List of colloquium

Date : 03-10-2018
Time : 16:00:00
Speaker : Prof. Debabrata Goswami
Area : DEAN'S OFFICE
Venue : Nanosims Lecture Hall, PRL

Abstract

Femtosecond laser pulses have been shaped in a programable manner for coherent control at molecular level and for several coherent optical processes that have resulted in applications to fast switching, data compression, ultrasensitive detection, computing, etc. Optical and quantum interaction and their detection remain at the forefront of all such efforts. Typically, however, it is not common for ultrashort time to be connected to ultra-small dimension. Use of femtosecond optical tweezers (FOTs) makes this connection possible. We have developed a novel on-the-fly calibration method of FOT that enables in situ control and contactless measure of absolute temperature and viscosity at nanoscale dimensions. Such measurements and control at the nanoscale have been challenging since the present techniques can only provide relative off-line measurements that are of low spatial resolution. Such spatiotemporal control with ultrashort pulses provides the possibility of manipulation at nanoscale that can yield several interesting results that include visualization of colloidal aggregation in real time, computational logical operation in localized zone that is then reset with the subsequent pulse train. We simultaneously apply the high temporal sensitivity of position autocorrelation and equipartition theorem to precisely measure and control in situ temperature and the corresponding microrheological property around the focal volume of the trap at high spatial resolution. The FOTs use a single-beam high repetition rate laser for optical trapping to result in finer temperature gradients in comparison to the continuous-wave laser tweezers. Thermal effects are often treated delirious and most spectroscopy efforts remain in removing them. We have, on the other hand, used highly repetitive femtosecond laser heating to develop time-resolved photothermal lens spectroscopy that provide molecule level sensitivity.

Date : 29-08-2018
Time : 16:00:00
Speaker : Dr. Navinder Singh
Area : DEAN'S OFFICE
Venue : Nanosims Lecture Hall, PRL

Abstract

Air travel has become one of the most common means of transportation. One wonders about the lifting capacity of uniquely designed wings of Boeing airliners. You might have peeped through the window of an airliner and have noticed the moment of ailerons and flaps when plane takes off or lands, and that might have excited your curiosity. The physics behind these mechanisms is both interesting and challenging. The common question which is generally asked is: How does an airplane gain lift? And the most common answer is via the Bernoulli principle. It turns out that it is wrongly applied in common explanations, and there are certain misconceptions in this field. In an alternative explanation the push of air from below the wing is argued to be the lift generating force via Newton's law. There are problems with this explanation too. In this presentation we will try to clear these misconceptions, and the correct explanation, using the Lancaster-Prandtl circulation theory, will be discussed. The physical meaning of the Kutta-Joukowski condition will be illustrated. At the end, a brief discussion of a new viewpoint advanced in PRL will also be presented which goes beyond the Lancaster-Prandtl theory. This talk will discuss the physics of paragliders and powered paragliders.

Date : 01-08-2018
Time : 16:00:00
Speaker : Prof. Deshdeep Sahdev
Area : DEAN'S OFFICE
Venue : K. R. Ramanathan Auditorium, PRL

Abstract

It is an interesting and remarkable fact that every Nobel-prize winning piece of work in Experimental Physics was carried out on apparatus designed and developed by the physicist in question, be it Rutherford, Raman, Mossbauer or Binnig. I will start by taking the audience through a fascinating journey which saw my team developing Scanning Probe Microscopes, Physical Properties Measurement Systems and hi-end CVDs all the way out to internationally competitive standards. I will then describe how we have gone about enhancing the base so developed for research in material science, condensed matter physics and nano-technology, with packages for scientific computation, many designed and developed (like our instruments) essentially from scratch. By the end of the talk, I hope to have convinced the audience that the complete & seamless, indigenous integration of theory, computation, experiment and instrumentation, which we are beginning to achieve at QuazarTech holds out the promise (not only for us but for centers all over India) of tackling some really interesting physics problems, a few of which I will describe.

Date : 30-05-2018
Time : 16:00:00
Speaker : Dr. Navinder Singh
Area : DEAN'S OFFICE
Venue : K. R. Ramanathan Auditorium, PRL

Abstract

Every child has at one time or another played with a magnet and been fascinated by its mysterious ways. It is an uncanny feeling to experience the repulsion between the like poles of two magnets. The "magical" properties of magnets have fascinated mankind over the centuries. Questions like why only iron, cobalt, nickel, or their alloys show ferromagnetic behaviour whereas other elements do not, comes to every curious mind? This presentation is devoted to the historical development of the key ideas in the vast field of magnetism. The presentation follows a chronological order (which is also the logical one from the conceptual point of view). We start from the Greeks, to medieval times to and the 20th century, and highlight the key contributions of people line William Gilbert; Coulomb; Poisson; Oersted; Ampere; Faraday; Maxwell; Pierre Curie; Langevin; Weiss; van Vleck; Heisenberg; Pauli; Slater; Stoner; Anderson; Moriya, Hubbard and others. It will be shown how the advent of quantum mechanics resolved some baffling problems in the field. The current problems in the magnetic properties of strongly correlated electronic systems will be presented, and finally we will summarize the current status of the field of magnetism.

Date : 23-05-2018
Time : 16:00:00
Speaker : Dr. Shanti Pappu
Area : DEAN'S OFFICE
Venue : K. R. Ramanathan Auditorium, PRL

Abstract

In the history of scientific thought, the story of our origins, has been one of the endless fascination and heated debates. The study of human evolution has been approached in recent years through interdisciplinary research including archaeology, palaeoanthropology and genetics, situated within a geochronological and palaeoenvironmental framework. Much of the early fossil and archaeological evidence for the story of human evolution arises from discoveries in Africa. Debates range around the timing and nature of dispersals of differing species out of Africa, with alternate theories being periodically proposed. In this context, the geographical position of South Asia, and its rich and diverse prehistoric archaeological record, critically informs our understanding of cultural aspects of human evolution, behavioral changes and adaptation of populations to past environmental variability. Here, we first situate the South Asian prehistoric record in a global context. We then move to our specific research project comprising excavations at the site of Attirampakkam, Tamil Nadu and other sites along the SE coast of India. Archaeological, geomorphological and geochronological studies here have led to paradigm shifts in our understanding of the prehistoric record of India, reframing current concepts of the age and nature of the early Palaeolithic (Stone Age) occupation of India. In particular age estimates for different cultural phases at Attirampakkam ranging from around 1.7 million years ago to around 172,000 years ago have stimulated global debates on existing theories of the timing and nature of population dispersals out of Africa and across Asia. Implications of these studies in terms of paradigm shifts in viewing trajectories of cultural evolution and population dispersals across Eurasia are discussed here. We conclude by emphasising the crucial importance of Indian archaeology and associated sciences in contributing towards a global perspective of human origins.

Date : 14-03-2018
Time : 16:00:00
Speaker : Dr. Kishore Dutta
Area : DEAN'S OFFICE
Venue : K. R. Ramanathan Auditorium, PRL

Abstract

The recent discovery of superconductivity below 1K within a limited pressure range in uranium ferromagnetic superconductors triggered many experimental and theoretical investigation on the coexistence of superconductivity and ferromagnetism, revealing their detail electric and magnetic properties. The Curie temperatures for paramagnetic to ferromagnetic (PM-FM) phase transition in these compounds are found to depend strongly on pressure, indicating that magnetic energy is coupled to the lattice. The recent experimental results for critical behavior related to their PM-FM phase transition does not belong to any known universality classes of critical phenomena. In order to capture their critical behavior related to PM-FM phase transition, spin-lattice coupling needs to be considered in the critical theory. Through renormalization-group analysis of such a model Hamiltonian, it is shown that it can capture well the experimentally determined critical exponents for such compounds. This talk will also discuss the importance of magneto elastic interaction in the vicinity of quantum critical points in strongly correlated systems.

Date : 07-02-2018
Time : 16:00:00
Speaker : Prof. P. C. Deshmukh
Area : DEAN'S OFFICE
Venue : K. R. Ramanathan Auditorium, PRL

Abstract

Einstein’s insightful analysis of the symmetry in the laws of electrodynamics changed our perception of space and time in a manner that continues to challenge common intuition. Even as time is not an observable, and perhaps not comprehensible, time-intervals are measurable. Physical atomic processes occur at ultra-fast speeds over attoseconds. In this talk, the Wigner-Eisenbud-Smith (WES) measure of time delay in atomic dynamics will be introduced. Exploiting the time-reversal symmetry, the WES time-delay is well-adapted to estimate the time-delay in the atomic photoelectric effect. Einstein’s explanation of photoionization laid the very foundation of the quantum theory. For over a hundred years, it was considered to be an ‘instantaneous’ process, but in the last decade, there have been pioneering studies, both experimental and theoretical, in which photoionization time-delays on the attosecond time scale have been reported. These are of importance for the atomic-clock technology, and to understand fundamental relativistic effects and many-body electron-correlations in atomic dynamics. This research field is very young, yet quite vast. This talk will provide a brief introduction to this exciting field and discuss our understanding of the photoionization WES time-delay, and its anisotropic character, especially in the energy regions of the Cooper-minimum, and also in the energy regions of autoionization resonances, and the shape resonances.

Date : 15-11-2017
Time : 16:00:00
Speaker : Prof. Amita Das
Area : DEAN'S OFFICE
Venue : K. R. Ramanathan Auditorium, PRL

Abstract

Understanding electron beam transport and energy deposition in plasma is crucial in the context of many applications such as fast ignition etc., where it is desirable to dump energy in an over dense compressed core of the target where lasers are unable to penetrate. The talk will cover complex collective physics associated with electron beam plasma instabilities, the associated evolution of magnetic fields and the ensuing turbulence leading to possible anomalous behavior of transport. The experimental evidences in support of anomalous transport will be provided. A novel effect arising due to finite transverse beam size will also be demonstrated.

Date : 30-08-2017
Time : 16:00:00
Speaker : Dr. Urbasi Sinha
Area : DEAN'S OFFICE
Venue : K. R. Ramanathan Auditorium,PRL

Abstract

Quantum mechanics is a cornerstone of modern physics. Just as the 19th century was called the Machine Age and the 20th century the Information Age, the 21st century promises to go down in history as the Quantum Age. In this talk, key properties of quantum systems called Quantum Superposition & Quantum Entanglement and the world of single & entangled photons will be discussed. Also, in this colloquium the ongoing work towards quantum technology in Quantum Information and Computing lab at the Raman Research Institute, Bengaluru will be discussed.

Date : 26-07-2017
Time : 16:00:00
Speaker : Prof. Sreerup Raychaudhuri
Area : DEAN'S OFFICE
Venue : K. R. Ramanathan Auditorium, PRL

Abstract

The story of how research into the physics of cosmic rays and elementary particles began in India will be told in simple and non-technical language. Starting from the days before the First World War, the growth of research in this area will be traced till the nineteen-sixties. On the way small anecdotes of the major personalities will be told. Finally, we shall discuss some lessons which can be learned from this historical exercise.