Colloquia

Historically, two paradigms competed to explain superconductivity (i) Bose Einstein Condensation of weakly interacting Charge 2e pairs (Schafroth), and (ii) Pairing instability of the Fermi liquid (BCS). BCS theory was the unquestionable winner until the late 80's. BCS approximations however, have suffered major setbacks in the advent of high temperature, short coherence length superconductors, such as cuprates, pnictides, and granular superconducting films. A third paradigm has offered itself: Hard Core lattice Bosons (HCB), which are experimentally realized in cold atoms on optical lattices. HCB behave less like weakly interacting bosons or fermions, but (strangely) more like quantum spins. Their static correlations are very well understood by theories of quantum antiferromagnets. Recent calculations of the conductivity of Hard Core Bosons suggests a new route to understanding linear in temperature resistivity and other strange metallic properties above the transition temperature.