Abstract
The quasi-two-dimensional electronic gas at the (111) ${\mathrm{SrTiO}}_{3}$-based heterostructure interfaces is described by a multiband tight-binding model providing electronic bands in agreement at low energies with photoemission experiments. We analyze both the roles of the spin-orbit coupling and of the trigonal crystal-field effects. We point out the presence of a regime with sizable strain where the band structure exhibits a Dirac cone whose features are consistent with ab initio approaches. The combined effect of spin-orbit coupling and trigonal strain gives rise to nontrivial spin and orbital angular momenta patterns in the Brillouin zone and to quantum spin Hall effect by opening a gap at the Dirac cone. The system can switch from a conducting to a topological insulating state via modification of trigonal strain within a parameter range which is estimated to be experimentally achievable.
Highlights
The discovery [1] of a quasi-two-dimensional electronic gas (q2DEG) formed at the (001) interface between the SrTiO3 (STO) and LaAlO3 (LAO) grown on it gave rise to a very rich research field
Compared with Ref. [37], which obtained the same behavior with density functional theory (DFT) methodologies, we accurately discussed the role of spin-orbit coupling (SOC) and assessed the regime of the trigonal strain where a Dirac cone is expected
We showed the presence of nontrivial spin and orbital angular momentum patterns in the Brillouin zone (BZ), finding that in the presence of the trigonal distortion there can be a nonvanishing magnetic dipole moment between the two layers of Ti at a fixed k in the BZ
Summary
The discovery [1] of a quasi-two-dimensional electronic gas (q2DEG) formed at the (001) interface between the SrTiO3 (STO) and LaAlO3 (LAO) grown on it gave rise to a very rich research field. Compared to previous works which adopted TB methodologies, we emphasize the role of the strain at the interface and the atomic SOC in the band-structure properties Such an approach is useful to have a physical understanding of the mechanisms giving rise to the peculiar features of the system. The use of TB methodology allows an effective modeling of the band structure near the Dirac point, including the effects of the SOC with a small computational effort, opening up the way to study the transport properties and the topological invariants of this interface that can be very demanding for first-principles approaches.
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