Orbital-Ordering-Induced Ferroelectricity inSrCrO3

Abstract

Using density functional theory calculations, ultrathin films of SrVO3(d1) and SrCrO3(d2) on SrTiO3 substrates have been studied as possible multiferroics. Although both are metallic in the bulk limit, they are found to be insulating as a result of orbital ordering driven by lattice distortions at the ultrathin limit. While the distortions in SrVO3 have a first-order Jahn-Teller origin, those in SrCrO3 are ferroelectric in nature. This route to ferroelectricity results in polarizations comparable with conventional ferroelectrics.

Surface polarization and edge charges

“…In contrast, our surface polarization P lies in-plane and is nonzero only when the symmetry of the terminating surface supports a nonzero in-plane vector, as for example on the (110) surface of GaAs. It can also arise from a spontaneous symmetrylowering surface reconstruction, as observed recently at the Pb 1−x Sn x Se (110) surface [6] and predicted for an ultrathin film of SrCrO 3 on SrTiO 3 substrate (001) [7]. The surface polarization will be most evident when the bulk P vanishes, as will be the case for the systems discussed below.…”

Coupled Nonpolar-Polar Metal-Insulator Transition in1∶1SrCrO3/SrTiO3<

“…It is correlated to a partial orbital ordering d 1 xy ,(d yz d xz ) 1 , where the d xy is nearly occupied while d yz and d xz orbitals are both half occupied [8,9]. For the single layer film of SCO epitaxially grown on SrTiO 3 , due to the missing apical oxygen of the CrO 5 octahedra at the surface, d yz and d xz orbitals become lower in energy than d xy , leading to a d 1 yz d 1 xz d 0 xy orbital ordering and an insulating state [11]. However, recently Zhou et al claimed that SCO is an insulator while the insulator-metal transition occurs under sufficient pressure [12], due to the bond instability found around 4 GPa, suggesting the strong interaction between structure and electronic structure.Layering a d-band perovskite oxide in a superlattice with a d 0 insulating perovskite will lead to large changes in the d-band states near the Fermi level, depending on the thickness of the d-band layer [13][14][15].…”

Data analysis method to achieve sub-10 pm spatial resolution using extended X-ray absorption fine-structure spectroscopy

“…However, sub-10 pm spatial resolution is required in many important fields of research, such as lattice distortion studies in colossal magnetic resistance (CMR) materials (Sen et al, 2010), high-temperature superconductivity materials (Saha et al, 2009), antiferromagnetic materials (de la Cruz et al, 2010) and multiferroic materials (Gupta et al, 2013). It is believed that the lattice distortion plays an important role in the special properties of these materials and a detailed structural analysis can help to better understand the physics of these materials.…”