AI 中文总结
该研究揭示加压La₃Ni₂O₇中未掺杂时为s±波超导配对，空穴掺杂会诱导其向d_{xy}波转变，而电子掺杂下s±波配对始终稳定，表明γ费米口袋并非超导必需，为检验双层镍酸盐的配对机制提供了新方向。
AI 中文摘要
我们研究了加压La$_3$Ni$_2$O$_7$的超导配对对称性及其掺杂演化规律。对于未掺杂的化合物，最有利的配对态为$s_{\text{±}}$波，其特征是费米口袋之间的能隙函数存在符号反转。对配对相互作用的详细分析表明，这种非常规态源于双层镍酸盐的磁奇模介导的排斥相互作用。\n空穴掺杂时，$γ$费米口袋发生膨胀，放大了该口袋上的口袋内排斥作用。这些由磁偶模驱动的排斥作用逐渐主导配对相互作用，最终在重空穴掺杂区域推动配对对称性从$s_{\text{±}}$波转变为$d_{xy}$波。\n与之形成鲜明对比的是，电子掺杂下$s_{\text{±}}$波配对始终存在，甚至在发生Lifshitz（利夫希茨）转变的重电子掺杂区域也依然稳定。这一发现表明，$γ$费米口袋并非双层镍酸盐中超导出现的必要条件。实际上，在不存在$γ$口袋的情况下，$s_{\text{±}}$波配对会变得更加稳定，因为$α$和$β$口袋之间有利的嵌套会强烈增强自旋涨落——这一条件由Luttinger定理（卢廷格定理）和费米面拓扑结构所保证。我们认为，探索超导配对的掺杂演化将为检验加压La$_3$Ni$_2$O$_7$的配对机制开辟新的领域。
英文摘要
We investigate the superconducting pairing symmetry and its doping evolution in pressurized La$_3$Ni$_2$O$_7$. For the undoped compound, the most favorable pairing state is found to be $s_{\pm}$-wave, characterized by sign reversal of the gap functions between the Fermi pockets. A detailed analysis of the pairing interactions reveals that this unconventional state originates from repulsive interactions mediated by the magnetic odd modes of the bilayer nickelate. Upon hole doping, the $γ$ Fermi pocket expands, which amplifies the intrapocket repulsions on this pocket. These repulsions, driven by the magnetic even modes, gradually dominates the pairing interactions and ultimately drive a transition in pairing symmetry from $s_{\pm}$-wave to $d_{xy}$-wave in the heavily hole-doped regime. In stark contrast, the $s_{\pm}$-wave pairing persists under electron doping, even deep into the heavily electron-doped regime where a Lifshitz transition occurs. This finding suggests that the $γ$ Fermi pocket is not essential for the emergence of superconductivity in bilayer nickelates. In fact, the $s_{\pm}$-wave pairing becomes more robust in the absence of the $γ$ pocket, as spin fluctuations are strongly enhanced by the favorable nesting between the $α$ and $β$ pockets --- a condition guaranteed by Luttinger's theorem and the Fermi surface topology. We believe that exploring the doping evolution of superconducting pairing will open a new realm for testing the pairing mechanism in pressurized La$_3$Ni$_2$O$_7$.
Comments8 pages, 5 figures
