The moment of inertia and the scissors mode of a Bose-condensed gas

We relate the frequency of the scissors mode to the moment of inertia of a trapped Bose gas at finite temperature in a semi-classical approximation. We apply these theoretical results to the data obtained in our previous study of the properties of the scissors mode of a trapped Bose-Einstein condensate of Rb-87 atoms as a function of the temperature. The frequency shifts that we measured show quenching of the moment of inertia of the Bose gas at temperatures below the transition temperature-the system has a lower moment of inertia than that of a rigid body with the same mass distribution, because of superfluidity.