Starts 22 Oct 2009 12:00
Ends 22 Oct 2009 20:00
Central European Time
Leonardo da Vinci Building Seminar Room
Strada Costiera, 11 I - 34151 Trieste (Italy)
Because of their very small carrier density, bismuth and graphite allow to attain the quantum limit in a bulk metal with available magnetic fields. The fate of a three-dimensional electron gas pushed to this ultra-quantum regime remains an open question. Recent measurements of the Nernst effect in graphite and in graphene combined to what was reported in bulk bismuth a few years ago, and in two-dimensional electron systems a decade earlier, permits to draw a striking correlation between the field profile of the Nernst response and dimensionality. When a Landau level intersects the Fermi level, the Nernst signal peaks in three-dimensional systems and vanishes in two-dimensional systems. We argue that this qualitative difference is a signature of a topological phase transition exclusive to three-dimensional systems. Beyond the quantum limit, when all carriers are confined to the first Landau level, Nernst effect in bismuth detects field scales, which are not expected in the one-particle picture. The field profile of these anomalies points to a bulk origin. According to our recent angular-dependent Nernst measurements, the band picture is quite successful in explaining the complex electronic spectrum of bismuth up to 9 T, but is inadequate as the quantum limit is crossed. In particular, in the vicinity of 40 T, that is more than four times the quantum limit, large anomalies in all transport properties point to an enigmatic reorganization of bulk electrons. Unexpectedly, this electronic instability leads to an enhanced conductivity and a better metallicity.
  • M. Poropat