Phenomenological dynamics for two-dimensional superfluids

The dynamical properties of the superfluid transition in two dimensions are studied at a phenomenological level. The formulations of the dynamic theory by Minnhagen and by Ambegaokar, Halperin, Nelson, and Siggia are compared with each other and with experiments. The discussion centers around the dynamic diffusion length and the Kramers-Kronig relation between the superfluid density and the dissipation. The comparison with experiments is sharpened by the presence of new high-precision data on systems prepared with lithographic techniques and on YBa₂{Cu}₃O₇ films. It is shown that the prediction from Minnhagen's theory that the ratio of the dissipation peak height and the superfluid density equals 2/{π} is supported by experiments.