Topological Phase Transitions and Quantum Hall Effect in the Graphene Family

Monolayer staggered materials of the graphene family present intrinsic spin-orbit coupling and can be driven through several topological phase transitions using external circularly polarized lasers, and static electric or magnetic fields. We show how topological features arising from photo-induced phase transitions and the quantum Hall effect coexist in these materials, and simultaneously impact their Hall conductivity through their corresponding charge Chern numbers. We also show that the spectral response of the longitudinal conductivity contains signatures about the various phase transition boundaries, that the transverse conductivity encodes information about the topology of the band structure, and that both present resonant peaks which can be unequivocally associated to one of the four inequivalent Dirac cones present in these materials. This complex optoelectronic response can be probed with straightforward Faraday rotation experiments, allowing the study of the crossroads between quantum Hall physics, spintronics, and valleytronics.Comment: 8 pages, 6 figure

Quantized beam shifts in graphene

We predict quantized Imbert-Fedorov, Goos-H\"anchen, and photonic spin Hall shifts for light beams impinging on a graphene-on-substrate system in an external magnetic field. In the quantum Hall regime the Imbert-Fedorov and photonic spin Hall shifts are quantized in integer multiples of the fine structure constant $\alpha$, while the Goos- H\"anchen ones in multiples of $\alpha^2$. We investigate the influence on these shifts of magnetic field, temperature, and material dispersion and dissipation. An experimental demonstration of quantized beam shifts could be achieved at terahertz frequencies for moderate values of the magnetic field.Comment: Correction of typos, title change, and updated references. 5 pages, 4 figure

Blood lead and blood pressure: some implications for the situation in The Netherlands.

Studies performed earlier have shown a positive relation between blood lead (a parameter for lead body burden) and blood pressure, whereas such a relation between urine cadmium (a parameter for cadmium body burden) and blood pressure could not be shown. Median (i.e., 50th percentile, P50) blood levels in the general population in the Netherlands are in the range of 80 to 150 micrograms/L. Persons occupationally exposed to lead show median blood lead levels that may exceed 400 micrograms/L. To study causality, a prospective study among lead workers is desired

Molding the flow of light with a magnetic field: plasmonic cloaking and directional scattering

We investigate electromagnetic scattering and plasmonic cloaking in a system composed by a dielectric cylinder coated with a magneto-optical shell. In the long-wavelength limit we demonstrate that the application of an external magnetic field can not only switch on and off the cloaking mechanism but also mitigate losses, as the absorption cross-section is shown to be minimal precisely at the cloaking operation frequency band. We also show that the angular distribution of the scattered radiation can be effectively controlled by applying an external magnetic field, allowing for a swift change in the scattering pattern. By demonstrating that these results are feasible with realistic, existing magneto-optical materials, such as graphene epitaxially grown on SiC, we suggest that magnetic fields could be used as an effective, versatile external agent to tune plasmonic cloaks and to dynamically control electromagnetic scattering in an unprecedented way, we hope that these results may find use in disruptive photonic technologies.Comment: 7 pages, 8 figure

Tuning plasmonic cloaks with an external magnetic field

We propose a mechanism to actively tune the operation of plasmonic cloaks with an external magnetic field by investigating electromagnetic scattering by a dielectric cylinder coated with a magneto-optical shell. In the long wavelength limit we show that the presence of an external magnetic field may drastically reduce the scattering cross-section at all observation angles. We demonstrate that the application of external magnetic fields can modify the operation wavelength without the need of changing material and/or geometrical parameters. We also show that applied magnetic fields can reversibly switch on and off the cloak operation. These results, which could be achieved for existing magneto-optical materials, are shown to be robust to material losses, so that they may pave the way for developing actively tunable, versatile plasmonic cloaks.Comment: 5 pages and 4 figures Figure 4 has been remad

Enhancing Near-Field Heat Transfer in Composite Media: Effects of the Percolation Transition

We investigate the near-field heat transfer between a semi-infinite medium and a nanoparticle made of composite materials. We show that, in the effective medium approximation, the heat transfer can be greatly enhanced by considering composite media, being maximal at the percolation transition. Specifically, for titanium inclusions embedded in a polystyrene sphere, this enhancement can be up to thirty times larger than in the case of the corresponding homogeneous titanium sphere. We demonstrate that our findings are robust against material losses, to changes in the shape of inclusions and materials, and apply for different effective medium theories. These results suggest the use of composite media as a new, versatile material platform to enhance, optimize, and tailor near-field heat transfer in nanostructures.Comment: 8 pages, 6 figures, 2 table

Purcell effect at metal-insulator transitions

We investigate the spontaneous emission rate of a two-level quantum emitter next to a composite medium made of randomly distributed metallic inclusions embedded in a dielectric host matrix. In the near-field, the Purcell factor can be enhanced by two-orders of magnitude relative to the case of an homogeneous metallic medium, and reaches its maximum precisely at the insulator-metal transition. By unveiling the role of the decay pathways on the emitter's lifetime, we demonstrate that, close to the percolation threshold, the radiation emission process is dictated by electromagnetic absorption in the heterogeneous medium. We show that our findings are robust against change in material properties, shape of inclusions, and apply for different effective medium theories as well as for a wide range of transition frequencies.Comment: 8 pages, 7 figure

The influence of a surface in the non-retarded interaction between two atoms

In this work we obtain analytical expressions for the non-additivity effects in the dispersive interaction between two atoms and perfectly conducting surface of arbitrary shape in the non-retarded regime. We show that this three bodies quantum-mechanical problem can be solved by mapping it into a two-bodies electrostatic one. We apply the general formulas developed in this paper in several examples. Firstly we re-derive the London interaction as a particular case of our formalism. Then we treat two atoms in the presence of a plane, re-obtained the result displayed in the literature. After we add some new examples. A particularly interesting one is two atoms inside a plate capacitor, a situation where non-additivity is very manifest since the plates lead to the exponentially suppression of the interaction of the atoms, provided the atoms are separated by a distance of the order of the distance between the plates or greater. Our results holds even in the presence of other atoms inside the plate capacitor. As a last example we deal with two atoms in the presence of a sphere, both grounded and isolated. We show that for realistic experimental parameters the non-additivity may be relevant for the force in each atom

Tuning quantum fluctuations with an external magnetic field: Casimir-Polder interaction between an atom and a graphene sheet

We investigate the dispersive Casimir-Polder interaction between a Rubidium atom and a suspended graphene sheet subjected to an external magnetic field B. We demonstrate that this concrete physical system allows for an unprecedented control of dispersive interactions at micro and nanoscales. Indeed, we show that the application of an external magnetic field can induce a 80% reduction of the Casimir-Polder energy relative to its value without the field. We also show that sharp discontinuities emerge in the Casimir-Polder interaction energy for certain values of the applied magnetic field at low temperatures. Moreover, for sufficiently large distances these discontinuities show up as a plateau-like pattern with a quantized Casimir-Polder interaction energy, in a phenomenon that can be explained in terms of the quantum Hall effect. In addition, we point out the importance of thermal effects in the Casimir-Polder interaction, which we show that must be taken into account even for considerably short distances. In this case, the discontinuities in the atom-graphene dispersive interaction do not occur, which by no means prevents the tuning of the interaction in ~50% by the application of the external magnetic field.Comment: The first two authors listed contributed equally to this work and are joint first authors. 5 pages, 4 figure

Microscale electromagnetic heating in heterogeneous energetic materials based on X-ray CT imaging

Electromagnetic stimulation of energetic materials provides a noninvasive and nondestructive tool for detecting and identifying explosives. We combine structural information based on X-ray computed tomography, experimental dielectric data, and electromagnetic full-wave simulations, to study microscale electromagnetic heating of realistic three-dimensional heterogeneous explosives. We analyze the formation of electromagnetic hot spots and thermal gradients in the explosive-binder meso-structures, and compare the heating rate for various binder systems.Comment: 8 pages, 5 figure