arXiv subjects

T. V. C. Antão

Publications and source records attributed to T. V. C. Antão.

6 recordsLinked to original sources

arXiv2024

Su-Schrieffer-Heeger quasicrystal: Topology, localization, and mobility edge

In this paper we discussed the topological transition between trivial and nontrivial phases of a quasi-periodic (Aubry-André like) mechanical Su-Schrieffer-Heeger (SSH) model. We find that there exists a nontrivial boundary separating the two topological phases and an analytical expression for this boundary is found. We discuss the localization of the vibrational modes using the calculation of the inverse participation ratio (IPR) and access the localization nature of the states of the system. We find three different regimes: extended, localized, and critical, depending on the intensity of the Aubry-André spring. We further study the energy dependent mobility edge (ME) separating localized from extended eigenstates and find its analytical expression for both commensurate and incommensurate modulation wavelengths, thus enlarging the library of models possessing analytical expressions for the ME. Our results extend previous results for the theory of fermionic topological insulators and localization theory in quantum matter to the classical realm.

cond-mat.mes-hall↗

arXiv2023

Effects of dilution in a 2D topological magnon insulator

We study the effect of diluting a two-dimensional ferromagnetic insulator hosting a topological phase in the clean limit. By considering the ferromagnetic Heisenberg model in the honeycomb lattice with second nearest-neighbor Dzyanshikii-Moriya interaction, and working in the linear spin-wave approximation, we establish the topological phase diagram as a function of the fraction $p$ of diluted magnetic atoms. The topological phase with Chern number $C=1$ is robust up to a moderate dilution $p_{1}^{*}$, while above a higher dilution $p_{2}^{*}>p_{1}^{*}$ the system becomes trivial. Interestingly, both $p_{1}^{*}$ and $p_{2}^{*}$ are below the classical percolation threshold $p_{c}$ for the honeycomb lattice, which gives physical significance to the obtained phases. In the topological phase for $p p_{2}^{*}$, when all states become localized, the system shows $C=0$ as expected for a trivial phase. Replacing magnetic with non-magnetic atoms in a systems hosting a magnon Chern insulator in the clean limit puts all the three phases within experimental reach.

cond-mat.dis-nn↗

arXiv2023

Strain Engineering of Photo-induced Topological Phases in 2D Ferromagnets

We argue that strain engineering is a powerful tool which may facilitate the experimental realization and control of topological phases in laser-driven 2D ferromagnetic systems. To this extent, we show that by applying a circularly polarized laser field to a 2D honeycomb ferromagnet which is uniaxially strained in either the zig-zag or armchair direction, it is possible to generate a synthetic Dzyaloshinskii-Moriya interaction (DMI) tunable by the intensity of the applied electric field, as well as by the magnitude of applied strain. Such deformations enable transitions to phases with opposite sign of Chern number, or to trivial phases. These are basic results that could pave the way for the development of a new field of Strain Engineered Topological Spintronics (SETS).

cond-mat.mes-hall↗

arXiv2022

Laser induced enhanced coupling between photons and squeezed magnons in antiferromagnets

In this paper we consider a honeycomb antiferromagnet subject to an external laser field. Obtaining a time-independent effective Hamiltonian, we find that the external laser renormalizes the exchange interaction between the in-plane components of the spin-operators, and induces a synthetic Dzyaloshinskii-Moria interaction (DMI) between second neighbors. The former allows the control of the magnon dispersion's bandwidth and the latter breaks time-reversal symmetry inducing non-reciprocity in momentum space. The eigen-excitations of the system correspond to squeezed magnons whose squeezing parameters depend on the properties of the laser. When studying how these spin excitations couple with cavity photons, we obtain a coupling strength which can be enhanced by an order of magnitude via careful tuning of the laser's intensity, when compared to the case where the laser is absent. The transmission plots through the cavity are presented, allowing the mapping of the magnons' dispersion relation.

cond-mat.mes-hall↗

arXiv2021

Two-level Systems Coupled to Graphene plasmons: A Lindblad equation approach

In this paper we review the theory of open quantum systems and macroscopic quantum electrodynamics, providing a self-contained account of many aspects of these two theories. The former is presented in the context of a qubit coupled to a electromagnetic thermal bath, the latter is presented in the context of a quantization scheme for surface-plasmon polaritons (SPPs) in graphene based on Langevin noise currents. This includes a calculation of the dyadic Green's function (in the electrostatic limit) for a Graphene sheet between two semi-infinite linear dieletric media, and its subsequent application to the construction of SPP creation and annihilation operators. We then bring the two fields together and discuss the entanglement of two qubits in the vicinity of a graphene sheet which supports SPPs. The two qubits communicate with each other via the emission and absorption of SPPs. We find that a Schödinger cat state involving the two qubits can be partially protected from decoherence by taking advantage of the dissipative dynamics in graphene. A comparison is also drawn between the dynamics at zero temperature, obtained via Schrodinger's equation, and at finite temperature, obtained using the Lindblad equation.

cond-mat.mes-hall↗

arXiv2021

The polarizability of a confined atomic system: An application of Dalgarno-Lewis method

In this paper we give an application of Dalgarno-Lewis method, the latter not usually taught in quantum mechanics courses. This is very unfortunate since this method allows to bypass the sum over states appearing in the usual perturbation theory. In this context, and as an example, we study the effect of an external field, both static and frequency dependent, on a model-atom at fixed distance from a substrate. This can happen, for instance, when some organic molecule binds from one side to the substrate and from the other side to an atom or any other polarizable system. We model the polarizable atom by a short range potential, a Dirac$-δ$ and find that the existence of a bound state depends on the ratio of the effective "nuclear charge" to the distance of the atom to the substrate. Using an asymptotic analysis, previously developed in the context of a single $δ-$function potential in an infinite medium, we determine the ionization rate and the Stark shift of our system. Using Dalgarno-Lewis theory we find an exact expression for the static and dynamic polarizabilities of our system valid to all distances. We show that the polarizability is extremely sensitive to the distance to the substrate creating the possibility of using this quantity as a nanometric ruler. Furthermore, the line shape of the dynamic polarizability is also extremely sensitive to the distance to the substrate, thus providing another route to measure nanometric distances. The ditactic value of the $δ-$function potential is well accepted in teaching activities due to its simplicity, while keeping the essential ingredients of a given problem.

quant-ph↗