Clock Shift in a Strongly Interacting Two-Dimensional Fermi Gas.

We derive universal relations for the rf spectroscopy of a two-dimensional Fermi gas consisting of two spin states interacting through an S-wave scattering length. The rf transition rate has a high-frequency tail that is proportional to the contact and displays logarithmic scaling violations, decreasing asymptotically like l/(&ohgr;2ln2&ohgr;). Its coefficient is proportional to ln2(a′2D/a′2D)> where a2D and a′2D are the two-dimensional scattering lengths associated with initial-state and final-state interactions. The clock shift is proportional to the contact and to ln(a′2D/a2D). If∣ ln(a′2D/a2D)∣ » 1. the clock shift arises as a cancellation between much larger contributions proportional to ln2(a′2D/a2D) from bound-bound and bound-free rf transitions. [ABSTRACT FROM AUTHOR]