1,155 research outputs found
Transport through a double barrier in Large Radius Carbon Nanotubes in the presence of a transverse magnetic field
We discuss the Luttinger Liquid behaviour of Large Radius Carbon Nanotube
e.g. the Multi Wall ones (MWNT), under the action of a transverse magnetic
field . Our results imply a reduction with in the value of the
critical exponent, , for the tunneling density of states, which
is in agreement with that observed in transport experiments. Then, the problem
of the transport through a Quantum Dot formed by two intramolecular tunneling
barriers along the MWNT, weakly coupled to Tomonaga-Luttinger liquids is
studied, including the action of a strong transverse magnetic field . {We
predict the presence of some peaks in the conductance G versus , related to
the magnetic flux quantization in the ballistic regime (at a very low
temperature, ) and also at higher , where the Luttinger behaviour
dominates}. The temperature dependence of the maximum of the
conductance peak according to the Sequential Tunneling follows a power law,
with linearly dependent on the critical
exponent, , strongly reduced by .Comment: 8 pages, 3 figures, PACS numbers: 05.60.Gg, 71.10.Pm, 73.63.-b,
71.20.Tx, 72.80.R
Large N Effects and Renormalization of the Long-Range Coulomb Interaction in Carbon Nanotubes
We develop a dimensional regularization approach to deal with the low-energy
effects of the long-range Coulomb interaction in 1D electron systems. The
method allows us to avoid the infrared singularities arising from the
long-range Coulomb interaction at D = 1, providing at the same time insight
about the fixed-points of the theory. We show that the effect of increasing the
number N of subbands at the Fermi level is opposite to that of approaching the
bare Coulomb interaction in the limit D --> 1. Then, we devise a double scaling
limit, in which the large N effects are able to tame the singularities due to
the long-range interaction. Thus, regular expressions can be obtained for all
observables right at D = 1, bearing also a dependence o the doping level of the
system. Our results imply a variation with N in the value of the exponent for
the tunneling density of states, which is in fair agreement with that observed
in different transport experiments involving carbon nanotubes. As the doping
level is increased in nanotubes of large radius and multi-walled nanotubes, we
predict a significant reduction of order N^{-1/2} in the critical exponent of
the tunneling density of states.Comment: 16 pages, 5 figures, PACS codes: 73.40, 11.10.
Envelope solitons induced by high-order effects of light-plasma interaction
The nonlinear coupling between the light beams and non-resonant ion density
perturbations in a plasma is considered, taking into account the relativistic
particle mass increase and the light beam ponderomotive force. A pair of
equations comprising a nonlinear Schrodinger equation for the light beams and a
driven (by the light beam pressure) ion-acoustic wave response is derived. It
is shown that the stationary solutions of the nonlinear equations can be
represented in the form of a bright and dark/gray soliton for one-dimensional
problem. We have also present a numerical analysis which shows that our bright
soliton solutions are stable exclusively for the values of the parameters
compatible with of our theory.Comment: 9 pages, 5 figure
Warm turbulence in the Boltzmann equation
We study the single-particle distributions of three-dimensional hard sphere
gas described by the Boltzmann equation. We focus on the steady homogeneous
isotropic solutions in thermodynamically open conditions, i.e. in the presence
of forcing and dissipation. We observe nonequilibrium steady state solution
characterized by a warm turbulence, that is an energy and particle cascade
superimposed on the Maxwell-Boltzmann distribution. We use a dimensional
analysis approach to relate the thermodynamic quantities of the steady state
with the characteristics of the forcing and dissipation terms. In particular,
we present an analytical prediction for the temperature of the system which we
show to be dependent only on the forcing and dissipative scales. Numerical
simulations of the Boltzmann equation support our analytical predictions.Comment: 4 pages, 5 figure
Board characteristics and financial performance in the insurance industry: An international empirical survey
There are few studies in the literature on how the characteristics of boards of directors affect the performance of insurance companies. The purpose of this research is to investigate the characteristics of a company’s board that can have a significant impact on financial performance in the insurance sector. For this purpose, we performed a dynamic pooled regression model to test the impact of a wide range of board-specific factors. The survey has been conducted on an international sample of 119 listed insurance companies operating in the period 2009-2019. The sample includes companies from three geographical areas: North America, Europe and Asia. Our findings
provide evidence that board structure and board independence are the most relevant governance factors, with a potentially positive impact on insurers’ market performance. These findings indirectly outline the opportunity for insurance companies to improve corporate fair value by strengthening internal governance models through effective board policies, an adequate qualification of board members and a well-balanced membership of the board. At the same time, there is still room for improvement as regards the level of board independence by
strengthening internal governance policies in order to maintain an adequate number of independent and non-executive board
members. The study upgrades the evidence arising from the existing literature by providing new elements to support a deeper understanding of the effects of insurance companies’ board characteristics on financial performance. Empirical results may also have important implications for both managers and policy makers
Crossover from Luttinger liquid to Coulomb blockade regime in carbon nanotubes
We develop a theoretical approach to the low-energy properties of 1D electron
systems aimed to encompass the mixed features of Luttinger liquid and Coulomb
blockade behavior observed in the crossover between the two regimes. For this
aim we extend the Luttinger liquid description by incorporating the effects of
a discrete single-particle spectrum. The intermediate regime is characterized
by a power-law behavior of the conductance, but with an exponent oscillating
with the gate voltage, in agreement with recent experimental observations. Our
construction also accounts naturally for the existence of a crossover in the
zero-bias conductance, mediating between two temperature ranges where the
power-law behavior is preserved but with different exponent.Comment: 5 pages, 3 figure
Electronic screening and correlated superconductivity in carbon nanotubes
A theoretical analysis of the superconductivity observed recently in Carbon
nanotubes is proposed. We argue that ultra-small (diameter )
single wall carbon nanotubes (with transition temperature )
and entirely end-bonded multi-walled ones () can superconduct
by an electronic mechanism, basically the same in both cases. By a Luttinger
liquid -like approach, one finds enhanced superconducting correlations due to
the strong screening of the long-range part of the Coulomb repulsion. Based on
this finding, we perform a detailed analysis on the resulting
Hubbard-like model, and calculate transition temperatures of the same order
of magnitude as the measured ones.Comment: 6 pages, 1 figure, PACS: 71.10.Pm,74.50.+r,71.20.Tx, to appear in
Phys. Rev.
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