At small momenta, the Girvin-MacDonald-Platzman (GMP) mode in the fractional quantum Hall (FQH) effect can be identified with gapped nematic fluctuations in the isotropic FQH liquid. This correspondence would be exact as the GMP mode softens upon approach to the putative point of a quantum phase transition to a FQH nematic. Motivated by these considerations as well as by suggestive evidence of an FQH nematic in tilted field experiments, we have sought evidence of such a nematic FQHE in a microscopic model of interacting electrons in the lowest Landau level at filling factor 1/3. Using a family of anisotropic Laughlin states as trial wave functions, we find a continuous quantum phase transition between the isotropic Laughlin liquid and the FQH nematic. Results of numerical exact diagonalization also suggest that rotational symmetry is spontaneously broken, and that the phase diagram of the model contains both a nematic and a stripe phase.
We analyse various microscopic properties of the nematic fractional quantum Hall effect (FQHN) in the thermodynamic limit, and present necessary conditions required of the microscopic Hamiltonians for the nematic FQHE to be robust. Analytical expressions for the degenerate ground state manifold, ground state energies, and gapless nematic modes are given in compact forms with the input interaction and the corresponding ground state structure factors. We relate the long wavelength limit of the neutral excitations to the guiding center metric deformation, and show explicitly the family of trial w…
Two-dimensional multi-valley electronic systems in which the dispersion of individual pockets has low symmetry give rise to quantum Hall ferroelectric and nematic states in the presence of strong quantising magnetic fields. We investigate local signatures of these states arising near impurities that can be probed via Scanning Tunnelling Microscopy (STM) spectroscopy. For quantum Hall ferroelectrics, we demonstrate a direct relation between the dipole moment measured at impurity bound states and the ideal bulk dipole moment obtained from the modern theory of polarisation. We also study the many…
We theoretically study the correlated insulator states, quantum anomalous Hall (QAH) states, and field-induced topological transitions between different correlated states in twisted multilayer graphene systems. Taking twisted bilayer-monolayer graphene and twisted double-bilayer graphene as examples, we show that both systems stay in spin polarized, $C_{3z}$-broken insulator states with zero Chern number at 1/2 filling of the flat bands under finite displacement fields. In some cases these spin polarized, nematic insulator states are in the quantum valley Hall phase by virtue of the nontrivial…
Understanding the nature of the mysterious pseudogap phenomenon is one of the most important issues associated with cuprate high-$T_c$ superconductors. Here, we report $^{17}$O nuclear magnetic resonance (NMR) studies on two planar oxygen sites in stoichiometric cuprate YBa$_2$Cu$_4$O$_8$ to investigate the symmetry breaking inside the pseudogap phase. We observe that the Knight shifts of the two oxygen sites are identical at high temperatures but different below $T_{\rm nem} \sim$ 185 K, which is close to the pseudogap temperature $T^{\ast}$. Our result provides a microscopic evidence for int…
Graphene-based moiré systems have attracted considerable interest in recent years as they display a remarkable variety of correlated phenomena. Besides insulating and superconducting phases in the vicinity of integer fillings of the moiré unit cell, there is growing evidence for electronic nematic order both in twisted bilayer graphene and twisted double-bilayer graphene (tDBG), as signaled by the spontaneous breaking of the threefold rotational symmetry of the moiré superlattices. Here, we combine symmetry-based analysis with a microscopic continuum model to investigate the structure of the n…
Microscopic origin of the nemato-elastic coupling and dynamics of hybridized collective nematic-phonon excitations
Niels Bohr Institute, University of Copenhagen(哥本哈根大学尼尔斯·玻尔研究所);Carl Zeiss SMT GmbH(卡尔蔡司SMT有限公司);Ariel University(阿里埃勒大学);University of Illinois Urbana-Champaign(伊利诺伊大学厄巴纳-香槟分校)
Momentum Dependence of the Nematic Order Parameter in Iron-Based Superconductors
铁基序参量的动量依赖性是铁基高温超导体微观描述的重要组成部分。虽然最近关于FeSe的报道表明,电子和空穴带之间的电子序参量改变符号,但对于其他化合物仍然缺少详细的知识。结合角度分辨光电子能谱(ARPES)与单轴应变调谐,我们测量的两个FeSe和BaFe $_2$ As $_2$的能带分裂没有干扰的孪生或磁序。我们发现,在布里渊散射中心和角点之间的符号变化的两种化合物中,量子序参量表现出相同的动量依赖性。这表明,尽管相图非常不同,但相同的微观机制驱动着有序。
Microscopic Theory of the Phonon Thermal Hall Effect in Chiral Mott Insulators
Seoul National University(首尔大学);Soongsil University(崇实大学);Origin of Matter and Evolution of Galaxies (OMEG) institute, Soongsil University(崇实大学物质起源与星系演化研究所)
The use of ultra-low temperature cooling and of high hydrostatic pressure techniques has significantly expanded our understanding of the two-dimensional electron gas confined to GaAs/AlGaAs structures. This chapter reviews a selected set of experiments employing these specialized techniques in the study of the fractional quantum Hall states and of the charged ordered phases, such as the reentrant integer quantum Hall states and the quantum Hall nematic. Topics discussed include a successful cooling technique used, novel odd denominator fractional quantum Hall states, new transport results on e…
相关电子流体可以表现出一系列令人惊讶的复杂相,其中一个更令人惊讶的是电子自旋,一个自发产生的空间各向异性的几何不变的金属相。经典向列相通常出现在棒状分子的液体中;考虑到电子是点状的,考虑电子向列相的最初理论动机来自于将电子流体视为量子熔化的电子晶体,而不是费米气体的强相互作用产物。1999年在超净量子霍尔系统中进行的戏剧性传输实验和2007年在强磁场中的Sr 3Ru 2 O 7中进行的戏剧性传输实验证实了这种相在自然界中的存在。在本文中,我们简要地回顾了理论上的考虑,管理的顺序,总结量子霍尔和Sr 3Ru 2 O 7实验,明确地建立了这个阶段的存在,并调查了一些目前的证据,这样一个阶段的铜酸盐和铁基高温超导体。
Unveiling a nematic quantum critical point in multi-orbital systems
电子向列性,提出存在于一些过渡金属材料,可以有不同的微观起源。特别是,在Sr 3Ru 2 O 7中观察到的各向异性电阻率和元磁跳变与早先的提议一致,即各向同性-磁跳变一般是一阶的,并且当由磁场调谐时伴随着元磁。然而,其他引人注目的实验特征,如非费米液体电阻率和临界热力学行为意味着存在一个身份不明的量子临界点(QCP)。在这里,我们表明,轨道的自由度发挥了至关重要的作用,揭示了一个超临界QCP,即使它是蒙上阴影附近的亚临界转变在低温下。我们进一步提出了一个有限的温度相图,包括熵景观和讨论我们的研究结果中观察到的现象Sr 3Ru 2 O 7。