Transport and excitations in a negative-U quantum dot at the LaAlO₃/SrTiO₃ interface

In a solid-state host, attractive electron-electron interactions can lead to the formation of local electron pairs which play an important role in the understanding of prominent phenomena such as high T _c superconductivity and the pseudogap phase. Recently, evidence of a paired ground state without superconductivity was demonstrated at the level of single electrons in quantum dots at the interface of LaAlO₃ and SrTiO₃. Here, we present a detailed study of the excitation spectrum and transport processes of a gate-defined LaAlO₃/SrTiO₃ quantum dot exhibiting pairing at low temperatures. For weak tunneling, the spectrum agrees with calculations based on the Anderson model with a negative effective charging energy U, and exhibits an energy gap corresponding to the Zeeman energy of the magnetic pair-breaking field. In contrast, for strong coupling, low-bias conductance is enhanced with a characteristic dependence on temperature, magnetic field and chemical potential consistent with the charge Kondo effect.Complex oxide devices provide a platform for studying and making use of strongly correlated electronic behavior. Here the authors present a LaAlO₃/SrTiO₃ quantum dot and show that its transport behavior is consistent with the presence of attractive electron interactions and the charge Kondo effect.