Presentation Information
[PC8-02]Theoretical study on ambient pressure superconductivity in La3Ni2O7 thin films: robustness of wave pairing
Kensei Ushio1, Shu Kamiyama2, Yuto Hoshi1, Ryota Mizuno3, Masayuki Ochi2,3, Kazuhiko Kuroki2, *Hirofumi Sakakibara4 (1. Fac. of Eng.,Tottori Univ. (Japan), 2. Dept. of Phys., Univ. of Osaka (Japan), 3. FRC, Univ. of Osaka (Japan), 4. AMES, Tottori Univ. (Japan))
Keywords:
high-temperature superconductivity,nickelates,spin-fluctuations,unconventional pairing,Thin film
[Purpose]
Since the discovery of high-temperature superconductivity in the Ruddlesden-Popper-type nickelate La3Ni2O7 and the observation of a significant superconducting volume fraction in (La,Pr)3Ni2O7, multi-layered nickelates have garnered considerable attention. More recently, ambient-pressure superconductivity has been reported in thin films of La3Ni2O7 and (La,Pr)3Ni2O7. In these experiments, three different substrates were examined, but ambient-pressure superconductivity was observed only in films grown on SrLaAlO4 (SLAO). As SLAO has the smallest lattice constant of the three substrates, this suggests that compressive strain from the substrate plays a crucial role in stabilizing superconductivity. Motivated this background, we theoretically analyze the influence of the strain coming from the substrates on superconductivity.
[Method]
Firstly, we theoretically determine the crystal structure using first-principles calculations. We optimize the c-axis length while assuming that the in-plane lattice constants of the substrate and the thin film are equal. From the obtained structures, we construct maximally localized Wannier orbitals to derive a two-orbital bilayer model, consisting of the x2-y2 and 3z2−r2 orbitals in each layer. Finally, we apply the fluctuation-exchange (FLEX) approximation to this model to evaluate the relative strength of superconductivity.
[Results]
For thin films grown on an SLAO substrate, the energetic splitting between the x2-y2 and 3z2−r2 orbitals is enhanced due to the in-plane compression of the NiO6 octahedra. Consequently, the small Fermi surface around (kx,ky)=(π,π), often called the γ-surface, tends to disappear more readily than in bulk materials. Given the significant interest in the existence of the γ-surface in this research field, we also examined how the inclusion of a +U correction affects its presence or absence. Our current analysis, based on the fluctuation-exchange (FLEX) approximation, shows that s±-wave superconductivity is robust regardless of whether the γ-surface is present.
[Consideration]
This robustness may be attributed to finite-energy spin fluctuations arising from the 3z2−r2 orbitals. In the talk, we will also discuss the origin of relatively low Tc ~ 40 K in the thin films than in bulk La3Ni2O7 (Tc ~ 80 K).
[Conclusion]
We have constructed a two-orbital bilayer model of thin film La3Ni2O7. We investigate several models having the different condition of the γ-Fermi surface. Our main massage is that s±-wave superconductivity is robust regardless of the γ-surface.
Since the discovery of high-temperature superconductivity in the Ruddlesden-Popper-type nickelate La3Ni2O7 and the observation of a significant superconducting volume fraction in (La,Pr)3Ni2O7, multi-layered nickelates have garnered considerable attention. More recently, ambient-pressure superconductivity has been reported in thin films of La3Ni2O7 and (La,Pr)3Ni2O7. In these experiments, three different substrates were examined, but ambient-pressure superconductivity was observed only in films grown on SrLaAlO4 (SLAO). As SLAO has the smallest lattice constant of the three substrates, this suggests that compressive strain from the substrate plays a crucial role in stabilizing superconductivity. Motivated this background, we theoretically analyze the influence of the strain coming from the substrates on superconductivity.
[Method]
Firstly, we theoretically determine the crystal structure using first-principles calculations. We optimize the c-axis length while assuming that the in-plane lattice constants of the substrate and the thin film are equal. From the obtained structures, we construct maximally localized Wannier orbitals to derive a two-orbital bilayer model, consisting of the x2-y2 and 3z2−r2 orbitals in each layer. Finally, we apply the fluctuation-exchange (FLEX) approximation to this model to evaluate the relative strength of superconductivity.
[Results]
For thin films grown on an SLAO substrate, the energetic splitting between the x2-y2 and 3z2−r2 orbitals is enhanced due to the in-plane compression of the NiO6 octahedra. Consequently, the small Fermi surface around (kx,ky)=(π,π), often called the γ-surface, tends to disappear more readily than in bulk materials. Given the significant interest in the existence of the γ-surface in this research field, we also examined how the inclusion of a +U correction affects its presence or absence. Our current analysis, based on the fluctuation-exchange (FLEX) approximation, shows that s±-wave superconductivity is robust regardless of whether the γ-surface is present.
[Consideration]
This robustness may be attributed to finite-energy spin fluctuations arising from the 3z2−r2 orbitals. In the talk, we will also discuss the origin of relatively low Tc ~ 40 K in the thin films than in bulk La3Ni2O7 (Tc ~ 80 K).
[Conclusion]
We have constructed a two-orbital bilayer model of thin film La3Ni2O7. We investigate several models having the different condition of the γ-Fermi surface. Our main massage is that s±-wave superconductivity is robust regardless of the γ-surface.