TILTING OF OXYGEN OCTAHEDRA IN SrTiO3 (001) SURFACE

FRANCISCO GONZALEZ PINTO; V. L. VILDOSOLA; RUBEN WEHT

BsAs

Workshop; LT27; 2014

p { margin-bottom: 0.08in; direction: ltr; color: rgb(0, 0, 0); font-family: "Arial",sans-serif; font-size: 11pt; font-style: normal; font-weight: normal; line-height: 115%; text-align: left; widows: 2; orphans: 2; text-decoration: none; page-break-before: auto; page-break-after: auto; } The discovery of a 2-dimensional electron gas (2DEG) at the interface between the two insulating perovskite oxides LaAlO_3 and SrTiO_3 [1] opened a spectrum of possibilities in exploiting its properties in the development of all-oxide devices. Recently, ARPES experiments revealed the presence of a 2DEG of similar characteristics at the vacuum-cleaved SrTiO_3 (001) surface[2,3]. Although these ARPES measurements[2] were performed at temperatures (10K - 20K) far below the temperature corresponding to the bulk SrTiO_3 structural phase transition from tetrahedral to cubic symmetry (110K), the Fermi surface maps observed for this system show a Brillouin zone consistent with the SrTiO_3 cubic structure. In this work, we analyze, by means of density functional theory (DFT), the angle of tilting around the z axis of the oxygen octahedra in SrTiO_3 stoichiometric. We observe a gradual reduction of the tilting angle with respect to the oxygen ions positions in the cubic structure as we move through the successive layers of the slab, from its centre to the surface. This reduction becomes more abrupt for the oxygen octahedron closest to the surface. This is in agreement with the common belief  that the 2DEG states are associated with the d orbitals of Titanium ions located at the surface.