6,714 research outputs found
NbSe3: Effect of Uniaxial Stress on the Threshold Field and Fermiology
We have measured the effect of uniaxial stress on the threshold field ET for
the motion of the upper CDW in NbSe3. ET exhibits a critical behavior, ET ~ (1
- e/ec)^g, wher e is the strain, and ec is about 2.6% and g ~ 1.2. This
ecpression remains valid over more than two decades of ET, up to the highest
fields of about 1.5keV/m. Neither g nor ec is very sensitive to the impurity
concentraction. The CDW transition temperature Tp decreases linearly with e at
a rate dTp/de = -10K/%, and it does not show any anomaly near ec. Shubnikov
de-Haas measurements show that the extremal area of the Fermi surface decreases
with increasing strain. The results suggest that there is an intimate
relationship between pinning of the upper CDW and the Fermiology of NbSe3.Comment: 4 pages, 5 figure
Infrared Spectroscopy of Quantum Crossbars
Infrared (IR) spectroscopy can be used as an important and effective tool for
probing periodic networks of quantum wires or nanotubes (quantum crossbars,
QCB) at finite frequencies far from the Luttinger liquid fixed point. Plasmon
excitations in QCB may be involved in resonance diffraction of incident
electromagnetic waves and in optical absorption in the IR part of the spectrum.
Direct absorption of external electric field in QCB strongly depends on the
direction of the wave vector This results in two types of
dimensional crossover with varying angle of an incident wave or its frequency.
In the case of QCB interacting with semiconductor substrate, capacitive contact
between them does not destroy the Luttinger liquid character of the long wave
QCB excitations. However, the dielectric losses on a substrate surface are
significantly changed due to appearance of additional Landau damping. The
latter is initiated by diffraction processes on QCB superlattice and manifests
itself as strong but narrow absorption peaks lying below the damping region of
an isolated substrate.SubmiComment: Submitted to Phys. Rev.
Plasmon excitations and 1D - 2D dimensional crossover in quantum crossbars
Spectrum of boson fields and two-point correlators are analyzed in quantum
crossbars (QCBs, a superlattice formed by m crossed interacting arrays of
quantum wires), with short range inter-wire capacitive interaction. Spectral
and correlation properties of double (m=2) and triple (m-3) QCBs are studied.
It is shown that the standard bosonization procedure is valid, and the system
behaves as a sliding Luttinger liquid in the infrared limit, but the high
frequency spectral and correlation characteristics have either 1D or 2D nature
depending on the direction of the wave vector in the 2D elementary cell of
reciprocal lattice. As a result, the crossover from 1D to 2D regime may be
experimentally observed. It manifests itself as appearance of additional peaks
of optical absorption, non-zero transverse space correlators and periodic
energy transfer between arrays ("Rabi oscillations")
Del Pezzo surfaces with 1/3(1,1) points
We classify del Pezzo surfaces with 1/3(1,1) points in 29 qG-deformation
families grouped into six unprojection cascades (this overlaps with work of
Fujita and Yasutake), we tabulate their biregular invariants, we give good
model constructions for surfaces in all families as degeneracy loci in rep
quotient varieties and we prove that precisely 26 families admit
qG-degenerations to toric surfaces. This work is part of a program to study
mirror symmetry for orbifold del Pezzo surfaces.Comment: 42 pages. v2: model construction added of last remaining surface,
minor corrections, minor changes to presentation, references adde
Prospect of determining the Dirac/Majorana state of neutrino by Multi-OWL experiment
We consider the non-radiative two body decay of a neutrino to a daughter
neutrino with degraded energy and a very light particle (Majoron). Ultrahigh
energy neutrinos from an astrophysical source like a Gamma Ray Burst undergoing
this decay process are found to produce different number of events in the
detector depending on whether they are Majorana or Dirac particles. The next
generation large scale experiments like Multi-OWL is expected to provide us an
accurate determination of the flux of neutrinos from astrophysical sources and
this may enable us to distinguish between the Dirac and Majorana nature of
neutrino.Comment: 18 pages latex, no figure. Journal of Phys. G in pres
Twisted boundary states in c=1 coset conformal field theories
We study the mutual consistency of twisted boundary conditions in the coset
conformal field theory G/H. We calculate the overlap of the twisted boundary
states of G/H with the untwisted ones, and show that the twisted boundary
states are consistently defined in the diagonal modular invariant. The overlap
of the twisted boundary states is expressed by the branching functions of a
twisted affine Lie algebra. As a check of our argument, we study the diagonal
coset theory so(2n)_1 \oplus so(2n)_1/so(2n)_2, which is equivalent with the
orbifold S^1/\Z_2. We construct the boundary states twisted by the
automorphisms of the unextended Dynkin diagram of so(2n), and show their mutual
consistency by identifying their counterpart in the orbifold. For the triality
of so(8), the twisted states of the coset theory correspond to neither the
Neumann nor the Dirichlet boundary states of the orbifold and yield the
conformal boundary states that preserve only the Virasoro algebra.Comment: 44 pages, 1 figure; (v2) minor change in section 2.3, references
adde
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