Colossal thermomagnetic response in the exotic superconductor URu2Si2

The superconducting fluctuation effect, due to preformed Cooper pairs above the critical temperature T-c, has been generally understood by the standard Gaussian fluctuation theories in most superconductors(1). The transverse thermoelectric (Nernst) effect is particularly sensitive to the fluctuations, and the large Nernst signal found in the pseudogap regime of the underdoped cuprates(2,3) has raised much debate. Here we report on the observation of a colossal Nernst signal due to the superconducting fluctuations in the heavy-fermion superconductor URu2Si2. The Nernst coeffcient is anomalously enhanced (by a factor of similar to 10(6)) as compared with the theoretically expected value of the Gaussian fluctuations. Moreover, contrary to the conventional wisdom, the enhancement is more significant with a reduction of the impurity scattering rate. This unconventional Nernst effect intimately reflects the highly unusual superconducting state of URu2Si2. The results invoke possible chiral or Berry-phase fluctuations associated with the broken time-reversal symmetry(4-7) of the superconducting order parameter.