Quantum Cafe: Kamran Behnia

Date & Time

Title: Superconductivity, Charge Transport and Phonon Hydrodynamics in Strontium Titanate


Long-range ferroelectric order is aborted in strontium titanate because of quantum fluctuations. As a consequence, the low-temperature static electric permittivity becomes extremely large and the effective Bohr radius of the order of a micron. This is why removing a tiny fraction of oxygen atoms turns the system to a dilute metal, which has both a sharp Fermi surface and a superconducting instability. Substituting strontium with calcium stabilizes a long-range ferroelectric order in Sr1-xCaxTiO3 coexisting with metallicity and its superconducting instability in a narrow window of doping. As the carrier concentration is increased, the ferroelectric order is eventually destroyed by a quantum phase transition and the superconducting critical temperature is enhanced. Recent analysis points to the failure of Boltzmann-Drude picture of conductivity in explaining charge transport of this dilute metal. Thermal transport in the insulator detects the Poiseuille flow of phonons in a narrow temperature window as a consequence of strong coupling between the ferroelectric soft mode and acoustic phonons.

About the Speaker

Kamran Behnia obtained his Ph.D. working on heavy-fermion systems in Grenoble. He then spent two years as a postdoctoral fellow at University of Geneva. In 1992, he was employed by Centre National de la Recherche Scientifique (CNRS) and spent seven years working on organic and cuprate superconductors at Paris-Sud University. Since 2000, he has been based at Ecole Supérieure de Physique et de Chimie Industrielles (ESPCI) in Paris. He is interested in collective quantum phenomena in a variety of solids ranging from semimetals to superconductors. His book Fundamentals of Thermoelectricity was recently published by Oxford University Press.

Advancing Research in Basic Science and MathematicsSubscribe to Flatiron Institute announcements and other foundation updates