Electronic phase transitions under hydrostatic pressure in ${\mathrm{LaMnO}}_3$ (111) bilayers sandwiched between ${\mathrm{LaAlO}}_3$

Using ab initio calculations, we investigate the effect of hydrostatic pressure on the electronic structure of ${\mathrm{LaMnO}}_3$ (111) bilayers sandwiched between ${\mathrm{LaAlO}}_3$. In the ideal heterostructure we observe Dirac cones at the Fermi energy. However, octahedral tiltings open a band gap and thus destroy the Dirac nature. We show that the effect of the tiltings can be suppressed by hydrostatic pressure from 40 GPa to 60 GPa. At higher pressure further phase transitions are encountered.

Figure 1

(a) Structure at ambient pressure without (top) and with (bottom) octahedral tiltings. (b) Corresponding band structures. Red (solid) lines represent the superlattice without tiltings and green (dashed) lines that with tiltings. Only the spin-up bands are shown.

Figure 2

(a) Octahedral tilting and (b) Jahn-Teller distortion as functions of the hydrostatic pressure.

Figure 3

(a) Mn magnetic moment and (b) occupation of the $d_{3z^2-r^2}$ and $d_{x^2-y^2}$ orbitals as functions of the hydrostatic pressure. (c) Slice through the charge density of the Mn occupied bands showing an orbitally ordered pattern. Interactions are mediated by O, giving rise to a ferromagnetic coupling.

Figure 4

Band structure evolution with pressure. The green (solid) and blue (dashed) lines represent spin-up and spin-down, respectively.

Figure 5

Density of states. (a) 0 GPa without octahedral tilting, (b) 0 GPa with octahedral tilting, (c) 20 GPa, and (d) 40 GPa.