Tuning electronic structure via epitaxial strain in Sr2IrO4 thin films

Abstract

We have synthesized epitaxial Sr 2 IrO 4 thin-films on various substrates and studied their electronic structures as a function of lattice-strain. Under tensile (compressive) strain, increased (decreased) Ir-O-Ir bond-angle is expected to result in increased (decreased) electronic bandwidth. However, we have observed that the two optical absorption peaks near 0.5 eV and 1.0 eV are shifted to higher (lower) energies under tensile (compressive) strain, indicating that the electronic-correlation energy is also affected by in-plane lattice-strain. The effective tuning of electronic structures under lattice-modification provides an important insight into the physics driven by the coexisting strong spin-orbit coupling and electronic correlation. PACS: 71.70.Ej, 72.80.Sk, 81.15 In this letter, we report on the growth and optical properties of Sr 2 IrO 4 (SIO-214) thin films. The in-plane lattice mismatches between SIO-214 and various oxide substrates can exert both tensile (+) and compressive (-) strains to films, as shown in Fig. 1(a). We find that the electronic structure of SIO-214 films are effectively altered by lattice strain, and we observe 3 shifted optical transitions (absorptions) between the J eff = 1/2 lower Hubbard band (LHB) and the J eff = 1/2 upper Hubbard band (UHB), and between the J eff = 3/2 band and the J eff = 1/2 UHB band. Our observations strongly suggest that not only the electronic bandwidth, but also the magnitude of the effective electronic correlation energy (U eff ), can be manipulated by lattice strain. Our results demonstrate that epitaxial SIO-214 thin films can be used as a model system to study the physics of coexisting strong electron correlation and strong spin-orbit coupling under lattice modification.We have used a custom-built, pulsed laser deposition system equipped with in-situ Table I. The epitaxial growth conditions are found to be the following: an oxygen partial pressure (P O2 ) of 10 mTorr, a substrate temperature of 700 °C, and a laser (KrF excimer, λ = 248 nm) fluence of 1.2 J/cm 2 . Figure 2 shows θ-2θ X-ray diffraction scans of the samples discussed herein. Well-defined 00l-peaks are present due to the films' 00l-orientation along the perpendicular to the substrates. The full widths at half maximum in rocking-curve scans of the 00l peaks are all less than 0.05°, which confirms the high crystallinity of the films. Note that the thin films' 0012-peaks are shifted to low angles as the substrate lattice parameters decrease (from GSO to LAO). This behavior is consistent with the schematic diagrams in Fig. 1(b), since elongated (contracted) out-of-plane lattice parameters are expected as compressive (tensile) in-plane strain is exerted on thin films. 4Figure 3(a) shows X-ray reciprocal space maps, which reveal important information about both the in-plane and the out-of-plane lattice parameters of the SIO-214 thin films near the 332-reflection (103-reflection) of orthorhombic (pseudo-cubic) substrates. The 1118-peaks from the thin films are clearly observed, and are...

Noncollinear versus collinear description of the Ir-based one-t2g-hole perovskite-related compounds:SrIrO3andSr2Lado1, Pardo2 2015Phys. Rev. B12580View full textAdd to dashboardCite

“…22 and in disagreement with gap estimates as a function of strain in Ref. 21, that show the opposite trend. Figure 2 shows the results of our ab initio calculations for the evolution of the gap with strain for a particular U value (U= 3 eV).…”

Electronic structure and magnetic properties of iridate superlattice SrIrO3/SrTiO3

“…Note that the equilibrium in-plane lattice constant of Sr 2 IrO 4 is ∼3.88Å 11,24 . If we assume the IrO 6 octahedra are rigid (i.e., no change in the Ir-O bond lengths), it is natural to expect the enhancement (reduction) of the octahedral rotation for the compressive (tensile) strain.…”

Epitaxial Ba2IrO4 thin-films grown on SrTiO3 substrates by pulsed laser deposition

“…This behavior has also been observed in compressively strained SIO thin-films. 19 The rocking curve scan of the BIO (006) peak ( Fig. 1 (c)), whose full-width half-maximum (FWHM) is 0.07°, confirms the good crystallinity of the BIO thin-films.…”

“…4,5 However, superconductivity has not been observed in SIO samples even under various physical tuning parameters such as electrochemical doping, 23,26,27 hydrostatic pressure, 17 and lattice strain. 19 Our experimental observations on BIO thin-films suggest that BIO is a better candidate for intriguing transport properties such as unconventional superconductivity since its electronic structure is closer to the metal-insulator transition due to significantly reduced transport and optical gap energies.…”

“…This means the electronic bandwidth (W) is larger for BIO thin-films than for SIO thin-films. Although  and  occur at higher energies, the significantly larger W results in the optical gap energy, as estimated from the onset of the optical spectra, of BIO thin-films being smaller than not only SIO thin-films deposited on STO, but for bulk 24 and other thin-film 18,19 samples of SIO as well.…”