School of Physics Hard Condensed Matter & AMO Seminar: Prof. Yoonseok Lee, University of Florida

Superfluid helium three (3He) is the first kown superfluid system formed by finite angular momentum Cooper pairs. Unlike other unconventional superconductors the symmetry of the order paramter in this system is fully understood as p-wave spin triplet pairing. From the maximal symmetry group in its normal state, all of the continuous symmetry except for the translational symmetry are broken in the superfluid phase, exhibiting extraordinarily rich physical phenomena. In particular, the surface scattering in unconventional superfluids/superconductors induces quasi-particle sub-gap bound states spatially localized near the surface within the coherence length, called the Andreev surface bound states (ASBS). We investigated 3He-B properties using a micro-machined mechanical oscillator developed in our laboratory. Our recent results reveal unexpected features in the damping of the oscillator and in its nonlinear behavior in the zero temperature limit. We will discuss a unique process involving multiple Andreev scattering in the surface states that might be the underlying physics for the observed behavior.