arXiv subjects

P. R. Silva

Publications and source records attributed to P. R. Silva.

22 records · Page 2Linked to original sources

arXiv2000

An Effective Field Model to High Temperature Superconductors: Fitting of The Energy Gap to the Experimental Results of the $Bi_2Sr_2CaCu_2O_8$

We use an effective field model (transverse Ising model) to describe the dependence on the temperature of the energy gap of some two-dimensional $(2-D)$ superconducting systems. The order parameter of this model is put in a direct correspondence with that of the Ising model. Then, we use the exact relations for the spontaneous magnetization of the Ising model in some $2-D$ lattices as a means to fit the experimental results of $Bi_2Sr_2CaCu_2O_8 $ films obtained through reflectivity measurements by Brunel et al [Phys. Rev. Lett. 66, 1346 (1991)] and the argon-annealed $Bi_2Sr_2CaCu_2O_8$ samples investigated by Staufer et al [Phys. Rev. Lett. 68, 1069 (1992)] through Raman scattering. The zero temperature energy gap $E_g(0)$ relations were evaluated in various $2-D$ lattices and also in the $(3-D)$ simple cubic lattice, for comparison. In the square lattice case we obtained $E_g(0)=3.52kT_c$, coincidentally the same number as the BCS result, and in the triangular lattice case we get $E_g(0)=3.30kT_c$ in agreement with the experimental findings of Brunel et al.

cond-mat.supr-con↗

arXiv2000

Unified treatment of $A+B\to 0 $ and $A+A\to 0$ chemical reactions through Thompson's approach

In this work we propose an action to describe diffusion limited chemical reactions belonging to various classes of universality. This action is treated through Thompson's approach and can encompass both cases where we have segregation as in the $A+B\to 0$ reaction, as well the simplest one, namely the $A+A\to 0$ reaction .Our results for long time and long wavelength behaviors of the species concentrations and reaction rates agree with exact results of Peliti for $A+A\to 0$ reaction and rigorous results of Bramson and Lebowitz for $A+B\to 0$ reaction, with equal initial concentrations.The different classes of universality are reflected by the obtained upper critical dimensions varying continuously from $d_{c}=2$ in the first case to $d_{c}=4$ in the last one. Just at the upper critical dimensions we find universal logarithmic corrections to the mean field behavior.

hep-ph↗

arXiv2000

Thompson's Method applied to Quantum Electrodynamics (QED)

In this work we apply Thompson's method (of the dimensions) to study the quantum electrodynamics (QED). This method can be considered as a simple and alternative way to the renormalisation group (R.G) approach and when applied to QED lagrangian is able to obtain the running coupling constant behavior $α(μ)$, namely the dependence of $α$ on the energy scale. We also obtain the dependence of the mass on the energy scale. The calculations are evaluated just at $d_c=4$, where $d_c$ is the upper critical dimension of the problem, so that we obtain logarithmic behavior both for the coupling $α$ and the mass $m$ on the energy scale $μ$.

hep-th↗

arXiv2000

A Model to Describe Transport Properties in $Bi_2Sr_2(Ca_zPr_{1-z})Cu_2O_{8+y}$

A pseudo-spin model is proposed, as a means to describe some transport properties (resistivity and Hall mobility) in $Bi_2Sr_2(Ca_zPr_{1-z})Cu_2O_{8+y}$. Our model is based in a double-well potential where tunneling in a given site and interaction between different lattice sites are allowed only through the excited states. Doping of the pure system by the addition of $Pr$ increases the ratio between the activation energy and the tunneling constant. The model Hamiltonian displays some features which are present in the hydrogen-bonded ferroelectrics. Its dynamics is treated in the random phase approximation and the characteristic frequency (time) is used in a Drude formula in order to obtain some transport properties of the system, namely the electric resistivity and the Hall mobility. The quantities calculated in this work are compared with the experimental data of B. Beschoten, S. Sadewasser, G. Güntherodt and C. Quitmann [Phys. Rev. Lett.77, 1837(1996)].

cond-mat.supr-con↗