Physics Colloquium: Superconductivity at low density
Thursday, March 9, 2023
3:30 PM-5:00 PM
Vladyslav Kozii, PhD
Assistant Professor, Carnegie Mellon University
Superconductivity at low density:
Superconductivity – the loss of all electrical resistance at very low temperature – is one of the most remarkable quantum phenomena found in materials. The explanation of conventional superconductivity as a condensate of electron pairs constitutes a great triumph of 20th century solid state physics. In this conventional theory of superconductivity, the attraction that keeps the electron pairs together is provided by lattice vibrations, which provides an excellent description of many classic superconductor. This theory breaks down, however, when applied to unconventional superconductors discovered more recently. The failure of the conventional is approach is particularly acute in materials with low – or very low – electron density. In this talk, I present a mechanism for superconductivity in a special class of low-density systems, i.e., the three-dimensional topological materials, which are close to a polar structural instability represented by the ferroelectric quantum critical point. I show that while the Coulomb repulsion between electrons is strongly screened by the lattice polarization near the critical point, the electron-phonon coupling is significantly increased by critical fluctuations, even in the case of vanishing carrier density. Applying these results to low-density systems, I show that the superconducting transition temperature is strongly enhanced upon approaching the quantum critical point. Furthermore, I will describe how ferroelectricity and topology may lead to a superconducting instability at vanishing density.