Anomalous transport near the Lifshitz transition at the LaAlO_3/SrTiO_3 interface

摘要

The two-dimensional electron liquid, at the (001) interface between band insulators LaAlO_3 and SrTiO_3, undergoes Lifshitz transition as the interface is doped with carriers. At a critical carrier density, two additional orbitals populate at the Fermi level, with a concomitant change in the Fermi surface topology. Using dynamical mean-field theory, formulated within a realistic three-orbital model, we study the influence of the Lifshitz transition and local electron correlations on the transport properties. We look at the thermal conductivity, optical conductivity, Seebeck coefficient, and angle-resolved photoemission spectra and find that at a critical density, both the thermal and dc conductivities rise sharply to higher values while the Seebeck coefficient shows a cusp. The interorbital electron-electron interaction transfers spectral weight near the Γ point towards lower energy, thereby reducing the critical density. In the presence of external magnetic field, the critical density further reduces due to exchange splitting. Beyond a sufficiently large field, multiple cusps appear in the Seebeck coefficient revealing multiple Lifshitz transitions.