Colossal thermomagnetic response in the exotic superconductor URu2Si2

Abstract

The Nernst coefficient is a measure of the transverse thermoelectric effect in a conductor. Superconducting fluctuations magnify this effect but in URu2Si2, the million-fold enhancement suggests that the fluctuations have an exotic origin. The superconducting fluctuation effect, due to preformed Cooper pairs above the critical temperature Tc, has been generally understood by the standard Gaussian fluctuation theories in most superconductors1. The transverse thermoelectric (Nernst) effect is particularly sensitive to the fluctuations, and the large Nernst signal found in the pseudogap regime of the underdoped cuprates2,3 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 coefficient is anomalously enhanced (by a factor of ∼106) 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 symmetry4,5,6,7 of the superconducting order parameter.