Electronic structure and optical properties of Sr₂IrO₄ under epitaxial strain

Abstract

We study the modification of the electronic structure in the strong spin-orbit coupled Sr 2 IrO 4 by epitaxial strain using density-functional methods. Structural optimization shows that strain changes the internal structural parameters such as the Ir-O-Ir bond angle, which has an important effect on the band structure. An interesting prediction is the Γ−X crossover of the valence band maximum with strain, while the conduction minimum at M remains unchanged. This in turn suggests strong strain dependence of the transport properties for the hole-doped system, but not when the system is electron doped. Taking the measured value of the Γ−X separation for the unstrained case, we predict the Γ−X crossover of the valence band maximum to occur for the tensile epitaxial strain e xx ≈3%. A minimal tight-binding model within the J eff =1/2 subspace is developed to describe the main features of the band structure. The optical absorption spectra under epitaxial strain are computed using densityfunctional theory, which explains the observed anisotropy in the optical spectra with the polarization of the incident light. We show that the optical transitions between the Ir (d) states, which are dipole forbidden, can be explained in terms of the admixture of Ir (p) orbitals with the Ir (d) bands.

Strain engineering of the charge and spin-orbital interactions in Sr 2 IrO 4

“…Namely, tensile (compressive) strain tends to increase (decrease) the Ir-O-Ir bond angle (26,27). However, to what extent this rotation would be "rigid" in Sr 2 IrO 4 is not clear, as a concomitant modulation of the Ir-O bond length is likely at play (28,30,50). In the following, we will first address the effect of strain on the isospin excitations and then discuss the evolution of the lowenergy band structure by analyzing the electron-hole pair excitations.…”

“…Namely, tensile (compressive) strain tends to increase (decrease) the Ir–O–Ir bond angle ( 26 , 27 ). However, to what extent this rotation would be “rigid” in Sr 2 IrO 4 is not clear, as a concomitant modulation of the Ir–O bond length is likely at play ( 28 , 30 , 50 ).…”

Stability of the antiferromagnetic state in the electron doped iridates

“…where H σ (k) = −σ∆ + h 11 h 12 h 12 σ∆ + h 11 (4) Figure 1. (color online) The square lattice, relevant for Sr 2 IrO 4 considered in the paper, with two different sublattices, A and B, marked in different colors denoting Ir atoms with two different pseudo-spins.…”

“…The NN, next NN, and third NN hoppings are also indicated. (color online) (a) Tight-binding band structure of SIO with the parameters (in eV): t 1 = -0.095, t 2 = 0.015, t 3 = 0.035, and U = 0.65, obtained by fitting to the density-functional bands [12]. The doped electrons form an electron pocket at the M point.…”

Spin-orbital entangled two-dimensional electron gas at the LaAlO3/Sr2IrO4 interface

“…This model has been successfully used to describe the band structure of bulk SIO. 27,28 With c † iα being the creation operator at site i (sublattice A or B) for the two |J eff , m states,…”