APERIODIC QUANTUM OSCILLATIONS IN THE TWO-DIMENSIONAL ELECTRON GAS AT THE LaAlO₃/SrTiO₃ INTERFACE

Walter Escoffier, Michel Goiran, LNCMI Toulouse and Km Rubi, HFML Nijmegen.

The discovery of a two-dimensional electron gas (2DEG) at the interface between the two insulators LaAlO₃ (LAO) and SrTiO₃ (STO) has not only enhanced the expectations of oxide-electronics but has also brought new and exciting opportunities to explore the novel physics of 2DEG with unmapped parameters. First principles calculations of the band structure reveal the occupancy of several non-degenerate sub-bands d_xy, d_xz, and d_yz, originating from crystal-field-split Ti 3d − t_2g orbitals; located at the interface or in its vicinity. The existence of many anisotropic and non-parabolic sub-bands, together with a large spin-orbit splitting at the crossing point of the d_xy and d_xz/yz bands, provides a complex band structure which has received only partial support from transport experiments. In this study, we investigated the transport properties of a high-mobility quasi-2DEG at this interface under high magnetic field (55 T) and provided new insights in its electronic band structure by analyzing the Shubnikovde Haas oscillations. Interestingly, the quantum oscillations are not periodic in 1/B and produce a highly non linear Landau plot (Landaulevel index versus 1/B). The aperiodic character of the oscillations entails the failure of standard Fourier-transformation data processing. Very low temperatures combined with high-field measurements are necessary to address the multi-band origin of the measured non 1/B-periodic oscillations. We explore several alternative scenarios, and in particular the generalized Onsager relation involving the magnetic response functions of the system. This study brings further evidence for a non-trivial band structure at the Fermi energy of this system, consistent with density-functional-theory calculations.

Figure: (a) Main panel: Inverse-field dependence of relative resistance oscillations, ΔR_xx, for zero gate voltage. Inset: Corresponding Landau plot. (b) Landau level plots (symbols) for various gate voltages together with fits derived from the generalized Onsager relation (solid lines). The dashed line represents the asymptote for zero gate voltage. The index N is given within an integer offset N‘.

Aperiodic quantum oscillations in the two-dimensional electron gas at the LaAlO₃/SrTiO₃ interface, K. Rubi, J. Gosteau, R. Serra, K. Han, S. Zeng, Z. Huang, B. Warot-Fonrose, R. Arras, E. Snoeck, Ariando, M. Goiran, and W. Escoffier, npj Quantum Mater. 5, 9 (2020).

DOI: https://arxiv.org/abs/1903.03038

Contact: walter.escoffier@lncmi.cnrs.fr