Examinando por Materia "Funciones de Green"

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    From Kondo to Anderson : time-dependent quantum transport through an interacting quantum dot within the Schwinger-Keldysh field theory formalism
    (Universidad del Valle, 2024) Fernández Sánchez, Jhoan Alexis; Rodriguez-Ramirez, Karen
    This work delves into the theory of interacting electrons and local moment formation, modeled by the single impurity Anderson model (SIAM) and the Kondo effect, under the framework of nanoscale quantum transport theories. We explore the connection between these models through the Schrieffer-Wolff transformation (SWT) and study time-dependent quantum transport through an interacting quantum dot, serving as a bridge between practical quantum transport systems and the Kondo model. Using the intricate Schwinger-Keldysh nonequilibrium Green’s functions (NEGF) technique, we investigate the system’s response to a bias voltage applied to metallic leads, analyzing the Jauho-Meir-Wingreen (JMW) charge current within stationary and wide- band limit (WBL) approximations. Applying the non-canonical Hubbard-I approximation to the electron-electron interaction term, we derived analytical expressions for the time-dependent charge current and electron spin occupation through the quantum dot for different Coulomb interaction strengths between electrons. The results obtained align well with previously reported literature and reveal enhanced mean-field correlation effects on the charge dynamics while assessing the model’s capacity to describe Kondo effects in transport phenomena. This study lays the groundwork for more realistic models and paves the way for advanced theoretical and computational approaches in the quantum transport unit of the theoretical solid-state physics group at Universidad del Valle.
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    PublicaciónAcceso abierto
    Photosynthetic efficiency in FMO complex : a dynamical study using the lindblad and non-equilibrium greens functions frameworks
    (Universidad del Valle, 2024) Valencia Guzmán, Gabriela; Vasquez Jaramillo, Juan David
    This work aimed to study the efficiency of the photosynthetic complex Fenna-Matthews Olso (FMO). For this purpose, the behavior of the average efficiency in the reduced FMO system (FMO- 123) was analyzed employing two formalisms: the Lindblad master equation, and the Green functions. First, the dynamics of the system were found with the Lindblad formalism, which allowed to establish the Dynamical Efficiency of the FMO-123, defined by the ratio between the output and input power, which presented a maximum peak for a value of 50 ps−1 of the dephasing rate (γdeph). Second, through the retarded Green’s function, the density of states, and the use of Parseval’s theorem, an analogous expression for the Dynamical Efficiency was defined in this formalism. It has also a maximum for a value of 1.8 meV of the coupling of FMO with the reservoirs (Γ). From the two results obtained, it stands out how the calculation of the Dynamical Efficiency takes into account the dynamics reflected in the input power at site 1, different from how the efficiency of FMO has been treated in previous studies, providing a more complete understanding of the system behavior. On the other hand, the use of the Lindblad formalism indicated that the high efficiency of this complex is achieved by the environment-assisted quantum transport (ENAQT) regime. This could show that the efficiency can be maximum for a certain value of the dephasing rate, i.e. of the support from the environment, regardless of whether this support leads to the presence of long-lived coherences in the system. As a perspective, we plan to use both formalisms again to study the excitonic current of FMO.