arXiv subjects

P. Contreras

Publications and source records attributed to P. Contreras.

15 recordsLinked to original sources

arXiv2022

On the azimuthal dependence of orthorhombic fractures for vertical seismic profiles using the ellipsoidal approximation

The analysis of travel times with move-out velocities represents one of the most widely used seismic signal processing techniques for the exploration and monitoring of Oil and Gas reservoirs. In travel time analysis for anisotropic elastic media with fractures, the knowledge of the conversion point at interfaces with incident longitudinal, and reflected transversal elastic response impulses that take into account the azimuthal dependence is important for seismic data analysis acquired in multicomponent surveys, and for the correct interpretation of seismic in reservoirs. Henceforth, this work shows how to derive analytical expressions for the longitudinal to transverse response impulse $P -S_i$ conversion points using the ellipsoidal approximation for fractured orthorhombic elastic media under kinematical considerations. These expressions can be used for vertical seismic profiles with small polar angles of aperture and azimuthal dependence in orthorhombic media when the elastic slowness is used as a main theoretical tool to solve the Christoffel equation. We also explain some of the differences within the ellipsoidal inversion procedure of the elastic stiffnesses $c_{13}$ and $c_{23}$.

physics.geo-ph↗

arXiv2022

Coalescence of Impurity Strontium Atoms in Lightly-Substituted Samples of Lanthanum Cuprate

By comparing experimental results obtained in the study of the electron transport and magnetic properties of samples of lightly strontium-substituted lanthanum cuprates and the results of a previously published numerical analysis in the reduced elastic scattering space (RPS) of the elastic scattering cross-section, we construct a phenomenological classical self-consistent strong-binding energy density profile in the superconducting $La_{2-x}Sr_xCuO_4$ cuprate. It is found that the imaginary part of the reduced phase scattering space can be zero, almost constant, or strongly self-consistent, depending on the Sr substituted concentration. If the Sr atomic concentration is dilute, a constant imaginary part of the elastic scattering cross-section brings a sub-melted coalescent superconducting metallic profile similar to the one with a constant scattering lifetime in the metallic state of normal metals, except for the unitary narrow, sharp peak at zero frequency. A self-consistent broadening of this peak occurs for a higher concentration of Sr atoms, and finally, for very small amounts of nonmagnetic dirt, only the narrow unitary peak prevails around the zero frequency.

cond-mat.supr-con↗

arXiv2022

The two-dimensional density of states in normal and superconducting compounds

The present work represents a review for the numerical calculation of the density of states (DoS) for two-dimensional tight-binding models with first neighbors in its normal state and for two superconducting order parameters. One is a singlet scalar state and the other is a triplet vector state. At the beginning an emphasis is given to the general expressions commonly used to the calculation of the density of states as the number of partial and total number of states, the degrees of freedom and the ab-initio methods most commonly used to its calculation. Then, the transition happening to the DoS normal states by varying the Fermi energy and the hopping parameter is investigated. After that, the numerical calculation of the superconducting density of states using the zero-temperature scattering cross-section is performed for the two order parameters. Finally, the residual density of states depending on disorder and the scattering potential strength using the Larkin equation are calculated for the two order parameter symmetries different in nature.

cond-mat.supr-con↗

arXiv2021

Quasi-point versus point nodes in $Sr_2RuO_4$, the case of a flat tight binding $\gamma$ sheet

We perform a numerical study of the unitary regime as a function of disorder concentration in the imaginary part of the elastic scattering cross-section for the compound $Sr_2RuO_4$ in the flat band non-disperse limit. By using a self-consistent tight-binding (TB) method, we find a couple of families of Wigner probabilistic functions that help to explain macroscopically the distribution between Fermion dressed quasiparticles and Cooper pairs, and also the position of nodes in the order parameter for $Sr_2RuO_4$. Therefore, we are able to show that a TB model for the $\gamma$ sheet numerically shows 4 point nodes in a flat $\gamma$ sheet limit or 4 quasi-point nodes for strong dispersion $\gamma$ sheet limit in the reduced phase scattering space (RPS).

cond-mat.supr-con↗

arXiv2021

Dressed behavior of the quasiparticles lifetime in the unitary limit of two unconventional superconductors

We compare the quasiparticle lifetime behavior in the unitary limit of two unconventional superconductors dressed by non-magnetic impurity scattering to differentiate an anomalous functional behavior in its shape when the disorder concentration is changed in a triplet paired model with respect to the well behave singlet model. For singlet paired superconductors, the functional shape of the lifetime due to elastic scattering around the nodal regions does not change with the change of the disorder concentration, but for a triplet model with a tiny gap, an anomalous drop in shape is observed only when small values of disordering are added. We use a 2D tight-binding parametrization to study the reduced phase space of the first Brillouin zone, where the low energy scattering is restricted to the nodal/quasinodal regions for two irreducible representations of the crystal lattice.

cond-mat.supr-con↗

arXiv2021

Non-magnetic tight binding disorder effects in the $\gamma$ sheet of $Sr_2RuO_4$

Inspired by the physics of the Miyake - Narikiyo model (MN) for superconductivity in the {\gamma} sheet of $Sr_2RuO_4$ to investigate numerically the behavior caused by a non-magnetic disorder in the imaginary part of the elastic scattering matrix for an anisotropic tight-binding model. We perform simulations by going from the Unitary to the Born scattering limit, varying the parameter c which is inverse to the strength of the impurity potential. It is found that the unitary and intermedia limits persist for different orders of magnitude in simulating the disorder concentration. Subsequently and in order to find the MN tiny gap, we perform a numerical study of the unitary limit as a function of disorder concentration, to find the tiny anomalous gap.

cond-mat.supr-con↗

arXiv2021

The role of transverse anisotropic elastic waves and Ehrenfest relationships in the superconducting state of the compound Sr$_2$RuO$_4$

In this short review, some bulk threshold phenomena of the unconventional superconductivity in the strontium ruthenate compound (Sr2RuO4) are mentioned. Particularly, in Sr2RuO4, the Ehrenfest relations, the velocity propagation of the elastic field modes, and the ultrasound attenuation find a common point to study elastic anisotropic lattice field effects at the transition temperature (Tc) between the normal and the superconducting state. Ehrenfest relations are suitable for establishing a phase diagram of the Tc point according to symmetry consideration of the electrons pairs in unconventional superconductors. Further studies in this direction could turn into a new role for the spin polarization of the transverse phonon field and its interaction with the conduction electrons in anisotropic crystals with several conducting/superconducting bands such as Sr2RuO4.

cond-mat.supr-con↗

arXiv2021

Scattering due to non-magnetic disorder in 2D anisotropic d-wave high Tc superconductors

Inspired by the studies on the influence of transition metal impurities in high Tc superconductors and what is already known about nonmagnetic suppression of Tc in unconventional superconductors, we set out to investigate the behavior of the nonmagnetic disordered elastic scattering for a realistic 2D anisotropic high Tc superconductor with line nodes and a Fermi surface in the tight-binding approximation. For this purpose, we performed a detailed self-consistent 2D numerical study of the disordered averaged scattering matrix with nonmagnetic impurities and a singlet line nodes order parameter, varying the concentration and the strength of the impurities potential in the Born, intermediate and unitary limits. In a high Tc anisotropic superconductor with a tight binding dispersion law averaging over the Fermi surface, including hopping parameters and an order parameter in agreement with experimental data, the tight-binding approximation reflects the anisotropic effects. In this study, we also included a detailed visualization of the behavior of the scattering matrix with different sets of physical parameters involved in the nonmagnetic disorder, which allowed us to model the dressed scattering behavior in different regimes for very low and high energies. With this study, we demonstrate that the scattering elastic matrix is affected by the non-magnetic disorder, as well as the importance of an order parameter and a Fermi surface in agreement with experiments when studying this effect in unconventional superconductors.

cond-mat.supr-con↗

arXiv2021

TDOS Quantum Mechanical visual analysis for single molecules

We have analyzed with pedagogical purposes the relation of the total densities of states (TDOS/PDOS/OPDOS) and molecular orbital diagrams (MOD) for single and isolated molecules of Water and Nitrogen. We use a calculation level HF/6-311G, spreading the energy eigenvalues around the TDOS spikes and using the Mulliken visual analysis in Multiwfn to showcase our findings. We discuss the possibility to use these electrons orbit population diagrams, in conjunction with the more intuitive MOD diagrams to teach the Quantum Mechanics of simple molecular isolated structures.

physics.chem-ph↗

arXiv2021

An Eigenvalue Analysis of Damping in Optical Thin Plasmas

In this work, the behavior of magnetohydrodynamic waves in optically thin plasmas considering dissipative processes, thermal and magnetic diffusion, a given ionization, and the heating and cooling functions are investigated for several particular cases. A numerical eigenvalues analysis of the dimensionless secular equations according to various cases is performed for the entire set of MHD equations.

physics.plasm-ph↗

arXiv2019

Anisotropic shear stress $\sigma_{xy}$ effects in the basal plane of Sr$_2$RuO$_4$

In this short note, we repeat the calculations the jumps for the specific heat C$_{\sigma_{xy}}$, the elastic compliance S$_{xyxy}^{\sigma_{xy}}$ and the thermal expansion $\alpha_{\sigma_{xy}}$ due to a shear stress $\sigma_{xy}$ in the basal plane of $Sr_2RuO_4$. Henceforth we clarify some issues regarding the elastic theoretical framework suitable to explain the sound speed experiments of Lupien et al. (2001,2002), and partially the strain experiments of Hicks et al. (2014), and Steppke et al. (2016) in strontium ruthenate. We continue to propose that the discontinuity in the elastic constant C$_{xyxy}$ of this tetragonal crystal gives unambiguous experimental evidence that the superconducting order parameter $\Psi$ has two components with a broken time-reversal symmetry state, and that the $\gamma$ band couples the anisotropic electron-phonon interaction to the $[xy]$ in-plane shear stress according to Walker and collaborators [4] and [3]. Some importants words about the roll of the spin equal to one for the transversal phonons are added in the conclusion following Levine [34].

cond-mat.supr-con↗

arXiv2019

Perfectly matched layers simulation in 2-D VTI media

Implementing computational boundary conditions, such as perfectly matched layers PML does have advantages for forwarding modeling of the earth's crust. The mathematical modeling of many physical problems encountered in industrial applications often leads to a system of linear partial differential equations-PDEs. It considerably improves the visualization of seismic events relevant to oil and gas exploration. In this work, we present an efficient numerical scheme for hyperbolic partial differential equations where a computational technique takes care of reflections at the borders domain using a linear 2-D elastic-wave system of decoupled equations with PML-type boundary conditions. The key idea is to introduce a layer that absorbs the reflections from the borders improving images visualization. Anisotropy has been reported to occur in the Earth's three main layers. The crust, the mantle, and the core; but this implementation refers to the case of a vertical transversal anisotropic medium VTI in the crust-layer. Images and screen-shots of the longitudinal P impulse-response and the SV transverse impulse-response are obtained at different times. This computational method enables us to achieve images for the P and SV response-impulses, and to obtain high quality synthetic seismograms for the PP and PS reflection events in a 2-D VTI two-layer model.

physics.geo-ph↗

arXiv2018

A non-linear minimization calculation of the renormalized frequency $\tilde{\omega}$ in dirty d-wave superconductors

This work performs a comparative numerical study of the impurity average self-frequency $\tilde{\omega}$ in an unconventional superconducting alloy with non-magnetic impurities. Two methods are used: the Levenberg-Marquardt algorithm as a non-linear minimization problem, and a fixed-point iteration procedure. The unconventional superconducting renormalized by impurities \bw is a self-consistent complex non-linear equation with two varying parameters: the impurity concentration $\Gamma^+$ and the strength of the impurities c, for which its numerical solution is a computational challenge. Throughout this study $\tilde{\omega}$ is the renormalized frequency, \bg represents the inverse of the residual average lifetime $\tau$ at zero frequency, and $N/N_0$ is the normalized superconducting density of states (DOS). This study uses an order parameter that corresponds to the high-temperature superconducting ceramics (HTS) with a well-established gap symmetry. The results reveal the computational efficiency of the non-linear minimization technique by improving the calculations of the $\tilde{\omega}$ computation when using a 2D parameter space ($\Gamma^+$, c), particularly in the unitary regime, where the imaginary part of $\tilde{\omega}$ is a complicated expression of those parameters; this allows to enhance the study of the universal behavior of this particular quantum mechanical state.

cond-mat.supr-con↗

arXiv2018

Electronic heat transport for a multiband superconducting gap in Sr$_2$RuO$_4$

This paper gives a detailed numerical study of the superconducting electronic heat transport in the unconventional multiband superconductor Strontium Ruthenate Sr$_2$RuO$_4$. The study demostrates that a model with different nodal structures on different sheets of the Fermi surface is able to describe quantitatively experimental heat transport data. The contribution of the density of states DOS is given for each sheet of the Fermi surface and the total contribution is also calculated. Finally, a discussion of the universal character of the electronic heat transport in unconventional superconductors and its relation to the DOS based on the type of nodal structure of the superconducting gap in Sr$_2$RuO$_4$ is given.

cond-mat.supr-con↗

arXiv2018

Gamma-ray imaging system for real-time measurements in nuclear waste characterisation

A compact, portable and large field-of-view gamma camera to identify, locate and quantify gamma-ray emitting radioisotopes in real-time has been developed. The device delivers spectroscopic and imaging capabilities, which allow one to use it in a variety of nuclear waste characterisation scenarios, such as radioactivity monitoring in nuclear power plants and more specifically for the decommissioning of nuclear facilities. The technical development of this apparatus and some examples of its application in field measurements are reported in this article. The performance of the presented gamma-camera is also benchmarked against other conventional techniques.

physics.ins-det↗