Theoretical analysis on the possibility of superconductivity in the trilayer Ruddlesden-Popper nickelate <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>La</mml:mi><mml:mn>4</mml:mn></mml:msub><mml:msub><mml:mi>Ni</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>10</mml:mn></mml:msub></mml:mrow></mml:math> under pressure and its experimental examination: Comparison with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>La</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>Ni</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>7</mml:mn></mml:msub></mml:mrow></mml:math>
Hirofumi Sakakibara, Masayuki Ochi, Hibiki Nagata, Yuta Ueki, Hiroya Sakurai, Ryo Matsumoto, Kensei Terashima, Keisuke Hirose, Hiroto Ohta, Masaki Kato, Yoshihiko Takano, Kazuhiko Kuroki
Abstract
We study the possibility of superconductivity in a trilayer Ruddlesden-Popper nickelate ${\mathrm{La}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{10}$ under pressure both theoretically and experimentally, making comparison with the recently discovered high ${T}_{c}$ superconductor ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$, a bilayer nickelate. Through DFT calculations, we find that a structural phase transition from monoclinic to tetragonal takes place around 10--15 GPa. Using the tetragonal crystal structure, we theoretically investigate the possibility of superconductivity, where a combination of fluctuation exchange approximation and linearized Eliashberg equation is applied to a six-orbital model constructed from first-principles band calculations. The obtained results suggests that ${\mathrm{La}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{10}$ may also become superconducting under high pressure with ${T}_{c}$ comparable to some cuprates, although it is not as high as ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$. We also perform experimental studies using our polycrystalline samples of ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7.01}$ and ${\mathrm{La}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{9.99}$. The superconducting transition of ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7.01}$, with a maximum onset ${T}_{c}$ of 67.0 K at a pressure of 26.5 GPa, is confirmed by a drop in the electrical resistance as well as the magnetic-field dependence of the resistance. Quite interestingly, similar temperature and magnetic field dependencies of the resistance are also observed for ${\mathrm{La}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{9.99}$, where a drop in the resistance is observed at lower temperatures compared to ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7.01}$, under pressures of 32.8 GPa and above. Given the theoretical expectation, the reduction in the resistance can most likely be attributed to the occurrence of superconductivity in ${\mathrm{La}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{9.99}$. The temperature at which the resistance deviates from linear behavior, considered as the onset ${T}_{c}$, monotonically increases up to 23 K at 79.2 GPa, which is opposite to the pressure dependence of ${T}_{c}$ in ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7.01}$.