21,286 research outputs found
Deficiency of MecA in Streptococcus mutans causes major defects in cell envelope biogenesis, cell division, and biofilm formation
Fractionalization, topological order, and cuprate superconductivity
This paper is concerned with the idea that the electron is fractionalized in
the cuprate high- materials. We show how the notion of topological order
may be used to develop a precise theoretical characterization of a
fractionalized phase in spatial dimension higher than one. Apart from the
fractional particles into which the electron breaks apart, there are
non-trivial gapped topological excitations - dubbed "visons". A cylindrical
sample that is fractionalized exhibits two disconnected topological sectors
depending on whether a vison is trapped in the "hole" or not. Indeed, "vison
expulsion" is to fractionalization what the Meissner effect ("flux expulsion")
is to superconductivity. This understanding enables us to address a number of
conceptual issues that need to be confronted by any theory of the cuprates
based on fractionalization ideas. We argue that whether or not the electron
fractionalizes in the cuprates is a sharp and well-posed question with a
definite answer. We elaborate on our recent proposal for an experiment to
unambiguously settle this issue.Comment: 18 pages, 7 figure
Gapless Fermions and Quantum Order
Using 2D quantum spin-1/2 model as a concrete example, we studied the
relation between gapless fermionic excitations (spinons) and quantum orders in
some spin liquid states. Using winding number, we find the projective symmetry
group that characterizes the quantum order directly determines the pattern of
Fermi points in the Brillouin zone. Thus quantum orders provide an origin for
gapless fermionic excitations.Comment: 23 pages. LaTeX. Homepage http://dao.mit.edu/~we
Spin- generalization of fractional exclusion statistics
We study fractional exclusion statistics for quantum systems with SU(2)
symmetry (arbitrary spin ), by generalizing the thermodynamic equations with
squeezed strings proposed by Ha and Haldane. The bare hole distributions as
well as the statistical interaction defined by an infinite-dimensional matrix
specify the universality class. It is shown that the system is described by the
level- WZW model and has a close relationship to non-abelian fractional
quantum Hall states. As a low-energy effective theory, the sector of {\it
massless} Z parafermions is extracted, whose statistical interaction is
given by a finite-dimensional matrix.Comment: 11pages, REVTE
Bosonic model with fractionalization
Bosonic model with unfrustrated hopping and short-range repulsive interaction
is constructed that realizes fractionalized insulator phase in two
dimensions and in zero magnetic field. Such phase is characterized as having
gapped charged excitations that carry fractional electrical charge 1/3 and also
gapped vortices above the topologically ordered ground state.Comment: 7 pages, 3 figure
Quantum Hall Ferromagnets
It is pointed out recently that the quantum Hall states in bilayer
systems behave like easy plane quantum ferromagnets. We study the
magnetotransport of these systems using their ``ferromagnetic" properties and a
novel spin-charge relation of their excitations. The general transport is a
combination of the ususal Hall transport and a time dependent transport with
time average. The latter is due to a phase slippage process in
and is characterized by two topological constants. (Figures will be
provided upon requests).Comment: 4 pages, Revtex, Ohio State Universit
Topological orders and Edge excitations in FQH states
Fractional quantum Hall (FQH) liquids contain extremely rich internal
structures which represent a whole new kind of ordering. We discuss
characterization and classification of the new orders (which is called
topological orders). We also discuss the edge excitations in FQH liquids, which
form the so-called chiral Luttinger liquids. The chiral Luttinger liquids at
the edges also have very rich structures as a reflection of the rich
topological orders in the bulk. Thus, edge excitations provide us a practical
way to measure topological orders in experiments.Comment: 67 pages, plain-tex, 3 figures. The section about spin vector was
rewritten to make it more readabl
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