Curriculum Vitae

Publication List

Publications (highlights)

Germanium microparticles as optically induced oscillators in optical tweezers

Oscillatory dynamics is a key tool in optical tweezer applications. It is usually implemented by mechanical interventions that cannot be optically controlled. In this paper, we show that germanium semiconductor beads behave as optically induced oscillators when subjected to a highly focused laser beam. In turn, the well-defined direction of oscillations can be manipulated by the polarization of the light beam. Such unusual motion is due to the competition between the usual optical forces and the radiometric force related to thermal effects, which pushes the beads from the focal region. We characterize the behavior of the germanium beads in detail and propose a model accounting for the related forces in good agreement with the experimental data. Such kind of system can potentially revolutionize the field of optical manipulation, contributing to the design of single molecule machines and to the application of oscillatory forces in fundamental physics, cellular manipulation, fluid dynamics, and other soft-matter systems.

W. H. Campos, T. A. Moura, O. J. B. J. Marques, J. M. Fonseca, W. A. Moura-Melo, M. S. Rocha and J. B. S. Mendes. “Germanium microparticles as optically induced oscillators in optical tweezers”, Phys. Rev. Research 1, 033119 (2019).

Topological Insulator Particles As Optically Induced Oscillators: Toward Dynamical Force Measurements and Optical Rheology

We report the first experimental study upon the optical trapping and manipulation of topological insulator (TI) particles. By virtue of the unique TI properties, which have a conducting surface and an insulating bulk, the particles present a peculiar behavior in the presence of a single laser beam optical tweezers: they oscillate in a plane perpendicular to the direction of the laser propagation. In other words, TI particles behave as optically induced oscillators, allowing dynamical measurements with unprecedented simplicity and purely optical control. Actually, optical rheology of soft matter interfaces and biological membranes, as well as dynamical force measurements in macromolecules and biopolymers, may be quoted as feasible possibilities for the near future.

W. H. Campos, J. M. Fonseca, V. E. Carvalho, J. B. S. Mendes, M. S. Rocha and W. A. Moura-Melo. “Topological Insulator Particles As Optically Induced Oscillators: Toward Dynamical Force Measurements and Optical Rheology”, ACS Photonics 5 (3), 741-745 (2018).

Geometrically induced reversion of Hall current in a topological insulator cavity

An electric charge near the surface of a topological insulator induces an image magnetic monopole. Here, we show that if the topological insulator surface has a negative curvature, namely in the case of a semispherical cavity, the induced Hall current reverses its rotation as the electric charge crosses the semisphere geometric focus. Such a reversion is shown to be equivalent of inverting the charge of the image magnetic monopole. We also discuss upon the case of a semicylindrical cavity, where Hall current reversion appears to be feasible of probing in realistic experiments.