Research Areas
Quantum Magnetism and Related Phenomena
Optical and Opto-electronic Properties
Transport in Nanostructures and Biomolecular Systems
Hydrogen Storage in Organic Molecular Solids
Physics and Chemistry of New Carbon based Materials
Quantum Magnetism and Related Phenomena
Quantum Magnetism is as old as quantum mechanics. There have been a number of celebrated models in this area, and although the field was initially completely theoretical in nature, the last couple of decades have witnessed the synthesis of an innumerable number of novel systems with far-reaching applications in magnetic recording, data storage and magneto-electronic circuitry. This field offers the promise of manipulating purely quantum objects like spin for applications in fields such as quantum computing, spintronics and quantum qubit technology. Our interest lies in the interface of structural aspects and quantum ordering: mostly in insulating oxides, sulphides and related materials. Different structural manifestations of magnetic ions, together with the interactions among the spin degrees of freedom in various forms, open up a host of possibilities. This is more evident in low-dimensional systems, where quantum effects may give rise to completely unconventional and exotic quantum phases. We have been involved in developing quantum many-body theories to accurately calculate several static and dynamic properties of low-dimensional magnetic systems. In particular, the effects of competing exchange interactions and lattice dimerizations have been analysed in detail for a large class of systems including Kagome antiferromagnets, sawtooth lattices and ladder structures. We have also been extending our theory to design novel magnetic clusters with desired technological applications in magneto-electronics.
Optical and Opto-electronic Properties
Materials with large non-linear optical absorption and emission properties find tremendous applications in lasers, optical switches and optoelectronics. To fully realize the potential offered by optically active materials, one has to be able to optimize properties of individual molecular species at a microscopic level, as well as come up with efficient ways of arranging molecules macroscopically, so as to achieve maximum density and acentricity. Our interest lies in developing theories that can help in understanding and predicting a priori, the optical response functions in a wide variety of systems ranging from organic crystals composed of charge-transfer species to dipolar crystals and inorganic materials. We design strategies that enhance the opto-electronic response functions at the molecular as well as at the crystalline aggregate level. We also have proposed for the first time a number of all-metallic sandwich type aluminium complexes together with strategies for future experimental synthesis.
Transport in Nanostructures and Biomolecular Systems
Due to possible applications in miniature circuits, the study of charge conduction through single molecules and nanosystems has gained tremendous impetus. Our theoretical investigations focus on the parameters that critically influence conductance across such systems. We consider real experimental systems that exhibit such phenomena. We have been involved in developing effective theories that describe the spatial electrostatic potential across electrode-nanosystem interfaces as well as nonequilibrium dynamical properties like conductance, current and capacitance. Landauer-Buttiker equations together with configuration interactions methods have been successfully applied through non-equilibrium Green function formalisms to understand various transport characteristics in a number of nanosystems. We have been also able to design nanomaterials for molecular memory and switching devices. We have also been actively involved in the field of bio inspired nanoelectronics. We have studied the effect on incorporating magnetic ions into the DNA helix for possible applications in spintronics. We find that the alignment of magnetic ions within the DNA helix creates a spin channel due to the efficient orbital interactions between the magnetic ions. This also gives rise to odd-even effects in the low frequency region of the optical spectra, which can be used as a signature to identify the spin-spin interactions. We have also designed various bio-molecular systems for potential applications in current rectification and switching, and as low dimensional half-metallic ferromagnetic devices. Initial studies for understanding the mechanisms of light absorption and electron transport in photosynthetic centers are currently underway. The primary interest of the project is to understand the correlation between the active Magnesium-chlorin centers and various side chain functionalities of LHCs (Light harvesting complexes) present in photosynthetic centers of bacterial species and plants.
Hydrogen Storage in Organic Molecular Solids
The storage of molecular hydrogen in a safe and affordable manner is one of the most challenging problems of the current decade. The ever-increasing demand on energy, limited resources and polluting nature of fossil fuels has led to an interest in materials that are capable of storing molecular hydrogen. Microporous materials such as zeolites, activated carbon, nano-tubes, and open-framework architectures, which have many molecular size sieves have been recognized as suitable candidates for hydrogen storage, although the critical limit of 6.5% (by weight) efficiency is yet to be realized for commercial marketing. Hence, there is a very focused research towards the design of new materials with enhanced hydrogen storage capacity. Most of the inorganic open-framework materials which have large pore sizes and are capable of adsorbing large volumes of hydrogen, become non-reusable since very often due to the formation of strong chemical bonds with hydrogen hinders hydrogen desorption. Hence the ideal hydrogen storage materials will be the molecules that physically adsorb the molecular hydrogen and require mild conditions for their removal. Our major goal has been to design the molecular solids of high hydrogen adsorption efficiency computationally. For this purpose we look into various organic systems with different structures like Sulflower and Sumanene. Whether such systems also could be used for effective field effect transistor actions is also being actively pursued.
Physics and Chemistry of New Carbon based Materials
The two dimensional flat monolayer of carbon atoms packed into a honeycomb lattice, i.e., graphene, has started gaining prominence very recently owing to the recent progress in experimental techniques. Because of its sophisticated low-dimensional electronic properties and huge application possibility, it has attracted a big scientific army to explore it in various aspects. This material has been modeled both within Schrodinger and Dirac formalism. In our group, we are studying the electronic structure, electronic conduction and storage properties of this interesting material within both manybody and DFT formalism. We observe magnetic ground state of zigzag edge graphene nano ribbons, which shows intrinsic half-metallic property on hole doping over a large temperature domain, opening up a huge application possibility in spintronics devices. Our calculations suggest graphene as a promising storage material for both hydrogen and carbon dioxide.