Danfeng Li

Tunable conductivity threshold at polar oxide interfaces

The physical mechanisms responsible for the formation of a two-dimensional electron gas at the interface between insulating SrTiO(3) and LaAlO(3) have remained a contentious subject since its discovery in 2004. Opinion is divided between an intrinsic mechanism involving the build-up of an internal electric potential due to the polar discontinuity at the interface between SrTiO(3) and LaAlO(3), and extrinsic mechanisms attributed to structural imperfections. Here we show that interface conductivity is also exhibited when the LaAlO(3) layer is diluted with SrTiO(3), and that the threshold thickness required to show conductivity scales inversely with the fraction of LaAlO(3) in this solid solution, and thereby also with the layers formal polarization. These results can be best described in terms of the intrinsic polar-catastrophe model, hence providing the most compelling evidence, to date, in favour of this mechanism.

Giant oscillating thermopower at oxide interfaces

Understanding the nature of charge carriers at the LaAlO3/SrTiO3 interface is one of the major open issues in the full comprehension of the charge confinement phenomenon in oxide heterostructures. Here, we investigate thermopower to study the electronic structure in LaAlO3/SrTiO3 at low temperature as a function of gate field. In particular, under large negative gate voltage, corresponding to the strongly depleted charge density regime, thermopower displays high negative values of the order of 104–105μVK−1, oscillating at regular intervals as a function of the gate voltage. The huge thermopower magnitude can be attributed to the phonon-drag contribution, while the oscillations map the progressive depletion and the Fermi level descent across a dense array of localized states lying at the bottom of the Ti 3d conduction band. This study provides direct evidence of a localized Anderson tail in the two-dimensional electron liquid at the LaAlO3/SrTiO3 interface.

Growth-induced electron mobility enhancement at the LaAlO3/SrTiO3 interface

We have studied the electronic properties of the 2D electron liquid present at the LaAlO3/SrTiO3 interface in series of samples prepared at different growth temperatures. We observe that interfaces fabricated at 650 °C exhibit the highest low temperature mobility ( ≈10 000 cm2 V−1 s−1) and the lowest sheet carrier density ( ≈5×1012 cm−2). These samples show metallic behavior and Shubnikov-de Haas oscillations in their magnetoresistance. Samples grown at higher temperatures (800–900 °C) display carrier densities in the range of ≈2−5×1013 cm−2 and mobilities of ≈1000 cm2 V−1 s−1 at 4 K. Reducing their carrier density by field effect to 8×1012 cm−2 lowers their mobilities to ≈50 cm2 V−1 s−1 bringing the conductance to the weak-localization regime.

Large modulation of the Shubnikov?de Haas oscillations by the Rashba interaction at the LaAlO3/SrTiO3 interface

We investigate the two-dimensional Fermi surface of high-mobility LaAlO3/SrTiO3 interfaces using Shubnikov-de Haas oscillations. Our analysis of the oscillation pattern underscores the key role played by the Rashba spin–orbit interaction brought about by the breaking of inversion symmetry, as well as the dominant contribution of the heavy dxz/dyz orbitals on electrical transport. We furthermore bring into light the complex evolution of the oscillations with the carrier density, which is tuned by the field effect.

Weak localization and spin-orbit interaction in side-gate field effect devices at the LaAlO 3 /SrTiO 3 interface

Using field effect devices with side gates, we modulate the 2-dimensional electron gas hosted at the LaAlO3/SrTiO3 interface to study the temperature and doping evolution of the magnetotransport. The analysis of the data reveals different transport regimes depending on the interplay between the different (elastic, inelastic, and spin-orbit) scattering times and their temperature dependencies. We find that the spin-orbit interaction strongly affects the low-temperature transport in the normal state in a very large region of the phase diagram, extending beyond the superconducting dome.

Fabricating superconducting interfaces between artificially grown LaAlO3 and SrTiO3 thin films

Realization of a fully metallic two-dimensional electron gas at the interface between artificially-grown LaAlO

Large phonon-drag enhancement induced by narrow quantum confinement at the LaAlO3/SrTiO3 interface

_3

Magneto-transport study of top- and back-gated LaAlO3/SrTiO3 heterostructures

and SrTiO

Characterization of atomic force microscopy written conducting nanowires at LaAlO3/SrTiO3 interfaces

_3

Probing Quantum Confinement and Electronic Structure at Polar Oxide Interfaces

thin films has been an exciting challenge. Here we present for the first time the successful realization of a superconducting 2DEG at interfaces between artificially-grown LaAlO