Physics Colloquium, March 28, 2006

Detecting boson-vortex duality in experiments: how superfluids become solids in two dimensions

Subir Sachdev

Harvard University

Superconductivity or superfluidity is realized in a wide variety of systems in nature. Although the microscopic constituents and interactions differ greatly, the underlying mechanism which allows matter to flow without dissipation is essentially the same. A bosonic degree of freedom (Cooper pairs, 4He, 87Rb atoms...) condenses by macroscopically occupying an extended state, and this condensate can set up a supercurrent. I will discuss the properties of superfluids that are near a transition to an insulating solid. A superfluid-to-insulator transition has been observed recently for ultracold 87Rb atoms trapped in an optical lattice, and it is believed that the cuprate superconductors are near such a transition. I will focus on the quantum mechanical properties of vortices (i.e. whorls of superflow) in such a superfluid, and show that the vortex wavefunctions provide a dual description of the crystalline order in the solid. I will argue that essential characteristics of this vortex wave function may already have been detected in recent scanning tunneling microscopy experiments on the cuprate superconductors.

4:00 p.m., Physics Research Building (PRB), Room 1080

Reception at 3:45 p.m., Atrium, PRB