德拜温度、电子-声子耦合常数以及高度压缩La$_3$Ni$_2$O$_{7-δ}$中晶体应变随压力的三穹形状
Debye temperature, electron-phonon coupling constant, and three-dome shape of crystalline strain as a function of pressure in highly compressed La$_3$Ni$_2$O$_{7-δ}$
AI总结：
本研究通过分析电阻数据，确定了高度压缩镍酸盐La$_3$Ni$_2$O$_{7-δ}$的德拜温度与电子-声子耦合常数，发现其应变随压力呈三穹形状，并提出了观察零电阻态的条件。
摘要：
除了对最近发现的高度压缩高温超导体La$_3$Ni$_2$O$_{7-δ}$的相结构转变、配对机制和物理性质进行持续研究外，我们在此探索了电子-声子配对机制作为超导态起源的可能性，并确定了该镍酸盐在高压$Fmmm$相和低压$Ammm$相中的微晶应变$ε(P)$。为此，我们分析了温度依赖的电阻，并提取了La$_3$Ni$_2$O$_{7-δ}$中压力依赖的德拜温度$Θ_D(P)$，其近似值为$Θ_D(P = 25 GPa) = 550$ K。由此我们确定La$_3$Ni$_2$O$_{7-δ}$是强耦合超导体，其电子-声子耦合常数$λ_{e-ph}(P=22.4 GPa) = 1.75$。该值接近常压超导体$Nb_3R (R = Sn, Al)$的$λ_{e-ph} = 1.70$。为了解决关于晶格应变可能是La$_3$Ni$_2$O$_{7-δ}$中高温超导性出现起源的持续讨论，我们确定了高压$Fmmm$相中的微晶应变$0.011 < ε(P)$，以及低压$Fmmm$相中的$ε(P) < 0.011$。我们的分析表明，在$1.6 GPa < P < 41.2 GPa$的压力范围内，$ε(P)$呈三穹形状。这两个$ε(P)$低谷之一位于$P \approx 15 GPa$，与$Ammm$相到$Fmmm$相的相变压力一致。基于我们的分析，我们提出了在La$_3$Ni$_2$O$_{7-δ}$中观察到零电阻态的可能条件。
英文摘要：
Besides ongoing studies of phase structural transitions, pairing mechanism, and physical properties of recently discovered highly compressed high-temperature superconductor La$_3$Ni$_2$O$_{7-δ}$, here we explored a possibility for the electron-phonon pairing mechanism as an origin of the superconducting state and determined the microcrystalline strain, $ε(P)$, in high pressure $Fmmm$-phase, and low-pressure $Ammm$-phase of this nickelate. To do this, we analyzed temperature dependent resistance and extracted pressure dependent Debye temperature, $Θ_D(P)$, in La$_3$Ni$_2$O$_{7-δ}$ with an approximate value of $Θ_D(P = 25 GPa) = 550$ $K$. From this we established that the La$_3$Ni$_2$O$_{7-δ}$ is strong-coupled superconductor with the electron-phonon coupling constant $λ_{e-ph}(P=22.4 GPa) = 1.75$. This value is close to $λ_{e-ph} = 1.70$ of ambient pressure superconductors $Nb_3R (R = Sn, Al)$. To address ongoing discussion that the lattice strain can be the origin for the emergence of high-temperature superconductivity in the La$_3$Ni$_2$O$_{7-δ}$, we determined the microcrystalline strain, $0.011 < ε(P)$, in the high-pressure $Fmmm$-phase, and $ε(P) < 0.011$ of low-pressure $Fmmm$-phase. Our analysis showed that $ε(P)$ has three-dome shape in the pressure range of $1.6 GPa < P < 41.2 GPa$. One of these two $ε(P)$ deeps at $P \approx 15 GPa$ coincides with the pressure at which the $Ammm$-phase into the $Fmmm$-phase phase transition occurs. Based on our analysis, we proposed probable condition to observe the zero-resistance state in La$_3$Ni$_2$O$_{7-δ}$.
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