CPM Seminar

Quenched Disorder in Superfluids

Bill Halperin

Northwestern University

One of the most intriguing phenomena in condensed matter physics is superfluidity, macroscopic quantum states that allow frictionless flow. Superconductors may be the most familiar example, in which case the superfluid carries charge. But in recent years new superfluids and superconductors have been discovered that have unusual spontaneously broken symmetries such as rotational symmetry and time reversal symmetry. The paradigm for such systems is superfluid ³He, discovered by Osheroff, Richardson, and Lee (Nobel prize, 1996) and Tony Leggett (Nobel prize, 2003). Now there is strong evidence that certain heavy fermion superconductors, high temperature superconductors, and others, behave in a similar way. This class of so-called unconventional superfluids is very fragile in the presence of impurities. However, we can learn a lot about the superfluid or superconducting state by intentionally introducing impurities thereby disturbing the system. Until recently, this approach has been impossible in superfluid ³He, arguably the cleanest and purest material known to man. With the discovery of superfluid ³He in highly porous silica aerogel that situation has changed. I will discuss this new superfluid phenomenon and outstanding problems in this system, and what we can learn about pure superfluid interactions; and I will make comparison to related behavior in unconventional superconductors.