14,695 research outputs found
Emergent Many-Body Translational Symmetries of Abelian and Non-Abelian Fractionally Filled Topological Insulators
The energy and entanglement spectrum of fractionally filled interacting
topological insulators exhibit a peculiar manifold of low energy states
separated by a gap from a high energy set of spurious states. In the current
manuscript, we show that in the case of fractionally filled Chern insulators,
the topological information of the many-body state developing in the system
resides in this low-energy manifold. We identify an emergent many-body
translational symmetry which allows us to separate the states in
quasi-degenerate center of mass momentum sectors. Within one center of mass
sector, the states can be further classified as eigenstates of an emergent (in
the thermodynamic limit) set of many-body relative translation operators. We
analytically establish a mapping between the two-dimensional Brillouin zone for
the Fractional Quantum Hall effect on the torus and the one for the fractional
Chern insulator. We show that the counting of quasi-degenerate levels below the
gap for the Fractional Chern Insulator should arise from a folding of the
states in the Fractional Quantum Hall system at identical filling factor. We
show how to count and separate the excitations of the Laughlin, Moore-Read and
Read-Rezayi series in the Fractional Quantum Hall effect into two-dimensional
Brillouin zone momentum sectors, and then how to map these into the momentum
sectors of the Fractional Chern Insulator. We numerically check our results by
showing the emergent symmetry at work for Laughlin, Moore-Read and Read-Rezayi
states on the checkerboard model of a Chern insulator, thereby also showing, as
a proof of principle, that non-Abelian Fractional Chern Insulators exist.Comment: 32 pages, 9 figure
Diffusive-Ballistic Crossover and the Persistent Spin Helix
Conventional transport theory focuses on either the diffusive or ballistic
regimes and neglects the crossover region between the two. In the presence of
spin-orbit coupling, the transport equations are known only in the diffusive
regime, where the spin precession angle is small. In this paper, we develop a
semiclassical theory of transport valid throughout the diffusive - ballistic
crossover of a special SU(2) symmetric spin-orbit coupled system. The theory is
also valid in the physically interesting regime where the spin precession angle
is large. We obtain exact expressions for the density and spin structure
factors in both 2 and 3 dimensional samples with spin-orbit coupling.Comment: 4 pages, 3 figure
Berry-phase description of Topological Crystalline Insulators
We study a class of translational-invariant insulators with discrete
rotational symmetry. These insulators have no spin-orbit coupling, and in some
cases have no time-reversal symmetry as well, i.e., the relevant symmetries are
purely crystalline. Nevertheless, topological phases exist which are
distinguished by their robust surface modes. Like many well-known topological
phases, their band topology is unveiled by the crystalline analog of Berry
phases, i.e., parallel transport across certain non-contractible loops in the
Brillouin zone. We also identify certain topological phases without any robust
surface modes -- they are uniquely distinguished by parallel transport along
bent loops, whose shapes are determined by the symmetry group. Our findings
have experimental implications in cold-atom systems, where the crystalline
Berry phase has been directly measured.Comment: Latest version is accepted to PR
Recursions of Symmetry Orbits and Reduction without Reduction
We consider a four-dimensional PDE possessing partner symmetries mainly on
the example of complex Monge-Amp\`ere equation (CMA). We use simultaneously two
pairs of symmetries related by a recursion relation, which are mutually complex
conjugate for CMA. For both pairs of partner symmetries, using Lie equations,
we introduce explicitly group parameters as additional variables, replacing
symmetry characteristics and their complex conjugates by derivatives of the
unknown with respect to group parameters. We study the resulting system of six
equations in the eight-dimensional space, that includes CMA, four equations of
the recursion between partner symmetries and one integrability condition of
this system. We use point symmetries of this extended system for performing its
symmetry reduction with respect to group parameters that facilitates solving
the extended system. This procedure does not imply a reduction in the number of
physical variables and hence we end up with orbits of non-invariant solutions
of CMA, generated by one partner symmetry, not used in the reduction. These
solutions are determined by six linear equations with constant coefficients in
the five-dimensional space which are obtained by a three-dimensional Legendre
transformation of the reduced extended system. We present algebraic and
exponential examples of such solutions that govern Legendre-transformed
Ricci-flat K\"ahler metrics with no Killing vectors. A similar procedure is
briefly outlined for Husain equation
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