二维超导体中由相位涨落与尺度层级产生的涌现磁性赝能隙
Emergent magnetic pseudogap from phase fluctuations and hierarchy of scales in two-dimensional superconductors
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中文总结 AI 辅助
该研究在二维超导体中，仅通过相位涨落识别出涌现磁性赝能隙，分析了NMR弛豫率1/T₁T的演化，明确了其与各尺度的相互作用机制。
中文摘要 AI 辅助
预配对与相位涨落被认为在预测二维超导体正常态的电荷赝能隙中发挥关键作用。本研究扩展了这一思路，进一步识别出仅由纯相位涨落产生的涌现磁性赝能隙，无需引入任何竞争序。我们通过微扰理论计算气泡贡献与领头阶顶点修正，分析了NMR弛豫率1/T₁T。研究发现，磁性赝能隙表现为正常态中1/T₁T的平滑抑制，其特征温度尺度为TₘPG，与超导能隙Δ_SC和转变温度T_c不同。电荷与磁性赝能隙的 onset 尺度均由BKT关联长度ξ(T)与BCS相干长度ξ_BCS的竞争决定。此外，顶点修正对d波配对无关，但在s波体系中变得显著，会在T_c以上的较低温度驱动1/T₁T的相干增强。我们将1/T₁T的正常态增强归因于s波超导能隙边缘发散的相干峰，这与BCS理论中著名的Hebel-Slichter峰具有相同的物理本质。与相干Hebel-Slichter峰类似，费米液体型散射的正则化至关重要，其特征为散射长度ℓ。因此，1/T₁T的正常态相干增强可通过ξ(T)与ℓ的竞争来描述，由此确定相干尺度T_coh。最终，1/T₁T的完整演化可通过尺度层级ξ(T)、ξ_BCS与ℓ之间的相互作用，在统一图像中得到定量理解。
英文摘要
Preformed pairs and phase fluctuations are believed to play a vital role in predicting the charge pseudogap in the normal state of two-dimensional superconductors. In this work, we extend this idea and further identify the emergent magnetic pseudogap from pure phase fluctuations without invoking any competing order. We examine the NMR relaxation rate $1/T_1T$ by evaluating the bubble contribution and leading-order vertex correction within perturbation theory. It is found that the magnetic pseudogap, manifesting as a smooth suppression of $1/T_1T$ in the normal state, is characterized by a temperature scale $T_\text{mPG}$ distinct from the superconducting gap $Δ_\text{SC}$ and transition temperature $T_c$. The onset scales of both charge and magnetic pseudogap are dominated by the competition of BKT correlation length $ξ(T)$ and BCS coherence length $ξ_\text{BCS}$. Moreover, the vertex correction is shown to be irrelevant for $d$-wave pairing, while it becomes prominent in $s$-wave systems and drives a coherent enhancement of $1/T_1T$ at lower temperatures just above $T_c$. We attribute this normal-state enhancement of $1/T_1T$ to the diverging coherence peak at the $s$-wave superconducting gap edge, which shares the same spirit as the celebrated Hebel-Slichter peak in the BCS theory. Analogous to the coherent Hebel-Slichter peak, regularization by Fermi-liquid-like scatterings is important and is characterized by a scattering length $\ell$. The normal-state coherent enhancement of $1/T_1T$ is hence described by the competition of $ξ(T)$ and $\ell$, through which the coherence scale $T_\text{coh}$ is determined. As a result, the complete evolution of $1/T_1T$ is understood quantitatively in a unified picture as the interplay among hierarchy of scales $ξ(T)$, $ξ_\text{BCS}$ and $\ell$.
