Three-dimensional character of the Fermi surface in ultrathin LaTiO3/SrTiO3 heterostructures

${\mathrm{LaTiO}}₃$ films on ${\mathrm{SrTiO}}₃$ single crystal substrates exhibit metallic behavior attributed to the ${\mathrm{LaTiO}}₃$ film, the interface as well as part of the ${\mathrm{SrTiO}}₃$. In the limit of ultrathin ${\mathrm{LaTiO}}₃$ films on ${\mathrm{SrTiO}}₃$, the contribution to the metallicity from strain-induced electronic structure modification of the ${\mathrm{LaTiO}}₃$ film is minimized so that the dominant contribution to metallicity is from the interface and part of the ${\mathrm{SrTiO}}₃$ due to charge transfer of $3d$ electrons from ${\mathrm{LaTiO}}₃$ to ${\mathrm{SrTiO}}₃$. In such a limit, we observe quantum oscillations whose angular dependence indicates a three-dimensional Fermi surface. Such angular dependence is observed in two sets of quantum oscillations---one low frequency and one high frequency---that we have attributed to an inner and outer Fermi surface associated with a Rashba-like spin split hybridized ${d}_xz+yz$ band.