Spectroscopic evidence for competing reconstructions in polar multilayers LaAlO3/LaVO3/LaAlO3

Phys Rev Lett. 2009 Jun 12;102(23):236401. doi: 10.1103/PhysRevLett.102.236401. Epub 2009 Jun 10.

Abstract

We have studied the valence redistribution of V in LaAlO(3)/LaVO(3)/LaAlO(3) trilayers, which are composed of only polar layers grown on SrTiO3 (001) substrates, by core-level photoemission spectroscopy. We have found that the V valence is intermediate between V3+ and V4+ for thin LaAlO3 cap layers, decreases with increasing cap-layer thickness, and finally recovers the bulk value of V3+ at approximately 10 unit-cell thickness. In order to interpret these results, we propose that the atomic reconstruction of the polar LaAlO3 surface competes with the purely electronic V valence change so that the polar catastrophe is avoided at the cost of minimum energy.