Mahi R. SinghWestern Science

Research Activities

Nanomaterials and nanocomposites

5-1The aim of the proposed research program is to advance both the basic science and practical applications of light-matter interactions in nanocomposite materials. This will be achieved through theoretical design, modeling, simulation, and collaborative research to synthesize the required functional nanocomposite architectures. Nanocomposite materials are engineered materials fabricated by combining two or more semiconductor, biological or metallic nanostructures. By using various combinations of these nanostructures an enormous number of nanocomposites can be fabricated with varying physical and optical properties. The most prominent examples of nanostructures which can be used to build nanocomposites are quantum dots, graphene, carbon nanotubes, semiconductor nanowires, and metallic nanospheres, nanorods or nanowiresfor more information please click here    back to home page 

Nanophotonics, plasmonics and polaritonics


Plasmonics: Plasmonic is the study of collective motions of electrons in metallic nanomaterials. We proposed new types of hybrid systems made from quantum dots and metallic nanoparticles. We also propose metallic nanowires and waveguides made from metallic nanoparticles. They are made from embedding a periodically arranged metallic spheres into a host dielectric or metallic photonic crystal. It is found that when pump laser is applied and plasmon coupling is absent the system has one minimum (i.e. transparent state) between two absorption peaks (fig 4a). In the presence of the plasmon coupling the system has three peaks and two minima (two transplant states) (fig 4b). For certain experimental conditions two transparent states can be merged into the one transparent state (fig. 4c). This means that the system can be switched from two transparent states to one and vice versa. The present study can be used to make new types of plasmonic devices such as plasmonic switches, transistors, light sources, integrated optical circuits, incandescent application lamp and thermal photovoltaic power generation. Click here for more information. for more information please click here  back to home page 

Graphene and carbon nanostructure


We study quantum optics and energy transfer in a graphene nanostructures and carbon nanotubes. Graphene is made from two-dimensional carbon atoms. Here the quantum dot (QD)-graphene system is embedded in a photonic crystal, which acts as a tunable photonic reservoir for the QD (see figure). Photonic crystals are engineered, periodically ordered microstructures that facilitate the trapping and control of light on the microscopic level. Applications for photonic crystals include all-optical microchips for optical information processing, optical communication networks, sensors and solar energy harvesting. In our investigation we consider a nonlinear photonic crystal, which has a refractive index distribution that can be tuned optically. The nonlinear photonic crystal surrounds the QD-graphene system and is used to manipulate the interaction between the QD and graphene nanodisk.

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Metallic nanostructures


We have studied energy transfer and photoluminescence in donor and acceptor quantum dots embedded in a nonlinear photonic crystal. The quantum dots are interacting with each other via the dipole-dipole interaction. The nonlinear photonic crystal modles the dielectric constant of the hybrid system. Using the density matrix method, it is found that the energy transfer and photoluminescence in the donor quantum dot can be controlled by a pump .eld due to the nonlinearity of the photonic crystal. Additionally, our theoretical calculations agree with recent experiments. This hybrid system can be used to fabricate ultrafast switching and sensing nanodevices.for more information please click here  back to home page 

Second harmonic generatio

1Currently there is considerable interest in the study of nonlinear semiconductor and metallic nanoparticles as new light sources in the nanoscale regime. For example, nanoparticles consisting of non-centrosymmetric metallic nanoparticles (MNPs) exhibit two-photon second-harmonic generation (SHG) which can be used for nonlinear optical microscopy. Nanoparticles made of pure noble metals have high electron polarizabilities and produce a giant enhanced local electric field. Strong local fields are particularly important for nonlinear optical processes, such as surface-enhanced Raman scattering and SHG which scale with the power of the applied field. Two-photon photoluminescence has been studied in nanostructured noble metals, and was found to be more sensitive to the local field than single-photon luminescence. SHG in semiconductor nanoparticles such as quantum dots has also been investigated experimentally and theoretically. Two-photon excitation has many advantages over one-photon excitation including higher spatial resolution, deeper penetration and less photo-damage. Nonlinear nanoparticles have applications nanoscale antennae nanoscale lenses and photolithography and two-photon microscopy. for more information please click here   back to home page 

Photonic and polaritonic band gap materials

1Photonic and polaritonic crystals: Recently there is considerable interest in finding a new class of materials which can be used to fabricate faster and smaller photonic and optoelectronic devices since semiconductor industry has reached its highest limit. In this research project we study photonic, plasmonics and optoelectronic properties of nanomaterials made form polaritonic/photonic band gap materials and doped with nanoparticles. These materials have energy gap in their energy spectrum. Energy gap in polaritonic/excitonic materials appears due to the phonon/exciton-photon coupling [fig 1a/1b]. In other words radiation signals in polaritonic materials are carried out by an admixture of photons and optical phonons/excitons rather than photons. On the other hand the energy gap in photonic materials is due the scattering of photons with periodicity of the dielectric constant (fig 1c). Examples for photonic materials are photonic crystals and example for polaritonic materials are quantum dots and wires, III-V, II-VI semiconductors, polymers, dispersive materials; oxides, halides, organic and inorganic materials etc.for more information please click here  back to home page  


1We study quantum optics of metamaterials and metamaterials nanocomposites. Metamaterials are a new class of artificial materials whose optical properties are determined not only by their classical atomic composition, but also by the nanoscale organization of their structural components. As a result, metamaterials possess unique electromagnetic properties which cannot be obtained from naturally occurring materials. Metamaterials have the dielectric permittivity and magnetic permeability simultaneously negative for a range of frequencies in the electromagnetic spectrum, effectively leading to a negative refractive index. We study photoluminescence and spontaneous emission in quantum dots doped in a dielectric substrate-metamaterial heterostructure. A schematic diagram of the heterostructure is shown in Figure. The heterostructure is formed by fabricating a split-ring resonator and metallic rod metamaterial on a dielectric substrate. Quantum dots are doped near the interface in the heterostructure. Our results indicate that the photoluminescence and spontaneous emission of the QDs are enhanced in the presence of the metamaterial when the exciton and surface plasmon frequencies are resonant. Click here for more information.

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We have also developed theoretical models for charge and spin transport due to equilibrium and non-equilibrium processes in semiconductor nanowires and quantum wells DNA nanowires and DNA derivatives. The theory is able to explain the existing experiments. Excitons phase transitions in semiconductor heterostructures has also been studied.

Semiconductors and semiconductor heterostructures

Surfaces and interfaces

High temperature superconductors