| Summary: | <p>Alkali-doped fullerides are strongly correlated organic superconductors that exhibit high transition temperatures, exceptionally large critical magnetic fields, and a number of other unusual properties. The proximity to a Mott insulating phase is thought to be a crucial ingredient of the underlying physics and may also affect precursors of superconductivity in the normal state above <strong><em>T<sub>C</sub></em></strong>. We report on the observation of a sizable magneto-thermoelectric (Nernst) effect in the normal state of <strong>K<sub>3</sub>C<sub>60</sub></strong>, which displays the characteristics of superconducting fluctuations. This nonquasiparticle Nernst effect emerges from an ordinary quasiparticle background below a temperature of 80 K, far above <strong><em>T<sub>C</sub></em> = 20 K</strong>. At the lowest fields and close to <strong><em>T<sub>C</sub></em></strong>, the scaling of the effect is captured by a model based on Gaussian fluctuations. The behavior at higher magnetic fields displays a symmetry between the magnetic length and the correlation length of the system. The temperature up to which we observe fluctuations is exceptionally high for a three-dimensional isotropic system, where fluctuation effects are expected to be suppressed.</p>
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