ELECTRON-PHONON BASED SUPERCONDUCTIVITY: A NEW FANTASY FOR HIGH TEMPERATURE SUPERCONDUCTIVITY

Abstract

Superconductivity has been most fascinating phenomenon in condensed matter physics since the day of its discovery in 1911. It was almost after half century later that underlying mechanism of superconductivity was discovered by Bardeen-Cooper-Schrieffer (BCS) in terms of electron-phonon coupling in 1956. Although, following decades have witnessed lot of exceptions to BCS theory of superconductivity and a large class of exotic superconductors have been discovered. One of the disappointments associated with BCS theory was belief that electronphonon based superconductivity cannot be observed at high temperatures owing to weak nature of electron-phonon coupling. The isotope effect displayed that strength of electron-phonon coupling and hence transition temperature (Tc) is related to mass of constituent atoms and lighter atoms results in higher Tc. Motivated by this, N. W. Ashcroft advocated the idea that due to lighter mass of hydrogen and strong covalent bonding, the metallic hydrogen or hydrogen rich compounds can have higher Debye frequency and electron-phonon coupling leading to high Tc value. This idea has recently been pursued by many theoretical predictions on hydride superconductors which have been predicted to have Tc as high as 250 K for Lanthanum hydrides which is close to room temperature. These compounds are although stable at very high pressures (hundreds of GPa). In my talk I shall present a quick overview of BCS theory of superconductivity and then scan recent developments in hydride superconductors. I will also present few results of my theoretical calculations highlighting possibility of electron-phonon superconductivity with high Tc in some intercalated non-hydride materials at ambient pressures.