Thursday, 19 September, 2013

Massive Symmetry Breaking in LaAlO₃/SrTiO₃(111) Quantum Wells: A Three-Orbital Strongly Correlated Generalization of Graphene

D. Doennig, W. Pickett, and R. Pentcheva -
Phys. Rev. Lett., Vol. 111 (12), 126804 (2013)

Density functional theory calculations with an on-site Coulomb repulsion term reveal competing ground states in (111)-oriented (LaAlO₃)_M/(SrTiO₃)_Nsuperlattices with n-type interfaces, ranging from spin, orbitally polarized (with selective e_g, a_1g, or d_xy occupation), Dirac point Fermi surface, to charge-ordered flat band phases. These phases are steered by the interplay of (i) Hubbard U, (ii) SrTiO₃ quantum well thickness, and (iii) crystal field splitting tied to in-plane strain. In the honeycomb lattice bilayer N=2 under tensile strain, inversion symmetry breaking drives the system from a ferromagnetic Dirac point (massless Weyl semimetal) to a charge-ordered multiferroic (ferromagnetic and ferroelectric) flat band massive (insulating) phase. With increasing SrTiO₃quantum well thickness an insulator-to-metal transition occurs.

Article on journal's website