Nernst effect, the transverse voltage generated by a longitudinal thermal
gradient in presence of magnetic field has recently emerged as a very
sensitive, yet poorly understood, probe of electron organization in solids.
Here we report on an experiment on graphite, a macroscopic stack of graphene
layers, which establishes a fundamental link between dimensionality of an
electronic system and its Nernst response. In sharp contrast with single-layer
graphene, the Nernst signal sharply peaks whenever a Landau level meets the
Fermi level. This points to the degrees of freedom provided by finite
interlayer coupling as a source of enhanced thermoelectric response in the
vicinity of the quantum limit. Since Landau quantization slices a
three-dimensional Fermi surface, each intersection of a Landau level with the
Fermi level modifies the Fermi surface topology. According to our results, the
most prominent signature of such a topological phase transition emerges in the
transverse thermoelectric response.Comment: 13 pages, 4 figures and supplementary information; To appear in
Nature Physic