Pseudogaps in SrTiO$_{3}$ Quantum Wells

A departure from Fermi liquid behavior appears in molecular beam epitaxy grown SrTiO$_{3}$ quantum wells embedded in the antiferromagnetic insulator SmTiO$_{3,\, }$suggesting proximity to a quantum critical point. We will report on the observation of pseudogap behavior in SmTiO$_{3}$/SrTiO$_{3}$/SmTiO$_{3}$ quantum wells via tunneling spectroscopy measurements. Tunnel junction devices with SrZrO$_{3}$ barriers grown in-situ were fabricated from quantum wells of varying thickness. The tunneling conductance spectra of these devices revealed the formation of a pseudogap in the density of states upon cooling, indicating the onset of non-Fermi liquid behavior. The pseudogap state was most pronounced in thin quantum wells, persisting up to nearly 200 K in the well containing only 2 SrO layers. The pseudogap was absent in the thickest wells, which showed only a small suppression of the density of states with a logarithmic dependence on bias resulting from disorder. The results are compared to tunneling spectra of GdTiO$_{3}$/SrTiO$_{3}$/GdTiO$_{3}$ quantum wells, providing insight into the role of structural distortion and octahedral tilts on the electronic structure and quantum critical behavior in oxide heterostructures.