ir bond angle plays in determining the ground state. Indeed, as also demonstrated in this study, applied electric current readily weakens the antiferromagnetic order via the straightening of the Ir-O-Ir bond angle, highlighting that even slight change in the local structure can disproportionately affect the physical properties in the spin-orbit-coupled system.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Emergent interlayer magnetic order via strain-induced orthorhombic distortion in the 5 d Mott insulator Sr 2 IrO 4

In this letter, we report a La 2 CuO 4 -like interlayer antiferromagnetic order in Sr2IrO4 films with large orthorhombic distortion (>1.5%). The biaxial lattice strain in epitaxial heterostructures of Sr 2 IrO 4 /Ca 3 Ru 2 O 7 lowers the crystal symmetry of Sr 2 IrO 4 from tetragonal ($C_4$) to orthorhombic ($C_2$), guiding the Ir $5d J_{text{eff}}$ = 1/2 pseudospin moment parallel to the elongated b axis via magnetic anisotropy. From resonant x-ray scattering experiments, we observed an antiferromagnetic order in the orthorhombic Sr 2 IrO 4 film whose interlayer stacking pattern is inverted from that of the tetragonal Sr 2 IrO 4 crystal. This interlayer stacking is similar to that of the orthorhombic La 2 CuO 4 , implying that the asymmetric interlayer exchange interactions between $\textit{a}$ and $\textit{b}$ directions exceed the anisotropic interlayer pseudodipolar interaction. Our result suggests that strain-induced distortion can provide a delicate knob for tuning the long-range magnetic order in quasi-two-dimensional systems by evoking the competition between the interlayer exchange coupling and the pseudodipolar interaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗