Physics Colloquium Spring 2022

Thursdays 4:00 p.m. 104 Physics or online via Zoom.

Contact colloquium organizer Dr. Shun Saito at for the Zoom link.

(Link to main colloquium page)


Title: Pairing at Zero Density 

Abstract: As far as we know all superconductors are condensates of paired electrons. Thus, pairing is an essential stage in the formation of a superconductor. According to standard lore, the key to overcoming the strong electron-electron repulsion lies in their ability to exchange phonons, which vibrate at low frequency (the Debye frequency), orders of magnitude smaller than the electronic frequency (the Fermi energy). Moreover, the superconducting transition temperature is an emergent scale that is exponentially sensitive to the density of free charge carriers, thus bounding the density from below. The discovery of superconductivity in doped materials (semimetals, semiconductors, doped Mott insulators, twisted bilayer graphene etc.) challenges this understanding by defying these basic requirements. In this talk I will discuss these issues in detail. I will then present a concrete example exhibiting superconductivity at any charge density including zero; A Dirac semimetal in a crystal that is undergoing a structural quantum phase transition. Thus, providing a new mechanism for superconductivity that does not suffer from a vanishing density and possibly opens a path to understand the low-density superconductors.