Electronic Reconstruction in (LaVO₃)_m/SrVO₃ (_m = 5, 6) Superlattices

Abstract

ferromagnetic (AFM) to a paramagnetic state. [13] In contrast, bulk SrVO 3 is a paramagnetic metal with cubic symmetry. [14] The electronic configurations of the V ions in LaVO 3 and SrVO 3 , respectively, are 3d 2 (V 3+ ) and 3d 1 (V 4+ ). It has been found that the solid solution La 1-x Sr x VO 3 , containing mixed V 3+ and V 4+ states, shows a non-Fermi liquid behavior up to very high temperatures and is subject to an insulator-to-metal transition under hole doping. [15,16] Appearance of both V 3+ and V 4+ states at the interfaces of (LaVO 3 ) 6 /(SrVO 3 ) 3 superlattices has been reported in ref.[10] without identifying a specific spatial pattern. In addition, it is known that the magnetization in (LaVO 3 ) m /SrVO 3 superlattices depends on the thickness of the LaVO 3 layer, with m = 4, 6 yielding larger saturation magnetization than m = 3, 5. [6] The fact that in the latter case the saturation magnetization does not exceed the threshold of the substrate impurities indicates that there is no macroscopic magnetization. The mechanism responsible for the deviating behaviors of superlattices with odd and even thicknesses is not fully understood so far. While it could be a pure strong correlation effect, [17] results on the bulk compounds indicate that strain introduced into the superlattices by the substrate may also influence the magnetic behavior (as well as other physical properties). [18] Distortions in vanadate superlattices generated by charge disproportionation into V 3+ and V 4+ ions have the potential to result in ferroelectricity [19] and distortions of the VO 6 octahedra can have complex effects on the orbital occupations. [20] Based on these considerations, we will study in the present work (LaVO 3 ) m /SrVO 3 superlattices by numerical calculations within density functional theory, using experimental lattice parameters. Our considerations will focus on the cases m = 5 and 6, as examples for superlattices with odd and even thicknesses. We will establish the magnetic ground state, provide detailed insight into the electronic reconstruction (in particular with respect to the V ions at the interfaces of the superlattices), and explain the observed m-dependence of the electronic and magnetic properties. MethodologySpin-polarized first-principles calculations are performed employing the projector augmented wave method of the Vienna The (LaV 3+ O 3 ) m /SrV 4+ O 3 (m = 5, 6) superlattices are investigated by first principles calculations. While bulk LaVO 3 is a C-type antiferromagnetic semiconductor and bulk SrVO 3 is a paramagnetic metal, semiconducting A-type antiferromagnetic states for both superlattices are found due to epitaxial strain. At the interfaces, however, the V spins couple antiferromagnetically for m = 5 and ferromagnetically for m = 6 (m-dependence of the magnetization). Electronic reconstruction in form of charge ordering is predicted to occur with V 3+ and V 4+ states arranged in a checkerboard pattern on both sides of the SrO layer. As compared to bulk LaVO 3 , the presence of V 4+ ions...

(LaCrO3)m/SrCrO3 superlattices as transparent p-type semiconductors with finite magnetization

“…It is remarkable that the results in Table 1 are comparable to previous reports on the appearance of short (1.84 Å for m = 5 and 1.83 Å for m = 6) and long (2.04 Å for m = 5 and 2.03 Å for m = 6) out-of-plane V–O bonds at the interface of the (LaVO 3 ) m /SrVO 3 superlattice (combined with V–O–V bond angles of 163° for m = 5 and 172° for m = 6, decreasing to the bulk value of LaVO 3 , 157°, as one moves away from the interface). 26…”

“…Notably, in the case of the (LaVO 3 ) 5 /SrVO 3 superlattice the same orbitals give rise to localized in-gap states, however, located about 0.8 eV above the valence band edge. 26…”

“…In the case of the (LaVO 3 ) 6 /SrVO 3 superlattice localized in-gap states, due to the same orbitals, appear about 0.7 eV above the valence band edge. 26…”

“…The analysis of the magnetic coupling between these ions points to strong electronic correlations and reveals an even-odd m -dependence of the magnetization, 25 in agreement with theoretical results for m = 5 and 6. 26…”

Effects of oxygen vacancies on the electronic structure of the (LaVO3)6/SrVO3 superlattice: a computational study

“…The key for understanding the experimental situation may be the observation of simultaneous appearance of both V 3+ ions (as in bulk LaVO 3 ) and V 4+ ions (as in bulk SrVO 3 ) at the interface of the (LaVO 3 ) 6 /(SrVO 3 ) 3 superlattice in [22]. Under the assumption that there are no O vacancies, first principles calculations show that these V 3+ and V 4+ ions form a checkerboard pattern adjacent to the SrO layer [23]. However, in a real sample, O vacancies are inevitable during the growth process [24], which may affect the electronic reconstruction of the V ions and, thus, the properties of the superlattice.…”