1,817 research outputs found
On bipartite Rokhsar-Kivelson points and Cantor deconfinement
Quantum dimer models on bipartite lattices exhibit Rokhsar-Kivelson (RK)
points with exactly known critical ground states and deconfined spinons. We
examine generic, weak, perturbations around these points. In d=2+1 we find a
first order transition between a ``plaquette'' valence bond crystal and a
region with a devil's staircase of commensurate and incommensurate valence bond
crystals. In the part of the phase diagram where the staircase is incomplete,
the incommensurate states exhibit a gapless photon and deconfined spinons on a
set of finite measure, almost but not quite a deconfined phase in a compact
U(1) gauge theory in d=2+1! In d=3+1 we find a continuous transition between
the U(1) resonating valence bond (RVB) phase and a deconfined staggered valence
bond crystal. In an appendix we comment on analogous phenomena in quantum
vertex models, most notably the existence of a continuous transition on the
triangular lattice in d=2+1.Comment: 9 pages; expanded version to appear in Phys. Rev. B; presentation
improve
One-particle and collective electron spectra in hot and dense QED and their gauge dependence
The one-particle electron spectrum is found for hot and dense QED and its
properties are investigated in comparison with the collective spectrum. It is
shown that the one-particle spectrum (in any case its zero momentum limit) is
gauge invariant, but the collective spectrum, being qualitatively different, is
always gauge dependent. The exception is the case for which the
collective spectrum long wavelength limit demonstrates the gauge invariance as
well.Comment: 9 pages, latex, no figure
Heat transport through quantum Hall edge states: Tunneling versus capacitive coupling to reservoirs
We study the heat transport along an edge state of a two-dimensional electron
gas in the quantum Hall regime, in contact to two reservoirs at different
temperatures. We consider two exactly solvable models for the edge state
coupled to the reservoirs. The first one corresponds to filling and
tunneling coupling to the reservoirs. The second one corresponds to integer or
fractional filling of the sequence (with odd), and capacitive
coupling to the reservoirs. In both cases we solve the problem by means of
non-equilibrium Green function formalism. We show that heat propagates chirally
along the edge in the two setups. We identify two temperature regimes, defined
by , the mean level spacing of the edge. At low temperatures, , finite size effects play an important role in heat transport, for both
types of contacts. The nature of the contacts manifest themselves in different
power laws for the thermal conductance as a function of the temperature. For
capacitive couplings a highly non-universal behavior takes place, through a
prefactor that depends on the length of the edge as well as on the coupling
strengths and the filling fraction. For larger temperatures, ,
finite-size effects become irrelevant, but the heat transport strongly depends
on the strength of the edge-reservoir interactions, in both cases. The thermal
conductance for tunneling coupling grows linearly with , whereas for the
capacitive case it saturates to a value that depends on the coupling strengths
and the filling factors of the edge and the contacts.Comment: 15 pages, 5 figure
Double point contact in Quantum Hall Line Junctions
We show that multiple point contacts on a barrier separating two laterally
coupled quantum Hall fluids induce Aharonov-Bohm (AB) oscillations in the
tunneling conductance. These quantum coherence effects provide new evidence for
the Luttinger liquid behavior of the edge states of quantum Hall fluids. For a
two point contact, we identify coherent and incoherent regimes determined by
the relative magnitude of their separation and the temperature. We analyze both
regimes in the strong and weak tunneling amplitude limits as well as their
temperature dependence. We find that the tunneling conductance should exhibit
AB oscillations in the coherent regime, both at strong and weak tunneling
amplitude with the same period but with different functional form.Comment: 4 pages, 3 figures; new version, edited text, 2 new references;
figure 2 has been edited; new paragraph in page 1 and minor typos have been
correcte
Some Computations in Background Independent Open-String Field Theory
Recently, background independent open-string field theory has been formally
defined in the space of all two-dimensional world-sheet theories. In this
paper, to make the construction more concrete, I compute the action for an
off-shell tachyon field of a certain simple type. From the computation it
emerges that, although the string field action does not coincide with the
world-sheet (matter) partition function in general, these functions do coincide
on shell. This can be demonstrated in general, as long as matter and ghosts are
decoupled.Comment: 14 p
Artificial electric field in Fermi Liquids
Based on the Keldysh formalism, we derive an effective Boltzmann equation for
a quasi-particle associated with a particular Fermi surface in an interacting
Fermi liquid. This provides a many-body derivation of Berry curvatures in
electron dynamics with spin-orbit coupling, which has received much attention
in recent years in non-interacting models. As is well-known, the Berry
curvature in momentum space modifies naive band dynamics via an artificial
magnetic field in momentum space. Our Fermi liquid formulation completes the
reinvention of modified band dynamics by introducing in addition an "artificial
electric field", related to Berry curvature in frequency and momentum space. We
show explicitly how the artificial electric field affects the renormalization
factor and transverse conductivity of interacting U(1) Fermi liquids with
non-degenerate bands. Accordingly, we also propose a method of momentum
resolved Berry's curvature detection in terms of angle resolved photoemission
spectroscopy (ARPES)
Topological superconducting phases from inversion symmetry breaking order in spin-orbit-coupled systems
We analyze the superconducting instabilities in the vicinity of the
quantum-critical point of an inversion symmetry breaking order. We first show
that the fluctuations of the inversion symmetry breaking order lead to two
degenerate superconducting (SC) instabilities, one in the -wave channel, and
the other in a time-reversal invariant odd-parity pairing channel (the simplest
case being the same as the of He-B phase). Remarkably, we find that unlike
many well-known examples, the selection of the pairing symmetry of the
condensate is independent of the momentum-space structure of the collective
mode that mediates the pairing interaction. We found that this degeneracy is a
result of the existence of a conserved fermionic helicity, , and the two
degenerate channels correspond to even and odd combinations of SC order
parameters with . As a result, the system has an enlarged symmetry
, with each corresponding to one value of
the helicity . Because of the enlarged symmetry, this system admits
exotic topological defects such as a fractional quantum vortex, which we show
has a Majorana zero mode bound at its core. We discuss how the enlarged
symmetry can be lifted by small perturbations, such as the Coulomb interaction
or Fermi surface splitting in the presence of broken inversion symmetry, and we
show that the resulting superconducting state can be topological or trivial
depending on parameters. The symmetry is restored at the
phase boundary between the topological and trivial SC states, and allows for a
transition between topologically distinct SC phases without the vanishing of
the order parameter. We present a global phase diagram of the superconducting
states and discuss possible experimental implications.Comment: 14 pages, 5 figures, to match the published versio
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