Motivated by the evidence in PCCO and NCCO of a magnetic quantum critical point at which Neel order is destroyed, we study the evolution with doping of the T=0 quantum phases of the electron doped cuprates. At low doping, there is a metallic Neel state with small electron Fermi pockets, and this yields a fully gapped d_{x^2-y^2} superconductor with co-existing Neel order at low temperatures. We analyze the routes by which the spin-rotation symmetry can be restored in these metallic and superconducting states. In the metal, the loss of Neel order leads to a topologically ordered `doublon metal' across a deconfined critical point with global O(4) symmetry. In the superconductor, in addition to the conventional spin density wave transition, we find a variety of unconventional possibilities, including transitions to a nematic superconductor and to valence bond supersolids. Measurements of the spin correlation length and of the anomalous dimension of the Neel order by neutron scattering or NMR should discriminate these unconventional transitions from spin density wave theory.
We investigate in underdoped cuprates possible coexistence of the superconducting (SC) order at zero momentum and pair density wave (PDW) at momentum ${\bf Q}=(π, π)$ in the presence of a Neel order. By symmetry, the $d$-wave uniform singlet pairing $dS_0$ can coexist with the $d$-wave triplet PDW $dT_{\bf Q}$, and the $p$-wave singlet PDW $pS_{\bf Q}$ can coexist with the $p$-wave uniform triplet $pT_0$. At half filling, we find the novel $pS_{\bf Q}+pT_0$ state is energetically more favorable than the $dS_0+dT_{\bf Q}$ state. At finite doping, however, the $dS_0+dT_{\bf Q}$ state is more fav…
Metallic Néel order stabilized by coupling between inequivalent Hubbard layers
Institute for Advanced Study in Physics, Zhejiang University（浙江大学前沿物理研究院）；Leinweber Institute for Theoretical Physics, Stanford University（斯坦福大学莱因韦伯理论物理研究所）；Department of Applied Physics, Stanford University（斯坦福大学应用物理系）；Institute for Advanced Study, Tsinghua University（清华大学高等研究院）；Department of Physics, Stanford University（斯坦福大学物理系）
It is inferred from bulk-sensitive muon Knight shift measurement for a Bi$_{1.76}$Pb$_{0.35}$Sr$_{1.89}$CuO$_{6+δ}$ single-layer cuprate that metal-insulator (MI) transition (in the low temperature limit, $T\rightarrow0$) occurs at the critical hole concentration $p=p_{\rm MI}=0.09(1)$, where the electronic density of states (DOS) at the Fermi level is reduced to zero by the pseudogap irrespective of the Néel order or spin glass magnetism. Superconductivity also appears for $p>p_{\rm MI}$, suggesting that this feature is controlled by the MI transition. More interestingly, the magnitude of the…
Effect of the pseudogap on T$_c$ in the cuprates and implications for its origin
铜氧化物的最有趣的方面之一是一个大的赝能隙与高的超导转变温度共存。在这里，我们研究配对中的铜酸盐从电子-电子相互作用，通过构建对顶点使用的光谱函数来自角度分辨的光电发射数据为近最佳掺杂的Bi $_2$ Sr $_2$ CaCu $_2$ O $_{8+δ}$样品，具有明显的赝隙。假设赝能隙是{ \it not}，我们发现超导不稳定性被强烈抑制，与实际观察到的形成鲜明对比。使用的光谱函数的解析近似，我们可以跟踪这种抑制BCS对数奇异性的破坏的赝能隙和寿命加宽的组合。我们的研究结果强烈支持这些理论的pseudogap是由于配对的铜酸盐。
We perform quantum Monte Carlo simulations of the itinerant-localized periodic Kondo-Heisenberg model for the underdoped cuprates to calculate the associated spin correlation functions. The strong electron correlations are shown to play a key role in the abrupt destruction of the quasi long-range antiferromagnetic order in the lightly doped regime.
In the present work we address a long standing problem of the magnetic ground state and magnetic excitations in underdoped cuprates. Modelling cuprates by the extended $t-J$ model we show that there is a hidden dimensionless parameter $λ$ which drives magnetic criticality at low doping $x$. Hence we derive the zero temperature $λ-x$ phase diagram of the model. It is argued that all underdoped cuprates are close to the quantum tricritical point $x=0$, $λ=1$. The three phases "meet" at the tricritical point: (i) Néel antiferromagnet, (ii) spin spiral with antinodal direction of the spiral wave v…
Motivated by the widespread experimental observations of nematicity in strongly underdoped cuprate superconductors, we investigate the possibility of enhanced nematic fluctuations in the vicinity of a Mott insulator that displays Néel-type antiferromagnetic order. By performing a strong-coupling expansion of an effective model that contains both Cu-$d$ and O-$p$ orbitals on the square lattice, we demonstrate that quadrupolar fluctuations in the $p$-orbitals inevitably generate a biquadratic coupling between the spins of the $d$-orbitals. The key point revealed by our classical Monte Carlo simu…
Numerous experiments have reported discrete symmetry breaking in the high temperature pseudogap phase of the hole-doped cuprates, including breaking of one or more of lattice rotation, inversion, or time-reversal symmetries. In the absence of translational symmetry breaking or topological order, these conventional order parameters cannot explain the gap in the charged fermion excitation spectrum in the anti-nodal region. Zhao et al. (1601.01688) and Jeong et al. (arXiv:1701.06485) have also reported inversion and time-reversal symmetry breaking in insulating Sr2IrO4 similar to that in the meta…
It has been experimentally established that the occurrence of charge density waves is a common feature of various under-doped cuprate superconducting compounds. The observed states, which are often found in the form of bond density waves (BDW), often occur in a temperature regime immediately above the superconducting transition temperature. Motivated by recent optical experiments on superconducting materials, where it has been shown that optical irradiation can transiently improve the superconducting features, here, we propose a new approach for the enhancement of superconductivity by the targ…
Elucidating the nature of the magnetism of a high-temperature superconductor is crucial for establishing its pairing mechanism. The parent compounds of the cuprate and iron-pnictide superconductors exhibit Néel and stripe magnetic order, respectively. However, FeSe, the structurally simplest iron-based superconductor, shows nematic order (Ts = 90 K), but not magnetic order in the parent phase, and its magnetic ground state is intensely debated. Here, we report inelastic neutron-scattering experiments that reveal both stripe and Néel spin fluctuations over a wide energy range at 110 K. On enter…
The orthorhombic Haldane spin chain compound Tb2BaNiO5 (Neel order, TN1= 63 K) has been shown to be an exotic multiferroic system below (TN2) 25 K due to various fascinating features, pointing to a strong potential for the advancement of concepts in this field. In particular, the rare-earth ions play a direct decisive role unlike in many other well known multiferroic materials and there appears to be a critical canting angle, developing below TN2, subtended by Tb 4f and Ni 3d moments to trigger this cross coupling phenomenon. However, for a small replacement of Sr for Ba, viz. in Tb2Ba0.9Sr0.1…
Relation between cuprate superconductivity and magnetism: A Raman study of (CaLa)(BaLa)$_{2}$Cu$_{3}$O$_{y}$
利用拉曼散射和μ子自旋转动研究了电荷补偿反铁磁（Ca $_{x}$ La $_{1-x}$）（Ba $_{1.75-x}$ La $_{0.25+x}$）Cu $_{3}$ O $_{y}$单晶.在该体系中，参数$x$通过键距和屈曲角控制Cu-O-Cu超交换相互作用。氧含量$y$控制电荷掺杂。在没有掺杂的情况下，双磁振子峰位置与超交换强度$J$成正比。我们发现，$x$和$y$影响的峰值位置相当大。从μ子自旋旋转确定的Néel温度在相同的样品上独立地证实了磁相互作用对$x$和$y$的强烈依赖性。我们发现一个相当大的增加，在最高超导转变温度$T_{c}^{max}$与$J$。这是强有力的证据，轨道重叠的重要性，超导在这个家庭的铜酸盐。
Most of solid-state spin physics arising from spin-orbit coupling, from fundamental phenomena to industrial applications, relies on symmetry-protected degeneracies. So does the Zeeman spin-orbit coupling, expected to manifest itself in a wide range of antiferromagnetic conductors. Yet, experimental proof of this phenomenon has been lacking. Here, we demonstrate that the Néel state of the layered organic superconductor $κ$-(BETS)$_2$FeBr$_4$ shows no spin modulation of the Shubnikov-de Haas oscillations, contrary to its paramagnetic state. This is unambiguous evidence for the spin degeneracy of…
Motivated by experimental observations, Samajdar et al. [Nature Physics 15, 1290 (2019)] have proposed that the insulating Neel state in the parent compounds of the cuprates is proximate to a quantum phase transition to a state in which Neel order coexists with semion topological order. We study the manner in which proximity to this transition can make the phonons chiral, by inducing a significant phonon Hall viscosity. We describe the spinon-phonon coupling in a lattice spinon model coupled to a strain field, and also using a general continuum theory constrained only by symmetry. We find a no…
Frustration from Localized Zhang-Rice States: A Unified Theory of Doping-Driven Magnetic Transitions in Cuprates
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University（上海交通大学物理与天文学院人工结构与量子控制教育部重点实验室）
Particle-hole symmetry in the pseudogap phase of moderately underdoped cuprate high temperature superconductors evidenced from joint density of states analysis
We present a new method to treat the two-dimensional (2D) Hubbard model for parameter regimes which are relevant for the physics of the high-$T_c$ superconducting cuprates. Unlike previous attempts to attack this problem, our new approach takes into account all fluctuations in different channels on equal footing and is able to treat reasonable large lattice sizes up to 32x32. This is achieved by the following three-step procedure: (i) We transform the original problem to a new representation (dual fermions) in which all purely local correlation effects from the dynamical mean field theory are …
Motivated by the rich physics of honeycomb magnetic materials, we obtain the phase diagram and analyze magnetic properties of the spin-1/2 and spin-1 J1-J2-J3 Heisenberg model on the honeycomb lattice. Based on the SU(2) and SU(3) symmetry representations of the Schwinger boson approach, which treats disordered spin liquids and magnetically ordered phases on an equal footing, we obtain the complete phase diagrams in the (J2,J3)plane. This is achieved using a fully unrestricted approach which does not assume any pre-defined Ansatze. For S=1/2, we find a quantum spin liquid (QSL) stabilized betw…
We use the Nernst effect to delineate the boundary of the pseudogap phase in the temperature-doping phase diagram of cuprate superconductors. New data for the Nernst coefficient $ν(T)$ of YBa$_{2}$Cu$_{3}$O$_{y}$ (YBCO), La$_{1.8-x}$Eu$_{0.2}$Sr$_x$CuO$_4$ (Eu-LSCO) and La$_{1.6-x}$Nd$_{0.4}$Sr$_x$CuO$_4$ (Nd-LSCO) are presented and compared with previous data including La$_{2-x}$Sr$_x$CuO$_4$ (LSCO). The temperature $T_ν$ at which $ν/T$ deviates from its high-temperature behaviour is found to coincide with the temperature at which the resistivity deviates from its linear-$T$ dependence, which…
This thesis deals with the Hubbard model as prototypical model to describe the physics of electrons in the two-dimensional copper-oxide planes of high-$T_c$ cuprates. To get approximate solutions, we employ functional renormalization group (fRG) and dynamical mean-field theory (DMFT) methods. We deal with the problem of identifying bosonic fluctuations in the vertex function, exhibiting an intricate dependence on momenta and frequencies already at moderate coupling. In the normal, paramagnetic phase, the goal is achieved by employing the recently introduced single-boson exchange decomposition.…
