Prof. Bhupendra Dev
Prof. Bhupendra Dev
Indian Institute of Technology Kharagpur, India
Title: Superconductivity of cobalt in nanoscale cobalt thin films

The phenomenon of superconductivity was discovered over a century ago. So far more than half of the number of elements in the periodic table have shown superconductivity. Usually metals possessing strong long-range magnetic order, as in antiferromagnetism or ferromagnetism, do not exhibit superconductivity. This includes cobalt – a ferromagnetic transition metal. Recently, we discovered a high-density nonmagnetic (HDNM) fcc phase of Co in Co thin films [1]. As this phase of Co is nonmagnetic, it was logical to explore superconductivity in this HDNM phase of Co. We have indeed discovered superconductivity in these HDNM Co thin films with a superconducting transition temperature (Tc) of ~ 5 K. The transition to the superconducting state has been detected by four-probe measurements. Point-contact spectroscopy has provided a Tc value of ~ 9.5 K. The higher value of Tc obtained in point contact spectroscopy is apparently due to unavoidable pressure at the contact point. First-principles density functional theory calculations for this dense fcc phase of Co show that this phase is nonmagnetic, characterized by zero elementary moment, and the estimated TC within the BCS theory is 0.30 K. A volume preserving strain in fcc Co is shown to result in anomalous softening of zone boundary phonons which couple strongly with electrons, and stabilize superconductivity at a relatively high temperature (> 5 K) [2]. The value of TC can indeed be higher for other strain conditions. That the superconding Co layer (~ 4 nm) is in contact with a ferromagnetic Co layer (18 nm) indicates its potential application in the area of quantum information.

[1] Nasrin Banu et al., Sci. Rep. 7, 41856 (2017); Nanotechnology 29, 195703 (2018). 

[2] Nasrin Banu, B. N. Dev et. al., arXiv:1710.06114

Prof. Dev received his PhD from University at Albany, The State University of New York, USA. He was a Guest Scientist at DESY, Hamburg, Germany, before he accepted a faculty position in India. Having served two institutions over the past 30 years and developed major research programmes in surface and nanoscale science, currently he is a Visiting Professor at Indian Institute of Technology Kharagpur. He has supervised 21 Ph.D. theses and published about 160 papers in reputed international journals. He has been serving as editorial board or advisory editorial board members of several international journals. As principal investigator, he has carried out international bilateral Indo-US, Indo-German and Indo-Japan collaborative research projects. He is a fellow of national academies of India. Among many awards Prof. Dev received is the 2010 International Alumni Award for Exceptional Achievement from the University at Albany, State University of New York, U.S.A.