Time-reversal invariant three-dimensional topological insulators can be defined fundamentally by a topological field theory with a quantized axion angle theta of zero or pi. It was recently shown that fractional quantized values of theta are consistent with time-reversal invariance if deconfined, gapped, fractionally charged bulk excitations appear in the low-energy spectrum due to strong correlation effects, leading to the concept of a fractional topological insulator. These fractionally charged excitations are coupled to emergent gauge fields which ensure that the microscopic degrees of freedom, the original electrons, are gauge-invariant objects. A first step towards the construction of microscopic models of fractional topological insulators is to understand the nature of these emergent gauge theories and their corresponding phases. In this work, we show that low-energy effective gauge theories of both Abelian or non-Abelian type are consistent with a fractional quantized axion angle if they admit a Coulomb phase or a Higgs phase with gauge group broken down to a discrete subgroup. The Coulomb phases support gapless but electrically neutral bulk excitations while the Higgs phases are fully gapped. The Higgs and non-Abelian Coulomb phases exhibit multiple ground states on boundaryless spatial 3-manifolds with nontrivial first homology, while the Abelian Coulomb phase has a unique ground state. The ground state degeneracy receives an additional contribution on manifolds with boundary due to the induced boundary Chern-Simons term.
The D3-probe-D7 brane system, oriented so as to have 2+1-dimensional Poincare symmetry, is argued to be the holographic representation of a strongly correlated fractional topological insulator which exhibits a zero-field quantized Hall effect with half-units of Hall conductivity. The phase diagram of the system with charge density and external magnetic field is found and, as well as charge gapped quantum Hall states, it exhibits metallic and semi-metallic phases with interesting behaviours. The relationship of this to other models of fractional topological insulators is discussed.
Reply to "Comment on `Floquet Fractional Chern Insulators'"
我们对L. D'Alessio in arXiv:1412.3481 on our work“Floquet Fractional Chern Insulators”[Phys. Rev. Lett. 112,156801(2014)]。我们证实了有效哈密顿量的基态是一个相互作用的分数Chern绝缘体的中心结果。
We study transitions between topological phases featuring emergent fractionalized excitations in two-dimensional models for Mott insulators with spin and orbital degrees of freedom. The models realize fermionic quantum critical points in fractionalized Gross-Neveu$^\ast$ universality classes in (2+1) dimensions. They are characterized by the same set of critical exponents as their ordinary Gross-Neveu counterparts, but feature a different energy spectrum, reflecting the nontrivial topology of the adjacent phases. We exemplify this in a square-lattice model, for which an exact mapping to a $t$-…
We construct the symmetric-gapped surface states of a fractional topological insulator with electromagnetic $θ$-angle $θ_{em} = \fracπ{3}$ and a discrete $\mathbb{Z}_3$ gauge field. They are the proper generalizations of the T-pfaffian state and pfaffian/anti-semion state and feature an extended periodicity compared with their of "integer" topological band insulators counterparts. We demonstrate that the surface states have the correct anomalies associated with time-reversal symmetry and charge conservation.
Motivated by work on the bulk topological proximity effect and the topological bootstrap, we consider two coupled layers of quantum anomalous Hall (QAH) insulators with opposite signs of time-reversal breaking, which leads to a trivial band insulator at half-filling. We study the impact of interactions in this model within slave rotor theory, which leads to a layer-selective Mott transition, resulting in a fractionalized quantum anomalous Hall insulator QAH$^*$ where a Chern band insulator coexists with a chiral spin liquid. We also compute the edge electron spectral function in the vicinity o…
Dirac Quantization and Fractional Magnetoelectric Effect on Interacting Topological Insulators
利用Dirac量子化方法研究了相互作用拓扑绝缘体中的分数电荷和轴子角θ。在相互作用的拓扑绝缘体中,由于边界处的常规奇通量量子化和非平凡偶通量量子化,存在两种类型的分数轴子角。在带隙时反不变系统的偶通量量子化中,我们证明了在霍尔电导为p/4 qe ~(2/2)h(p,q为奇数)的表面上存在减半的四分之一分数量子霍尔效应.能隙表面模的特征是偶通量量子化产生的非平凡的Z2反常。在复旋量场Dirac量子化的基础上,提出了电子可以看作是一个非阿贝尔色规范场约束的分数荷电夸克束缚态。
We formulate a Chern-Simons composite fermion theory for Fractional Chern Insulators (FCIs), whereby bare fermions are mapped into composite fermions coupled to a lattice Chern-Simons gauge theory. We apply this construction to a Chern insulator model on the kagome lattice and identify a rich structure of gapped topological phases characterized by fractionalized excitations including states with unequal filling and Hall conductance. Gapped states with the same Hall conductance at different filling fractions are characterized as realizing distinct symmetry fractionalization classes.
Lattice construction of pseudopotential Hamiltonians for Fractional Chern Insulators
分数Chern绝缘体是分数量子霍尔态在无轨道磁场晶格系统中的新实现。这些状态可以通过Wannier状态表示(Phys. Rev. Lett. 107,126803(2011))。本文利用Wannier态表象构造了分数阶Chern绝缘体的赝势哈密顿量,它是以某些理想模型波函数作为精确基态的相互作用哈密顿量。我们表明,这些赝势哈密顿可以近似的短程相互作用的分数陈省身绝缘体,和他们的范围将被最小化的最佳规范选择的Wannier状态。作为说明性的例子,我们明确地写出了几个分数陈绝缘体模型的最低赝势的形式,包括晶格狄拉克模型和棋盘模型与陈数1,和d波模型和三角晶格模型与陈数2。当Chern数C=1时,赝势哈密顿算符的基态为1/3 Laughlin态;当C=2时,赝势哈密顿算符的基态为拓扑的330态.还包括d-波模型和两个解耦层的晶格狄拉克模型之间的插值的结果,这明确地证明了C=2分数陈绝缘体和双层分数量子霍尔态之间的关系。所提出的状态可以通过未来的数值工作进行验证,特别是提供了一个模型哈密顿量的拓扑结构的状态,还没有实现数字。
Fractional topological insulators of Cooper pairs induced by proximity effect
某些具有强自旋轨道耦合的绝缘材料可以沿着其边缘或表面传导电流。这一现象源于电子能带结构的非平凡拓扑性质,与强磁场中电子的整数量子霍尔效应有些相似。类似于分数量子霍尔效应的拓扑绝缘体也是可能的,但尚未在任何材料中观察到。在这里,我们表明,一个量子阱的拓扑带绝缘体,如Bi 2 Se 3或Bi 2 Te 3,放置在与超导体接触,可以用来实现一个二维的拓扑状态与宏观多体量子纠缠的激发携带分数电子的电荷和自旋。这种分数拓扑绝缘体是诱导自旋p波库珀对的“赝能隙”态,对量子场论具有重要意义,并可应用于自旋电子器件和量子计算.
Motivated by the recent work of QED$_3$-Chern-Simons quantum critical points of fractional Chern insulators (Phys. Rev. X \textbf{8}, 031015, (2018)), we study its non-Abelian generalizations, namely QCD$_3$-Chern-Simons quantum phase transitions of fractional Chern insulators. These phase transitions are described by Dirac fermions interacting with non-Abelian Chern-Simons gauge fields ($U(N)$, $SU(N)$, $USp(N)$, etc.). Utilizing the level-rank duality of Chern-Simons gauge theory and non-Abelian parton constructions, we discuss two types of QCD$_3$ quantum phase transitions. The first type h…
In this paper, we propose a generalization of the $S$-duality of four-dimensional quantum electrodynamics ($\text{QED}_4$) to $\text{QED}_4$ with fractionally charged excitations, the fractional $S$-duality. Such $\text{QED}_4$ can be obtained by gauging the $\text{U(1)}$ symmetry of a topologically ordered state with fractional charges. When time-reversal symmetry is imposed, the axion angle ($θ$) can take a nontrivial but still time-reversal invariant value $π/t^2$ ($t\in\mathbb{Z}$). Here, $1/t$ specifies the minimal electric charge carried by bulk excitations. Such states with time-reversa…
We investigate the problem of intertwined orders in fractional Chern insulators by considering lattice fractional quantum Hall (FQH) states arising from pairing of composite fermions in the square-lattice Hofstadter model. At certain filling fractions, magnetic translation symmetry ensures the composite fermions form Fermi surfaces with multiple pockets, leading to the formation of finite-momentum Cooper pairs in the presence of attractive interactions. We obtain mean-field phase diagrams exhibiting a rich array of striped and topological phases, establishing paired lattice FQH states as an id…
Fractional topological insulators (FTI) are electronic topological phases in $(3+1)$ dimensions enriched by time reversal (TR) and charge $U(1)$ conservation symmetries. We focus on the simplest series of fermionic FTI, whose bulk quasiparticles consist of deconfined partons that carry fractional electric charges in integral units of $e^\ast=e/(2n+1)$ and couple to a discrete $\mathbb{Z}_{2n+1}$ gauge theory. We propose massive symmetry preserving or breaking FTI surface states. Combining the long-ranged entangled bulk with these topological surface states, we deduce the novel topological orde…
We perform an exact-diagonalization study of quasihole excitations for the two-component Halperin $(221)$ state in the lowest Landau level and for several $ν=1/3$ bosonic fractional Chern insulators in topological flat bands with Chern number $|C|=2$. Properties including the quasihole size, charge, and braiding statistics are evaluated. For the Halperin $(221)$ model state, we observe isotropic quasiholes with a clear internal structure, and obtain the quasihole charge and statistics matching the theoretical values. Interestingly, we also extract the same quasihole size, charge, and braiding …
Moir{é} superlattice realized in two-dimensional heterostructures offers an exciting platform to access strongly-correlated electronic states. In this work, we study transition metal dichalcogenides (TMD) Moir{é} superlattices with time-reversal-symmetry and nontrivial spin{/valley}-Chern numbers. Utilizing realistic material parameters and the method of exact diagonalization, we find that at a certain twisting angle and fractional filling, gapped fractional topological states, i.e., fractional Chern insulators, are naturally {stabilized} by simply introducing the Coulomb repulsion. In contras…