550 research outputs found
On the Intracluster Medium in Cooling Flow & Non-Cooling Flow Clusters
Recent X-ray observations have highlighted clusters that lack entropy cores.
At first glance, these results appear to invalidate the preheated ICM models.
We show that a self-consistent preheating model, which factors in the effects
of radiative cooling, is in excellent agreement with the observations.
Moreover, the model naturally explains the intrinsic scatter in the L-T
relation, with ``cooling flow'' and ``non-cooling flow'' systems corresponding
to mildly and strongly preheated systems, respectively. We discuss why
preheating ought to be favoured over merging as a mechanism for the origin of
``non-cooling flow'' clusters.Comment: 4 pages, to appear in the proceedings of the "Multiwavelength
Cosmology" Conference held in Mykonos, Greece, June 2003, ed. M. Plionis
(Kluwer
Low-energy local density of states of the 1D Hubbard model
We examine the local density of states (DOS) at low energies numerically and
analytically for the Hubbard model in one dimension. The eigenstates represent
separate spin and charge excitations with a remarkably rich structure of the
local DOS in space and energy. The results predict signatures of strongly
correlated excitations in the tunneling probability along finite quantum wires,
such as carbon nanotubes, atomic chains or semiconductor wires in scanning
tunneling spectroscopy (STS) experiments. However, the detailed signatures can
only be partly explained by standard Luttinger liquid theory. In particular, we
find that the effective boundary exponent can be negative in finite wires,
which leads to an increase of the local DOS near the edges in contrast to the
established behavior in the thermodynamic limit.Comment: 6 pages, 4 figures, more information can be found at
http://www.physik.uni-kl.de/eggert/papers/index.htm
Tomonaga-Luttinger liquid parameters of magnetic waveguides in graphene
Electronic waveguides in graphene formed by counterpropagating snake states in suitable inhomogeneous magnetic fields are shown to constitute a realization of a Tomonaga-Luttinger liquid. Due to the spatial separation of the right- and left-moving snake states, this non-Fermi liquid state induced by electron-electron interactions is essentially unaffected by disorder. We calculate the interaction parameters accounting for the absence of Galilei invariance in this system, and thereby demonstrate that non-Fermi liquid effects are significant and tunable in realistic geometries
Local spectral properties of Luttinger liquids: scaling versus nonuniversal energy scales
Motivated by recent scanning tunneling and photoemission spectroscopy
measurements on self-organized gold chains on a germanium surface we
reinvestigate the local single-particle spectral properties of Luttinger
liquids. In the first part we use the bosonization approach to exactly compute
the local spectral function of a simplified field theoretical low-energy model
and take a closer look at scaling properties as a function of the ratio of
energy and temperature. Translational invariant Luttinger liquids as well as
those with an open boundary (cut chain geometry) are considered. We explicitly
show that the scaling functions of both setups have the same analytic form. The
scaling behavior suggests a variety of consistency checks which can be
performed on measured data to experimentally verify Luttinger liquid behavior.
In a second part we approximately compute the local spectral function of a
microscopic lattice model---the extended Hubbard model---close to an open
boundary using the functional renormalization group. We show that as a function
of energy and temperature it follows the field theoretical prediction in the
low-energy regime and point out the importance of nonuniversal energy scales
inherent to any microscopic model. The spatial dependence of this spectral
function is characterized by oscillatory behavior and an envelope function
which follows a power law both in accordance with the field theoretical
continuum model. Interestingly, for the lattice model we find a phase shift
which is proportional to the two-particle interaction and not accounted for in
the standard bosonization approach to Luttinger liquids with an open boundary.
We briefly comment on the effects of several one-dimensional branches cutting
the Fermi energy and Rashba spin-orbit interaction.Comment: 19 pages, 5 figures, version as accepted for publication in J.
Phys.:Condensed Matte
Lattice Twisting Operators and Vertex Operators in Sine-Gordon Theory in One Dimension
In one dimension, the exponential position operators introduced in a theory
of polarization are identified with the twisting operators appearing in the
Lieb-Schultz-Mattis argument, and their finite-size expectation values
measure the overlap between the unique ground state and an excited state.
Insulators are characterized by . We identify with
ground-state expectation values of vertex operators in the sine-Gordon model.
This allows an accurate detection of quantum phase transitions in the
universality classes of the Gaussian model. We apply this theory to the
half-filled extended Hubbard model and obtain agreement with the level-crossing
approach.Comment: 4 pages, 3 figure
Phase diagram of an asymmetric spin ladder
We investigate an asymmetric zig-zag spin ladder with different exchange
integrals on both legs using bosonization and renormalization group. When the
leg exchange integrals and frustration both are sufficiently small,
renormalization group analysis shows that the Heisenberg critical point flows
to an intermediate-coupling fixed point with gapless excitations and a
vanishing spin velocity. When they are large, a spin gap opens and a dimer
liquid is realized. Here, we find a continuous manifold of Hamiltonians with
dimer product ground states, interpolating between the Majumdar-Ghosh and
sawtooth spin-chain model.Comment: 4 pages, 2 EPS figures, to be published in PR
Upper Critical Field in a Spin-Charge Separated Superconductor
It is demonstrated that the spatial decay of the pair propagator in a
Luttinger liquid with spin charge separation contains a logarithmic correction
relative to the free fermi gas result in a finite interval between the spin and
charge thermal lengths. It is argued that similar effects can be expected in
higher dimensional systems with spin charge separation and that the temperature
dependence of the upper critical field curve is a probe of this
effect.Comment: 3 pages, postscript file (compressed and uuencoded
Mechanism of CDW-SDW Transition in One Dimension
The phase transition between charge- and spin-density-wave (CDW, SDW) phases
is studied in the one-dimensional extended Hubbard model at half-filling. We
discuss whether the transition can be described by the Gaussian and the
spin-gap transitions under charge-spin separation, or by a direct CDW-SDW
transition. We determine these phase boundaries by level crossings of
excitation spectra which are identified according to discrete symmetries of
wave functions. We conclude that the Gaussian and the spin-gap transitions take
place separately from weak- to intermediate-coupling region. This means that
the third phase exists between the CDW and the SDW states. Our results are also
consistent with those of the strong-coupling perturbative expansion and of the
direct evaluation of order parameters.Comment: 5 pages(REVTeX), 5 figures(EPS), 1 table, also available from
http://wwwsoc.nacsis.ac.jp/jps/jpsj/1999/p68a/p68a42/p68a42h/p68a42h.htm
Flux-free conductance modulation in a helical Aharonov-Bohm interferometer
A novel conductance oscillation in a twisted quantum ring composed of a
helical atomic configuration is theoretically predicted. Internal torsion of
the ring is found to cause a quantum phase shift in the wavefunction that
describes the electron's motion along the ring. The resulting conductance
oscillation is free from magnetic flux penetrating inside the ring, which is in
complete contrast with the ordinary Aharonov-Bohm effect observed in untwisted
quantum rings.Comment: 10 pages, 4 figure
Electron transport through a mesoscopic metal-CDW-metal junction
In this work we study the transport properties of a finite Peierls-Fr\"ohlich
dielectric with a charge density wave of the commensurate type. We show that at
low temperatures this problem can be mapped onto a problem of fractional charge
transport through a finite-length correlated dielectric, recently studied by
Ponomarenko and Nagaosa [Phys. Rev. Lett {\bf 81}, 2304 (1998)]. The
temperature dependence of conductance of the charge density wave junction is
presented for a wide range of temperatures.Comment: Latex, Revtex 3.0, 7 pages, 2 EPS figures (uses epfs
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