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Spin Effects in Condensed Matter Systems and Opto-spin physics
Magneto-optical phenomena
| Faraday rotation describes a magneto-optical phenomenon i.e, interaction of optical radiation and magnetic field. It is the rotation of plane of polarization of linearly polarized monochromatic light transmitting through an optically inactive medium under the action of an axial magnetic field and is usually very small in magnitude, of the order of micro radians so, a large dc magnetic field is usually required. However, with the help of lock-in technique using the small ac magnetic field, this requirement can be bypassed. We have devised an experiment using the phase sensitive technique to study the Faraday rotation in different materials. We have also adapted this system to look at reflections, the experiment is the typical magneto-optical Kerr effect. Measurements have been performed investigating reflections from thin nanomagnetic layers. The ultimate goal is to use Kerr rotations to probe the spin structure of materials, notably the spin Seebeck and spin Hall effects. |  |
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Spin caloritronics
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The spin Hall effect is the spin analogue of the famed Hall effect, a spin voltage (difference in Fermi levels for oppositely polarized spins) develops across a current-carrying conductor. The spin accumulation should be detectable by the differing interaction of circularly polarized light with opposite spins. Similarly, we also have the spin Seebeck effect which uses a temperature gradient to induce the spin voltage, similar to the traditional Seebeck effect taking place in thermocouples, where a temperature difference produces an electrical voltage. The origin of both of these effects lies in the spin-orbit interaction. The magneto-optical characterization of these spin-dependent processes requires careful control, generation and detection of light polarization, controlled heating and precise temperature measurement, vacuum production and low-temperatures. We have, in our lab, acquired sufficient expertise in all of these areas individually and are now in a position to integrate our preliminary investigations. (For the low temperature studies, we have acquired a custom designed optical cryostat.) Traditionally, these so-called spin caloritronic effects are measured by electrical means. The electrical methods require cumbersome electrical connections and one is limited by the electrical noise of the system, the weak detected electrical signals may be overwhelmed with the intrinsic noise processes. The optical detection bypasses this limitation, thanks to very sensitive photon detectors which have high sensitivities (output current/incident light intensity). The final goals of this project are the:
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Biophysics
Compact hyperpolarized NMR and MRI
| There has been considerable progress in the invention and refinement of low-field and zero-field magnetic systems. In our research group, we are developing a compact and mobile spin polarizer to augment a benchtop NMR/MRI apparatus that is currently under development in the lab. This will enable the miniaturization of both the NMR and hyperpolarization mechanisms. |  |
Polarized, miniaturized and mobilized magnetic resonance can revolutionize the applicability of this widespread technique, extending it to developing countries, on-field inspections and testing, ambulatory medical care in disaster-struck areas, and the chemistry lab benchtop or the fume hood. For example, the high polarizations achieved from para-hydrogen enable us to detect trace amounts of chemical species and image their spatio-temporal profile, circumventing the low sensitivity issue plaguing NMR. In addition, the polarized para-hydrogen can be used as a magnetization storage vector for portable, mobile MRI instrumentation. It is known that the storage time can be extended beyond the conventional T1 times by exploiting the symmetry properties of the quantum singlet state. Such a long-lived and transferrable polarization agent can be achieved, for example, by the endohedral hydrogen fullerene, H2@C60 which is a molecule capable of surviving high temperature conditions (~500 deg C) for extended periods of time (~10 min). We are studying the use of endohedral fullerenes for the hyperpolarization storage and physical migration of the polarized product from one spatial location to another. Another experiment we will design, once our hardware is completely ready, is the in-situ and real-time study of polymerization reaction catalyzed by supported catalysts. The goals of this project include:
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Microfluidic real-time pocket-sized PCR
| The Polymerase Chain Reaction (PCR) is a very important tool for medical diagnostics and finds applications in genomic analysis, infectious diseases detection, mutation studies and forensics. Available PCR machines are expensive, and the real challenge is to make them pocket sized and low cost, bringing them within reach of Pakistani clinical laboratories. In PCR, we amplify DNA using a thermocycling process, which involves three steps including Denaturing (at 95C), Annealing (50-60C) and Extension (72C). We have used TO-220 pacakaged BJT and FET for heating purposes. The temperature at each zone is controlled by LabVIEW based PID Controller. Real time analysis will be performed by optical means. |  |
Development of a Portable Atomic Force Microscope
| AFM (Atomic Force Microscope) is used in very high resolution microscopy, with typical resolution of 0.16 nanometer. With different operational modes AFM can be used to image almost any type of samples from solid metals to biomedical specimens. The physlab is developing a teaching and basic-research grade AFM in-house. The basic principle lies on cantilever deflection when scanned very close to the sample. A laser beam is used to detect the deflection of cantilever by using photo detector. |  |
Completed Projects
Please click here to visit previous research and development directions pursued in this Laboratory.