该研究描述了一种被提出的量子自旋液体的约束不稳定性，该液体存在于空穴掺杂铜氧化物中的赝能隙金属态下。这种自旋液体可以用Nf = 2个携带基本规范电荷的无质量狄拉克费米子的SU(2)规范理论来描述，该理论是在具有π通量的Z2中心的方形晶格上移动的费米子自旋子的平均场态的低能理论。该理论具有新兴的SO(5)f全局对称性，并被认为在低能下约束为Néel态。在非零掺杂（或在半填充Hubbard排斥U较小时），研究人员认为约束通过具有基本SU(2)规范电荷的玻色子荷子的Higgs凝聚来实现，这些荷子也在具有π Z2通量的环上移动。在半填充状态下，Higgs扇区的低能理论包括Nb = 2个相对论玻色子，并且可能存在一个新兴的SO(5)b全局对称性，并描述了d波超导体、周期-2电荷纹波和破坏时间反演的“d密度波”态之间的旋转。
研究人员提出了一个共形的SU(2)规范理论，其中包括Nf = 2个基本费米子、Nb = 2个基本玻色子和SO(5)f×SO(5)b全局对称性，该理论描述了一个无约束的量子临界点，位于破坏SO(5)f和破坏SO(5)b的约束态之间。在这个临界点上，两个SO(5)对称性的破缺模式由可能在临界点处是不相关的项决定，可以通过选择适当的参数获得从Néel序到d波超导的相变。同样的理论也适用于非零掺杂和大U的情况，其中荷子之间具有更长程的耦合，导致具有更长周期的电荷序出现。
附：英文原文
Title: A model of d-wave superconductivity, antiferromagnetism, and charge order on the square lattice
Author: Christos, Maine, Luo, Zhu-Xi, Shackleton, Henry, Zhang, Ya-Hui, Scheurer, Mathias S., Sachdev, Subir
Issue&Volume: 2023-5-16
Abstract: We describe the confining instabilities of a proposed quantum spin liquid underlying the pseudogap metal state of the hole-doped cuprates. The spin liquid can be described by a SU(2) gauge theory of Nf = 2 massless Dirac fermions carrying fundamental gauge charges—this is the low-energy theory of a mean-field state of fermionic spinons moving on the square lattice with π-flux per plaquette in the Z2 center of SU(2). This theory has an emergent SO(5)f global symmetry and is presumed to confine at low energies to the Néel state. At nonzero doping (or smaller Hubbard repulsion U at half-filling), we argue that confinement occurs via the Higgs condensation of bosonic chargons carrying fundamental SU(2) gauge charges also moving in π Z2-flux. At half-filling, the low-energy theory of the Higgs sector has Nb = 2 relativistic bosons with a possible emergent SO(5)b global symmetry describing rotations between a d-wave superconductor, period-2 charge stripes, and the time-reversal breaking “d-density wave” state. We propose a conformal SU(2) gauge theory with Nf = 2 fundamental fermions, Nb = 2 fundamental bosons, and a SO(5)f×SO(5)b global symmetry, which describes a deconfined quantum critical point between a confining state which breaks SO(5)f and a confining state which breaks SO(5)b. The pattern of symmetry breaking within both SO(5)s is determined by terms likely irrelevant at the critical point, which can be chosen to obtain a transition between Néel order and d-wave superconductivity. A similar theory applies at nonzero doping and large U, with longer-range couplings of the chargons leading to charge order with longer periods.
DOI: 10.1073/pnas.2302701120
Source: https://www.pnas.org/doi/10.1073/pnas.2302701120