${\mathrm{SrRuO}}_3\text{−}{\mathrm{SrTiO}}_3$ heterostructure as a possible platform for studying unconventional superconductivity in ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$

There is intense controversy around the unconventional superconductivity in strontium ruthenate, where the various theoretical and experimental studies suggest diverse and mutually exclusive pairing symmetries. Currently, the investigation is solely focused on only one material, ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$, and the field suffers from the lack of comparison targets. Here, employing a density-functional-theory-based analysis, we show that the heterostructure composed of ${\mathrm{SrRuO}}_3$ and ${\mathrm{SrTiO}}_3$ is endowed with all the key characteristics of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$, and, in principle, can host superconductivity. Furthermore, we show that competing magnetic phases and associated frustration, naturally affecting the superconducting state, can be tuned by epitaxial strain engineering. This system thus offers an excellent platform for gaining more insight into superconductivity in ruthenates.

Figure 1

(a) Crystal structure of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ and SRO-STO. Gray and blue octahedera denote ${\mathrm{RuO}}_6$ and ${\mathrm{TiO}}_6$ octahedra, and red and green spheres represent oxygen and strontium atoms, respectively (b) Partial DOS of Ru-$d$ orbitals for ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ and SRO-STO for $xy$ and $yz/zx$.

Figure 2

The energy landscape as a function of strain (a) with and (b) without octahedral rotation of ${\mathrm{RuO}}_6$, for three magnetic configurations schematically depicted in (c): FM (ferromagnetic), Néel antiferromagnetic, and SDW $[\mathbf{q}=(1,1,0)\frac{2\pi }{3a}]$ phases. (d) The change in Lindhard susceptibility obtained from the unfolded band for Ru $yz/zx$ orbitals. Octahedral rotations are linearly interpolated between the unrotated case (0.0) and the fully rotated one (1.0). (e), (f) The change in Fermi surfaces (e) with and (f) without octahedral rotation. (d)–(f) are for the unstrained (0%) structure. The arrows in the Fermi surfaces indicate ${\mathbf{q}}_3$ nesting vector which activates both the $xz$ and $yz$ quasi-1D Fermi surfaces.

Figure 3

Partial DOS of Ru $xy$ (red) and Ru $yz/zx$ (blue) bands for strains $-4\%$, $0\%$, and $4\%$. Corresponding Fermi surfaces including the $\mathrm{\Gamma }$ point are shown in the right column with the same color code. The contribution of other orbitals at the Fermi surface is marked by the green color.