Superconductivity at extremely low carrier density: Bismuth
ABSTRACT :
Bismuth(Bi) has played a very important role in uncovering many interesting physical properties in condensed matter research and continues to draw enormous scientific interests due to its anomalous electronic properties. Unlike metals where there is roughly one mobile electron per atom, in a semi-metal like Bi, the concentration of mobile electrons is extremely low (100,000 atoms share a single mobile electron). Hence, the superconductivity (SC) in bulk Bi is thought to be very unlikely at a currently achievable temperature (~40 mK). In this talk, I will describe the first-ever observation of bulk SC in Bi single crystals (99.9999%) below 530 mK under ambient pressure with an estimated critical magnetic field of 5.2 mT (one eighth of earth’s magnetic field) at absolute zero. The standard models (superconductivity) cannot explain this phenomenon because the characteristic thermal energy is comparable to the Fermi energy in Bi and a new theory is necessary.
ABOUT THE SPEAKER:
Professor Srinivasan Ramakrishnan did his MSc. Physics in I.I.T. Madras in the year 1977-1979. He joined TIFR for his Ph.D (1979-1985) to study superconductivity in transition metal compounds. Subsquently, he joined TIFR as a faculty in 1985 and currently he is a senior professor. He is a recipient of many awards, to name a few, Satyamurthy (IPA, India), Humboldt (Germany), JSPS (Japan) and NWO (Netherlands). He is also a member of Indian Academy of Sciences and currently vice president of IUPAP5 (Low Temperature Physics). He is one of the well known low temperature physicists in India and his laboratory is the only place in the country where one can do experiments over seven decades in temperature from 400 K to 40 mK. He has authored more than 300 publications in reputed International Journals spanning 3 decades of research work. The central theme of his research is study of strongly correlated electron systems with the emphasis on investigating competing ground states in a variety of systems that exhibit multiple phase transitions at low temperatures. Such a study required setting up of a complex low temperature laboratory with a capability to measure various bulk properties of intermetallic and insulating compounds at low and ultra low temperatures.