  One of the hallmarks of high-temperature superconductors is a pseudogap
regime appearing in the underdoped cuprates above the superconducting
transition temperature Tc. The pseudogap continously develops out of the
superconducting gap. In addition, high-frequency conductivity experiments show
a superconducting scaling of the optical response in the pseudogap regime,
pointing towards a superconducting origin of the pseudogap. The
phase-fluctuation vortex scenario is further supported by the measurement of an
unusually large Nernst signal above Tc and the recently observed field-enhanced
diamagnetism which scales with the Nernst signal. In this paper, we use a
simple phenomenological model to calculate the paraconductivity and magnetic
response caused by phase fluctuations of the superconducting order parameter
above Tc. Our results are in agreement with experiments such as the
superconducting scaling of the optical response and the spin (or Pauli)
susceptibility, and further strengthen the idea of a phase-fluctuation origin
of the pseudogap.
