Isaac Newton, Robert Boyle, Carl Gauss, Augustin Cauchy, George Ohm, James Maxwell, Albert Einstein, Srinivasa Ramanujan, Niels Bohr, Max Planck, Erwin Schrödinger, Werner Heisenberg, Richard Feynman and Stephen Hawking. The world’s most accomplished scientists have one thing in common: they have all been members of the elite Royal Society. Founded in 1660 ‘to promote knowledge of the natural world through observation and experiment’, the Royal Society in London felicitates outstanding researchers. To join the ranks of these pioneers in the field of science, Professor Ajay Sood from the Department of Physics at the Indian Institute of Science (IISc) has recently been elected as one of the fellows of this prestigious society.
Prof. Sood is India’s leading experimental physicist working in the field of condensed matter. In a career spanning over 35 years, his contributions to the field have been original, diverse and vastly significant. “The excitement of discovery motivates me. I am always trying to explore the unexplored,” said Prof. Sood.
In recent times, Prof. Sood and his team at IISc have been working on two broad topics of research within the field of condensed matter. “The first can be called ‘Quantum Condensed Matter’ under which we study materials like carbon nanotubes, graphene and superconductors. The second topic is ‘Soft Condensed Matter’. Both topics are interdisciplinary and require knowledge of various different fields,” he explains. His laboratory aims to primarily understand the physics behind each observed phenomenon before delving into the questions of their commercial applications.
Over the last 15 years, their research in Quantum Condensed Matter has focused on nanomaterials. They have designed Field Effect Transistors (FETs) using materials like carbon nanotubes, graphene , Molybdenum disulphide and, most recently, black phosphorus ;superconductors such as iron pnictides. They perform Raman spectroscopy on the device, while it is working, in order to study the electron-phonon coupling process in the device. This technique helps them understand and optimise device performance. Additionally, they study the opto-electronic properties of such materials by exciting them with the help of ultrafast (femtosecond) LASERs. “This method is called ‘time-resolved pump probe spectroscopy’ which lets us investigate the amount of time optically excited electrical carriers take to return to their ground state. Such analysis can aid, for example, in the design of photovoltaic devices,” elaborates Prof. Sood.
His latest research interest in Soft Condensed Matter is something he calls “active granular matter”, which are asymmetric grains of brass that are thicker at one end than at the other. When these grains are vibrated vertically on a plate, they move like living objects or “active matter” by exhibiting a cooperative motion that is frequently observed in birds, ants and fish. This provides them with an opportunity to understand the natural phenomenon of “flocking” by studying non-living objects. A widely-accepted theory in flocking is the Nearest Neighbour Model that simply states each member of the flock aligns itself with its nearest neighbour. Prof. Sood’s team was the first to show that flocking can be achieved even going beyond nearest neighbour interactions. Prof. Sood said, “If we add some aluminium beads on the plate with the brass grains, the brass grains exhibit perfect flocking behaviour. This implies that the motion is being transferred from one grain to another through the beads, even when the grains are not nearest neighbours”.
Once the analysis of these projects is complete, one can expect far-reaching commercial applications based on these phenomena. “Carbon nanotube or graphene FETs coated with very specific antibodies to detect biological matter could act as extremely sensitive biosensors. When the desired analyte is detected, there will be a change in transistor characteristics,” describes Prof. Sood. The team has also recently designed a protein detector that was made from optical fibre Bragg grating . A small portion of the shell of an optical fibre is removed and the core under it is engraved with gratings and then coated with a layer of graphene that has antibodies attached to it. “When the antibodies come in contact with the antigen, the refractive index of the optical fibre changes,” says Prof. Sood. They have used this device to detect a protein called CRP which is a marker for heart attacks in the human body. Another important application arises from the phenomenon of “shear thickening”, the increase in viscosity of a liquid when shear force is applied, which finds its use in the design of bullet-proof vests. Most bullet-proof articles are made by using sheets of polymer( Kevlar) and there is a liquid between the sheets that becomes thicker when a bullet hits the article. Prof. Sood said, “Conventional bullet-proof vests require 50 to 60% silica colloid by weight, in order to achieve shear thickening. We have found that using carbon nanotubes instead of silica colloid can reduce this quantity to merely 1% by weight and still achieve shear thickening”.
Prof. Sood has been bestowed with many honours for his exceptional contributions to science. He was awarded the Padma Shri by the Government of India in the year 2013. He was formerly the President of the Indian Academy of Sciences , the Vice-President of the Indian National Science Academy and now is Secretary General of The World Academy of Sciences. On being elected as a fellow of the Royal Society this year, he says, “I feel happy to be recognised for our work; honoured to be elected and humbled when I realise that I have been placed in the company of so many geniuses”.
Professor Ajay Sood photographed at the Signing Ceremony of the Royal Society, which took place on 10th July 2015 in London. Image source: The Royal Society.