Electronic reconstruction and surface two-dimensional electron gas in a polarized heterostructure with a hole-doped single copper-oxygen plane

We show that confinement together with intrinsic polarization induce hole doping of the CuO${}_2$ plane in the proposed SrTiO${}_3$/[SrO-La${}_2$CuO${}_4$-SrO]/LaAlO${}_3$ heterostructure without resorting to chemical substitution, using the generalized gradient approximation and its combination with Coulomb correlation $U$. Hole concentration can be rationally manipulated via tuning the LaAlO${}_3$ thickness and in-plane strain. The stable antiferromagnetic insulating bulk state up to 8$\%$ doping in this disorder-free structure is remarkable; moreover, this antiferromagnetic state coexists with two-dimensional electron gas on the top surface of LaAlO${}_3$, which originates from out-of-plane charge transfer mainly between the La-$d_{3z^2-1}$ state at the surface and Cu-$e_g$ states in the CuO${}_2$ plane. In addition, a possible SrTiO${}_3$ capping layer is introduced in which, instead of La-$d_{3z^2-1}$, Ti-$t_{2g}$ orbitals exchange holes with electrons of Cu-$e_g$ orbitals.

Figure 1

Top panel: Schematic geometrical structures of 4(STO)/La${}_2$Sr${}_2$CuO${}_6$/3(LAO) HS. Bottom panel: Calculated oxygen dimpling away from cation planes for 4(STO)/La${}_2$Sr${}_2$CuO${}_6$/$n$(LAO) HSs ($1\le n\le 5$) in $z$ direction.

Figure 2

(a) Planar average and macroscopic average of electrostatic potential for metallic 4STO/LSCO/3LAO HS. Valence-band shift $E_{\mathrm{VBS}}^{\mathrm{LAO}}$ of LAO part of interface (b) for different 4STO/LSCO/$n$LAO HSs obtained by layer-projected density of states.

Figure 3

Layer-projected density of states of 4STO/LSCO/2LAO (left panel) and 4STO/LSCO/3LAO (right panel) HSs from GGA calculations.

Figure 4

GGA band structures of (a) bulk La${}_2$CuO${}_4$, (b) 4STO/LSCO/1LAO, (c) 4STO/LSCO/2LAO, and (d) 4STO/LSCO/3LAO HSs. The Fermi level ${\varepsilon }_F$ is set at zero. (e) The 0.04 Å${}^{-3}$ partial charge density isosurfaces for the two partially occupied conduction bands (Ti-$3d$ and La-$5d$) at the $\Gamma$ point for 4STO/LSCO/2LAO HS.

Figure 5

(a) The amount of hole in Cu-$e_g$ orbitals, (b) energy of the partially occupied upper Cu-$e_g$ band at the X point, and (c) energy differences $E_{\mathrm{NM}}-E_{\mathrm{AFM}}$ and $E_{\mathrm{NM}}-E_{\mathrm{FM}}$ as a function of LAO layer number $n$ in HS.

Figure 6

$\text{GGA}+U_d$ AFM band structure of 4STO/LSCO/3LAO HS. The Fermi level ${\varepsilon }_F$ is set at zero.