LLow dimensionality, broken symmetry and easily-modulated carrier concentrations provoke novel electronic phase emergence at oxide interfaces. However, the spatial extent of such reconstructions-i.e. the interfacial "depth"-remains unclear. Examining LaAlO3/SrTiO3 heterostructures at previously unexplored carrier densities n2D≥ 6.9 × 1014 cm-2, we observe a Shubnikov-de Haas effect for small in-plane fields, characteristic of an anisotropic 3D Fermi surface with preferentialdxz,yz orbital occupancy extending over at least 100 nm perpendicular to the interface. Quantum oscillations from the 3D Fermi surface of bulk doped SrTiO3 emerge simultaneously at higher n2D. We distinguish three areas in doped perovskite heterostructures: narrow (<20 nm) 2D interfaces housing superconductivity and/or other emergent phases, electronically isotropic regions far (>120 nm) from the interface and new intermediate zones where interfacial proximity renormalises the electronic structure relative to the bulk.
Bibliographical noteFunding Information:
The authors gratefully acknowledge discussions with H. Hilgenkamp, A. Fujimori and I. Martin. This work was supported by the National Research Foundation, Singapore, through Grant NRF-CRP4-2008-04. The research at the University of Nebraska-Lincoln (UNL) was supported by the National Science Foundation through the Materials Research Science and Engineering Center (Grant No. DMR-0820521) and the Designing Materials to Revolutionize and Engineer our Future (DMREF) Program (Grant No. DMR-1234096). Computations were performed at the UNL Holland Computing Center and the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.
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