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arXiv 2402.09502cond-mat.str-elcond-mat.supr-conhep-th
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半填充方格上节点 d 波超导、Néel 序与电荷序的解禁闭量子临界性

Deconfined quantum criticality of nodal $d$-wave superconductivity, Néel order, and charge order on the square lattice at half-filling

Maine Christos, Henry Shackleton, Subir Sachdev, Zhu-Xi Luo

AI总结:

本文构建方格 SU(2) 规范理论并映射到扩展 Hubbard 模型,刻画 d 波超导、Néel 与电荷等相之间的解禁闭共形量子临界性,并预测蜂窝晶格上的三相交会双临界点。

摘要:

我们考虑方格上的一个 SU(2) 晶格规范理论,每个晶格位点上有一个基础复费米子和一个基础复玻色子。带规范荷费米子的投影对称性被选取为与 π 通量自旋液体中的自旋子相匹配。所有规范不变可观测量的整体对称性则被选取为与半填充时粒子-空穴对称的电子 Hubbard 模型相匹配。因此,基础费米子和基础玻色子都在平均 π 通量背景中运动,它们的规范不变复合粒子是物理电子;在强规范耦合展开中消去规范场后,可得到电子的有效扩展 Hubbard 模型。该 SU(2) 规范理论展现出若干禁闭/Higgs 相:一个节点 d 波超导体,以及具有 Néel、价键固体、电荷或交错电流序的状态。这些相之间还存在许多量子相变,极有可能由 2+1 维解禁闭共形规范理论描述,我们给出了此类理论的大味道数展开。其中包括现象上富有吸引力的情形:具有电荷能隙和 Néel 序的传统绝缘体,与在 Brillouin 区 4 个节点处具有无隙 Bogoliubov 准粒子的传统 d 波超导体之间的转变。我们还将该方法应用于蜂窝晶格,在 Néel、价键固体(Kekulé)和 Dirac 半金属相的交汇处发现了一个双临界点。

英文摘要:

We consider a SU(2) lattice gauge theory on the square lattice, with a single fundamental complex fermion and a single fundamental complex boson on each lattice site. Projective symmetries of the gauge-charged fermions are chosen so that they match with those of the spinons of the $π$-flux spin liquid. Global symmetries of all gauge-invariant observables are chosen to match with those of the particle-hole symmetric electronic Hubbard model at half-filling. Consequently, both the fundamental fermion and fundamental boson move in an average background $π$-flux, their gauge-invariant composite is the physical electron, and eliminating gauge fields in a strong gauge-coupling expansion yields an effective extended Hubbard model for the electrons. The SU(2) gauge theory displays several confining/Higgs phases: a nodal $d$-wave superconductor, and states with Néel, valence-bond solid, charge, or staggered current orders. There are also a number of quantum phase transitions between these phases which are very likely described by 2+1 dimensional deconfined conformal gauge theories, and we present large flavor expansions for such theories. These include the phenomenologically attractive case of a transition between a conventional insulator with a charge gap and Néel order, and a conventional $d$-wave superconductor with gapless Bogoliubov quasiparticles at 4 nodal points in the Brillouin zone. We also apply our approach to the honeycomb lattice, where we find a bicritical point at the junction of Néel, valence bond solid (Kekulé), and Dirac semi-metal phases.

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