367 research outputs found
Conformal quantum mechanics as the CFT dual to AdS
A 0+1-dimensional candidate theory for the CFT dual to AdS is
discussed. The quantum mechanical system does not have a ground state that is
invariant under the three generators of the conformal group. Nevertheless, we
show that there are operators in the theory that are not primary, but whose
"non-primary character" conspires with the "non-invariance of the vacuum" to
give precisely the correlation functions in a conformally invariant theory.Comment: 6 page
Corner Junction as a Probe of Helical Edge States
We propose and analyze inter-edge tunneling in a quantum spin Hall corner
junction as a means to probe the helical nature of the edge states. We show
that electron-electron interactions in the one-dimensional helical edge states
result in Luttinger parameters for spin and charge that are intertwined, and
thus rather different than those for a quantum wire with spin rotation
invariance. Consequently, we find that the four-terminal conductance in a
corner junction has a distinctive form that could be used as evidence for the
helical nature of the edge states.Comment: 4+ pages, 3 figure
Colored noise in the fractional Hall effect: duality relations and exact results
We study noise in the problem of tunneling between fractional quantum Hall
edge states within a four probe geometry. We explore the implications of the
strong-weak coupling duality symmetry existent in this problem for relating the
various density-density auto-correlations and cross-correlations between the
four terminals. We identify correlations that transform as either ``odd'' or
``anti-symmetric'', or ``even'' or ``symmetric'' quantities under duality. We
show that the low frequency noise is colored, and that the deviations from
white noise are exactly related to the differential conductance. We show
explicitly that the relationship between the slope of the low frequency noise
spectrum and the differential conductance follows from an identity that holds
to {\it all} orders in perturbation theory, supporting the results implied by
the duality symmetry. This generalizes the results of quantum supression of the
finite frequency noise spectrum to Luttinger liquids and fractional statistics
quasiparticles.Comment: 14 pages, 3 figure
Out-of-equilibrium dynamical fluctuations in glassy systems
In this paper we extend the earlier treatment of out-of-equilibrium
mesoscopic fluctuations in glassy systems in several significant ways. First,
via extensive simulations, we demonstrate that models of glassy behavior
without quenched disorder display scalings of the probability of local two-time
correlators that are qualitatively similar to that of models with short-ranged
quenched interactions. The key ingredient for such scaling properties is shown
to be the development of a critical-like dynamical correlation length, and not
other microscopic details. This robust data collapse may be described in terms
of a time-evolving Gumbel-like distribution. We develop a theory to describe
both the form and evolution of these distributions based on a effective
sigma-model approach.Comment: 20 pages, RevTex, 9 figure
Interaction of Phonons and Dirac Fermions on the Surface of Bi2Se3: A Strong Kohn Anomaly
We report the first measurements of phonon dispersion curves on the (001)
surface of the strong three-dimensional topological insulator Bi2Se3. The
surface phonon measurements were carried out with the aid of coherent helium
beam surface scattering techniques. The results reveal a prominent signature of
the exotic metallic Dirac fermion quasi-particles, including a strong Kohn
anomaly. The signature is manifest in a low energy isotropic convex dispersive
surface phonon branch with a frequency maximum of 1.8 THz, and having a
V-shaped minimum at approximately 2kF that defines the Kohn anomaly.
Theoretical analysis attributes this dispersive profile to the renormalization
of the surface phonon excitations by the surface Dirac fermions. The
contribution of the Dirac fermions to this renormalization is derived in terms
of a Coulomb-type perturbation model
Correlation of eigenstates in the critical regime of quantum Hall systems
We extend the multifractal analysis of the statistics of critical wave
functions in quantum Hall systems by calculating numerically the correlations
of local amplitudes corresponding to eigenstates at two different energies. Our
results confirm multifractal scaling relations which are different from those
occurring in conventional critical phenomena. The critical exponent
corresponding to the typical amplitude, , gives an almost
complete characterization of the critical behavior of eigenstates, including
correlations. Our results support the interpretation of the local density of
states being an order parameter of the Anderson transition.Comment: 17 pages, 9 Postscript figure
Quantizing Majorana Fermions in a Superconductor
A Dirac-type matrix equation governs surface excitations in a topological
insulator in contact with an s-wave superconductor. The order parameter can be
homogenous or vortex valued. In the homogenous case a winding number can be
defined whose non-vanishing value signals topological effects. A vortex leads
to a static, isolated, zero energy solution. Its mode function is real, and has
been called "Majorana." Here we demonstrate that the reality/Majorana feature
is not confined to the zero energy mode, but characterizes the full quantum
field. In a four-component description a change of basis for the relevant
matrices renders the Hamiltonian imaginary and the full, space-time dependent
field is real, as is the case for the relativistic Majorana equation in the
Majorana matrix representation. More broadly, we show that the Majorana
quantization procedure is generic to superconductors, with or without the Dirac
structure, and follows from the constraints of fermionic statistics on the
symmetries of Bogoliubov-de Gennes Hamiltonians. The Hamiltonian can always be
brought to an imaginary form, leading to equations of motion that are real with
quantized real field solutions. Also we examine the Fock space realization of
the zero mode algebra for the Dirac-type systems. We show that a
two-dimensional representation is natural, in which fermion parity is
preserved.Comment: 26 pages, no figure
Phase-Coherent Transport through a Mesoscopic System: A New Probe of Non-Fermi-Liquid Behavior
A novel chiral interferometer is proposed that allows for a direct
measurement of the phase of the transmission coefficient for transport through
a variety of mesoscopic structures in a strong magnetic field. The effects of
electron-electron interaction on this phase is investigated with the use of
finite-size bosonization techniques combined with perturbation theory
resummation. New non-Fermi-liquid phenomena are predicted in the FQHE regime
that may be used to distinguish experimentally between Luttinger and Fermi
liquids.Comment: 4 pages, 3 figures, Revte
Disorder and interaction induced pairing in the addition spectra of quantum dots
We have investigated numerically the electron addition spectra in quantum
dots containing a small number (N < 11) of interacting electrons, in presence
of strong disorder. For a short-range Coulomb repulsion, we find regimes in
which two successive electrons enter the dot at very close values of the
chemical potential. In the strongly correlated regime these close additions, or
pairing, are associated with electrons tunneling into distinct electron puddles
within the dot. We discuss the tunneling rates at pairing, and we argue that
our results are related to a phenomenon known as "bunching", recently observed
experimentally.Comment: 4 pages, 5 figure
- …