Inelastic electronic transport in single-layer graphene and at the surface of topological insulator Bi2Se3
1ICN2 - Institut Catala de Nanociencia i Nanotecnologia, Campus UAB, Bellaterra, 08193 Barcelona, Spain
2Universitat Autónoma de Barcelona, Bellaterra, 08193 Barcelona, Spain
3ICREA - Institució Catalana de Recerca i Estudis Avançats, 08010 Barcelona, Spain
Understanding of the heating, energy flow and relaxation of two-dimensional Dirac carriers in graphene and topological insulators is essential for the design of electronic devices based on these materials. Elastic scattering by disorder imposes a limit to the conductivity at low temperatures; nevertheless, as disorder is reduced, the limit at finite temperatures will be ultimately set by the intrinsic electron-phonon (e-ph) coupling. In this talk, I will discuss our current understanding about the e-ph coupling in graphene and in the Bi2Se3 family of materials. In particular, I will describe recent results on electric-field and temperature-dependent transport measurements in exfoliated thin Bi2Se3 crystals  and on the generation of thermoelectric voltages due to hot electrons in graphene . In contrast to conventional metals with large Fermi surfaces, 2D Dirac electrons are largely decoupled from acoustic phonons leading to relatively low electron-lattice cooling rates. Temperature and bias dependent measurements reveal the presence of specific optical phonon modes that dominate the electronic response, with similar phenomenology in graphene and Bi2Se3. However, the large difference in the energy of the relevant modes (200 meV and 8 meV, respectively) results in dramatically different bias and temperature dependent transport characteristics. While in Bi2Se3 the resistivity changes strongly even at low temperatures (<100 K), reflecting inelastic scattering due to the thermal activation of optical phonons, the restriction of the acoustic phonons that can scatter off electrons in graphene leads to very long cooling times and unconventional high-order cooling pathways assisted by disorder in the same temperature range.
Acknowledgements: This work is supported by the European Research Council (ERC Grant Agreement No. 308023 SPINBOUND), and MINECO (MAT2013-146785-P, SEV-2013-0295).
 M. V. Costache, I. Neumann, J. F. Sierra, V. Marinova, M. M. Gospodinov, S. Roche, and S. O. Valenzuela, Phys. Rev Lett. 112, 086601 (2014)
 J. F. Sierra, I. Neumann, M. V. Costache, and S. O. Valenzuela, submitted