1,122 research outputs found
A conformal field theory description of the paired and parafermionic states in the quantum Hall effect
We extend the construction of the effective conformal field theory for the
Jain hierarchical fillings proposed in cond-mat/9912287 to the description of a
quantum Hall fluid at non standard fillings nu=m/(pm+2). The chiral primary
fields are found by using a procedure which induces twisted boundary conditions
on the m scalar fields; they appear as composite operators of a charged and
neutral component. The neutral modes describe parafermions and contribute to
the ground state wave function with a generalized Pfaffian term. Correlators of
Ne electrons in the presence of quasi-hole excitations are explicitly given for
m=2.Comment: 11 pages, plain Late
Tunnelling Effects in a Brane System and Quantum Hall Physics
We argue that a system of interacting D-branes, generalizing a recent
proposal, can be modelled as a Quantum Hall fluid. We show that tachyon
condensation in such a system is equivalent to one particle tunnelling. In a
conformal field theory effective description, that induces a transition from a
theory with central charge c=2 to a theory with c=3/2, with a corresponding
symmetry enhancement.Comment: 12 pages, no figures, Latex, some aspects clarified, sect.3 expanded,
references adde
A twisted conformal field theory description of the Quantum Hall Effect
We construct an effective conformal field theory by using a procedure which
induces twisted boundary conditions for the fundamental scalar fields. That
allows to describe a quantum Hall fluid at Jain hierarchical filling,
nu=m/(2pm+1), in terms of one charged scalar field and m-1 neutral ones. Then
the resulting algebra of the chiral primary fields is U(1)xW_m. Finally the
ground state wave functions are given as correlators of appropriate composite
fields (a-electrons).Comment: 11 pages, plain Late
A conformal field theory description of magnetic flux fractionalization in Josephson junction ladders
We show how the recently proposed effective theory for a Quantum Hall system
at "paired states" filling v=1 (Mod. Phys. Lett. A 15 (2000) 1679; Nucl. Phys.
B641 (2002) 547), the twisted model (TM), well adapts to describe the
phenomenology of Josephson Junction ladders (JJL) in the presence of defects.
In particular it is shown how naturally the phenomenon of flux
fractionalization takes place in such a description and its relation with the
discrete symmetries present in the TM. Furthermore we focus on closed
geometries, which enable us to analyze the topological properties of the ground
state of the system in relation to the presence of half flux quanta.Comment: 16 pages, 2 figure, Latex, revised versio
Paired states on a torus
We analyze the modular properties of the effective CFT description for paired
states, proposed in cond-mat/0003453, corresponding to the non-standard filling
nu =1/(p+1). We construct its characters for the twisted and the untwisted
sector and the diagonal partition function. We show that the degrees of freedom
entering our partition function naturally go to complete a Z_2-orbifold
construction of the CFT for the Halperin state. Different behaviours for the p
even and p odd cases are also studied. Finally it is shown that the tunneling
phenomenon selects out a twist invariant CFT which is identified with the
Moore-Read model.Comment: 24 pages, 1 figure, Late
New Results on the Phase Diagram of the FFXY Model: A Twisted CFT Approach
The issue of the number, nature and sequence of phase transitions in the
fully frustrated XY (FFXY) model is a highly non trivial one due to the complex
interplay between its continuous and discrete degrees of freedom. In this
contribution we attack such a problem by means of a twisted conformal field
theory (CFT) approach and show how it gives rise to the U (1)
symmetry and to the whole spectrum of excitations of the FFXY model.Comment: 7 pages; talk given by G. Niccoli at "Path Integrals - New Trends and
Perspectives International Conference", Max-Planck-Institut, Dresden,
Germany, September 23 - 28, 200
From vertex operators to Calogero-Sutherland models
The correlation function of the product of N generalized vertex operators satisfies an infinite set of Ward identities, related to a W_{\infty} algebra, whose extension out of the mass shell gives rise to equations which can be considered as a generalization of the compactified Calogero-Sutherland (CS) hamiltonians. In particular the wave function of the ground state of the compactified CS model is shown to be given by the value of the product of N vertex operators between the vacuum and exitated state. The role of vertex algebra as underlying unifying structure is pointed out
Topological order in Josephson junction ladders with Mobius boundary conditions
We propose a CFT description for a closed one-dimensional fully frustrated
ladder of quantum Josephson junctions with Mobius boundary conditions, in
particular we show how such a system can develop topological order. Such a
property is crucial for its implementation as a "protected" solid state qubit.Comment: 14 pages, 3 figures, to appear in JSTA
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