We report the observation of developing fractional quantum Hall states at Landau level filling factors $ν= 1/2$ and 1/4 in electron systems confined to wide GaAs quantum wells with significantly $asymmetric$ charge distributions. The very large electric subband separation and the highly asymmetric charge distribution at which we observe these quantum Hall states, together with the fact that they disappear when the charge distribution is made symmetric, suggest that these are one-component states, possibly described by the Moore-Read Pfaffian wavefunction.
Fractional quantum Hall states (FQHSs) exemplify exotic phases of low-disorder two-dimensional (2D) electron systems when electron-electron interaction dominates over the thermal and kinetic energies. Particularly intriguing among the FQHSs are those observed at even-denominator Landau level filling factors, as their quasi-particles are generally believed to obey non-Abelian statistics and be of potential use in topological quantum computing. Such states, however, are very rare and fragile, and are typically observed in the excited Landau level of 2D electron systems with the lowest amount of …
Motivated by the appearance of a `reflection symmetry' in transport experiments and the absence of statistical periodicity in relativistic quantum field theories, we propose a series of relativistic composite fermion theories for the compressible states appearing at filling fractions $ν=1/2n$ in quantum Hall systems. These theories consist of electrically neutral Dirac fermions attached to $2n$ flux quanta via an emergent Chern-Simons gauge field. While not possessing an explicit particle-hole symmetry, these theories reproduce the known Jain sequence states proximate to $ν=1/2n$, and we show …
Magnetic fields quench the kinetic energy of two dimensional electrons, confining them to highly degenerate Landau levels. In the absence of disorder, the ground state at partial Landau level filling is determined only by Coulomb interactions, leading to a variety of correlation-driven phenomena. Here, we realize a quantum Hall analog of the Neél-to-valence bond solid transition within the spin- and sublattice- degenerate monolayer graphene zero energy Landau level by experimentally controlling substrate-induced sublattice symmetry breaking. The transition is marked by unusual isospin transiti…
We study energy gaps of the $ν=7/2$ and $ν=5/2$ fractional quantum Hall states in a series of two-dimensional electron gases containing alloy disorder. We found that gaps at these two filling factors have the same suppression rate with alloy disorder. The dimensionless intrinsic gaps in our alloy samples obtained from the model proposed by Morf and d'Ambrumenil are consistent with numerical results, but are larger than those obtained from experiments on pristine samples published in the literature. The disorder broadening parameter has large uncertainties. However, a modified analysis relying …
Even denominator fractional quantum Hall states in a ZnO quantum well reveal interesting phase transitions in a tilted magnetic field. We have analyzed the planar electron gas in ZnO, confined in a parabolic potential in the third dimension, perpendicular to the plane of the electron gas. Since the Landau level gap is very small in this system we have included the screened Coulomb potential in order to include the effects of all the Landau levels. We observe an incompressible state - compressible state phase transition induced by the tilted field. Additionally, the 5/2 state has been experimen…
Even-denominator fractional quantum Hall states in the zeroth Landau level of ABA trilayer graphene
Indian Institute of Science（印度科学研究所）；National Institute for Materials Science（物质材料研究机构）；Physical Research Laboratory（物理研究实验室）；Institute of Mathematical Sciences（数学科学研究所）；Homi Bhabha National Institute（霍米·巴巴国立研究所）
研究 ABA 三层石墨烯零朗道能级中偶数分母分数量子霍尔态，通过实验观察到特定分数态及相关子态，确定其出现在特定位移场窗口与朗道能级交叉处，发现是朗道能级混合及反演对称性破缺所致，拓展了该领域并建立了可调平台。
Displacement field stabilizes even-denominator and partonic fractional quantum Hall states in the $\mathcal{N}{=}2$ Landau levels of Bernal-stacked bilayer graphene
Institute of Mathematical Sciences（数学科学研究所）；Homi Bhabha National Institute（霍米·巴巴国立学院）；Department of Physics, Indian Institute of Technology Bombay（印度理工学院孟买分校物理系）；Theoretical Physics Division, Physical Research Laboratory（物理研究实验室理论物理部）
Fractional quantum Hall states (FQHSs) at even-denominator Landau level filling factors ($ν$) are of prime interest as they are predicted to host exotic, topological states of matter. We report here the observation of a FQHS at $ν=1/2$ in a two-dimensional electron system of exceptionally high quality, confined to a wide AlAs quantum well, where the electrons can occupy multiple conduction-band valleys with an anisotropic effective mass. The anisotropy and multi-valley degree of freedom offer an unprecedented tunability of the $ν=1/2$ FQHS as we can control both the valley occupancy via the ap…
Recent Experimental Progress of Fractional Quantum Hall Effect: 5/2 Filling State and Graphene
分数量子霍尔效应（Fractional Quantum Hall Effect，简称FQHE）是在33年前首次在实验中观察到的。电子间的库仑相互作用和关联导致准粒子带有分数元电荷。30年过去了，太阳能电池领域仍然活跃着新的发现和新的技术发展。填充因子5/2态是量子物理学中的一个重要研究方向，因为它具有不寻常的偶数分母和在拓扑量子计算中的应用。传统上，在高迁移率GaAs异质结构中观察到了异质结HE，但石墨烯等新材料也为异质结HE开辟了新的领域。本文综述了石墨烯中5/2态的量子阱和量子阱的最新研究进展。
At even-denominator Landau level filling fractions, such as $ν=1/2$, the ground state, in most cases, has no energy gap, and there is no quantized plateau in the Hall conductance. Nevertheless, the states exhibit non-trivial low-energy phenomena. Open questions concerning the proper description of these systems have attracted renewed attention during the last few years. Issues at $ν=1/2$ include consequences of particle-hole symmetry, which should be present for a spin-aligned system in the limit where one can neglect mixing between Landau levels. Other issues concern questions of anisotropy a…
Non-Abelian states with negative flux: a new series of quantum Hall states
将仿费米子成团的思想应用于具有正负通量的复合玻色子，提出了一系列新的描述分数量子霍尔态的试探波函数。这些非阿贝尔态与其他基态如条纹或复合费米子态竞争填充因子k/（3 k +/- 2）。这两个系列包含了潘等人最近发现的所有状态。90，016801（2003）]，包括偶数分母情况。精确对角化的研究领域和环面点，他们可能的相关性填充因子3/7，3/11和3/8。
Fractional quantum spin Hall crystals from hidden density-wave order
University of California, Los Angeles（加州大学洛杉矶分校）；Mani L. Bhaumik Institute for Theoretical Physics, University of California Los Angeles（加州大学洛杉矶分校马尼·L·鲍姆克理论物理研究所）
The fractional quantum Hall effect (FQHE) is extensively studied, but the explanation for Hall plateau widths and excitation energy gaps remains elusive. We study the effective theory of FQHE built upon experimental inputs of Hall current distribution, edge dynamics, and many-body correlations. We argue that correlated composites of integer spin, comprising electrons and their images, localized at the edge of the incompressible strip are the basic transport entity. We show in the lowest Landau level that Zeeman interactions of these composites produce all odd denominator plateaus and effective…
We give a simple macroscopic phase-space explanation of fractional quantum Hall effect (FQHE), in a fashion reminiscent of the Landau-Ginsburg macroscopic symmetry breaking analyses. This is in contrast to the more complicated microscopic wavefunction approaches. Here, we employ a nonequilibrium quantum transport in the lattice Weyl transform formalism. This is coupled with the Maxwell Chern-Simons gauge theory for defining fractional filling of Landau levels. Flux attachment concept is inherent in fully occupied and as well as in partially occupied Landau levels. We derived the k-factor scali…
Half state at $ν_{tot}$ = -1/2 and its transition in Decoupled Twisted Double Bilayer Graphene
Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL)（洛桑联邦理工学院物理研究所）；Research Center for Functional Materials, National Institute for Materials Science（物质材料研究机构功能材料研究中心）；International Center for Materials Nanoarchitectonics, National Institute for Materials Science（物质材料研究机构国际纳米材料架构中心）；Center for Quantum Science and Engineering (QSE Center), École Polytechnique Fédérale de Lausanne (EPFL)（洛桑联邦理工学院量子科学与工程中心）
Large scale theoretical investigation of the phase diagram of twisted bilayer MoTe$_2$ at fractional fillings: agreements and contradictions with current experiments
Donostia International Physics Center（多诺西亚国际物理中心）；Department of Physics and Quantum Theory Project, University of Florida（佛罗里达大学物理系与量子理论项目）；Department of Physics, Princeton University（普林斯顿大学物理系）；Geballe Laboratory for Advanced Materials, Departments of Applied Physics, Stanford University（斯坦福大学应用物理系吉贝尔先进材料实验室）；IKERBASQUE, Basque Foundation for Science（伊克尔巴斯克，巴斯克科学基金会）；Center for Computational Quantum Physics, Flatiron Institute（平顿研究所计算量子物理中心）；Laboratoire de Physique de l’Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris-Diderot, Sorbonne Paris Cité（巴黎高等师范学校物理实验室，ENS，PSL大学，法国国家科学研究中心，索邦大学，巴黎狄德罗大学，索邦巴黎城）
Observation of Integer and Fractional Chern insulators in high Chern number flatbands
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）；Research Center for Electronic and Optical Materials, National Institute for Materials Science（物质材料研究机构电子光学材料研究中心）；Research Center for Materials Nanoarchitectonics, National Institute for Materials Science（物质材料研究机构材料纳米构造研究中心）；Songshan Lake Materials Laboratory（松山湖材料实验室）
