Spin bath dynamics and dynamical Renormalization Group

Abstract We discuss the quantum dynamics of the central spin model in a regime where the central spin and bath are slaved to each other. The exact solution is found when the bath is static, and is compared with the effect of an external field, finding that they are inequivalent due to the quantum nature of the environment. When the bath has dynamics, we analyze the differences between the numerical simulation using time-dependent perturbation theory and the equation of motion technique, which shows better accuracy. We demonstrate that the use of dynamical Renormalization Group (dRG), simultaneously with the equation of motion technique, provides a suitable analytical tool to understand the physics, to capture the main physical processes, and a powerful method to eliminate secular terms. In addition, this approach allows to separate classical non-linear behavior from corrections due to quantum correlations.Comment: Main text and Appendi

Merging of Dirac points and Floquet topological transitions in AC driven graphene

We investigate the effect of an in-plane AC electric field coupled to electrons in the honeycomb lattice and show that it can be used to manipulate the Dirac points of the electronic structure. We find that the position of the Dirac points can be controlled by the amplitude and the polarization of the field for high frequency drivings, providing a new platform to achieve their merging, a topological transition which has not been observed yet in electronic systems. Importantly, for lower frequencies we find that the multi-photon absorptions and emissions processes yield the creation of additional pairs of Dirac points. This provides an additional method to achieve the merging transition by just tuning the frequency of the driving. Our approach, based on Floquet formalism, is neither restricted to specific choice of amplitude or polarization of the field, nor to a low energy approximation for the Hamiltonian.Comment: 5 pages + supplementary material

¿Es posible graficar soluciones de ecuaciones diferenciales sin necesidad de derivar o integrar?

Para solucionar ecuaciones diferenciales es fundamental el uso de las integrales o de las derivadas, pero si queremos comprobar una de sus soluciones, en este documento se encontrará una manera alternativa de hacerlo teniendo en cuenta algunos aspectos como: qué es la pendiente de una recta y cómo se grafica, conocer algunas funciones y sus gráficas, tener una noción de derivada como la pendiente de una recta tangente a una curva, sabiendo esto es posible dar una solución aproximada a una ecuación diferencial haciendo un bosquejo de la función que al derivarse resultará la ecuación diferencial propuesta

Engineering Quantum Anomalous Hall Plateaus and Anti-Chiral States with AC Fields

We investigate the AC electric field induced quantum anomalous Hall effect in honeycomb lattices and derive the full phase diagram for arbitrary field amplitude and phase polarization. We show how to induce anti-chiral edge modes as well as topological phases characterized by a Chern number larger than $1$ by means of suitable drivings. In particular, we find that the Chern number develops plateaus as a function of the frequency, providing an time-dependent analogue to the ones in the quantum Hall effect.Comment: 4 pages and supplementary materia