We give a self-consistent theory of the scale dependent effective mass enhancement m*/m of quasiparticles by 3D antiferromagnetic (AFM) spin fluctuations in the presence of disorder at an AFM quantum critical point. The coupling of fermionic and bosonic degrees of freedom in the critical regime is described in terms of a critical quasiparticle theory. Using the fact that even in the "non-Fermi liquid" regime the quasiparticle width does not exceed the quasiparticle energy, we adopt relations from Fermi liquid theory to determine the dependence of the spin fluctuation spectrum on m*/m, from which the self energy and hence m*/m may be calculated. The self-consistent equation for m*/m has a strong coupling solution provided the initial value is sufficiently large. We argue that in YbRh2Si2, quasi-2D Gaussian fluctuations existing over a wide range drive the system into the 3D strongly coupled fluctuation regime. We find critical exponents of the temperature dependence of the specific heat coefficient γ\propto T^{-1/4} and of the resistivity ρ(T)=ρ(0)+ A T^{3/4} in good agreement with experiments on YbRh2Si2 in the temperature range T < 0.3K.
Signature of quantum criticality in photoemission spectroscopy at elevated temperature
重费米子（HF）化合物的量子相变（QPT）可能破坏费米液体基态。然而，这种崩溃的条件仍然不清楚。我们首次报道了在高温下用紫外光电子能谱直接研究了重准粒子在CeCu $_{6-x}$ Au $_x$正则体系中的形成和击穿过程，而没有考虑晶格相干性的复杂性.令人惊讶的是，单离子近藤能级$T_K$在量子临界金浓度$x_c=0.1$附近表现出突变。我们从理论上表明，这一步预计从一个高度非线性重整化的本地自旋耦合在每个Ce网站，诱导相邻网站上的自旋波动。它提供了一个通用的高温指标HF准粒子击穿在QPT。
The fluctuations-driven continuous quantum criticality has sparked tremendous interest in condensed matter physics. It has been verified that the gapless fermions fluctuations can change the nature of phase transition at criticality. In this paper, we study the fermionic quantum criticality with enlarged Ising$\times$Ising fluctuations in honeycomb lattice materials. The Gross-Neveu-Yukawa theory for the multicriticality between the semimetallic phase and two ordered phases that break Ising symmetry is investigated by employing perturbative renormalization group approach. We first determine th…
We consider spontaneous symmetry breaking transitions of strongly interacting two-dimensional Dirac fermions minimally coupled to mass and emergent gauge field order parameters. Using a renormalization group analysis, we show that the presence of gauge fields leads to novel fermion induced quantum (multi-)criticality where the putative emergent Lorentz invariance is violated. We illustrate this with the example of translational symmetry breaking due to charge-density wave order on the honeycomb lattice. Finally, we identify that topological phase transitions are well described by this effectiv…
Fermions in the Fermi gas obey the Pauli exclusion principle restricting any two fermions from filling the same quantum state. Strong interaction between fermions can completely change the properties of the Fermi gas. In our theoretical study we find a new exotic quantum phase in strongly interacting Fermi gases constrained to a certain condition imposed on the Fermi surfaces which we call the Fermi surface resonance. The new phase is quantum critical which can be identified by the power-law frequency tail of the spectral density and divergent static susceptibilities. An especially striking fe…
Quantum criticality beyond the Landau paradigm represents a fundamental problem in condensed matter and statistical physics. Heavy fermion systems with multipolar degrees of freedom can play an important role in the search for its universal description. We consider a Kondo lattice model with both spin and quadrupole degrees of freedom, which we show to exhibit an antiferroquadrupolar phase. Using a field theoretical representation of the model, we find that Kondo couplings are exactly marginal in the renormalization group sense in this phase. This contrasts with the relevant nature of the Kond…
Landau-Fermi liquid theory is conventionally believed to hold whenever the interacting single-particle density of states develops a $δ$-like component at the Fermi surface, which is associated with quasiparticles. Here we show that a microscopic justification can be actually achieved under more general circumstances, even in case coherent quasiparticles are totally missing and the interacting single-particle density of states vanishes at the chemical potential as consequence of a pole singularity in the self-energy.
Antiferromagnetic criticality at a heavy-fermion quantum phase transition
对强关联电子系统磁相图的解释仍有争议。特别是，在零温度下发生的量子相变的物理学仍然是个谜。重费米子化合物是量子临界性的教科书例子，因为掺杂、压力或磁场的应用可以导致磁有序态和顺磁态之间的量子相变。一个中心问题涉及临界量子涨落的微观性质。它们是反铁磁的还是本地的？在这里，我们证明，使用非弹性中子散射实验，量子相变在重费米子系统Ce 1-xLaxRu 2 Si 2的反铁磁序参量的波动控制。至少对于这个重费米子家族来说，赫兹-米利斯-森谷自旋涨落方法似乎是描述量子反铁磁-顺磁不稳定性的可靠基础。
We propose a general theoretical framework, using two layers of ancilla qubits, for deconfined criticality between a Fermi liquid with a large Fermi surface, and a pseudogap metal with a small Fermi surface of electron-like quasiparticles. The pseudogap metal can be a magnetically ordered metal, or a fractionalized Fermi liquid (FL*) without magnetic order. A critical 'ghost' Fermi surface emerges (alongside the large electron Fermi surface) at the transition, with the ghost fermions carrying neither spin nor charge, but minimally coupled to $(U(1) \times U(1))/Z_2$ or $(SU(2) \times U(1))/Z_2…
Anisotropic suppression of quasiparticle weight in two-dimensional electron system with partially flat Fermi surface: two-loop renormalization-group analysis
本文对具有部分平坦费米面的二维电子系统进行了双圈重整化群分析。我们发现，{ \it不考虑配对机制}，准粒子的重量是各向异性抑制由于在费米面的平坦区域的几何奇异过程。当能量标度减小时，准粒子重量在平坦区域的中心附近受到最强烈的抑制，这定性地同意通过角度分辨光电子能谱实验对欠掺杂Bi $_2$ Sr $_2$ CaCu $_2$ O $_8$提出的各向异性赝能隙行为。
We propose a simple solvable variant of the Sachdev-Ye-Kitaev (SYK) model which displays a quantum phase transition from a fast-scrambling non-Fermi liquid to disordered Fermi liquid. Like the canonical SYK model, our variant involves a single species of Majorana fermions connected by all-to-all random four-fermion interactions. The phase transition is driven by a random two-fermion term added to the Hamiltonian whose structure is inspired by proposed solid-state realizations of the SYK model. Analytic expressions for the saddle point solutions at large number $N$ of fermions are obtained and …
We consider a system of charged one-dimensional spin-$\frac{1}{2}$ fermions at low temperature. We study how the energy of a highly-excited quasiparticle (or hole) relaxes toward the chemical potential in the regime of weak interactions. The dominant relaxation processes involve collisions with two other fermions. We find a dramatic enhancement of the relaxation rate at low energies, with the rate scaling as the inverse sixth power of the excitation energy. This behavior is caused by the long-range nature of the Coulomb interaction.
Kondo Destruction in Heavy Fermion Quantum Criticality and the Photoemission Spectrum of YbRh$_2$Si$_2$
重费米子金属为研究量子临界性提供了原型。在实验上，量子临界点已经在越来越多的重费米子化合物中被识别和研究。从理论上讲，近藤破坏提供了一种手段来表征一类非常规的量子临界点，超越了朗道框架的序参数波动。这种局域量子临界性的突出证据之一是在YbRh $_2$ Si $_2$中的测量。在有限温度下观察到的霍尔系数和其他运输和热力学量的等温场的依赖性，这指定了一个$T^*(B)$线的温度（$T$）-磁场（$B$）相图中的快速交叉。在这里，我们通过分析交叉宽度与交叉位置的比率来讨论温度升高时会发生什么。在$T \gtrsim 0.5$ K下，该比值接近1，YbRh $_2$ Si $_2$在零磁场下属于量子临界涨落区，其中单粒子谱函数在小费米面和大费米面都具有显著的谱权重。这意味着，在这个温度范围内，任何对费米面敏感的测量也将在大费米面处看到显著的光谱权重。最近报道的YbRh $_2$ Si $_2$在$T>1$ K的角分辨光电子能谱（ARPES）实验与这一预期是一致的，因此支持$T^*(B)$线与近藤破坏物理学的关联。
The failure of Landau-Fermi liquid theory is often considered a telltale sign of universal, scale-invariant behavior in the emergent field theory of interacting fermions. Nevertheless, there exist borderline cases where weak scale invariance coupled with particle-hole asymmetry can coexist with the Landau quasiparticle paradigm. In this letter, I show explicitly that a Landau-Fermi liquid can exist for weak power-law scaling of the retarded Green's function. Such an exotic variant of the traditional Fermi liquid, although exhibiting a finite quasiparticle weight and large quasiparticle lifetim…
We present a comprehensive angle-resolved photoemission spectroscopy study of Ca$_{1.8}$Sr$_{0.2}$RuO$_4$. Four distinct bands are revealed and along the Ru-O bond direction their orbital characters are identified through a light polarization analysis and comparison to dynamical mean-field theory calculations. Bands assigned to $d_{xz}, d_{yz}$ orbitals display Fermi liquid behavior with fourfold quasiparticle mass renormalization. Extremely heavy fermions - associated with a predominantly $d_{xy}$ band character - are shown to display non-Fermi-liquid behavior. We thus demonstrate that Ca$_{1…
Unifying Dirac Spin Liquids on Square and Shastry-Sutherland Lattices via Fermionic Deconfined Criticality
Universität Würzburg（维尔茨堡大学）；Flatiron Institute（平顿研究所）；Massachusetts Institute of Technology（麻省理工学院）；Indian Institute of Technology Madras（马德拉斯印度理工学院）；Harvard University（哈佛大学）
Motivated by recent experimental realizations of polar metals with broken inversion symmetry, we explore the emergence of strong correlations driven by criticality when the polar transition temperature is tuned to zero. Overcoming previously discussed challenges, we demonstrate a robust mechanism for coupling between the critical mode and electrons in multiband metals. We identify and characterize several novel interacting phases, including non-Fermi liquids, when band crossings are close to the Fermi level and present their experimental signatures for three generic types of band crossings.
Resistivity of a non-Galilean--invariant Fermi Liquid near Pomeranchuk Quantum Criticality
分析了金属在波梅兰丘克量子相变（QPT）附近电子-电子相互作用对电阻率的影响。我们表明，Umklapp过程是不有效的QPT附近，必须考虑相互作用和无序获得有限的和T依赖的电阻率。通过功率计数，在Z=3 QPT附近，在低T下对剩余电阻率的校正标度为Δ T ^{（D+2）/3}。然而，我们表明，A=0的简单连接，凸费米面在2D中，由于隐藏的可积性的电子运动。我们认为，在一个两带（s-d）模型中，A >0，并提出这个模型作为所观察到的T^{（D+2）/3}行为的解释。
Scrutinizing Hall effect in Mn$_{1-x}$Fe$_{x}$Si: Fermi surface evolution and hidden quantum criticality
区分Mn $_{1-x}$ Fe $_{x}$ Si顺磁相中的正常（OHE）和异常（AHE）霍尔效应揭示了与隐藏的量子临界（QC）点$x^*\sim0.11$相关的OHE符号反转。在中等Fe含量下的半金属行为导致Mn $_{1-x}$ Fe $_{x}$ Si中的费米学、磁相互作用和QC领域中的可验证的预测。电子和空穴浓度的变化被认为是通过修改海森堡磁性模型中的RKKY交换相互作用来调节Mn $_{1-x}$ Fe $_{x}$ Si中QC区域的驱动力。
The thermopower as a signature of quantum criticality in heavy fermions
我们提出了一系列的论据表明，塞贝克系数可以作为一个决定性的实验来表征的性质的量子临界点（QCP）在重费米子化合物。作为反应几乎完全的离域熵载流子的存在下，塞贝克系数显示出剧烈的崩溃在近藤击穿QCP，作为重建的费米面发生。相反，在自旋密度波（SDW）QCP周围，塞贝克系数是广泛对称的。我们讨论了在QCP的符号变化的可能性，$| S / T | $的特性变化与温度和外部参数，以及塞贝克系数的能力，以区分本地化和巡回反铁磁性（AF）。对四种非常规化合物：YbRh $_2$ Si $_2$，Ce（Mn）In $_5$，CeCu $_{6-x}$ Au $_x$和URu $_2$ Si $_2$给出了实验建议。
