Browsing by Autor "Pedro Contreras"

Now showing 1 - 13 of 13

A constant self-consistent scattering lifetime in superconducting strontium ruthenate
(Mexican Society of Physics, 2024) Pedro Contreras
In this numerical work, we find a self-consistent constant scattering superconducting lifetime for two different values of the disorder parameters, the inverse atomic strength, and the stoichiometric impurity in the triplet paired unconventional super-conductor strontium ruthenate. This finding is relevant for experimentalists given that the expressions for the ultrasound attenuation and the electronic thermal conductivity depend on the superconducting scattering lifetime, and a constant lifetime fits well nonequilibrium experimental data. Henceforth, this work helps experimentalists in their interpretation of the acquired data. Additionally, we encountered tiny imaginary parts of the self-energy that resembles the Miyake-Narikiyo tiny gap out-side the unitary elastic scattering limit, and below the threshold zero gap value of 1.0 meV.
A CONSTANT SELF-CONSISTENT SCATTERING LIFETIME IN SUPERCONDUCTING STRONTIUM RUTHENATE
(2024) Pedro Contreras
In this numerical work, we find a self-consistent constant scattering superconducting lifetime for two different values of the disorder parameters, the inverse atomic strength, and the stoichiometric impurity in the triplet paired unconventional super-conductor strontium ruthenate. This finding is relevant for experimentalists given that the expressions for the ultrasound attenuation and the electronic thermal conductivity depend on the superconducting scattering lifetime, and a constant lifetime fits well nonequilibrium experimental data. Henceforth, this work helps experimentalists in their interpretation of the acquired data. Additionally, we encountered tiny imaginary parts of the self-energy that resembles the Miyake-Narikiyo tiny gap out-side the unitary elastic scattering limit, and below the threshold zero gap value of 1.0 meV.
A numerical calculation of the electronic specific heat for the compound Sr$_2$RuO$_4$ below its superconducting transition temperature
(Cornell University, 2018) Pedro Contreras; José Luis Burgos; Ender Ochoa; Daniel Uzcategui; Rafael Almeida
In this work, a numerical study of the superconducting specific heat of the unconventional multiband superconductor Strontium Ruthenate is performed. Two band gaps models are employed, and the results rendered for each of them are compared. One of the models, previously proposed by one of the authors to explain the experimental temperature behavior of the ultrasound attenuation, considers two gaps with point nodes of different magnitude on different gap surface sheets, while the other one is an isotropic and line node model, reported in the literature for describing quantitatively experimental specific heat data. The superconducting density of states DOS is computed by employing these two models and then, a detailed numerical study of the electronic specific heat, that includes the contribution from the different Fermi sheets, is carried out. It is found that the calculated point node model specific heat temperature behavior shows an excellent agreement with the existent Sr$_2$RuO$_4$ experimental data at zero field, particularly, it is obtained that the observed specific heat jump at T$_c$ is precisely reproduced. Also, it is found that the sum of the contributions from the different bands fits quantitatively the measured specific heat data. The results in this work evidence that the Sr$_2$RuO$_4$ superconducting states are of unconventional nature, corresponding to those of a point node superconductor, and show the importance of taking into account the multiband nature of the material when calculating thermodynamic superconducting quantities.
A Tale of the Scattering Lifetime and the Mean Free Path
(2023) Pedro Contreras; Dianela Osorio
The idea of applying the scattering lifetime calculated from the imaginary part of the zero temperature elastic scattering cross-section to study a hidden self-consistent damping in two spaces of importance for non-equilibrium statistical mechanics is proposed. It is discussed its relation with the classical phase space from statistical mechanics and the configuration space from nonrelativistic quantum mechanics. This idea is contrasted with the mean free path values in three elastic collision regimes. The main exercise is to study the behavior of a self-consistent probabilistic distribution function in a space we have called the reduced phase space, since it is related to the scattering lifetime. This exercise has been solved in two unconventional superconductors, for which several calculations are discussed. One of them is to obtain the scattering phase shift from the inverse strength of an atomic potential and the other is to build several phases with different nodal configuration of the superconducting order parameter and show that the imaginary self-consistent part of the scattering cross-section is always positive for two compounds: the triplet strontium ruthenate and the singlet doped with strontium lanthanum cuprate when three models of superconducting order parameters are used: the quasi-point, the point and the line nodal cases. We finally compare the frequency dispersion in the anomalous skin effect with singular shapes of the Fermi surface with the frequency dispersion in the scattering lifetime and their respective mean free paths. This idea is useful because it intuitively explores the nonlocality of this type of hidden self-consistent damping for those incoherent fermionic quasiparticles.
A Tale of the Scattering Lifetime and the Mean Free Path
(RELX Group (Netherlands), 2023) Pedro Contreras; Dianela Osorio
Aproximación elipsoidal del frente de ondas elástico en medios de simetría monoclínica
(European Organization for Nuclear Research, 2022) Pedro Contreras; Andrés Acosta P.; Demián Gutiérrez P.
En este trabajo se introduce una aproximación elipsoidal para las velocidades de fase de los modos longitudinal -P, y transversales -S1 y -S2 en medios que poseen simetría monoclínica. Esta nueva aproximación es válida para ángulos polares pequeños cerca de la dirección vertical, pero sin restricciones en el ángulo acimutal y para grados arbitrarios de anisotropía. A partir de un tratamiento analítico de la ecuación de Christoffel en términos de las lentitudes se logra conseguir expresiones matemáticas para las velocidades de fase en medios monoclínicos que resultan ser elipsoides 3D rotados respecto a los ejes de simetría. Para establecer el grado de validez de estas expresiones se resuelve numéricamente la ecuación de Christoffel y se visualizan los frentes de onda exactos y aproximados, encontrándose que cerca del eje vertical de simetría dan resultados similares. Aunque los modelos monoclínicos pueden presentarse en formaciones geológicas doblemente fracturadas, han sido poco utilizados en los métodos sísmicos multicomponentes de detección de fracturas debido principalmente a la gran cantidad de parámetros elásticos presentes. Las aproximaciones elipsoidales del frente de ondas pueden ser utilizadas para el cálculo de los tiempos de tránsito, así como el modelaje e inversión de las constantes elásticas en medios doblemente fracturados y para geometrías de adquisición del tipo perfil sísmico vertical y/o multi-acimutal.
Coalescence of Impurity Strontium Atoms in Lightly-Substituted Samples of Lanthanum Cuprate
(Cornell University, 2022) E. Yu. Beliayev; Dianela Osorio; Pedro Contreras
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.
Implicit Fermi Surface Evolution Using the Zero Temperature Elastic Scatteringcross-Section&nbsp;For La2−Xsrxcuo4
(RELX Group (Netherlands), 2022) Pedro Contreras; Dianela Osorio; Anjna Devi
Non-magnetic tight binding disorder effects in the γ sheet of Sr2RuO4.
(Mexican Society of Physics, 2022) Pedro Contreras; Dianela Osorio; Shikhgasan Ramazanov
Inspired by the physics of the Miyake - Narikiyo model (MN) for superconductivity in the γ sheet of Sr2RuO4, we set out 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.
The Effect of Nonmagnetic Disorder in the Energy Gap at Zero Temperature for the Fs Γ-Sheet of Strontium Ruthenate
(RELX Group (Netherlands), 2022) Pedro Contreras; Dianela Osorio; Anjna Devi
The Tight-Binding Flat Band Case in the Strontium-Substituted Lanthanum Cuprate
(RELX Group (Netherlands), 2022) Pedro Contreras; Dianela Osorio; Eugeniy Yurievich Beliayev
The two-dimensional density of states in normal and superconducting compounds
(Cornell University, 2022) Pedro Contreras; Anjna Devi; D C Helen Uzcátegui; E. Ochoa
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.
Tight-Binding Superconducting Phases in the Unconventional Compounds Strontium-Substituted Lanthanum Cuprate and Strontium Ruthenate
(Science Publishing Group, 2022) Pedro Contreras; Dianela Osorio; Eugeniy Yurievich Beliayev
We use the idea of the Wigner probability distribution (WPD) in a reduced scattering phase space (RPS) for the elastic scattering cross-section, with the help of a Tight-Binding (TB) numerical procedure allowing us to consider the anisotropic quantum effects, to phenomenologically predict several phases in these two novel unconventional superconductors. Unlike our previous works with pieces of evidences that these two compounds are in the unitary strong scattering regime and that superconductivity is suppressed by the atoms of strontium in both materials, several phases are built. In the case of the strontium-substituted lanthanum cuprate, it was found three phases from one family of Wigner probabilistic distributions, one corresponding to the antiferromagnetic compound La2CuO4 another one which consists of a coalescing metallic phase for very lightly doped La2-xSrxCuO4, and finally a strong self-consistent dependent strange metal phase with optimal levels of doping. In the case of a triplet superconductor strontium ruthenate, three phases can be differentiated from two families of Wigner distribution probabilities, one family of WDP with point nodes where Cooper pairs and dressed scattered normal quasiparticles are mixed for the whole range of frequencies and which correspond to a FS γ-flat-sheet in the ground metallic state, and two phases from another WPD family, where, in one of then, the Miyake-Narikiyo quasinodal tiny gap model allows the unique presence of Cooper pairs in a tiny interval of frequencies near the superconducting transition TC, the other phase corresponds to the mixed phase with Cooper pairs and dressed by stoichiometric strontium non-magnetic atoms, where strong self-consistent effects are noticeable. This approach allows comparing experimental results for samples in both compounds with numerical analysis studies.