发表机构
Hefei Institutes of Physical Science, Chinese Academy of Sciences; Graduate School of USTC; Southern University of Science and Technology; Shenzhen Pinghu Laboratory; Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area（中国科学院合肥物质科学研究院; 中国科学技术大学研究生院; 南方科技大学; 深圳平湖实验室; 粤港澳大湾区量子科学中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
通过测量 (La,Pr)$_3$Ni$_2$O$_7$ 薄膜的涡旋熔化相图，发现低温下各向异性参数趋近于1，表明超流体密度近各向同性，为 $\gamma$ 带对超导的显著贡献提供了热力学证据。
AI 中文摘要
块体双层镍酸盐中超导电性的发现为探索铜氧化物之外的高温超导电性建立了新的平台。Ni $3d_{z^2}$ 衍生的 $\gamma$ 带在双层镍酸盐超导电性中的作用仍未得到解决。通过对 (La,Pr)$_3$Ni$_2$O$_7$ 薄膜进行同步电阻和抗磁性测量，我们绘制了面内和面外磁场下的涡旋熔化相图。对于 $H\parallel c$，几何约束效应产生了饼状涡旋。值得注意的是，涡旋熔化场的各向异性参数 $\gamma_{H_m} \equiv H_m^{ab}/H_m^c$ 随温度降低而单调减小，并在低温下趋近于 1。在各向异性金兹堡-朗道标度下，$H_m^{ab}/H_m^c = \sqrt{\rho_s^{ab}/\rho_s^c}$ 追踪了超流体密度各向异性。这种涡旋固体意味着近各向同性的超流体密度，这与严格二维的 $3d_{x^2-y^2}$ 衍生带不可调和，但可以通过 $3d_{z^2}$ 衍生的 $\gamma$ 带产生的显著层间超流体贡献来自然解释。我们的结果为 $\gamma$ 带对双层镍酸盐薄膜超导电性的显著贡献提供了热力学证据。
英文摘要
The discovery of superconductivity in bulk bilayer nickelates has established a new platform for exploring high-$T_c$ superconductivity beyond the cuprates. The role of the Ni $3d_{z^2}$-derived $γ$ band in the superconductivity of bilayer nickelates remains unresolved. By performing simultaneous resistance and diamagnetism measurements on (La,Pr)$_3$Ni$_2$O$_7$ thin films, we map the vortex melting phase diagram for both in-plane and out-of-plane magnetic fields. For $H\parallel c$, the geometric confinement effect gives rise to pancake vortices. Remarkably, the anisotropy parameter of the vortex melting field $γ_{H_m} \equiv H_m^{ab}/H_m^c$ decreases monotonically with decreasing temperature and approaches unity at low temperatures. Within the anisotropic Ginzburg--Landau scaling, $H_m^{ab}/H_m^c = \sqrt{ρ_s^{ab}/ρ_s^c}$ tracks the superfluid-density anisotropy. Such a vortex solid implies a nearly isotropic superfluid density, which is irreconcilable with the strictly two-dimensional $3d_{x^2-y^2}$-derived bands, but naturally explained by a substantial interlayer superfluid contribution from the $3d_{z^2}$-derived $γ$ band. Our results provide thermodynamic evidence for a substantial contribution of the $γ$ band to superconductivity in bilayer nickelate thin films.
