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arXiv 2402.02785cond-mat.str-elcond-mat.supr-con
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两对之谜:论高Tc铜氧化物超导体中赝能隙终点的起源

A tale of two pairs: on the origin of the pseudogap end point in the high-T$_{c}$ cuprate superconductors

Jianhua Yang, Tao Li

AI总结:

本文从RVB视角研究无序二维t-J模型,用自旋-电荷分离解释d波配对的抗无序稳健性,并提出x*处Mott转变连接赝能隙终点与过掺杂侧超导消失。

摘要:

关于铜氧化物超导体存在两个看似无关的谜题。第一个谜题涉及超导圆顶在过掺杂侧终点x_c附近强烈的非BCS行为,而该区域的铜氧化物被认为可由费米液体理论很好地描述。这一点在观测到的ρ_s(0)-T_c标度关系以及低能区大量未凝聚光谱权重中表现得最为明显。第二个谜题涉及d波配对对此类掺杂体系中不可避免的无序效应所展现出的显著稳健性,这同样完全出乎传统BCS图像的预料。本文表明,这两个谜题与关于铜氧化物超导体的第三个谜题的起源深刻相关,即在所谓赝能隙终点x*附近观测到的神秘量子临界行为。通过从共振价键(RVB)视角对无序二维t-J模型进行系统的变分优化,我们发现该模型中的d波配对相比传统d波BCS超导体对无序效应具有显著更强的稳健性。我们发现,这种显著稳健性可归因于RVB图像中的自旋-电荷分离机制:通过该机制,电中性自旋子的d波RVB配对基本不受杂质势影响,仅存在与无序调制局域掺杂水平相关的次级效应。我们提出在x*处存在Mott转变,欠掺杂区域的RVB配对在x>x*时转变为越来越类似BCS的配对,其对无序效应日益增强的脆弱性导致了非BCS行为,并最终使超导在x_c附近受到抑制。

英文摘要:

There are two seemingly unrelated puzzles about the cuprate superconductors. The first puzzle concerns the strong non-BCS behavior around $x_{c}$, the end point of the superconducting dome on the overdoped side, where the cuparte is believed to be well described by the fermi liquid theory. This is the most evident in the observed $ρ_{s}(0)-T_{c}$ scaling and the large amount of uncondensed optical spectral weight at low energy. The second puzzle concerns the remarkable robustness of the d-wave pairing against the inevitable disorder effect in such a doped system, which is also totally unexpected from the conventional BCS picture. Here we show that these two puzzles are deeply connected to the origin of a third puzzle about the cuprate superconductors, namely, the mysterious quantum critical behavior observed around $x^{*}$, the so-called pseudogap end point. Through a systematic variational optimization of the disordered 2D $t-J$ model from the resonating valence bond(RVB) perspective, we find that the d-wave pairing in this model is remarkably more robust against the disorder effect than that in a conventional d-wave BCS superconductor. We find that such remarkable robustness can be attributed to the spin-charge separation mechanism in the RVB picture, through which the d-wave RVB pairing of the charge neutral spinons becomes essentially immune to the impurity potential except for the secondary effect related to the modulation of the local doping level by the disorder. We propose that there exists a Mott transition at $x^{*}$, where the RVB pairing in the underdoped regime is transmuted into the increasingly more BCS-like pairing for $x>x^{*}$, whose increasing fragility against the disorder effect leads to the non-BCS behavior and the ultimate suppression of superconductivity around $x_{c}$.

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