How the ground-state nature can be dramatically changed by the distinct underlying spin correlation is a central issue of doped Mott insulators. The two-leg XXZ ladder provides a prototypical spin background, which can be tuned from a long-range Néel order to a short-range spin liquid via the superexchange anisotropy, giving rise to a complex phase diagram at finite doping. By density matrix renormalization group method, we show that although the charge is always self-localized in the Néel ordered phase, a second insulating phase emerges in which the doped holes become paired but remain localized while the transverse spin-spin correlation reduces to short-ranged one to make the Néel order classical. Only when the Néel order totally disappears by further reducing anisotropy does the pairing become truly coherent as characterized by a Luther-Emery state. In sharp contrast, the pairing is totally absent in the in-plane ferromagnetic XXZ regime, where a direct transition from the charge self-localization in the Néel ordered phase to a Fermi-gas-like state in the spin liquid phase is found. A consistent physical picture is briefly discussed.

中文翻译：

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掺杂的XXZ阶梯的复杂相图：定位和配对

掺杂的Mott绝缘子的中心问题是如何通过不同的潜在自旋相关性来显着改变基态性质。两脚XXZ梯形图提供了典型的自旋背景，可以通过超交换各向异性将其从长距离Néel阶调到短距离自旋液体，从而在有限掺杂时产生了复杂的相图。通过密度矩阵重归一化群方法，我们表明，尽管电荷总是在Néel有序相中自定位，但出现了第二个绝缘相，其中掺杂的空穴成对，但保持局部，而横向自旋-自旋相关性减小至短-使Néel秩序经典。只有当Néel阶通过进一步减小各向异性而完全消失时，配对才真正以Luther-Emery状态为特征相干。与之形成鲜明对比的是，在平面铁磁XXZ模式中完全不存在该配对，在该区域中，发现从Néel有序相中的电荷自定位直接转变为自旋液相中的费米气体样状态。简要讨论了一致的物理图景。